p.1 

OAR Box 1877 

Prepped by Keeia Richards 

Document Number: 

43) ll-B-40 

Docket Number: 

A-90-19 

Primed 12/2/200810:36:50 AM Sheet 43 of 46 
* I 

P.2 

A-90-19 

ll-B-40 

MEMORANDU M 

TO: Process Vents Docket A-90-19 

FROM: Wanda Floyd 

DATE: December 1990 

SUBJECT: HON NESHAP: Industry Characteristics/Cresols 

Attached is a product-process summary (PPS) for the production of 

Cresols/Cresylic Acids (Mix) via Recovery from Spent Refinery Caustics 

category. This PPS was developed as part of the Industrial Profile project in 

support of the Hazardous Organic NESHAP (HON) regulatory effort. Information 

in this PPS is used as a basis for emissions and cost impact estimates for the 

HON program. 

Listed below are the key references used in developing the attached PPS. 

Genhartz, Wolfgang, ed. Ullmann's Encyclopedia of Industrial Chemistry. 5th 

edition. VCH Publishers, Florida, 1985. pp. 25-47. 

"Cresylics." In: Chemical Marketing Reporter. Schnell Publishing Company, 

New York, November 30, 1987. 

"Cresols & Cresylic Acid." In: Mannsville Chemical Products. New York, 

November 1985. 

1989 Directory of Chemical Producers USA. SRI International, California, 

p. 542. 

McKetta, John J., ed. Encyclopedia of Chemical Processing and Design, Marcel 

Dekker, Inc., NewYork, 1977. pp. 212-225. 

Kirk-Othmer. Concise Encyclopedia of Chemical Technology. John Wiley & Sons, 

New York, 1985. p. 73. 

Shreve, R. Norris and Brink, Jr., Joseph A. Chemical Process Industries. 

4th edition. McGraw-Hill Book Company, NewYork, 1977. pp. 72-77. 

Kirk-Othmer. Encyclopedia of Chemical Technology. 3rd edition. John Wiley 6c 

Sons, New York, 1978. Volume 22. p. 593. 

00:0*. A-90-19 

H-B-252 

cao.067 

cresols.ere 
P.3 

"i ff 

Preparer: 

Date: f/io/to 

Reviewer: 

ADMINISTRATIVE NOTES 

Product-Process Cod* /j / 9'?73/4 

Hours spent on this PPS f- -^ , 

create/ cfetytc, AjutU(p**f>Y,r 

P-P Name yie cover* /rc^ Seen1? Ac^ey ^<^/' W 

Incomplete Items (parts of 

form you cannot complete) 

(line # and description) Date Cleared Initials 

S.O jJo fy«, D/ 

'*? 

(-\\\lk0)6yk UJ 

X^l U ft. Crn^A ^ of + ^ Wl/trcsimio " ^ *^f 

Chemicals missing CAS numbers (y A ; a 

Plant with City but no County (plant name, city, state] 

Jee Sec tO* j , 0 . 
P.4 

Preparer: tod fr/t 

Date: f/sa/f* 

Reviewer: 

PRODUCT-PROCESS SUMMARY (PPS) 

ChenticaT Name C/'gols / Qyesi /rc. //c/g/s - ^///^/e r 

Alternative Chemical Name KJ ,_WT*_. : 

CASI /3/f?7? 

Karen Fidler Chemical Numm Monc 

CHEMICAL SPECIFIC INFORMATION 

1.0 U.S. Production Ref # Ik f . Pg # , Ref Year /f*>;/rtf 

(indicate the same reference information for any answers below from a 

different reference) 

1.1 Unfts of production {circle oneldninions ofka) or millions of gallons 

l.I U. S. Capacity 4*& 7<- * -*ss«. . ^&3_ . "_—,-

1.3 U. s. capacity VWU M * /?* ______4_1JXXJ' ><•<- .—r 

1.4 «. $, Oeaa&d *££=$- f,f Ll3_r3.3. .?/-.. .^ .._. 

i.5 Import* A 1 -3^^4-^kfr ^^yW.^ ^ 

1.5 Exports -^^ T Tt 7 ./v** ,^£3-^ 

1.7 Product Price 

1.7.1 Average Price ^>V / / / 35 /?3^

 / . £ D 

1.7.2 Units of price {-circle one) /f/Kft or S/oallon 

1.7.3 Concents on prj ci 

7 T ^ />/ ^ **<3 ref/**S CfCSyO.c tscOcff. 

1.8 Comments 

3£_u.i_3sf- -ray^^-c^ i 2-fjyLt*^* jts^-OUJ^ty--j j rXt.S /^t^^^e-c^ ^»*--<-<—"*<-•—=-3; /fi-a-Vt^sUtt-r 

O^^ydc ^^u- ~-<0$y^'-£ ^< ^ ~Z& 3w3>.4^ , <*w/ c?*t^<*^0 ^y«^ . 
P.5 

s 2.0 Chemical End-Use 

Jlii. 

Ref # £ 

txk/f*^} 

4 / ^ £^,—1< c&yZrr^ 

i4tA*4t>£<~Oo Cj-JZkZkk^ 

.. Pg # ., Ref Year Iff? 

Percent 

'2-6 

C-^y&l * ^ iC * ../-e^ 

^ 7 C^^^ y OPS f ^ x 

^ 
3.0 U.S. Producers Ref # 1 ., Pg # f?2 ., Ref Year 110 

Hffll Uffp'*

 qne J mjllioris oT]^> or millions of gallons 

3.2 Name, Location, and Capacity 

Location, 

Process Used 

(use P-P #) 

Capacity 

Units 3*-< -*t o 

jlC'C -VV Oo . 

6-,'Ca.iA) P-'l/.'j.'c* 

(gr/f-t'-d.^'e'-aj d.'tf'}''" 

//cUS^on TfKai 

y 

C A.-'e-'^o / f//. 

Jr& <i ft—-TT?- -^-yf^-^OsLA. 

fin* COS fr?} U*}/). 

r-f>s 

;£=S=^ S"^> " 

Total Capac ity 31l--£003£~ 7'' & 
P.7 

PRODUCT-PROCESS SPECIFIC INFORMATION 

4.0 Potential Product-Processes (P-P) Ref I '* Pg # ,7<3 

Commercially % Nat'l 

Name Viable fy/n) Capacity 

P-P 1 

P-P 2 

P-P 3 

P-P 4 

P-P. 5 

P-P 6 

fiet*vcf*j //em fycnl Rel''*e<-i (**j/.!c} £ _ /oc 

4.1 Documentation of P-Ps Excluded 

P-P not 

Commercially Viable Reasons 

TsoU f'0*- /li'/n Co*/ I*'} /If usee/ /n + e J "t 4- / 

UseJ * I'lHe ly one /<cc.Ok6yt 

4.2 Process described 

n.c process aescno-ea 0 / , . a r s /•> 

i» this W$ ISnccWy M>», jpervt /ie/'s-ey CA^/^C r 
P.8 

«;ST •T~t6t?e1<T*on*| Ref # u Pg #. 7* 

Air Oxidation Reaction 

Oxidation Reaction 

Alkylation Reaction 

Carbonylation Reaction 

Halogenation Reaction 

Condensation Reaction 

Dehydrogenation Reaction 

Dehydrohalogenation Reaction 

Esterification Reaction 

Hydrogenation Reaction 

Hydrohalogenation Reaction 

Hydroformylation Reaction 

Hydrolysis Reaction 

Nitration Reaction 

Oxyacety1 at1on React1 on 

Oxyhalogenation Reaction 

Sulfonation Reaction 

Catalytic Reformation 

Hydrodimerization Reaction 

V '4 /• ask'a rx 

4.4 Explain how you selected the reaction type in line 4.3. 

l^scJ-J ly +*f; 
P.9 

4.5 Written Description 

In the left margin, indicate references and page numbers throughout written 

description. 

^- /A iA d-0 / tsv*°& ff ?yu~^ <^- ^-^3//^-^u3^ -/^~~ k& ^Jfe* /^-t^}^, 

^ A~ yet* >-w^ y ZG*~$~ ^^^- ^ <~/<^. s^Llo< 

fi- rt^O-^**- sd^-pL-a u ^ gj_ &6&..<.Sy j /£**<£ p«~d/ CsUC?fa&/j' / 

_ fen oJ&t^V^>^ /^- ^^^^^L,^ . 
P.10 

30 Cresols and Xylenols 

will be expanded as the prices of oil and natural 

gas rise. This would yield more low-temperature 

tar, in which the content of cresols and xylenols 

is much greater than in high-temperature cokeoven tar. 

1.3.2. Recovery from Spent Refinery 

Caustics 

In the United States, cresols and xylenols are 

obtained mainly from the naphtha fractions produced by catalytic and thermal cracking in the 

petroleum industry, which contain, on the average, ca. 0.1 % C6 -C8 phenols [34], [36]. In the 

scrubbing of the sulfur compounds contained in 

these fractions (hydrogensulfides, alkyl- and 

arylthiols) with concentrated alkaline solutions, 

a process known as "sweetening," the acid 

cresols and xylenols are also extracted. The composition of the spent cresylate caustics fluctuates 

widely, and they contain on the average 

20-25% C6 -C8 phenols and 10-15% sulfur 

compounds. The caustics are collected by the reprocessing firms Merichem, Northwest Petrochemical, and Productol, and are reprocessed in 

central plants by a variety of processes. 

At the Northwest Petrochemical in Anacortes, Washington, the thiols in the alkaline 

solution are first oxidized with air to give disulfides, which are then decanted as an oily layer 

[37]: 

RSNa + R'SNa + 0.5 O, + 11,0 . RSSR: + 2 NaOl I 

The phenols are then precipitated from the 

aqueous alkaline phase in a packed column with 

a countercurrent stream of carbon dioxide (flue 

gas) and decanted. The phenols still present in 

the carbonate-hydrogen carbonate phase (2-

6%) are extracted with an organic solvent, from 

which they are extracted again with an aqueous 

alkaline phase, which is then returned to the column. A typical composition of the phenol mixture obtained in this way might be as follows: 

20% phenol, 18% o-cresol, 22% w-cresol, 9% 

p-cresol, 28 % xylenol (all six isomers plus ethylphenol), and 3 % higher phenols. This mixture is 

then separated by distillation into phenol, ocresol, m-/p-creso\ mixture, and xylenols, or mixtures in which particular constituents predominate. 

The Merichem Co. of Houston, Texas, is the 

biggest processor of spent refinery caustics, in the 

United States, and precipitates the phenols with 

Vol. A 8 

hydrogen sulfide, a waste product of the refineries in Houston [38], [39], instead of using 

carbon dioxide. After extraction with a solvent, 

the sulfide solution obtained in this process is 

concentrated in a triple-effect evaporator to give 

sodium sulfide for use in the paper industry and 

in ore dressing [39]. 

The water vapor condensate formed at this 

stage is stripped with natural gas to remove odorous compounds, after which it is passed to a 

cooling tower. The natural gas is then used as a 

fuel in the final process air incinerator. Before 

being introduced into the waste air incinerator, 

which is operated at ca. 1370°C, the process air 

from all of the other parts of the plant is 

scrubbed with alkaline solution. In addition, 

odor-neutralizing chemicals are sprayed alongside the plant area. All of the water at the plant 

(including rain water) is recycled in an integrated 

system. Water is released into the environment 

almost completely as water vapor from the cooling towers [39], [40]. 

According to the process operated until 1971 by the 

Pittsburgh Consolidated Chemical Co. [41], [42], the spent 

refinery caustics wereireated directly with flue gas containing 8-14% carbon dioxide.'From the crude phenol thus 

precipitated, a fraction boiling at 100-235 "C was removed 

by distillation and extracted continuously in a countercurrent of aqueous methanol-light naphtha. After removal of the final thiol and base residues with an ionexchange resin, the cresylic acids that had entered the 

aqueous methanolic phase were recovered by fractional 

distillation. 

In 1984, the "cresylics" capacities of Merichem, Northwest, and Productol were 55 000, 

15000, and 10000 t/a, respectively [43]. However, these figures include phenol, the xylenols, and 

several other alkylphenols. In addition, Merichem no longer isolates cresylics exclusively 

from spent refinery caustics, but also works up 

crude phenols from coal tars of various types. 

The recovery of cresols and xylenols from 

spent refinery caustics has so far been confined 

to the United States. Because different refinery 

techniques are used in the Federal Republic of 

Germany, the' production of cresol-containing 

spent caustics is insufficient for economical reprocessing; or no spent caustics are produced at 

all because desulfurization is carried out differently, e.g., by hydrotreating. In the United States 

as well, the recovery of cresol from spent refinery 

caustics is stagnating or even receding because 

the refineries are likewise changing over either to 

hydrotreating or to UOP's Merox process, partly 

because the price of sodium hydroxide has risen 
P.11 

5.0 Process Flow Diagram (attach at end of package) ^on*-

5.1 Flow Diagram Reference: Ref # , Pg # 

5.2 Comments on Flow Diagram 

/Jo /?**, />/«</*- J Prscefj C+rafne-Ss ef/<'~>tl/ / " — */*Scs y f> 

5.3 Process Component* Ref # A Pg # 3° 

Component Types Kpmber (jfftft tero f f !»0ne 

shown) 

Distillation Columns •? 

Absorbers o 

Strippers o 

Reactors o 

Condensers / 

Vaporizers / 

Others 

$<. su lies 2-

bi//.peradffS 

Tata? Huabei. JO 
6.0 Chemical Data 

6.1 Balanced Chemical Reactions 

P.12 

Ref I l& pg # Jo 

l/6 s^A+r^^ .fZ*S AJ^^0^ 

6.2 Chemical Tree Ref I l<> . pg # ?<? 

Jn^ fitA~*~y C^L^aUmC^1 C^U<f^Q. / /A^^SC^ SPCJ,. 
P.13 

'6.4 Stoichiometry Ref # /°, 3 Po # ^ " 

Show calculations and assumptions and then summarize in table on next 

page. 

fj.& fte/e-cjce J>'»CJ ferccS */k ff^ ,e£'~y c^frs 

<tW w< fLe„/s, «~X AV ^ I"**5 **•"* '"** "'r 

Com °S P***-/* - ** % fAe**' 

'° <*) - £*•*<•<• i 

1h-f) o f pkenc fs : xa t> 

' f I 

y „ _. ct><ei<>/ 

•>y$ % <yA*e' 

\ /kf-~J ^/'"/^3,^/. ^ *«**f'e 3 /^- ^ 

<•? - cse fo 

3 r ~ ~y (/y x ry /• ^jj^ ^ »v^/ . ^ - .^ 
$.4 Stoichiometry (continued) 

P.14 

StoicMbmetry 

OS I W*$ product} 

6.4.1 Product 

C'C f* /> /to** Jrc A/^S fa) ' pJf'Q?3 

6.4.2 Raw Material(s) 

#1 SpCn f /le/-'* (f/*v Ctu^rOcS 

#2 

#3 

#4 

#5 

6.4.3 Co-Products 

#1 n- Cres Q/ 

#2 rn - 'cese / 

n p - trako/ 

#4 (?IAJL-IA£> 

#5 yJ^s nJ 

6.4.4 Bv-Products 

#1 

#2 

#3 

#4 

#5 

6.4.5 Intermediates 

#1 . 

#2 

fi an e 

/£li2_£_ 

/£. 7 

?f 

_i_22£ 

MJki 
P.15 

6.4 Stoichiometry Conversion Factors 

a) q^H-oV Factor m ?mm r#£¥? /o 

b) CtMafcrslon Factor for Co-Product fl f- ° 

c) Conversion Factor for Co-Product 12 A ° 

d) Conversion Factor for Co«Product #3

 /

- ° 

e) Conversion Factor for Co-Product H 

f) Conversion Factor Comments 
P.16 

7.0 Process Vent Emission Sources 

7.1 ^OfP f process vent emissions? ' (Y/N) 

7.2 A1r Oxidation vent emissions? H (Y/N) Ref # , pg # 

7.3 Comments Ref # , Pg # 

7.4 Reactor vent emissions? rl (Y/N) Ref # , Pg # 

7.5 Comments Ref # , Pg # _ 
P.17 

r.r 

7.7 

vent emissions? L (Y/N) Ref # 

_^. 7 C<,\$ UAyJ-aVr \^c, J^L 

Pg # 

Ref # , Pg # 

r*# «W*J 

7.9 Comments 
r 

P.18 

8.0 Transfer Emission Sources 

8.1 Ai4vli$i&W€&-Prodeets Transferred* 

8.2 What mterials are transferred? 

Ref # 

/ (Y/N) 

., Pg # 

Name CAS timber 

8.2.1 Product 

C'eiils/Crerilrc flc'd ffrxU) 

a ' i****** ' 

8.2.2 Co-Products 

/n - cfesdf 

•A 

- LffS o/r 

/o?}?</ 

I* 6 <ff f 

8.3 Comments Ref # ., Pg # 
P.19 

9.0 Storage Emission Sources 

9.1 Arer'litttJfcftTs stored? . 3 

Ref # ., Pg # 

(Y/N) 

9.2 What materials are stored! 

Storage Service 

CAS I Type 

9.2.1 Product 

(f-e$o/s /(Ojresy/rc /PcOt/s />"'>/ 

9.2.2 Co-Products 

0 - CCfo/ 

fy\ - creto / 

•jcreta / 

9.2.3 Raw Materials 

Jpe'vf Ae /•'•»£'y Cgu.sf-a' 

/)/?7?J /T^/A/ 3 S6,«}g 

/Q%k) t ¥ (o:- pre J tic * rfc"-a>fe 

rio/ie ftotu /yur^r.*/ sCo^je 

9.2.4 Intermediates 

9.4 Comments 
P.20 

10.0. Wastewater Emission Sources 

10.2 Describe wastewater 

/ 

Ref # .. Pg # 

(Y/N) 

Stream 

Number 

#1 

n 

#3 

Equipment Component 

Producing Wastewater 

J}/jC'lui./''4A /a/a-rtt/t 

J ('/a/if* 

C6"c/e*f<" 

10.3 Stream Composition 

Comments on flow 

Ref # . . Pa # 

(provide only if readily available) 

Stream #1 Steam #2 

Organics Organics 

HAPs HAPs 

Water 

Other 

Water 

Other 
Stream #3 

Organics _ 

HAPs 

Water 

Other 

P.21 

•^El 

10.4 Comments Ref , __££__, Pg , ^ 

^ _ ,*#&-_-__ c , 
P.22_ 

SH-377 

fourth edition 

CHEMICAL 

PROCESS 

INDUSTRIES 

R. NORMS SHREVE 

Lau Profossor Emaritus of Chtmicat Engin—ring 

Purdttt Vnivttrsity 

JOSEPH A. BRINK, JR. 

Consulting Chtmicat Enginmmr 

Professor and Chairman of Oumieal Engimaring 

Washington Stat* Vnivtnitr 

MeCRAW-HILL BOOK COMPANY 

Horn IW* Ss. Lornls San Francisco Atddmmd Bog—. 

OtsssUorf Johamasburg Undo* Madrid Main 

Motmal >«r Dolhl Panama Paris _<__ Pamlm 

Singapore Sydnar Tokyo Toromsa 

mm LIBRARY 

DURHAM, N.C. 
Library of Congreaa Cataloging ia PabUeatioa Data 

Shreve, Randolph Norris, 1885-1975. 

Oiemical process industriea. 

Includes bibliographies and index. 

1. Chemistry, Technical. I. Brink, Joseph A., 

date, joint author. II. Tide. 

TP14S.S5 1977 660.2 77-4236 

ISBN 007^57145-7 

Copyright © 1977, 1967, 1956 by McGraw-Hill, Inc. All rigfats reserved. 

Copyright 1946 by McGraw-Hill, Inc. All rights reserved. 

Printed in the United States of America. No part of this 

publication may be reproduced, stored in a retrieval system, 

or transmitted, in any form or by any means, electronic, 

mechanical, photocopying, recording, or otherwise, without 

the prior written permission of die publisher. 

34567890 FGRFGR 7865432109 

The editon for this book vert Jeremy Robinion and Either Gelalt, 

and the production supervisor was Teresa F. Leaden. 

It vas set in Bodoni Book. 

Printed and bound by Fairfield Graphics. 

•tf 
72 [Chap. 5] Coal Chemicals 

ammonia liquor is pumped back into the pipes to help condensation; the rest goes to the ammonia 

still, which releases the ammonia for subsequent chemical combination in the saturator. All the tar 

flows to storage tanks for tar distillers or for fuel.8 

Figure 5.3 can be divided into different steps, representing the flow of material through the 

various pieces of equipment, wherein the proper physical operation or chemical conversion takes 

place. Figure 5.3 may be thus broken down into the following sequences: 

Coal is transferred, crushed, and screened (Op). 

Coal is charged to a hot, empty oven (Op)*. 

Coal is chemically transformed to coke and volatiles by pyrolysis (Ch). 

Hot coke is pushed out of the oven, quenched, and transported (Op). 

Condensable products of distillation are liquefied and collected in the hydraulic main (Op). 

Foul gas is cooled, and tar extracted (Op). 

Ammonia is removed from gas as ammonium sulfate (Ch). 

Cas is cooled and subjected to benzol and toluol removal by absorption in straw oil (Op). 

Hydrogen sulfide is removed (Ch). 

Purified gas is metered and transferred to consumers (Op). 

The tar separated from the collecting main and the tar extractor or electrostatic precipitators 

is settled from ammonia liquor and, together with light oil, subjected to the sequences represented 

by the flowchart (Fig. 5.6). 

Koppers-Becker ovens are the most widely used vertical-flue ovens in the United States. The 

elevation is shown in Fig. 5.4. These ovens are all of the regenerative type and have individual heat 

regenerators, generally from side to side, underneath the oven. The reversal of the air and waste 

gas flow is made from side to side every half hour. The gas burns upward, crosses over the top of 

the oven, comes downward on the other side, and exits through the regenerative oven underneath. 

This travel is completely reversed periodically. 

RECOVERY OF COAL CHEMICALS* The gaseous mixture leaving the oven is made up of 

permanent gases which form the final purified coke-oven coal gas for fuel, accompanied by condensable water vapor, tar, and light oils, with solid particles of coal dust, heavy hydrocarbons, and 

complex carbon compounds. The gas is passed from the foul main (Fig. 5.3) into the primary condenser and cooler at a temperature of about 165°F. Here the gases are cooled to 85°F by means 

of water. The gas is conducted to an exhauster, which serves to compress it. During the compression 

the temperature of the gas rises to as high as 120°F. The gas is passed to a final tar extractor, where 

the tar is thrown out by impingement of gas jets against metal surfaces. In newer plants the tar 

extractor may be replaced by electrostatic precipitators. On leaving the tar extractor, the gas carries 

three-fourths of the ammonia and 95% of the light oil originally present when it left the' oven. 

The gas is led to a saturator (Fig. 5.3), which contains a solution of 5 to 10%10 sulfuric acid, 

where the ammonia is absorbed with the formation of solid and crystalline ammonium sulfate. The 

saturator is a lead-lined, closed vessel, where the gas is fed in by a serrated distributor underneath 

the surface of the acid liquid. The acid concentration is maintained by the addition of 60°Be sulfuric 

acid, and the temperature is kept at 140°F by the reheater and the heat of neutralization. The 

crystallized ammonium sulfate is removed from the bottom of the saturator by a compressed-air 

injector, or a centrifugal pump, and drained on a table, from which the mother liquor is run back into 

the saturator. The salt is dried in a centrifuge and bagged, usually in 100-lb sacks (Chap. 18). 

"Lowly, op. cil.. Suppl. Vol., pp. 462-471. for other types of ovens. 

9Details for this recovery of the many coal chemicals are to be found in Lowry. op. cit., Suppl. Vol., pp. 618-628, for ur 

processing, pp. 629-674, for light-oil processing; ECT. 2d ed.. vol. 2. p. 299. 1963. 

10At the sun of t charge, the acidity is often aa high as 25%. but ammonium bisulfate is liable to be formed when free sulfuric 

acid exceeds 10 to 11%. 

VM" 

t 

OiP-r 

•30*/J-

» 

S-*-

I -
mmoma 

I the tar 

•ugli the 

>n takes 

'P.* 

(Op). 

ipttators 

resented 

tes. The 

lual heat 

id waste 

ie top of 

lerneath. 

le up of 

bv con-

•ons. and 

larv coniv means 

lpression 

>r. where 

s the tar 

is carries 

oven. 

trie acid, 

ate. The 

•derneath 

e sulfuric 

ion. The 

ressed-air 

back into 

p. 18). 

528, for ur 

free sulfuric 

Coking of Coal 73 

fP 

l-y.-vfirg.jgg? Wl^ _ -S-r_UJjr 

1 ' , gar? •*•* -

v^TW 

Fig. 5.6 Flowchart of coal-tar continuous distillation (without tar dehydration). The pipe .lill i. uf the radiant t* pe. The erude-tar 

feed inlet is at the lower right. Thia is filtered and pumped through the reflux vapor-tar heat exchanger, economizer, pitch-tar heat 

exchanger into the top of the lower third of the distillation column and out at the bottom, to the circulating pumps and into the pipe 

still (where the crude ur joins 4 to 5 volumes of the circulation pitch and on finallv to near the top of the distillation columnl. 

The vapors, steam-distilled and superheated, pass overhead from the top of the tray-tvpe distillation column, enter the bottom of the 

bubble-cap fractionating column, and are separated into four fractions: 1.2.3.4. with a residue. 5. leaving at the bottom of this 

fractionating column. The product pitch. 6. cascades from the top of the distillation column down through the superheated steaming 

section to establish the desired pitch hardness and to strip thb pitch of the higher-boiling volatile oils. It is then withdrawn from 

above the middle of the distillation column and conducted through the pitch-tar heal exchanger to storage. The products are: 

Side stream 1: Light oil. bp to 170°C. 

Side stream 2: Carbolic oil. bp 170-205°C. 

Side stream 3: Naphthalene "oil. bp 205-24O*'C. 

Side stream 4: Creosote or wash oil. bp 240-280"C. 

Residue 5: The residue or anthracene, bp 270-340°C. 

Pitch 6: Residuum or pitch, bp 325-400°C. 

lhere are standby steam pumps in the event of failure of the motor-driven pumps. The Wilton principle of recirculation of hoi 

pitch at 350°C mixed with the crude ur at 120°C rises the temperature of -the pitch-tar leaving the pipe still to onh 350°C and 

avoids thermal-cracking and vaporization in the pipe still. {Chemical Engineering. Wiltons Ltd.. London. See special pamphlets 

from this company for details.) 

The gas leaving the saturator at about 140°F is taken to final coolers or condensers, where 

" is scrubbed with water until its temperature is 75°F. During this cooling some naphthalene 

separates and is carried along with the wastewater and recovered. The gas is passed into a light-oil 

or benzol scrubber (Fig. 5.3), over which is circulated, at about 75°F as the absorbent medium, a 

heavy fraction of petroleum called straw oil. or sometimes a coal-tar oil. The straw oil is spraved 

mto the top of the absorption tower while the gas flows up through the tower. Most scrubbers use 

s

pual metal packing, although wooden grids were formerly used. The straw oil is allowed to absorb 

snout 2 to 3% of its weight of light oil, with a removal efficiency of about 957c of the light-oil vapor 

"1 the gas. 

Ine rich straw oil. after being warmed in heat exchangers bv vapors from the light-oil still and 

"•en by hoi debenzolized oil flowing out of the still, is passed to the stripping column, where the 

straw oil, flowing downward, is brought into direct contact with live steam. The vapors of the light 

°" and steam pass off and upward from the still through the heat exchanger previously mentioned 

into a condenser and water separator. The lean, or stripped, straw oil is returned through the 

eat exchanger ro the scrubbers. The gas. after being stripped of its ammonia and light oil, has the 

I 

• >! 

V 

if 5 

3 
74 [Chap. S] Coal Chemical* 

TABLE 5.3 Approximate Yield* per Ton of Coat Carbonized 

(Depending on Owl and Conditions L acd, 

Hightemperature. 

lb 

Lowtemperature, 

lb 

Furnace coke 

Coke breeze 

Semicoke (12% volatiles) 

Tar 

Ammonium sulfate 

Light oil (removed from gas 

oil scrubbing; see Table 5 

Cas 

bv 

-4) 

1.430 

93 

78 

20 

20 

3.500 

1.440 

150 

18 

16 

250 

Source. Ind. Eng. Chem. 48, 352 (1956). See also Fig. 3.3. Note that 4 lb of 

technical ammonium sulfate is equivalent to 1 lb of ammonia. 

sulfur removed in purifving boxes, which contain iron oxide on wood shavings, or bv a solution of 

ethanolamine (Girbotol) in scrubbing towers, the best present-dav practice. These procedures are 

fully described in Chaps. 6 and 7. 

U.S. Steel has built a coke-oven plant at Clairton. Pa.,11 which emplovs new processing, furnishing a clean gas for compression and hvdrogen recoverv and avoiding coproduction of ammonium 

sulfate. The kev to the new process is a recycled solution of ammonium phosphate that absorbs N'H3 

from the cooled (compressed?) coke-oven gas. In a typical absorption cvcle. lean 40% phosphate 

solution (the molar ratio of NH3 to H3P04 is less than 1.5) soaks up all but traces of NH3. The rich 

ammonium phosphate solution is reboiled in a distillation tower in which NH3 vapor and a lean 

phosphate solution are separated for reuse. 

LOW.TEMPERATURE CARBONIZATION15 In this century a large amount of experimental 

work has been carried out on the carbonization of coal at temperatures ranging from 750 to 1100°F. 

with the main object of obtaining maximum vields of liquid products and producing semicokes 

containing from 8 to 20% volatile matter. Here again the characteristics and vields of the various 

products depend upon the coal, the temperature.* and the treatment. Tables 5.3 and 5.5 show the 

difference in gas content and in yield products for high- and low-temperature svstems. The Disco 

plant at McDonald, Pa., is the onlv plant in this country to utilize a low-temperature carbonization 

process13 and has a daily capacity to convert high-volatile coal into 800 tons of Disco char, a domestic 

fuel. The tar is sold and refined to produce tar-acid oil, tar acids, "creosote,"14 and fuel pitch. The 

gas, after liquid-product removal, is used for firing. The maximum temperature used in this process 

is 1050°F. Low-temperature carbonization has been important in several European countries, 

especially England, for many decades, but has never been popular in the United States. 

DISTILLATION OF COAL TAR1 3 

Coal tar is a mixture of manv chemical compounds, mostly aromatic, which varv widely in composition 

(Figs. 5.2, 5.6. and 5.9). It is a coproduct of the destructive distillation or pyrolvsis of coal. Most 

of the tar in this country is produced bv steel companies as a coproduct from blast-furnace coke 

"Cool Cain for Ammonia Recovery. Chem. Keek. Feb. 27. 1965. p. 39: U.S. Pat. 3.024.090. 

'••Low*****, op. cit.. Suppl. Vol., chap. 10. pp. 395-460 (138 refs.). 

l3Lowrv, op. cit., Suppl. Vol.. p. 439. 

14Bv definition of the American Wood Preservers Association: however, creosote is a distillate of high-temperature coke-oven tar. 

15<_f. Bituminous Materials in Road Construction, pp. 26ff, Dept of Scientific and Industrial Research. HMSO, London. 
Distillation of Coal Tar 75 

production. The quality and quantity of tar from this operation will varv. depending on the rate of 

production of the ovens and the nature of the coal used. The specific gravity will varv from 1.15 to 

1.2. and the quantitv of tar will vary from 8 to 12 gal of tar per ton of coal. A tvpical light-tar 

composition is shown in Fig. 5.9. The end product of the distillation (Fig. 5.6) of coal tar is pitch, 

usually more than 60% of the crude tar. The objects of the distillation are to produce a salable end 

product, with a separation of the valuable products into useful cuts. In a modern refinerv equipped 

with a fractionating column (Figs. 5.6 and 5.8) for the primary distillation, these products must 

usuallv be sharply fractionated, with a minimum of overlapping. The process also should be thermally 

economical, and the furnace (Figs. 5.6 and 5.7) so designed and constructed that repairs and fuel 

usage are at a minimum. 

METHODS OF DISTILLATION There have been many improvements in coal-tar distillation 

over the vears. These can be divided into three general classifications: 

a solution of 

ocedures are 

sing, furnishf ammonium 

absorbs NH3 

7

c phosphate 

f3. The rich 

and a lean 

•xperimental 

itollOOT. 

» semicokes 

the various 

>.5 show the 

The Disco 

jrbonization 

. a domestic 

i pitch. The 

this process 

i countries. 

omposition 

coal. Most 

rnace coke 

••oke-oven tar. 

•ISO. London. 

1. The 3.000- to 10.000-gal batch still, which has been much improved and used for special 

end products such as pipe enamel (Fig. 5.7). 

2. The continuous still, with a single distillation column, using side streams (Fig. 5.6). 

3. The continuous unit, using multiple columns with reboilers (Fig. 5.8). 

PRODl'CTS OF DISTILLATION Modern practice, as exemplified by the pipe still and fractionating columns, is producing such clean cut fractions that often little further purification is 

necessary. However, in Fig. 5.6 and below are given the fractions obtained in an ordinary continuous 

distillation, which will varv with the coal and with conditions. 

a. Light oils usuallv comprise the cut up to 390°F. Thev are first crudelv fractionated and 

agitated at a low temperature with concentrated sulfuric acid, neutralized with caustic soda, and 

redistilled, furnishing benzene, toluene, and homologs (Table 5.4). 

b. Middle oils, or creosote oils, generally are the fraction from 390 to 480 or 520° F. which 

contains naphthalene, phenol, and cresols. The naphthalene settles out upon cooling, is separated 

:n 

in 

(,'*•••

 S *7 T«*distUlation batch tank still, heated bv gas or oil burning in large return bend 

« with about 70% thermal efficiency. Two stirrers. (Reilly Tar & Chemical Co.) 
•raB8SJg6WBW!«JP5< 

Fig. 5. 8 Fractionating distilling column (147 ft high) at Clairton. Pa., producing high-quality 

benzene, toluene, and xylene. (U.S. Steel Corp.) 

by centrifuging. and is purified by sublimation. After the naphthalene is removed, phenol and other 

tar acids16 are obtained by extraction with a 10% caustic soda solution and neutralization, or "springing," by carbon dioxide. These are fractionally distilled. 

c. Heavy oil may represent the fraction from 480 to 570°F, or it may be split between the 

middle oil and the anthracene oil. 

d. Anthracene oil is usually the fraction from 520 or 570°F up to 660 or 750°F. It is washed 

with various solvents to remove phenanthrene and carbazole: the remaining solid is anthracene. 

MISCELLANEOUS I SES OF COAL TAR In 1976 coal tar used as fuel amounted to about 15 

to 20% of the total consumption of tar for the vear. Coal tar is also utilized for roads and roofs. For 

these purposes the tar is distilled up to the point where thermal decomposition starts. This "base tar" 

is then oiled back with creosote oil to ensure satisfactory rapid drying. Somewhat similar tars are 

used to impregnate felt and paper for waterproofing materials. 

FRACTIONATION AND PURIFICATION OF COAL TAR CHEMICALS Largely because of the 

present competition among aromatic chemicals from petroleum (Chap. 38), interest in aromatics 

16"Tar acids," in the language of the tar distiller, represent phenol and its homologs, which are soluble in caustic soda. 

tV.,, 

*••>• , 

C

-,H 

H2 

• 3 

•V 
TABLE 5.4 Typical Composition of Light Oil from Gas 

Benzene 

Toluene 

Xylene and light solvent naphtha 

Acid washing loss (mostly unsaturated!) 

Heavy hydrocarbons and naphthalene 

Wash oil 

Total crude light oil 

Pure motor fraction 

Gallons per 

ton of coal 

1.85 

0.45 

0.30 

0.16 

0.24 

0.20 

3.20 

2.50 

Source: Lowry. Chemistry of Coal Utilization, vol. 2. 

p. 940: more detailed tabulation. Suppl. Vol.. pp. 633-642. 

Coal to Chemicals 77 

from coal tar has temporarily decreased (see Table 5.2 for main products). Also, svnthetic processes 

from acetaldehvde and ammonia are supplving the increased demands for pyridine, of which coal tar 

at one time was the sole supplier. This is also true of phenol (Chap. 34). In Europe.17 which has 

much coal and little petroleum, there is continued interest in coal chemicals. Table 5.6 lists some 

solid chemicals that couW be obtained from coal tar. The product of largest potential is phenanthrene 

(the second most abundant in coal tar), of which Franck estimates that 250,000 tons can be recovered 

in the Western world yearlv as soon as profitable uses can be found. This is based on a total recoverv 

of 10 million tons of crude tar and with a 50% yield. Anthracene, or rather anthraquinone (Chap. 

39), is the basis of many vat dyes, but here again it is cheaper to synthesize this compound (Chap. 39) 

from phthalic anhydride and benzene or preferably chlorobenzene. 

1 

ol and other 

. or "springbetween the 

It is washed 

anthracene, 

to about 15 

d roofs. For 

is "base tar" 

lilar tars are 

use of the 

•in aromatics 

in caustic soda. 

COAL TO CHEMICALS 

This section considers the rest of the processes listed in Table 5.1, except those designated for 

discussion in other chapters. In all cases further details are available in the references, especially in 

the monumental three volumes edited by Lowry. 

Solvent extraction of coals and lignites has been tried at temperatures below and above 300°C 

and with and without mild hydrogenation. Although various resins and waxes result, the processes 

have met only minor commercial acceptance.18 Alkaline hydrolysis19 has likewise been investigated, 

with meager results. Partial oxidation yields the tremendously important synthesis gas (Chap. 7). 

TABLE 5.5 Variation of Gas from Lose- and High-temperature Coal Carbonisation 

Cat 

co2 

CO 

CH« and homologs 

Coking temperature, 

500 C % 

9.0 

8.0 

5.5 

10.0 

65.0 

2.5 

Coking temperature, 

10OO C. % 

2.5 

3.5 

8.0 

50.0 

34.0 

2.0 

"Franck. The Challenge in Coal Tar Chemicals, Ind. Eng. Chem.. 55(5), 38 (1963). Manv coal chemicals described. 

'"Lowry, op. cit.. Suppl. Vol., p. 1089. 

Uwrv, op. cit.. Suppl. Vol., p. 1090. 
P.30 

(ty&nical PtwktcUS^ 

Subscription for: 

Rattan Corporation 

( 

7HnHH4<UlU Chemical Products 

Box 232 • Cortland, New York 13045 • (607)753-8700 
P.31 

PRODUCERS AMD CAPACITIES - CRESOLS AND CRESYLIC ACIDS - MILLIONS OF POUNDS 

NATURAL PRODUCERS LOCATION 1986 CAPACITY 

Merichem Houston, TX 120 

PMC Specialties Santa Fe Springs, CA 30 

Stimson Lumber Company Anacortes, WA 20 

Mobil Joliet, IL 4 

Crowley Tar Products Kent, OH 1 

SYNTHETIC PRODUCERS 

PMC Specialties Chicago, IL 30 

General Electric Plastics Selkirk, NY 200 

TOTAL Natural and Synthetic 405 

Sherwin Williams sold its para cresol plant to PMC Specialties in July 1985. Conoco closed 

a 50 mm lb., Newark, NJ, synthetic plant in May 1983. Diamond Shamrock closed a plant in 

Tuscaloosa, AL, and leases part to Merichem to manufacture naphthenic acid. General Electric 

produces synthetic 2,6-xylenol which is used to make polyphenylene oxide at Selkirk, NY. General 

Electric also produces 2,3,6-trimethyl phenol which is used as an antioxidant. PMC purchased 

the Ferro plant* in early 1986. 

END USES....The major end uses for cresols and cresylic acids are in wire enamel solvents, phenolic resins 

and agricultural chemicals. Para cresol is used to produce 2,6-di-tert-butyl-p-cresol (butylated hydroxytoluene or BHT). BHT is a leading antioxidant used in r er and plastics and to a lesser extent in food. 

Ortho cresol demand increased rapidly because of th: ise in consumption of epoxy cresol novai:- .': used 

to make computer chips. This led to an increase in pre*.* ..tion of synthetic o-cresol by*;such comp;. s as 

General Electric, Synthetic Chemical in the United Kingdom, and Nippon Steel in Japan. o-Cresol also 

used in the manufacture of MCPA, 4-chloro-2-methyl phenoxyacetic acid and 2,4-dinitro-ortho-cresol N0C). 

Meta cresol is used in the manufacture of thymol, an ingredient used by the pharmaceutical industry 

for cold and cough medicine. m-Cresol is also used in the production of synthetic pyrethroids for insecticide use in cotton for boll weevil control. 

Cresylic acid mixtures are used extensively as intermediates in the production of wire enamel solvents, phenolic resins, and phosphate esters. Various mixtures, mainly m-, p-cresols, or cresylic acids 

with high m-content are the preferred products for use in phenolic or epoxy resins. 

The market for phosphate esters has stabilized and now only represents about 8% of the demand for 

cresylics. In phosphate ester production, low ortho, meta-para and mixed xylenols are used extensively to 

produce a variety of grades for use as flame retardant plasticizers, fire resistant hydraulic fluids, and 

oil additives. 

Other end uses for cresols and cresylic acids include ore flotation frothers, disinfectants, fiber 

treatments, tanning agents, and metal degreasing agents. 

END USE PATTERN - 1985 ESTIMATED 

DERIVATIVE PERCENT 

Wire Enamel Solvents 

Phenolic Resins 

Agricultural Chemicals 

Phosphate Esters 

Disinfectants and Cleaning Compounds 

Ore Flotation 

Miscellaneous 

20 

18 

12 

9 

6 

5 

30 

MANUFACTURING....Cresylic acids and cresols are by-products of petroleum catalytic cracking or coal tar 

distillation. Natural cresols and cresylic acids are recovered by extraction of the spent caustic liquor 

used to wash petroleum distillates such as cracked naphtha. The cracked naphtha is passed through a vertical column and the filtrate containing phenol, cresols, and xylenols is extracted with sodium hydroxide. 

Further fractionation may be used to produce a variety of products tailored to meet specific requirements. 

Coal tar acids are recovered by extraction of the tar acid fraction, usually a light oil cut in the 

distillation process. The phenols, cresols, and xylenols are recovered in crude form by acidification of 

the aqueous solution usually by injecting carbon dioxide followed by gravity settling. The crude phenols 

are then fractionated to obtain phenols, cresols, and xylenol isomers. 

In the manufacture of synthetic cresols, there are several routes. The most commonly used process is 

the vapor phase methylation of phenol. PMC Specialties produces high-purity p-cresol by toluene sulfonation. Others produce cresol mixtures from cymene, obtained by the alkylation of toluene with propylene. 

ENVIRONMENTAL ASPECTS....Cresols and cresylic acids require a corrosive and poison label to meet DOT standards. Protective equipment is required. When handling, face shield, respirator, chemical gloves, and 

slicker suit also used. Exposure can cause damage to lung, liver, eyes, kidneys, and the nervous system. 

The EPA recently published a rule requiring cresol producers to initiate a testing program focusing on 

possible mutagenic and carcinogenic effects on exposure to three cresol isomers: ortho, para, and meta 

cresol, and cresylic acid. The first tier of test results will determine the need for ionger term assays 

and nuerotoxicity studies. Industrial sources indicate that a joint testing program is well underway to 

comply with all phases of the EPA requirements. 

To the best of our knowledge the information contained herein is accurate. However, we 

do not assume any liability whatsoever for the completeness or accuracy of this report. 
P.32 

(P/umi< '&IA4tuCt& m->ktt9flt\t,d 

NOVEMBER 198 5 

Previous Report — January 1980 

A Reporting Service of 

Chemical Products Corp. 

Cortland, New York 13043-0230 

CRESOLS & CRESYLIC ACIDS 

FOCUS....Cresols and cresylic acids are subcategories of a group of chemicals called tar acids. Tar acids 

consist of phenols and substituted phenols. These tar acids are recovered by extraction from chemical oil 

derived from either coal tar distillation or petroleum cracking. The extraction i6 usually accomplished by 

caustic solutions. The crude phenols are fractionated to obtain phenols, cresols, and higher boiling phenols and xylenols. These compounds or phenolic mixtures all have boiling points between 180-230°C. 

Cresols are defined as phenolic mixtures in which 505» of the material boils below 204°C. Cresols exist 

in several forms including ortho, meta, and para isomers. They are usually supplied as mixtures (meta, 

para) or as (ortho, meta, and para) but can also be purchased as individual isomers. 

Cresylic acids are defined as phenolic mixtures in which 50% of the material boils above 204°C. Cresylic acids include high boiling mixtures of cresol-xylenols, mixtures of xylenols and high boiling tar 

acids. In recent years, several companies including General Electric Plastics have started to produce synthetic alkylates such as 2,6-xylenols, ortho cresol, and cresylic acids. World demand for 2,6-xylenol is 

currently estimated at 120 thousand metric tons per year with General Electric manufacturing 100 thousand 

metric tons for making polyphenylene oxide (PP0). 

Cresols and cresylic acids are recovered by extraction of coal tars or petroleum naphtha from catalytic cracking. Production of the three cresol isomers, ortho, para and meta cresol and cresylic acid 

totalled 117.5 million pounds in 1985. Imports accounted for an additional 14.9 million pounds. Domestic 

production has declined steadily since 1974 when a high of 191 million pounds were produced. The decrease 

in output results from the decline in the production of phosphate esters produced from natural cresylic 

acids for use as flame retardant plasticizers and fire resistant hydraulic fluids. Over the past fifteen 

years, the trend has been toward the use of alkylphenols which are substitutes for the natural cresols 

used to make phosphate esters. The switch to synthetic phosphate esters was caused by performance and 

economic factors. The production of natural phosphate esters declined from 70 million pounds in 1970 to 

less than 10 million in 1985. Other factors affecting the decline are lower operating rates and increased 

efficiency at oil refineries and steel mills in recent years. These operating changes reduced the availability of spent refinery bottoms and coal-tars that can be fractionated for recovery of phenol alkylates. 

There have also been increasing environmental and health concerns about the use of natural cresols. 

OUTLOOK....the surplus of petroleum products will continue to be a factor in the availability of spent 

refinery bottoms and natural feedstocks. Industry forecasts indicate changes in demand for petroleum products will occur in 1989-90 which will increase the supply of natural feeds. The trend to produce selected 

grades of synthetic alkylates will continue as new production techniques are developed. Producers of specific grades of alkylates include Bayer, British Synthetic Chemical, Nippon Steel and General Electric. 

BHT (butylated hydroxytoluene), an antioxidant used primarily in rubber and plastics and manufactured 

from para cresol, will continue to decline in use as substitution of high molecular weight phenolic antioxidants are made. Also, the use of natural cresylic acids for phosphate ester production will continue to 

decline. The export market for cresols and cresylic acids will remain important. 

PRICING....Competition from synthetic cresols and cresylic acids will keep prices for the natural materials stable. Adequate supplies of all grades and depressed prices for petroleum feedstocks will also keep 

prices very sensitive to conditions of purchase. Depressed prices are expected to remain near current 

levels until 1988 or 1989. 

AVERAGE PRICE RANGE - CRESOLS AND CRESYLIC ACIDS 

Cents Per Pound - Tanks - Freight Equalized 

1960 1965 1970 1975 1980 1982 1983 1984 1985 1986 1988 1990 

Trade List 

o-Cresol 

m/p-Cresols 

p-Cresol 

Cresylic Acids-re 

SUPPLY AND DEMAND. 

Capacity 

Production 

o-Cresol 

Total Cresols 

Cresylic Acids 

Total Production 

Cresols-Cresylic 

16 18* 

22 18 

52 50 

•fined 

...Millions 

1960 

21 

67 

56 

Acids 123 

Synthetic Alkylates 

194 

20* 

47 

15' 

of Pounds 

1965 

203 

33 

71 

51 

122 

41* 

48 

72 

44 

614 

60 

125 

54 

....Estimated 

1970 

225 

23 

91 

98 

189 

1975 

250 

21 

93 

45 

138 

72 

61 

90 

49 

68 

65 

95 

52 

...Domestic U 

1980 

285 

30 

95 

30 

125 

1982 

325 

35 

80 

30 

110 

67 

68 

95 

53 

.S. 

1983 

405 

43 

75 

52 

127 

30 

65 

72 

65 

72 

100 100 

1984 

405 

55 

90 

40 

130 

50 

60 

1985 

405 

60 

118 

100 

65 

1986 

405 

65 

92 

28 

120 

110 

70 

75 

110 

75 

1988 

450 

73 

99 

. 31 

130 

130 

74 

85 

125 

85 

, 

1990 

450 

80 

106 

24 

130 

150 

AVAILABILITY....Several plant closings in recent years have been offset by the. entry of synthetic alkylates. Adequate capacity exists for all grades of cresols and cresylic acids. o-Cresol and 2,6-xylenol are 

growing at rates of 5-755 and 105. per year with adequate supplies available domestically and worldwide. 

In early 1986, Ferro Corporation sold its Productol Chemical Division to PMC Specialties Group Inc. of 

Rocky River, OH. Productol Chemical, with a plant in Santa Fe Springs, CA manufactures and markets alkylated phenols, cresylic acids and naphthenic acid. PMC produces synthetic materials in Chicago, IL. 
P.33 

CHEMICAL PROFILE 

CRESYLICS November 30,1987 

SUPPLY 

PRODUCER CAPACITY* 

Natural: 

Merichem, Houston, Tex 120 

Northwest, Anacortes, Wash 8 

PMC, Santa Fe Springs, Calif 30 

Synthetic: 

General Electric, Selkirk, N.Y 20 

PMC, Chicago, III ^30 

Total 208 

'Millions of pounds per year. Natural cresylics are coaltar- and petroleum-derived 

phenol, cresols and xylenols. PMC's synthetic plant makes p-cresol; General Electrics' makes o-cresol and xylenols. PMC acquired Productol's Santa Fe Springs 

facility in January, 1986. PMC has operated Sherwin-Williams' Chicago plant since 

July, 1985; acquisition of the plant was completed in September of this year. Profile 

last published 11/12/84; this revision, 11/30/87. 

DEMAND 

1986:100 million pounds; 1987:105 million pounds; 1991:110 million pounds 

(Includes exports; does not include phenol content). 

GROWTH 

Historical (1977-1986): minus 3.2 percent per year; future: 0 to 2 percent per 

year through 1991. ... -' 

PRICE 

Historical (1952-1987): High, 66c. per pound, cresylic acid, meta, para 

content 25 percent or less, tanks, frt. alld.; tow, 10.9c. per pound, same basis. 

Current: 55c. to 60c. per pound, same basis. 

USES 

Exports, 35 percent; antioxidants, 20 percent; phenolic, epoxy and novolac 

resins, 15 percent; wire enamel sblvent, 12 percent; phosphate esters, 5 percent; chemical intermediate, 5 percent; miscellaneous, including cleaning and 

disinfectant compounds and ore flotation, 8 percent. 

STRENGTH 

Antioxidants have benefitted from plastics growth, wire enamel use in motors 

from strong consumer spending, and resin use from a resurgence in US-based 

computer chip production. While other cresylics are well-balanced, p-cresol is 

currently snug. 

WEAKNESS 

Cresol-based phosphate esters have declined over the past several years. 

Ore flotation and cleaning compound use have been impacted by environmental 

concerns. Wire production, while currently on the upswing, has historically been 

falling. . — 

OUTLOOK 

Cresylics are generally very mature: while export opportunities are increasing, 

US growth prospects seem minimal. There is a potential, however, for availability 

of significant quantities of cresylic raw materials from the Great Plains coal 

gasification project that could eventually breathe new life into the market. 
P.34 

I 1 

ST-Ap - 00?39/>w£ 

1989 DIRECTORY OF 

CHEMICAL PRODUCERS 

UNITED STATES OF AMERICA 

Information in this Directory it for tho solo 

and privata usa of sponsors of tho 

Directory of Chemical Producers Program. 

RADIAN LIBRARY 

RESEARCH TRIANGLE PARK, NC 
P.35 

333 RAVENSWOOO AVENUE 

MENLO PARK, CALIFORNIA 94025 

(415) 859-3627 

FAX: (415)326-5512 

TWX. 910-373-2046 

TELEX: 334486 

Copyright O 1989 SRI International. Unauthorized use or reproduction of all or any part of this document is 

prohibited. Printed in U.S A 
P.36 

t98 9 DIRECTORY OF CHEMICAL PRODUCERS 

UNITED STATES PRODUCCrayon orange (See: Orange 15 in Organic Pigments under 

Pigments) 

Creatine hydrate 

Pfanstiehl Laboratories, Inc. Waukegan, Illinois 

Creatinine (1-MethyTglycocyamidine) (1-Methylhydantoin-2-

imide) 

Pfanstiehl Laboratories. Inc. Waukegan, Illinois 

Creosol (4-Hydroxy-3-methoxy-1-methylbenzene) (2-Methoxyp-cresol) (3-Methoxy-4-hydroxytoluene) (2-Methoxy-4-

methylphenol) (4-Methylguaiacol) 

Givaudan Corporation 

Chemicals Division Clifton, New Jersey 

p-Cresidine (m-Amino-p-cresol, methyl ester) (2-Methoxy-5-

methylaniline) (5-Methyl-o-anisidine) 

PMC, Inc. 

PMC Specialties Group Division Cincinnati, Ohio 

p-Cresidine sulfonic acid (5-Methyl-o-anisidine sulfonic acid) 

O-Cresol (o-Cresylic acid) (o-Hydroxytoluene) (2-Methyiphenoi 

(o-tolyj alcohol) 

Hilton-Davis Company 

p-Cresidine-o-sulfonic acid 

Bayer USA Inc. 

Mobay Corporation, subsidiary 

Dyes, Pigments and Organics 

Division 

Organics Department 

PMC, Inc. 

PMC Specialties Group Division 

Cincinnati, Ohio 

Bushy Park, South Carolina 

Cincinnati, Ohio 

m-Cresol (m-Cresylic acid) (m-Hydroxytoluene) (3-

Methylphenol) (m-Tolyl alcohol) 

Merichem Company Houston, Texas 

Neville-Synthese Organics, Inc. Oil City, Pennsylvania 

(m,p>-Cresol 

Merichem Company Houston, Texas 

Selkirk. New York 

Houston, Texas 

Chicago, Illinois 

Houston, Texas 

General Electric Company 

GE Plastics 

Merichem Company 

PMC, Inc. 

PMC Specialties Group Division 

(o,m,p)-Cresol 

Merichem Company 

p-Cresol (p-Cresylic acid) (p-Hydroxytoluene) (4-Methylphenoi 

(p-Tolyl alcohol) 

Bell Flavors & Fragrances inc. Northbrook, Illinois 

Oakland, New Jersey 

Merichem Company Houston, Texas 

PMC, Inc. 

PMC Specialties Group Division Chicago, Illinois 

p-Cresol, alkylated (See: Rubber Processing Chemicals) 

CresoMormaldehyde resins (unmodified) (See: Plastics ano 

Resins) 

CresoMormaldehyde sulfonate, sodium salt (See: 

Hydroxytoluenesulfonic acid, formaldehyde condensate, sodium 

salt) 

p-Cresol methyl ether (See: p-Methylanisole under Flavor and 

Fragrance Chemicals) 

o-Cresolphthalein 

Aldrich Chemical Company, Inc. 

Polysciences, Inc. 

Milwaukee, Wisconsin 

Warrington, Pennsylvania 

Cresotic acid methyl ester (See: Methyl cresotinate) 

m-Cresyl acetate (See: Medicinal (Pharmaceutical) Chemicals) 

p-Cresyl acetate (See: p-Tolyl acetate under Flavor and 

Fragrance Chemicals) 

Cresyl glycidyl ether (1,2-Epoxy-3-{tolyioxy] propane) 

(Glycidyl cresyl ether) 

Dow Chemical U.SA Freeport, Texas 

Cresylic acid 

General Electric Company 

GE Plastics 

Merichem Company 

PMC. Inc. 

PMC Specialties Group Division 

Stimson Lumber Company 

Northwest Petrochemical 

Corporation, division 

Selkirk, New York 

Houston, Texas 

Chicago, Illinois 

Santa Fe Springs, California 

Anacortes, Washington 

ADD TOTAL 

Annual Capacity 

(Millions of Pounds) 

na 

120 

30 

30 

•8 

188 

Raw Material 

Synthetic 

Petroleum 

Synthetic 

Petroleum 

Petroleum 

'Plant is currently shut down and up for sale. 

Note: Capacities from petroleum feedstock are for tar acids, including cresols, natural phenol, and^eme xylenols. They represent ability to produce tar acids,. 

provided feedstocks are available. tj, 

V • 

Source: SRI International estimates as of January 1, 1989. '• , 

m-Cresylic acid (See: m-Cresol) 

o-Cresylic acid (See: o-Cresol) 

p-Cresylic acid (See: p-Cresol) 

Cresylic acid-formaldehyde resins (See: Plastics and Resins) 

Cresylic acid, sodium salt (See: Sodium cresoxide) 

Cresylic dithiophosphoric acid 

American Cyanamid Company 

Chemical Products Division Linden, New Jersey 

542 SRI International 
P.37 

JCJ-ftF-MO 

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KIRK-OTHMER 

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ALLOSE 73 

or para-position give diphenylmethane derivatives on reaction with 

aldehydes which are important rubber antioxidants (see Antioxidants). 

Condensation of alkylphenols with formaldehyde and dimethylamine 

readily gives the expected Mannich bases. 

Alkylphenols condense under mild alkaline conditions with acrylate 

esters to give para-substituted propionates. Mild conditions are necessary for the nitration and halogenation of most phenols containing 

tertiary alkyl groups ortho or para to the hydroxyl group; otherwise, 

replacement of these groups or 2,5-cyclohexadienone formation can take 

place. Alkylphenols react readily with sulfur mono- and dichlorides 

giving, respectively, bisphenol disulfides and bisphenol monosulfides 

which are used as lubricating-oil detergents and antioxidants. 2,4,6-Trialkylphenols and halogens or nitric acid react to give the 2,5-cyclohexadienone derivatives. 

The only oxidation products that have been considered commercially, 

largely as antioxidants, are based on the coupling of 2,6-dialkylphenols 

to diphenoquinones by chemical oxidation or catalyzed air oxidation (see 

Polyethers). 

Manufacture 

The olefins used are propylene, 1- and 2-butene, isobutene, isopentene, 

isoheptene, diisobutylene, nonenes, dodecenes and styrene. The alkylation reaction takes place at or near atmospheric pressure in the presence 

of protonated acids or metal phenoxlde catalysts. Alkylations may also 

be performed over solid acidic clay or molecular-sieve catalysts. The 

nature of the products obtained in alkylation of substituted phenols, 

such as cresols and xylenols, depends to a large extent on the positions 

already occupied and the sizes of the alkyl groups as well as the size of 

the entering alkyl group. 

The ease of ring alkylation alkyl phenols follow the order tertiary > 

secondary > primary > alkyl. Ease of alkylation on the ring position is 

ortho > para > meta. On the other hand, the thermodynamic stability 

is just about the reverse of the above rates, ie, primary > secondary > 

tertiary and meta > para > ortho. 

Thus, ortho .-alkylation takes place readily even with mild metal 

phenoxide-type catalysts. More drastic conditions, eg, higher temperatures, stronger catalyst, and longer reaction time convert ortho-f-alkylphenols to the paraisomers and finally lead either to de-t-alkylation or 

isomerization to the meta-isomer. On the other end of the spectrum, one 

finds that meta-primary-alkylphenols are the most stable. Thus both 

coal tar (1000°C) with aluminum chloride catalysis (RT) produces a 2:1 

meta/para cresol isomer ratio. 

Alkylation-dealkylation with isobutylene was used to separate metafrom petra-cresol. This is based on the fact that p-cresol will di-f-butylate in the ortho positions giving the lower boiling derivative whereas 

m-cresol yields the higher boiling 2,4-di-_-butyl-5-methylphenol. (The 

6-position does not t-butylate owing to excessive steric hindrance). Some 

examples are shown in Table 1. Secondary alkyl groups, being more 

stable, are more difficult to remove from the ring than tert-alkyl groups. 

Acid catalysts used are the phosphoric acid on Fuller's earth, sulfuric 

acid, or oleum and aluminum chloride. 3-tert-Butylphenol is prepared by 

direct high temperature (190°C), reaction of phenol and isobutene, and 

by isomerization of the 2- or 4-isomers or mixtures. 

H.W.B. REED 

Imperial Chemical Industries Limited 

Reviewed by 

GERD LESTON 

Koppers Co., Inc. 

S.H. Patinkin and B_S. Friedman in GA. Olah, ed., FriedelCrafts and 

Related Reactions, Vol. 2, Part I, Intererience Publishers, a division of John 

Wiley & Sons, Inc., New York, 1964, pp. 75-97. 

R- Stroh and co-workers in W. Foerst, ed., Newer Methods of Preparative 

Organic Chemistry, Vol. 2, Academic Press, Inc., New York, 1963, pp. 337-359. 

M.W. Ranney, Antioxidants: Recent Developments, Noyee Data Corporation, 

Park Ridge, NJ., 1979. 

Table 1. Properties and Specification* of Important Alkylphenols 

Alkylphenol 

2-isopropyl-5-methyl-phenol( thymol) 

4-(_r(-butylph_nol 

5-methyl-2-(ert-butylphenol 

4-methyl-2*«ert-butylphenoi 

2-pheny lphenol 

4-phenylphenol 

2,4-dimethyl-6-£er r-butylphenol 

2.4-di-__r(.butylphenol 

2,6-di-fcrrbutylphenol 

4-octylphenol 

4,4'-i_opropylid_nediphenol {bisphenol 

A) 

2,4-diniethyl-6-(lmethylcyclohexyl)-

phenol 

nonylphenol 

4-methyl-2,6-di-_er(-butylphenol 

dodecylphenol 

2,2'thiobis(4-methyl-6--ertbutylphenol> 

4,4'-thiobis(5-methyl-2-<er<-butylphenol) 

2,2'-methylenebi_<4-methyl-6-_?*-M>utylphenol) 

2-methyl-4,6-di-«ert-nonylphenol 

2.2'*methylenebi_<4-methyl-6-(l methylcyclohexyllphenol) 

4,4'-methylenebis(2,6-di-«erf-butylphenol) 

octadecyl 3-(3,5-di-«**-f-butyl-4-

hydroxyphenyl)propionate 

l,l,3-tria<2-methyl-4-hydroxy-5-terr. 

butylphenylibutane 

tris<3,5-d_-«_rt-butyl-4-hydroxybenzyl) 

isocyan urate 

1.3.5-trimethyl-2,4,6-tri_<3,5-di-terf. 

butyl-4-hydroxyb_nzyl)benzene 

pentaerythlityl tetraJu_(3-(3,5-di-e_r(-

butyl-4-hydroxyphenyl)propionate] 

Mp, °C 

50.5 

99 

22 

51 

56-57 

159-163 

22 

52 

37 

81-8 3 

153 

70 

84-87 

Ifil 

130-132.5 

130 

155 

49-54 

183 

221 

244 

110-125 

Bp. 

°C/kPa ° 

231.8/101.3 

240/101.3 

244/101.3 

171/13.3 

241/101.3 

283-286 / 

101.3 

250/101.3. 

174/13.3 

264/101.3. 

190/1.1.3 

253/101.3. 

lfil/6.7 

280-302 / 

101.3 

220/0.53 

180/3.0 

295-320 / 

101.3 

265/101.3. 

190/13.3 

322-335• 

101.3 

217.II.1 3 

Solubility 

Water 

insol 

insol 

sl sol' 

si sol 

insol 

insol 

insol 

insol 

insol 

insol 

insol 

insol 

sl sol 

insol 

insol 

insol 

insol 

insol 

insol 

insol 

insol 

insol 

insol 

insol 

insol 

insol 

Hydrocarbons 

sol 

sl sol 

.sol 

sol 

sol 

sl sol 

sol 

sl sol 

sol 

slsol 

sl sol 

sol 

sl sol 

sol 

sl sol 

sol 

sol 

slsol 

.sol 

insol 

sol 

sol 

slsol 

sl sol 

sl sol 

sl sol 

"To convert kPa to mm Hg multiply by 7.50. 

"Forms hydrate CnH^O.jHjO, mp, 37°C. 

ALKYL PHOSPHATES. See Phosphoric acids and phosphates. 

ALKYL SULFATES. See Sulfuric acid and sulfurous esters. 

€ 

ALLANTOiN. See Uric acid. 

ALLENE. See Hydrocarbons. 

ALLERGENS. See Industrial hygiene and toxicology; Anti-asthmatic 

agents. 

ALLITOL See Alcohols, polyhydric. 

ALLOSE, C 6H , 2 0 6 . See Carbohydrates; Sugar. 
Ullmann's 

Encyclopedia of Industrial 

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Vol. M 

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About '.. 

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know how i 

Enzyklopddit 

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Encyclopedi. 

intoaconcis 

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P.42 

,.A8 

.ay et al.). 

.chene-Ma-

:h. 26(1976) . Machleidt, 

290. 

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harmacodyn. M. Matter). 6 (1956) 94. 

hmiedebergs ) 164. 

nacol. Che- 72 (1977) H. Bcrgcim, 

3710. 

id, Applied 

ler, J. Org. . A. Martin, 

Tner, A.G. i. 10 (1967) 

Chem. 16 

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hem. Ges. 63 . Chem. Soc. 

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74) 58. 

1963) 171. 

Forsch. 13 

i. 17 (1967) 

1967) 107. 

Forsch. 28 

Vol. A 8 

1 

*•* 

Cresols and Xylenols 25 

ovi'i'iuoriTED 

Cresols and Xylenols 

HELMUT FIEGE, Bayer AG, Leverkusen, Federal Republic of Germany 

1. Cresols 25 

1.1. Physical Properties 26 

1.2. Chemical Properties 27 

1.3. Formation and Isolation 28 

1.3.1. Isolation from Coal Tars 29 

1.3.2. Recovery from Spent Refinery Caustics 30 

1.4. Production 31 

1.4.1. Alkali Fusion of Toluencsulfonatcs ... 31 

1.4.2. Alkaline Chlorotoluene Hydrolysis ... 32 

1.4.3. Cymene Hydroperoxide Cleavage .... 33 

1.4.4. Methylation of Phenol 35 

1.4.5. Other Routes 38 

1.5. Separation of m- and p-Cresol 41 

1.5.1. Physicochemical Processes 41 

1.5.2. Separation via Addition Compounds . 42 

1.5.3. Separation via Ester or Salt 

Formation 43 

1.5.4. Separation by Nuclear Substitution ... 43 

1.6. Quality Specifications and Analysis ... 44 

1. Cresols [i]-[3] 

Cresol, methylphenol, C

7

H

8

0, M, 108.14, 

occurs in three isomeric forms: 

XcH, 

o-Cruol 

2-m«thylph«nol 

[93-48-7] 

& v 

m—Cresol p-Cresol 

3-m«U_ylph«nol 4-m*U_7lphenol 

[103-38-4] [108-44-3] 

Mixtures of m- and p-cresol and of o-, m-, 

and p-cresol are occasionally referred to in the 

technical literature as dicresol and tri- or isocre-

sol, respectively. 

Cresylic acids [1319'77-3] are mixtures of cre-

sols, xylenols, higher alkylated phenols, and pos-

sibly some phenol. Tar acids are cresylic acids 

obtained from tar. 

STADELBR first discovered cresol in cow's urine in 1851 

[4]. FAIRLIE and WILLIAMSON found it in coal-tar creosote 

1.7. Handling, Storage, and Transportation 44 

1.8. Uses 45 

1.9. Economic Aspects 46 

2. Xylenols 47 

2.1. Properties 47 

2.2. Isolation 47 

2.3. Separation 48 

2.4. Production 50 

2.5. Quality Specifications and Analysis ... 51 

2.6. Handling, Storage, and Transportation 52 

2.7. Uses 52 

2.8. Economic Aspects 52 

3. Environmental Protection 53 

4. Toxicology and Occupational Health .. 53 

5. References 54 

in 1854. (The word cresol, in which "creosote" and "phe-

nol" are combined, is partly explained by this fact.) Cresol 

was first synthesized in 1866 by GRIESS, who boiled diazo-

tized toluidine. All three cresol isomers were distinguished 

for the first time by ENGELHAROT and LATSCHINOFT in 

1869. 

Cresols and cresol derivatives (ethers and esters) are 

widely distributed in nature. They are formed as metabo-

lites of various microorganisms and ure found in the urine 

of mammals. Humans eliminate, on average, 87 mg of pcresol per day in the urine [5]. Cresol in its various forms is also detectable in the extracts and water vapor distillates of many plants, e.g., in jasmine flower oil, cassia flower oil, 

caster lily oil, and ylang ylang oil, in the floral oil of Yucca 

gloriosa, in peppermint, eucalyptus, and camphor oil, 

and in the essential oils of several plants of the genus 

Artemisia, of conifers, of oak wood, and of sandalwood. 

Small amounts of cresol are also found in certain foods and 

drinks, e.g., in tomatoes and tomato ketchup, cooked as-

paragus, certain types of cheese, butter oil, red wine, whis-

ky, rum, cognac, and other brandies [6], raw and roasted 

coffee, black tea, smoked foods, and tobacco and tobacco 

smoke. Considerable amounts of cresol may be formed and 

enter surface waten if forests are pyrolyzed by pyroclastic 

flow from erupting volcanorfas happened after the erup-

tion of Mount St. Helens in$980 (7). 

Cresols are important'chemical raw materi-

als. They were originally dbtained only from coal 
P.43 

26 Cresols and Xylenols Vol. A 8 

tar; after World War II, they were also obtained 

from spent refinery caustics. Since the mid1960s, they have been produced synthetically on 

an increasingly large scale. "Synthetic cresol" 

now provides ca. 60 % of the requirements of the 

United States, Europe, and Japan; only ca. 40% 

of the requirements are now met by "natural 

cresol," i.e., cresol from coal tar and spent 

refinery caustics. 

1.1. Physical Properties [1]!_p*H11] 

As pure substances, o- and p-cresol are 

crystalline; m-cresol is a viscous oil at room temperature. The cresols have a phenolic odor and 

are colorless, but become yellow to brown after 

a time. Because water dissolves freely in cresols, 

they absorb moisture from the-air. 

Physical data relating to the cresols have 

been compiled in Tables 1 and 2. Data concerning the temperature dependence of their thermodynamic properties are found in [8]-[ll]; many 

additional properties are contained in [10]. 

The solubility of the cresols in phenol and in 

many organic solvents, e.g., aliphatic alcohols, 

ethers, chloroform, and glycerol, is high. They 

are less soluble in water than phenol. The presence of other water-soluble organic compounds 

(e.g., methanol) raises their solubility in water 

and reduces the critical solution temperature 

[13]. Dissolved inorganic salts lower the water 

solubility of cresols. 

Table 1. Physical properties of pure cresols 

Property o-Cresol m-Cresol /j-Cresol 

Melling point at 101.3 kPa, "C 

Depression of nip by I mol% of impurity, "C 

Boiling point at 101.3 kPa, "C 

Density at 25 C (s or I). g/cm3 

at50°C(0 , g/cm3 

Viscosity at 50"C, mPa-s 

Refractive index al 50 "C 

Dielectric conslanl al 50 "C 

Specific conductance at 50 °C, S/cm 

Surface tension al SOT, N/m 

Dissociation constant at 25 "C 

Critical temperature, "C 

Critial pressure, MPa 

Critical density, kg/m3 

Heat capacity r al 25 "C (g), J mol"' K " ' 

c at25"C(i*or/). .lmo|-| K -• 

c•1,al 50"C(/), J mol"' K."' 

Enthalpy of fusion AW„ at mp. 101.3 kPa, kJ/mol 

Enthalpy of sublimation __#,_„ al 25 "C, 101.3 kPa, kJ/mol 

Enthalpy of vaporization A//„ at 25 "C, 101.3 kPa, kJ/mol 

<_/.„ at hp, 101.3 kPa. kJ/mol 

Enthalpy of combustion AW° al 25 "C, 101.3 kPa, kJ/mol 

Enthalpy of formation \H"r al 25 "C (.v or I), 101.3 kPa, kJ/mol 

M} at 25 "C (g), 101.3 kPa, kJ/mol 

Free energy of formation 6.G} at 25 "C (.. or I), 101.3 kPa, kJ/mol 

AC} at 25 °C (g). 101.3 kPa, kJ/mol 

Entropy Sa t 25 "C(s or/). 101.3 kPa, Jmol"' K."1 

Entropy S° at 25"C (g), 101.3 kPa, JmoP ' K"1 

Cubic expansion coefficient at 25 "C 

Solubility in water at 25 "C, wt% 

at 100°C, wt% 

of water in cresol at 25 °C, wt% 

at 100 °C, wt% 

Critical solution temperature in water, °C 

at % cresol, wt% 

Vapor density (air =1 ) j , 

Flash point (closed cup), "C .{J. 

Ignition temperature, "C V 

Flammability limit, lower, in air at 20**C, 101.3 kPa, vol% s • 

30.99 

0.596 

191.00 .„_. 

1.135 

1.0222 

3.06 

1.5310 

6.00 

0.43 xlO' 1 0 

34.4 xlO"6 

4.8x10" " 

424.4 

5.01 

384 

127.3 

154.7 

237.9 

15.830 

76.07 

-

45.222 

-369 6 

- 204.8 

- 128.7 

-55. 7 

-33. 0 

165.5 

352.8 ' 

2.6 

4.8 

13.4 

18.4 

164.8 

34 

3.72 

81 

555 

1.3 

12.22 

0.749 

202.23 

1-.03Q2 

1.0105 " 

4.17 

1.5271 

9.86 

63.4 xlO" 1 0 

33.4 xlO"6 

8.1x10-"* 

432.6 

4.56 

346 

124.6 

225.1 

235.0 

10.714 

-

61.76 

47.429 

-370 6 

- 194.2 

- 132.4 

-59. 2 

-40. 2 

212.7 

356.3 

0.759 xlO"3 

2.3 

5.3 

13.1 

20.8 

148.6 

36 

3.72 

86 

555 

1.0 

34.69 

0.915 

201.94 

1.154 

• 1.0116 

4.48 

1.5269 

10.18 

60.2x10"' ° 

'34.0x10"" 

5.4x10" " 

431.4 

5.15 

391 

124.6 

150.3 

233.3 

12.715 

73.98 

-

47.581 

-370 1 

- 199.5 

- 125.5 

-51. 0 

-31. 7 

167.4 

351.0 

1.9 

4.8 

15.8 

24.9 

143.7 

34 

3.72 

86 

555 

1.0 
Vol. A 8 Vol. A8 Cresols and Xylenols 27 

i after 

icrcsols. 

have 

bncemtthermofl]; many 

([10]. 

pi and in 

^alcohols, 

They 

be presnpounds 

Im water 

p'perature 

ithe water 

Table 2. Vapor pressure of pure cresols, for'/' 2. 260' C (in 

kPa)[8].[12] 

Temp., 

**C 

25 

50 

60 

80 

too 

120 

140 

160 

180 

200 

220 

260 

300 

340 

380 

o-Cresol, 

0.037 

0.25 

0.49 

1.57 

4.26 

10.10 

21.47 

41.72 

75.27 

127.6 

204.9 

471 

940 

1704 

2894 

m-Cresol, 

0.019 

0.12 

0.25 

0.86 

2.52 

6.36 

14.26 

29.01 

54.45 

95.52 

158.2 

378 

774 

1423 

2420 

p-Cresol, 

0.016 

0.11 

0.23 

0.83 

2.47 

6.29 

14.21 

29.07 

54.75 

96.24 

159.6 

388 

KK) 

1521 

2659 

and react with acyl anhydrides or acyl chlorides 

to give the corresponding tolyl esters, which are 

normally referred to as "cresyl" esters. Isocyanates react with the OH group to form urethanes. 

Substitution of the Hydroxyl Group. Under 

drastic conditions (420 °C, A1203), the OH 

group is replaced by ammonia, and the corresponding toluidine is obtained. If cresols are 

reacted with sulfur oxytetrafluoride at 150°C, 

with diphenylphosphine trichloride at 220 °C, or 

with phosphorus tribromide at 280 °C, the corresponding fluoro-, chloro-, or bromotoluene is 

obtained. Butylthiol in hydrochloric acid replaces the phenolic OH group by a thiobutyl 

group. Distillation with zinc powder gives 

toluene. 

["47.581 

x —3701 

.-199. 5 

•125.5 

£-51. 0 

'-31.7 

•-.167.4 

£351.0 

The cresols can be distilled with steam and 

form azeotropes with a number of compounds, 

e.g., decane, 1-decene, 1-undecene, dodecane, 

1,2,4,5-tetramethy lbenzene, divinylbenzene, ethylene glycol, diethylene glycol methyl and ethyl 

ether, diethylene glycol diethyl ether, ethylene 

glycol diacetate, benzyl formate, phenyl acetate, 

methyl benzoate, hexane-2,5-dione, 2-ocfanone, 

acetophenone, benzylamine, the toluidincs, and 

numerous pyridine derivatives. Vapor-liquid 

equilibrium data of the cresols with numerous 

other substances are compiled in [14]; those of 

m-cresol with carbon dioxide and nitrogen under 

pressure at 190-390°C are given in [15] 

(2-5 MPa) and [16] (2-25 MPa), respectively. 

1.2. Chemical Properties [2], [17] 

Acidity. The cresols are chemically similar to 

phenol. They are weak acids and dissolve in 

aqueous alkali to form water-stable salts known 

as cresolates. Therefore, they can be extracted 

into sodium hydroxide solution from solvents 

that are not miscible with water. Nevertheless, 

their acidity is so low (pK^ 10.1-10.3) that even 

hydrogen sulfide (pKa 7.2) and carbon dioxide 

{pK. 6.4) are able to liberate them from cresolates. Thus, they hardly dissolve at all in solutions of sodium carbonate or sodium hydrogen 

carbonate. 

Etherification and Esterification. The hydroxyl group can be etherified with alkyl halides, 

dialkyl sulfates, and toluenesulfonic acid esters. 

Hydrogenation. Hydrogenation in the vapor 

phase at 300-400 °C under pressure (up to 

8 MPa) in the presence of catalysts consisting of 

transition metals and aluminum oxide gives 

toluene (hydrodeoxygenation) [18]. Hydrogenolysis over catalysts at-400.-500 °C or purely thermally at 500-700 °C can bS*st>-cogtrolled that 

cresol is mainly demethylated to phenol (hydrodealkylation) [19]. Hydrogenation over Raney 

nickel or noble-metal catalysts under less severe 

conditions gives methylcyclohexanols or methylcyclohexanones. 

Oxidation. The cresols are sensitive to oxidation. Depending on the oxidizing agent, reaction 

conditions, and position of the methyl group, 

oxidative reactions, which occur by free radical 

mechanisms, lead to a large number of compounds such as hydroquinones, quinols, quinones, cyclic ketones, furans, dimeric and trimeric cresols, and tolyl ethers. Strongly oxidizing agents break down the phenol ring. 

After the hydroxyl group has been protected 

by esterification or etherification, the methyl 

group can be selectively mono-, di-, or trichlorinated, or selectively oxidized to a formyl group 

(e.g., with manganese dioxide or oxygen) or to a 

carboxyl group (with acid permanganate solution). Unlike the other two isomers, /?-cresol can 

be directly oxidized with oxygen to give phydroxybenzaldehyde, e.g., in methanolic sodium hydroxide in the presence of cobalt salts 

[20]. Alkali fusion of the cresols in the presence 

of leaJrbxide or manganese dioxide produces the 

corresponding hydroxybenzoic acids directly. 
tVol.A8 Vol. A8 Cresols and Xylenols 29 

9, [24] 

I on 

FRG 

0.12 

0.06 

0.12 

0.06 

0.06 

0.05 

0.47 

0.24 

coal [28], [29], oil shale [30], peat, wood [31], 

lignin [32], and other biomaluriuLs [33]. 

The yields of cresols, xylenols, and other phenols and their quantity ratio depend not only on 

the starting material, but also largely on the process conditions (especially the temperature and 

the residence time), the type of reactor, and the 

mode of operation. Hydrogenation provides the 

highest yields, low-temperature carbonization 

gives intermediate amounts, while high-temperature coking produces the lowest yields (Table 3). 

Small amounts of cresols, xylenols, and other 

phenol derivatives are also formed in the catalytic and thermal cracking (especially coking thermal cracking) of petroleum fractions [34]. 

At the present time cresols and xylenols are 

isolated from coal tars obtained in the. hightemperature coking process, low-tcmpcruturc 

carbonization, and Lurgi pressure gasification of 

coal (sec Table 3), and from spcnl refinery caustics. 

1.3.1. Isolation from Coal Tars 

The main source of tar cresols is the hightemperature coke-oven tar (composition and 

work up -• Tar and Pitch), obtained in the production of metallurgical coke by horizontal 

chamber coking of bituminous coal at 900-

1300°C [23]. This tar contains, on average, ca. 

0.4-0.6 wt% phenol, 0.8-1 wt% cresols, and 

0.2-0.5 wt% xylenols. In the United Kingdom, 

cresols arc also produced from low-tcmpcrature 

coal tars obtained in the production of smokeless 

fuels (semicoke) according to the Coalite process, where the content of C6 -C8 phenols is ca. 

10 times higher. Another source of cresols is provided by the liquid byproducts obtained by Sasol 

in South Africa in pressure gasification of bituminous coal by the Lurgi process, which are similar in composition to low-temperature tars. In 

addition, lignite tars are used in the German 

Democratic Republic, Czechoslovakia, the Soviet Union, and India [28]. 

When the starting product is high-lcmperature tar, the phenols are isolated by extraction 

with sodium hydroxide solution or, in the Lurgi 

phenoraffin process (-*-*• Tar and Pitch), from the 

carbolic oil that boils at 180-210°C, from the 

light oil, and from the filtrate of the naphthalene 

oil; where other coal tars are concerned the procedures are similar. The hydrocarbons and 

pyridine bases still present in the crude phenolate 

caustic are removed by distillation with steam. 

The crude phenol is then set free with carbon 

dioxide. Frequently, the phenolate caustics from 

coking plant effluents, which contain primarily 

phenol and cresol and only very small amounts 

of xylenols [35], are incorporated. The composition of the resulting crude phenol may, therefore, 

vary extensively. For example, the composition 

of crude phenol obtained in this way from German high-temperature coke-oven coal tar may 

be as follows [27]: 15 % water, 30 % phenol, 12 % 

o-cresol, 18% m-cresol, 12% p-cresol, 8% xylenols, and 5% trimethylphenols together with 

higher boiling phenols. 

After the alkali content of the crude phenol 

has been lowered from ca. 2% to ca. 0.3% by 

scrubbing with water, the crude phenol is dehydrated azeotropically and rectified under vacuum into the following fractions: phenol, o-cresol, 

w-/p-crcsol mixture, xylenol, and phenol tar. As 

the difference between the boiling points of mand p-cresol is very small (0.3 °C), these compounds are obtained as a single fraction, in 

which small amounts. o£_2.-6-xylenol and 2-ethylphenol are also present. The ratia.of w-cresol to 

p-cresol is ca. 60:40 for high-temperature tar and 

ca. 50:50 for low-temperature tar. 

Examples of firms that isolate cresols (and 

xylenols) from coal tar are the Koppers Co. and 

the Merictiem Co in the United States, Coalite & 

Chemical Products Ltd. and the Croda Synthetic Chemicals Ltd. in the United Kingdom, 

Riitgers-Werke AG and Chemisches Werk Lowi 

GmbH in the Federal Republic of Germany, 

CdF Chimie in France, and the Nippon Steel 

Chemical Co. in Japan. 

The scale on which cresols and xylenols are 

recovered from coal tar has decreased continuously over the past 25 years for the following 

primary reasons: the coke consumption of the 

iron- and steel-producing industry, which chiefly 

determines the supply of tar, has fallen; processes 

which lead to tars with lower cresol and xylenol 

contents are being increasingly used in coke production; and the tar output from gasworks has 

become insignificant due to the changeover to 

natural gas. 

The situation may change, however, because 

blast-furnace technology based on the use of 

high-temperature coke from bituminous coal as 

a reducing agent will retain at least its present 

importance, and because the gasification of coal 

to prodace synthetic natural gas and syncrude 
P.46 

30 Cresols and Xylenols 

will be expanded as the prices of oil ami natural 

gas rise. This would yield more low-temperature 

tar, in which the content of cresols and xylenols 

is much greater than in high-temperature cokeoven tar. 

1.3.2: Recovery from Spent Refinery 

Caustics 

In the United States, cresols and xylenols are 

obtained TYiainly from the naphtha fractions produced by catalytic and thermal cracking in the 

petroleum industry, which contain, on the average, ca. 0.1 % C6 -C8 phenols [34], [36]. In the 

scrubbing of the sulfur compounds contained in 

these fractions (hydrogensulfides, alkyl- and 

arylthiols) with concentrated alkaline solutions, 

a process known as "sweetening," the acid 

cresols and xylenols are also extracted. The composition of the spent cresylate caustics fluctuates 

widely, and they contain on the average 

20--25% C6-Ca phenols and 10-15% sulfur 

compounds. The caustics are collected by the reprocessing firms Merichem, Northwest Petrochemical, and Productol, and are reprocessed in 

central plants by a variety of processes. 

At the Northwest Petrochemical in Anacortes, Washington, the thiols in the alkaline 

solution are first oxidized with air to give disulfides, which arc then decanted as an oily layer 

[37]: 

ItSN-i + IfSNa + (1.5 0 , + 11/) • KSSIf i 2 NaOH 

The phenols are then precipitated from the 

aqueous alkaline phase in a packed column with 

a countercurrent stream of carbon dioxide (flue 

gas) and decanted. The phenols still present in 

the carbonate-hydrogen carbonate phase (2-

6%) are extracted with an organic solvent, from 

which they are extracted again with an aqueous 

alkaline phase, which is then returned to the column. A typical composition of the phenol mixture obtained in this way might be as follows: 

20% phenol, 18% o-cresol, 22% m-cresol, 9% 

p-cresol, 28% xylenol (all six isomers plus ethylphenol), and 3% higher phenols. This mixture is 

then separated by distillation into phenol, ocresol, w-/p-cresol mixture, and xylenols, or mixtures in which particular constituents predominate. 

The Merichem Co. of Houston, Texas, is the 

biggest processor of spent refinery caustics in the 

United States, and precipitates the phenols with 

Vol. A 8 

hydrogen sulfide, a waste product of the refineries in Houston [38], [39], instead of using 

carbon dioxide. After extraction with a solvent, 

the sulfide solution obtained in this process is 

concentrated in a triple-effect evaporator to give 

sodium sulfide for use in the paper industry and 

in ore dressing [39]. 

The water vapor condensate formed at this 

stage is stripped with natural gas to remove odorous compounds, after which it is passed to a 

cooling tower. The natural gas is then used as a 

fuel in the final process air incinerator. Before 

being introduced into the waste air incinerator, 

which is operated at ca. 1370CC, the process air 

from all of the other parts of the plant is 

scrubbed with alkaline solution. In addition, 

odor-neutralizing chemicals are sprayed alongside the plant area. All of the water at the plant 

(including rain water) is recycled in an integrated 

system. Water is released into the environment 

almost completely as water vapor from the cooling towers [39], [40]. 

According to the process operated until 1971 by the 

Pittsburgh Consolidated Chemical Co. [41], [42], the spent 

refinery caustics werejreated directly with flue gas containing 8-14% carbon dioxide.'From the crude phenol thus 

precipitated, a fraction boiling at 100-235 °C was removed 

by distillation and extracted continuously in a countercurrent of aqueous methanol-light naphtha. After removal of the final thiol and base residues with an ionexchange resin, the cresylic acids that had entered the 

aqueous methanolic phase were recovered by fractional 

distillation. 

In 1984, the "cresylics" capacities of Merichem, Northwest, and Productol were 55 000. 

15 000, and 10000 t/a, respectively [43]. However, these figures include phenol, the xylenols, and 

several other alkylphenols. In addition, Merichem no longer isolates cresylics exclusively 

from spent refinery caustics, but also works up 

crude phenols from coal tars of various types. 

The recovery of cresols and xylenols from 

spent refinery caustics has so far been confined 

to the United States. Because different refinery 

techniques are used in the Federal Republic of 

Germany, the' production of cresol-containing 

spent caustics is insufficient for economical reprocessing; or no spent caustics are produced at 

all because desulfurization is carried out differently, e.g., by hydrotreating. In the United States 

as well, the recovery of cresol from spent refinery 

caustics is stagnating or even receding because 

thi£refineries are likewise changing over either to 

hydrptreating or to UOP's Merox process, partly 

because the price of sodium hydroxide has risen 
P.47 

T 

• 

Vol. A 8 

very sharply in recent years. With the Merox 

process, substantial quantities of cresols remain 

in the gasoline, and considerably smaller 

amounts of spent caustics are obtained. 

1.4. Production 

Since 1965, when the recovery of cresols from 

coal tar and spent refinery caustics had become 

insufficient to meet the rising demand, these 

compounds have been increasingly produced by 

synthesis. The processes now in use are 

- alkali fusion of toluenesulfonates 

- alkaline chlorotoluene hydrolysis 

- splitting of cymene hydroperoxide 

- methylation of phenol in the vapor or liquid 

phase 

The first three processes start from toluene 

and were developed from the corresponding 

benzene-phenol syntheses (-<• Phenol); to some 

extent they are even carried out in converted 

plants that formerly produced phenol. In the fol-

lowing descriptions, attention will be primarily 

paid to the differences between these processes. 

The methylation of phenol is a process specifi-

cally developed to produce cresols and xylenols. 

Each process gives a different isomer distribu-

tion, and all are, therefore, of individual impor-

tance. 

1.4.1. Alkali Fusion of Toluenesulfonates 

[44], [45] 

The alkali fusion is used mainly to manufac-

ture p-cresgLand consists of four reaction steps: 

2CH,-C,H, + 2H.SO. 

•=i 2 CH,-C

<

H

4-S0J

H + 2 H,0 (1) 

2 CHJ-C.H.-SOJH + Na,SO, 

—. 2 CH,-C,H.-SO,Na + H,0 + SO, (2) 

2CH

)-C,H.-S0,Na-i-4Na0H —. 2CHJ-C,H«-ONa + 2Na,SO

, + 2 H.O (3) 

2 CHj-C.H.-ONa + SO, + H,0 

—.2CH

1-C<

H

<-OH*

f Na,SO, (4) 

2 CH.-C.H, + 2 H,S0

4 + 4 NaOH 

—. 2 CH.-C.H.-OH + 2 Na.SO, + 4 H,0 

The sulfonation of toluene (1) is normally 

carried out with concentrated sulfuric acid at 

120-130 °C and atmospheric pressure. To en-

sure that substantially all of the sulfuric acid has 

Cresols and Xylenols 

31 

been reacted, the water of the reaction is en-

trained with excess toluene vapor. The sulfonic 

acid mixture is neutralized with sodium sulfite 

(and/or sodium hydroxide) (2) and then fused 

with excess sodium hydroxide at 330-350 °C (3). 

The melt is introduced into water, the sodium 

sulfite filtered off, and the aqueous phase acidi-

fied with sulfur dioxide from reaction step (2) 

and/or with sulfuric • acid (4). This gives an 

aqueous phase containing sodium sulfite, which 

is returned to the neutralization unit (2), and a 

crude cresol phase, which is dehydrated by azeo-

tropic distillation. The plant and process are sim-

ilar to those formerly used in the synthesis of 

phenol by alkali fusion of sodium benzenesul-

fonate. The dehydrated crude cresol phase is sep-

arated by fractional distillation into phenol, o-

cresoi, m-/p-cresol mixture, and a residue con-

taining ditolyl sulfones, xylenols, higher phenols, 

and other compounds. The ditolyl sulfones are 

formed in the sulfonation; the phenols and xyle-

nols are formed in small quantities in the alkali 

fusion [46], [47]. See [46] for the mechanism of 

the fusion reaction. 

The distribution of the cresol isomers de-

pends mainly on the sulfonation conditions. 

Normally a mixture of the following composi-

tion is obtained: 6-12% o-cresol, 6-12% mcresol, 80-85%o p-cresol [44], [48]. After the ocresol has been removed by distillation, a 

p-cresol of ca. 90 % purity can be obtained by 

distillation. From this, p-cresol with a m-cresol 

content of only ca. 1 % can be isolated relatively 

easily by melt crystallization (see p. 41). 

A cresol yield of 80%, based on toluene, is 

possible [48]. The yield falls as the m-cresol con-

tent of the cresol mixture increases [44], [47]. 

Under kinetically controlled (mild) sulfona-

tion conditions and mild alkali fusion, it is pos-

sible to produce cresol mixtures with an even 

smaller content of m-cresol. It has been claimed 

that sulfonation with chlorosulfuric acid at 

33-45 °C gives a product free from m-cresol at a 

yield of 90 % (calculated on the basis of toluene) 

and with an o-/p-cresol ratio of 15:85 [49]. The 

sulfonation of toluene with sulfur trioxide -

sulfur dioxide mixtures at 25-50°C likewise 

leads to toluenesulfonic acid, mixtures almost 

devoid of the m-cresol isomejr, and which have an 

o-/p-isomer ratio as low a4J3:97 [50]. In the ab-

sence of a sulfur dioxide solvent, it may even be 

possible to obtain an o- and m-isomer content of 

only 0.5% when the processes carried out in a 

loop reactor at 0°C, and when gaseous S0

3

, di-
P.48 

32 Cresols and Xylenols Vol. A 8 

VS? 

luted with an inert gas, is introduced into the 

reactor at several locations [51]. The inert gas 

(waste gas) is not necessary if the process is carried out under vacuum [52]. 

Thermodynamically controlled sulfonation 

conditions (high temperature, long reaction 

time, and the use of a sulfonation mixture with a 

low water content) lead to an equilibrium containing ca. 5% o-, 54% m-, and 41% ptoluenesulfonic acid [53]. Alkali fusion of such 

- mixtures then gives an isomer distribution of ca. 

„'5% o-cresol, 56% m-cresol, and 39% p-cresol 

[47]. 

Technical-grade m-cresol can also be produced by toluene sulfonation according to a process used by ihc Honshu Chemical Industry Co. 

[54]. Steam at 165°C is introduced into an toluenesulfonic acid mixture rich in m-isomer obtained under thermodynamically controlled conditions as described above (isomerization for 

several hours at 190-200°C), whereupon o- and 

p-toluenesulfonic acid are hydrolyzed back to 

sulfuric acid and toluene. The toluene is distilled 

with the steam; m-toluenesulfonic acid with a 

purity above 90% remains, together with sulfuric acid. Side reactions during the isomerization 

and hydrolysis can be suppressed by adding sodium sulfate (5-10 mol%, calculated on the 

basis of sulfuric acid) to the sulfonation batch. In 

this way, removal of the sulfuric acid that is 

formed in the hydrolysis as a lower phase at ca. 

140-150 °C is also possible [55]. It is also possible to neutralize the hydrolysis mixture with concentrated sodium hydroxide solution, filler off 

the resulting sodium sulfate at 80 "C. introduce 

the solution of sodium ...-tolucncsulfonatc into 

a sodium hydroxide melt, containing 10-15% 

potassium hydroxide to facilitate stirring, at an 

initial temperature of 330 °C, and to fuse it at 

340 °C. 

The distillation of the crude cresol phase obtained after acidification gives m-cresol with a 

purity of up to 98 % in a yield of ca. 65 %, calculated on the basis of reacted toluene [55]. 

p-Cresol is produced according to the toluene sulfonation process by SheVwtp-Williams, 

(capacity 15 000 t/a) in the United States, by 

Croda Synthetic Chemicals Ltd. (capacity 

12000 t/a; sulfonating agent is S03) in the 

United Kingdom, and in Japan (ca. 5000 t/a). 

m-Cresol is produced in this way by the Honshu 

Chemical Industry Co. (ca. 2400 t/a). A plant 

designed to operate the Honshu process also 

reported to be capable of producing 3000-

5000 t/a of m-cresol has been built in India by 

Gujarat Aromatics. 

The toluenesulfonic acid-cresol process is 

relatively simple as regards the plant required. Its 

primary drawback is the unavoidable formation 

of sodium sulfite in aqueous solution. At Croda 

Synthetic Chemicals, the sodium sulfite is upgraded into a product suitable for the paper industry [56]. At Sherwin-Williams, sodium sulfite is oxidized with air to form sodium sulfate 

[57], but p-cresol is still present in the aqueous 

sulfite solution (3000-5000 ppm); to avoid 

stripping, thereby causing an odor problem in 

the neighborhood of the plant, the solution is 

first passed through columns of activated carbon 

to adsorb the cresol. The activated carbon is regenerated every 24 h with 10% sodium hydroxide solution. The amount of p-cresol recovered in this way is sufficient to pay for the additional installations [58]. 

1.4.2. Alkaline Chlorotoluene Hydrolysis 

The hydrolysis process is important in the 

production of cresol-with a high m-cresol content, and is used in the FederalRepublic of Germany by Bayer AG, the world's largest manufacturer of synthetic cresols (capacity more than 

30000 t/a). 

In the first reaction step, a mixture of o- and 

p-chlorotoluene in a 1:1 ratio is produced by 

chlorinating 1 mol of toluene with 1 mol of 

chlorine in the presence of iron(III) chloride and 

disulfur dichloride (-+ Chlorinated Hydrocarbons). 

CH,-C,H, + Cl, •--.. CHj C.H.-CI + HCl 

In the next reaction step, this mixture is hydrolyzed with excess sodium hydroxide solution (2.5-3.5 mol/mol) at 360-390°C and 280-

300 bar (28-30 MPa) [59]. 

CH,-C6H4-C1+ 2NaOH 

—. CH,-CtH4 -0Na + H,0 + NaCl 

The exothermic reaction is carried out continuously in high-pressure tubes several hundred 

meters long; the tubes are made of nickel steel to 

withstand the corrosive action of the reaction 

mixture. Separation of the components, which 

are introduced via a mixing chamber, is prevented'by causing the reaction mass to flow at 

high Telocity, with frequent changes in the direction ofr

 How; finally, the reaction mixture is 

homogeneous. 
P.49 

Vol. A8 Cresols and Xylenols 33 

fishyTjolu1280-

S+NiCI 

The cresol in the resulting sodium cresolate 

solution is set free by neutralization; for this pur-

pose the hydrochloric acid formed during chlori-

nation can also be used. The coproduct sodium 

chloride can be returned to the chlor-alkali elec-

trolysis. 

For economic reasons, it is important that 

the starting materials are produced at locations 

sufficiently close to one another that conveyance 

through pipelines is possible. The technology of 

the process largely corresponds to that of the 

Dow-Bayer chlorobenzene-phenol hydrolysis 

process [60]. In the manufacture of cresols, how-

ever, the amounts of the byproducts formed are 

larger than in this process: these include ditolyl 

ethers [bis(mcthylphenyl) ethers], in particular, 

tolylcresols [methyl(methylphenyl)phenols], and 

small amounts of toluene, phenol, benzoic acid, 

and off-gas from cracking (methane and hydro-

gen). The removal of small amounts of phenol by 

azeotropic distillation, e.g., with chlorotoluene, 

is dealt with in [61]. 

Whereas it is hardly possible to control the 

scale on which tolylcresol is formed, the forma-

tion of ditolyl ether can be controlled via the 

temperature, the residence time, and the sodium 

hydroxide concentration; in addition, the scale 

on which this byproduct is formed can be min-

imized by recycling. This possibility arises from 

the fact that ditolyl ethers are hydrolyzablc -

though less easily than the homologous di-

phenyl ether. Therefore, if the reaction is opti-

mally controlled, yields of ca. 80%, based on 

chlorotoluene, are attainable. However, ditolyl 

ether has several uses, e.g., as a heat transfer 

medium (Diphyl DT), as an electrical insulant 

(Baylectrol 4800; replacement for polychlori-

nated biphenyl), and as a precursor for tanning 

agents. Therefore, ditolyl ether is no longer re-

cycled; indeed, the conditions may be adjusted to 

increase the selectivity for this compound. 

The process gives very pure cresols, i.e., 

products that are almost free from other com-

pounds. The o-, m-, and p-isomers are present in 

a ratio of ca. 1:2:1. This ratio differs from that 

of the chlorotoluene input because isomerization 

via aryne intermediates is assumed to occur [62], 

[63] under the severe conditions of hydrolysis. 

After the o-cresol has been distilled, a m-jpcresol mixture containing ca. 70% m-cresol is 

obtained. 

The plant can also be operated on pure o- or 

p-chlorotoluene. The hydrolysis of p-chloro-

toluene then gives a 1:1 m-/p-cresol mixture, and 

hydrolysis of o-chlorotoluene gives a 1:1 o-\mcresol mixture. Technically pure m-cresol is obtainable from the latter by distilling off the ocresol. 

Hydrolysis of chlorotoluene without substantial isom-

crizalion is possible under milder conditions (200-350°C ) 

with alkali hydroxide [63], [64], alkali carbonates [65], or 

ammonium hydroxide [66], or with alkali acetate or alkali 

propionate solution [67] in the presence of copper or cop-

per compounds. These processes are not used industrially. 

1.4.3. Cymene Hydroperoxide Cleavage 

The synthesis via cymene hydroperoxide, 

which is also known as the cymene-cresol pro-

cess, permits the production of in- or p-crcsol 

from the corresponding cymenes (isopropyltol-

uenes). It is unsuitable for the production of ocrcsol. The process consists of three reaction steps: 1) Toluene propylation and cymene isomerization 

CH3 ,i ao-e

o oc 

+ CH,=CH-CH, > 

• s^ AltVHQ 

CH. 

CH3 3' / •CH 

o-Cymene I

 VCH_ 

CH 

/ \ 

H3C Ctt, 

^ 

CH, 1 /»* 

CH. 

m—Cymene 

2) Oxidation of cymene to cymene hydroperoxide 

Cll3 

CH, 

+ 0, 

/ CH 

(Air) 

'CH3 

3) Peroxide cleavage 

CH3 

(Alk-li) 

CH. 

ICH, 

C-OOH XCH, 

on 

+ CHg-CO-CHj 

OH 

m/p-Cresol 

By comparison with the analogous Hock 

cumene process (-> Acetone), the cymene-

cresol process has a lower space-time yield, in-

volves considerably more costly distillation proce-

dures, necessitates more extensive treatment of 

wastewater, and gives a jfroduct yield that is 

20-30% lower. The reasons-for this are as follows: i 

p—Cymene *•_. 
P.50 

34 Cresols and Xylenols Vol. A8 

1) All three isomers, o-, m-, and p-cymene, 

are formed in the propylation of toluene. Of the 

three isomers, o-cymene not only is hardly oxidized but also increasingly inhibits oxidation of 

the other cymenes [68] as its concentration in the 

isomer mixture rises. For continuous oxidation, 

the o-cymene content of the cymene mixture 

must be kept below 10% at all times [69], [70]. 

Thus, cymene mixtures are needed that contain 

as little o-cymene as possible. 

The lowtst w-cymcne content is that of a 

cymene mixture in thermodynamic equilibrium 

[70], [71]. Aluminum chloride must be used to 

reach this equilibrium as quickly as possible 

[72]-[74]. The isomer ratio obtainable with aluminum chloride under practical conditions is ca. 

3 % o-, 64 % m-, and 33 % p-cymene. As the ocymene concentration rises while the oxidation is 

in progress, a large amount of the cymene must 

be returned to the first stage of the process after 

the cymene hydroperoxide and other byproducts 

have been separated, so that the o-cymene content can again be lowered to ca. 3% through 

isomerization on aluminum chloride. The diisopropyltolucncs formed as byproducts in the 

alkylation and separated by distillation are also 

returned to this isomerization step. 

2) The oxidation rates of the cymenes are 

lower than that of cumene. In addition, the 

cymenes can be oxidized up to a peroxide content of only ca. 20%, whereas oxidation levels 

exceeding 30% arc possible with cumene. The 

proportion of unreacted cymene that must be 

distilled and returned to the reaction is, therefore, greater than in the cumene-phenol process. At higher degrees of oxidation, the formation of byproducts from excessive oxidation of 

the isopropyl group to dimethyl(tolyl)methanol 

and methylacetophenone is greatly increased. 

3) The methyl group of the cymenes is likewise oxidized; for details of the mechanism of 

p-cymene oxidation, see [75]. The ratio at which 

the methyl group and isopropyl group are subjected to oxidative attack may be as high as 1:4 

[76]. As the primary peroxide is less stable than 

the tertiary peroxide, it is more easily converted 

into secondary products (isopropylbenzyl alcohol, isopropylbenzaldehyde, cuminic acid). A 

more important drawback is that in the highly 

exothermic acid cleavage, in addition to isopropylphcnol, 1 mol of formaldehyde is formed per 

mole of primary peroxide still present; because 

formaldehyde is able to bind up lo 2 mol of cresol as a formaldehyde resin, the cresol yield is 

substantially diminished. Moreover, the presence of resin makes the product more difficult to 

work up. Various solutions to the problem have 

been proposed: (1) selective decomposition of 

the primary peroxide during the actual oxidation 

by adding catalytic amounts of picoline, pyrrole, 

thiophene [77], or triphenylphosphine [78]; (2) 

selective hydrogenation of the primary peroxide 

over a noble-metal catalyst [79] after the oxidation in a separate stage of the process (before the 

acid cleavage) or decomposition by passing the 

primary peroxide over a magnesium aluminate 

catalyst [80] or treatment with sodium hydroxide 

and heavy metals [81]; (3) extraction of the primary peroxide [82]—[85]. However, it is simpler 

to dissolve the products resulting from methyl 

group oxidation continuously and as fully as 

possible in excess alkali solution present during 

the actual oxidation itself [68], [69], [86]. The 

organic acids present in the spent caustics (ca. 

0.5 kg of cuminic acid, toluic acid, phthalic acid. 

and other products per kilogram of cresol) are 

largely precipitated during the acidification and 

can be removed by filtration. Additional 

removal from the filtrate.(wastewater) is possible 

by extraction [87]. "" ""• -

According to another suggestion, hydrogen peroxide 

should be present during cleavage of cymene hydroperoxide lo cresol [88]; alternatively, this cleavage could be 

effected under mildly hydrogenating conditions [89]. These 

measures decrease the extent of yield-lowering side reactions undergone either by the primary peroxide or by its 

secondary product, formaldehyde. 

4) The reaction mixture after acidic peroxide 

cleavage contains not only cresol, acetone, and 

unreacted cymene, but also isopropenyltoluene, 

2-tolylpropanol, isopropylbenzyl alcohol, isopropylbenzaldehyde, methylacetophenone, isopropylphenol, and numerous other compounds. 

The separation of these byproducts is relatively 

expensive because of their large number, their 

similar boiling points, and the formation of 

azeotropic mixtures [90]. 

Cymene-cresol plants, in which cymene mixtures are used and which have a nameplate capacity of 20 000 t/a each, have been operated in 

Japan by Mitsui and Sumitomo since 1969. The 

product has a m- and p-cresol content of more 

than 99.5%o and a m-/p-ratio of 60:40. The 

acetone coproduct is of high quality [91]. 

Ufoure p- or /;i-cymene is used, the high cost 

of recycling and isomerization necessitated by 

the presence of o-cymene is eliminated, and pure 

p- or to-cresol can be obtained directly. For ex-
P.51 

Vol. A 8 Cresols and Xylenols 35 

ample, until 1972 the Hercules Powder Co. oper-

ated a plant at Gibbstown in the United States 

for the manufacture of p-cresol from p-cymene 

obtained from natural terpenes [92]. 

Owing to the close proximity of the boil-

ing points of the cymene isomers (m-cymene 

175.1 'C, p-cymene 177.1 ''C, o-cymcnc 178.3 "C, 

at 101.3 kPa), the m-cymene, at most, may possi-

bly be isolated at reasonable cost from the 

cymene mixture resulting from the propylation 

of toluene (see above) [74]. However, both pure 

m-cymene and pure p-cymene can be isolated 

according to UOP's Cymex process on p-

cymcnc-sclcctivc 13X molecular sieves by using 

toluene as desorption agent [93]. The pro-

cess corresponds to UOP's Parex process for 

ihc isolation of p-xylene from C

8 aromatics 

(-•Xylene). A cymene-cresol plant, based on 

the UOP and Hercules Powder technologies, for 

the manufacture of pure m-cresol and p-cresol 

[for the antioxidant 2,6-di-.e//-butyl-4-methyl-

phenol (BHT)] is being constructed in China 

[94]. If in th

e Cymex process only one isomer, e.g.,. 

p-cymene, is required, the m-/o-cymene mixture 

leaving the adsorption column, which is impov-

erished with regard to p-cymene, can be re-

isomerized and returned to the separator [95]. 

Since it is less important in this case to have the 

lowest possible o-cymene content, the isomeriza-

tion (and the alkylation) can, for example, be 

carried out on phosphoric acid-aluminum oxide 

catalysts at 370 °C instead of using aluminum 

chloride [95]. 

In the manufacture of **i-cresol, •n-cymene can also be 

obtained by selective cracking of the p-cymene present in 

cymene mixtures with a low orlho isomer content. Cleav-

age of p-cymene (and to a lesser extent lhal of o-cymcnc) 

to toluene and propylene is accomplished al 300-400 "C on 

shape-selective ZSM5 zeolites [96] that are particularly 

selective in the MgO-modified I__T-ZSM5 form [97]. A 

further, technically less attractive way of isolating rncymene consists in complexing with anhydrous hydrofluoric acid-boron trifluoride at temperatures below - 40

 ;

C [98]. 

1.4.4. Methylation of Phenol 

Synthetic cresol, especially o-cresol, and xyle-

nol are now produced largely by methylation of 

phenol with methanol in the presence of cata-

lysts. 2.6-Xylenol is produced almost entirely by 

this method. 

The process consists of only one reaction 

step, but is based on phenol, which is relatively 

expensive; the separation of products from the 

reaction mixture is also costly. This is partly be-

cause the boiling points of several components 

are very near one another, and partly because in 

some cases the purity of the product must meet 

very strict requirements. 

The reaction can be carried out either in the 

vapor phase or in the liquid phase. 

Methylation in the Vapor Phase. Currently 

vapor-phasc methylation is used exclusively to 

manufacture pure o-cresol and/or pure 2,6-

xylenol: OH 

6 

• CHjOH 

OH OH 

CH3 

+ HJJO 

A

*

tf

2M = -104 kJ/mo l 

. CHjOH H3C

N-jkv^CH3 

\S HjO 

A#»_ 

Side reactions: 

CH30H —-. 

CO + HjO -

CO + 3 H

2 -

CO + 2 H

2 A/f ^ 

—"*"• COg + Hg tmH^gm 

= -48 kJ/mol 

-91 kJ/mo l 

-41 kJ/ mol 

CH« + HjO itH^ **** -206 kJ/mol 

At atmospheric or slightly elevated pressure, 

a superheated mixture of the vapors of phenol, 

methanol, and water is passed at a liquid hourly 

space velocity (LHSV) of 1-2 h" ' over a metal 

oxide catalyst fixed in a multitubular reactor of 

stainless steel at a temperature of 300-460 °C 

[99]-[101]. The reaction temperature required 

depends on the nature of the catalyst and on the 

desired composition of the product. The temper-

ature is permitted to deviate from this level by 

only a few degrees. 

The heat of the reaction is dissipated by boil-

ing organic heat transfer media [102], by circu-

lating salt melts [100], or through the generation 

of high-pressure steam [101]. The slight loss of 

catalytic activity that occurs in the course of time 

is compensated by raising the temperature'ac-

cordingly. Carbon deposits are removed from 

time to time by burning. The presence of water in 

the feedstock mixture suppresses the decom-

position of methanol, extends the regeneration 

cycle, and prolongs the lifetime of the catalyst 

[103], [104], which may then endure for several 

thousand hours. % 

The product mixture leaving the reactor gives 

up some of its heat to the feedstoak mixture in a 
P.52 

36 Cresols and Xylenols Vol. A 8 

heat exchanger, and is then condensed. The uncoiulensable reaction products formed from Ihe 

decomposition of methanol (H2, CH4, C02 , and 

CO) are used as fuel gas in steam production. 

Aqueous methanol is first distilled from the 

liquid reaction product and then recycled. Water 

remaining in the product is then removed either 

by azeotropic distillation with toluene [102] or as 

an azeotropic mixture with unreacted phenol 

[101]. In the latter case, it is necessary to strip the 

phenol from the wastewater. The dehydrated 

mixture is-then fractionated into phenol ether, 

phenol, o-cresol (> 99.5%), and 2,6-xylenol in 

an additional series of highly efficient distillation 

columns operated continuously under vacuum. 

The phenol ether-phenol fraction is recycled. 

The distillation residue, which contains, among 

other compounds, 2,3-, 2.4-, and 2,5-xylenol 

and 2,4,6- and 2,3,6-trimethylphenol. is usually 

burned as a fuel oil. If the catalyst has high ortho 

selectivity, pure (99.5%) 2,6-xylenol can be obtained directly. If that is not the case or if the 

reaction conditions are too severe (high temperature, long residence time), the 2,6-xylenol fraction will contain m- and p-cresol, which must be 

removed by special methods (cf. 49). The ratio of 

o-cresol to 2,6-xylenol can be controlled by altering the methanol-phenol ratio, and if the ocresol is recycled, 2,6-xylenol comprises the sole 

product. Over an extended production time, the 

yield (selectivity) of o-cresol and 2,6-xylenol, calculated on the basis of reacted phenol, is 

90-95%. 

With regard to the use of a fluidized-bed 

reactor for this reaction, see [105], [106]. Vaporliquid equilibrium data for the alkylation product arc given in [107], and details of the distillation in[108]-[110]. 

Magnesium oxide catalysts, in particular, are 

used. They require relatively high operating temperatures (420-460"C), but are so ortho-selective that m- and p-cresol are hardly formed, even 

at 540 'C [111]. The activity (phenol conversion), 

as well as the ratio of 2,6-xylenol to o-cresol and 

the ortho selectivity depend on the conditions 

under which the magnesium oxide is produced 

[112]—[114]. These properties can be further improved by combining magnesium oxide wilh other oxides, such as those of manganese [113], 

[115], copper [113]-[115], titanium, uranium, 

zirconium, chromium [116], and silicon [117]. At 

440 °C and at a liquid hourly space velocity 

(LHSV) of 2.0 h "' the continuous reaction of a 

mixture of phenol, methanol, and water in a 

1:4:2.4 molar ratio over a MgO catalyst thus 

gives a phenol conversion of ca. 82%, and a 

molar ratio of 2,6-xylenol, o-cresol, p-cresol, 

2,4-xylenol, and 2,4,6-trimethylphenol of 69.5: 

23.0:0.05:0.8:6.6. If the catalyst also contains 

ca. 1 % of copper, the conversion rate is 89%, 

and the corresponding molar ratio of the products is 73.3:18.9:0.06:0.07:7.0. The waste gas 

volume is in both cases 0.5 mol per mole of 

reacted phenol [114]. The mechanism of ortho 

methylation is discussed in [118]. 

With manganese oxide catalysts, the methylation can be carried out at ca. 420 °C [119]; on 

chromium oxide catalysts, at ca. 390 °C [120] — 

[122]; and on catalysts based on vanadium oxide 

[123], [124] or iron oxide [125]-[130], at ca. 

350

 CC, provided that these oxides are combined 

with smaller amounts of other oxides (e.g., of 

Co, Ni, Zn, Al, Ga, Si, Ge, Sn, Pb, Bi, Mg, and 

Na) or with one another [131]—[134]. These 

mixed oxide catalysts show excellent ortho selectivity and give a very high 2,6-xylenol/o-cresol 

ratio and virtually no p-cresol. At phenol/ 

methanol molar ratios of ca. 1:5-6 and liquid 

hourly space velocities'(*LH§\Q of ca. 1 h"' they 

permit almost complete conversion of phenol, 

with 2,6-xylenol yields of ca. 95% (calculated on 

the basis of phenol). Combination with other 

metal oxides also extends the catalyst lifetime 

(especially if alkali-metal compounds are added) 

and diminishes the extensive decomposition of 

methanol typically seen with manganese, chromium, vanadium, and iron,.oxide catalysts. In 

spite of this measure and the addition of water 

vapor (generally 1-2 mol per mole of phenol). 

1-2 mol of methanol are usually lost by decomposition for every mole of 2,6-xylenol manufactured. The proposed methods for reducing the 

loss include the addition of sulfur dioxide, hydrogen sulfide, nitric oxide, carbon monoxide, or 

carbon dioxide to the feedstock mixture [135], 

recycling a portion of the cracking gas [136], and 

introducing the methanol [137] or phenol at different parts of the .reactor [138]. Relatively little 

methanol is decomposed on Fe203 catalysts 

doped with silicon oxide and magnesium oxide 

[128]. For the mechanism of the reaction on 

mixed oxide contacts, see [139], [140]. 

y-Aluminum oxide catalyzes the methylation 

of phenol at a temperature as low as 300-320 °C. 

Under-rthese conditions, at a methanol:phenol 

molarTatio of 1:2, and at a liquid hourly space 

velocity (LHSV) of 1 h"1, o-cresol, 2,6-xylenol, 

and m-^p-cresol mixture are formed in a molar 
P.53 

Vol. A8 

ratio of ca. 82:17:1, wilh a total selectivity of 

97% and a phenol conversion of 33% [141]. In-

greasing the methanol:phenol ratio and recy-

cling the o-crcsol enables the ..-crcsol:2,6-

xvlenol ratio to be shifted toward 2,6-xylenol 

[142]. On y-AI

2

0;), unlike oilier methylation cata-

lysts, methanol is scarcely decomposed under the 

conditions described above. In addition, this cat-

alyst must be regenerated only once in ca. 

1000 h. and has a working lifetime of several 

years [143]. Its disadvantage is that to prevent 

the formation of significant quantities of other 

di-, tri-, and tetramethylphenols, the phenol con-

version rate must not substantially exceed 60%, 

which means that relatively large amounts of the 

product must be worked up and recycled. In 

addition, extensive operations, e.g., extractive 

distillation with diethylene glycol [142], are nec-

essary to free the 2.6-xylenol from the p-cresol 

that is unavoidably formed on this catalyst. 

Below 300'C. increasing amounts of anisole 

are formed on y-Al

2

0

3

; however, because ani-

sole is isomerized to cresol at elevated tempera-

tures [144], [145]. only a small amount (< 2.5%) 

is present in the reaction mixture under the pre-

viously mentioned conditions. As the tempera-

ture and residence time are increased, the rate of 

phenol conversion on Al

2

0

3 rises

, but the ortho 

selectivity falls. This is also basically true of oth-

er catalysts. Instead of o-cresol and 2,6-xylenol, 

increasingly large amounts of in- and p-cresol, 

other xylenols, multimethylphenols, and methyl-

benzenes, especially hexamethylbenzene, are 

formed [146], [147]. Demethylation occurs above 

500'C [148]. Increasing the temperature also re-

sults in the formation of larger amounts of 

gaseous cracking products, and accelerates the 

carbonization of the catalyst, thus necessitating 

more frequent regeneration. 

The reaction kinetics and the choice and cal-

culation of an optimum multitubular reactor for 

phenol methylation on -/-Al

2

0

3 ar

e discussed in 

[149] — [151]. Industrial plants are described in 

[99] and [142]. 

Aluminum oxides with sirong acid sites [152], 

silica-alumina [118], [153], zeolites [153]-[156], 

aluminum phosphates [147], [158], and phosphoric 

ticid-kicselgitlir [158] have enhanced isomeriza-

tion and transmethylation properties. Therefore, 

they lead to products with a relatively high m/p 

content, especially if the temperature is simul-

taneously raised to ca. 450

 C

C. In addition, at a 

temperature of 250-300 °C, shape-selective 

Cresols and Xylenols 37 

zeolites [154] [156], e.g.. of the HKY type [154], 

and also phosphoric acid-kieselguhr [158], 

show remarkably high selectivity for p-cresol, 

giving a m-/p-cresol mixture with p-cresol con-

tents of ca. 85% [154] or 77% [158], respectively. 

Titanium dioxide also shows para selectivity 

[158]. As alternative

s to methanol, methylbenzenes [160], 

[161], dimethyl ether [162], methylamine [163], methane 

[164], carbon monoxide-hydrogen mixtures [165], and 

formaldehyde-hydrogen mixtures [166] have been pro-

posed as methylaling agents. 

Methylation in the vapor phase is utilized by 

General Electric in the United States (capacity 

ca. 10000 t/a o-cresol and 70 000 t/a 2.6-xy-

lenol) and in the Netherlands (ca. 4000 t/a ocresol and 16000 t/a 2,6-xylenol); by Croda Synthetic Chemicals in the United Kingdom (ca. 

8000 t/a o-cresol and 2,6-xylenol); and in Japan 

by Nippon Crenol (joint venture of Asahi Chem-

ical and Nippon Steel Chemical; 5000 t/a o-

cresol and 10000 t/a 2,6-xylenol) and Gem-

Polymer (joint venture of General Electric and 

Mitsui; 2300 t/a o-cresol and 18000 t/a 2,6-

xylenol). The facilities of Conoco and Koppers 

in the United States were closed down (tem-

porarily) in 1983 for market reasons. Cindu, 

Riitag, and Midland Yorkshire Tar Distillers' 

(CRM) plant in the United Kingdom has been 

taken over by Croda. Vapor-phase methylation 

plants arc said to be in operation in the USSR 

[143] and in Czechoslovakia [150]. 

Methylation in the Liquid Phase. Results sim-

ilar to those achieved in the vapor phase are 

obtained if the oxide catalysts (particularly 

V-Al

2

0

3

) are suspended in a phenol-methanol 

mixture and heated in an autoclave to 300-

400°C [167]-[169]. The mixture of phenol and 

methanol [170] or of o-cresol and methanol [171] 

can also be passed as a liquid over a -/-A1

2

03 

catalyst forming a fixed bed in a tube reactor. At 

350"C and a phenol:methanol molar ratio of 

0.7:1, the pressure is ca. 35 bar [170]. 

According to a process operated by Chemi-

sches Werk Lowi, Federal Republic of Germany, 

phenol and an equimolar amount of methanol 

are reacted in an autoclave at 350-400 °C in the 

presence of 2-3 wt% aluminum methylate, with 

the water of the reaction, together with some of 

the methanol, being distilled through a small col-

umn. After the catalyst residue hasten re„ 

moved by filtration, the product is worked up by 

distillation. Methanol, anisole, and phenol are 
P.54 

38 Cresols and Xylenols Vol. A8 

recycled. The yield of cresols and xylenols is ca. 

80% [172], calculated on the basis of reacted 

phenol (ca. 60%). The main product is o-cresol; 

m- and p-cresol, 2,6-, 2,4-, and 2.3-xylenol, and 

trimethylphenols are also formed. The ratio of 

the products can be adjusted by altering the phenol .methanol ratio, the temperature, and the 

residence time. The presence of bases (e.g., pyridine) increases the conversion [173], whereas 

that of acids raises the proportion ofp-cresol and 

2,4-xylenol in the product [174]. Aluminum phenolate can also be used as a catalyst [175]. If 

necessary, the process can be operated in a multipurpose plant, the capacity of which may be ca. 

2000-3000 t/a. 

Union Rheinische Kraftstoff AG operates a 

process in the Federal Republic of Germany that 

uses liquid-phase catalysts [176], [177], preferably aqueous zinc halide-hydrogen halide solutions [178], at 200-240 °C and pressures of ca. 

25 bar (2.5 MPa). After the reaction, the organic 

components are separated from the aqueous catalyst phase by extraction with benzene or cyclohexane, washed with water several limes, and 

worked up by distillation. The catalyst solution 

is united with the washing water, concentrated, 

and recycled [179]. The main products are ocresol, p-cresol, 2,4-xylenol, and 2,6-xylenol. At 

a phenol: methanol molar ratio of 1:0.6, yields of 

up to 98%o arc obtainable, calculated on ihe 

basis of reacted phenol. Compared with other 

processes, this has the advantages not only that 

p-cresol and 2,4-xylenol are obtained in considerably larger quantities, but also that, provided 

the reaction conditions are carefully harmonized, the p-cresol is almost free of m-cresol. The 

extent of para substitution increases with the 

methanol content of the feedstock mixture, but 

the yield falls. The process requires materials 

that are highly resistant to corrosion, e.g., a reactor lined with tantalum. The plant has a capacity 

of ca. 16000 t/a. The product ratio is controllable within certain limits. As an example, the 

o-cresol, p-cresol, 2,4-xylenol, and 2,6-xylenol 

ratio can be 7:5:2:1. 

Transmethylation and Isomerization. After 

phenol has been added to the methylphenol residues either from the methylation of phenol or of 

different origin, or to 2,6-xylenol for which there 

is no other use, reaction can occur in ihc presence 

of alkylation catalysts to give a product consisting mainly of o-cresol, together with m-jpcresol. The reaction may proceed either in the 

vapor phase or in the liquid phase; the temperature is 400-500°C. Catalysts are aluminum 

oxide [180], chromium oxide-aluminum oxide 

[181], silica-alumina [182], metal oxide-iron 

oxide [183], ormagnesium oxide-tungsten oxide 

[184]. In the case of 2,6-xylenol, this transmethylation, accompanied by isomerization, can also 

be accomplished without a catalyst in the vapor 

phase at 550-600 °C or, batchwise, in the liquid 

phase at 420-470"C [185]. In this way, the ocresol yield from the methylation of phenol can 

be raised. 

Owing to the temporary lack of demand for 

o-cresol, opportunities for isomerizing it to mand p-cresol have been investigated. The results 

formerly obtained with aluminum chloride [186], 

[187], aluminum fluoride, boron trifluoride, aluminum silicates, or aluminum oxide were unsatisfactory [187], [188] because resinification 

and disproportionation to phenol, dimethylphenols, etc. occurred in addition to isomerization. 

Isomerization without substantial disproportionation is possible, however, on silica-alumina 

zeolites of the ZSM. groups at a temperature of 

ca. 400°C and o-cresol conversioh's'of 40-50%, 

/..-/p-cresol selectivities of 90% and an m:p ratio 

of 7:3 are possible [189]. 

1.4.5. Other Routes 

The rising demand for cresol has stimulated 

the development of numerous syntheses, especially those that lead selectively to certain cresol 

isomers. It appears, however, that these processes are not yet being used industrially. 

Gulf Oxychlorination. A cresol synthesis analogous to the Raschig phenol synthesis cannot be 

carried out satisfactorily under industrial conditions: at the temperature needed for oxychlorination in the vapor phase (5), toluene is oxidized to 

a considerably greater extent than benzene, and 

only low rates of toluene conversion are, therefore, possible. 

CH3-C6H5 + HC! + 0.5 Oj —- CHj-C,H4-CI + H,0 (5) 

CHj-C.H.-Cl + H,0 —. CHj-C„H4-0H + HCl (6) 

In a process developed by ihe Gulf Research Development Co., these disadvantages are avoided by oxychlorinating the tolirffie with aqueous hydrochloric acid and 

oxygen al a tcrffljerature of ca. 100°C in the presence of 

catalytic amounts pf nitric acid and a palladium or copper 

salt [190], [191]. At toluene conversion rates of 80%, 
P.55 

Vol. A8 Cresols and Xylenols 39 

primarily o- and /.-chlorotoluene are obtained in a 2:1 

molar ratio and wilh a selectivity of > 95%. 

The subsequent hydrolysis of the chlorotoluene mix-

lure is oarricd out in ihe vapor phase at 400-450°C, as in 

ihe Raschig process, but over improved catalysts, such as 

lanthanum phosphate that may be activated wilh copper 

[l.2|. At a chlorotoluene conversion of 20%, ihc cresol 

selectivity is ca. 95%. The isomer ralio differs from lhal 

given by the processes already being used industrially. A 

large amount of o-cresol is obtained in addition lo/.-cresol 

containing sonic »r-crcsol. 

If the hydrochloric acid set free in the hydro-

lysis step (6) is returned to the oxychlorination 

reactor, the process becomes equivalent to the 

oxidation of toluene with oxygen. This fact, to-

gether with the high conversion rates and selecti-

vities, makes the process interesting. Commer-

cial exploitation of the process necessitates the 

extensive recycling and piaces severe demands on 

the resistance of the plant to corrosion. 

The Gulf oxychlorination process is equally 

applicable to xylenes, and is, therefore, also suit-

able for the manufacture of xylenols. 

Oxidative Decarboxylation of Methyibenzoic 

Acids. As in the Dow process for the manufac-

ture of phenol from benzoic acid, methyibenzoic 

acids are decarboxylated to cresol when an air-

steam mixture is passed through their melt at 

200-240 °C in the presence of copper and mag-

nesium salts [193]. 

CH3 6" COOH + l/

2 0j 

OH + C02 

By comparison wilh the manufacture of phenol, ihe 

cresol process is more complex and 10-15% less selective 

(48). This is due partly to the fact thai cresols have higher 

boiling points; in consequence, optimal conlrol of Ihe reac-

tion is difficult, and a greater amount of lar is formed [193]. 

In addition, the simultaneous successive oxidation of the 

methyl group leads to numerous byproducts [194]. Oxida-

tion in the presence of benzoic acid has been proposed [195] 

as a mean of preventing the sublimation of methyibenzoic 

acid. 

Better results are achieved when a methyibenzoic acid-

steam mixture is oxidized in the vapor phase with oxygen -

nitrogen mixtures over mixed catalysts al a temperature of 

ca. 300°C [196], [197]. Thus, the reaction of a mixture of 

/•-methyibenzoic acid, water, oxygen, and nitrogen (molar 

ratio.of 1:18:1:9) al 300"C over a Mo-V-Cu-Zn-Na 

oxide catalyst supported on y-AI,Oj is reported to give a 

m-crcsol selectivity of 90% al a methyibenzoic acid conver-

sion rate of 80%; as byproducts. 2% toluene, 5% bis-

(methylphcnyl)-bis(mclhylphenyl) ether mixture, and 3% 

of additional carbon dioxide are formed [197]. 

The process could be of interest in the manu-

facture of pure ///-cresol. since only ///-cresol is 

formed from both the ortho and the para forms 

of methyibenzoic acid [48], [193]. m-Methyl-

benzoic acid gives (in the liquid phase) o- and 

p-cresol in a 1:2 ratio [198], [199]. Regarding the 

mechanism and kinetics, see [193], [194], and 

[200], respectively. 

The required methyibenzoic acids can be 

obtained by oxidation of the corresponding 

xylenes, which are, however, more expensive 

than toluene. 

Baeyer-Villiger Oxidation of p- or oMethylbenzaldehyde. This route leads to o-cresol 

or, more interestingly from the practical aspect, 

specifically to p-cresol. Hydrogen peroxide re-

acts with excess formic acid to give performic 

acid (7), which oxidizes p-methylbenzaldehyde 

top-tolyl formate (8); hydrolysis (9) then leads to 

p-cresol and formic acid. __ HGOOOH + H_0 (7) 

O-CHO 

(8) 

(B) 

Several variants ol" ihe process have been developed 

[201]-[203]. The most favorable process was probably in-

vented by Mitsubishi [2()4|. Hydrogen peroxide (1.2 mol; 

90%) is added to a mixture consisting of 1 mol of pmelhylbenzaldehyde. 14 mol of formic acid, and ca. 10% 

(4.5 mol) of water. The temperature of ihc mixture is main-

tained al 60 -90'C: ihe heal of the reaction is removed by 

reflux condensation under vacuum. Because of the pres-

ence of water, formate is hydrolyzed; aflcr a reaction lime 

of 1 li. the /'-mcthyllx-iizaldcliydc conversion rale is 100% 

and the p-cresol yield is 85%. If, instead of 90% hydrogen 

peroxide, performic acid is used, or if the process is carried 

out in the presence of a solid acid (zeolite or ion-exchange 

resin), the yield rises to 90-92%. The product is worked up 

by distilling the formic acid. Apart from the additional 

amount formed in the process, the formic acid, which has 

a concentration of ca. 90 %, is recycled. The p-cresol is then 

isolated from the residue, which still contains 10-20% of 

high-boiling constituents [204]. 

The starting material, p-methylbenzalde-

hyde, can be produced from toluene and carbon 

monoxide by the so-called MGC PTAL process 

developed by Mitsubishi [205]. It is an inter-

mediate in the manufacture of terephthalic acid. 

Nucleus Hydroxylation. The direcwfiydroxyl-

ation of toluene (or xylene), e.g., with, oxygen 

[206], hydrogen peroxide [207], [208], inorganic 
P.56 

40 Cresols and Xylenols Vol. A8 

peroxo compounds [209], or organic peroxides 

[210], [211], in the presence of various catalyst 

systems (Friedel-Crafts catalysts, transitionmetal compounds, or irradiation), has been extensively investigated. 

According lo Rhone-Poulenc , the most successful results so far have been obtained with 85 % hydrogen peroxide in the presence of a large amount of Irifluoroinethancsulfonic acid and a small amoun t of phosphoric acid (for 

complexing metal ions) [212]. 

CH, 

6" | + HgOj 

CH3 

_^°^^jf(

 + 

„0H 

CH3 

• 20 K 

OH 

1 

At — 20 to — 15"C and a molar ratio of H 2 0 , , 

toluene. CFjSOjH , and H^PO^ofca . 1:10:17:0.04. (--and 

/•-cresol are obtained in a 2:1 ratio in 80 % yield (calculated 

on ihc basis of hydrogen peroxide) al a toluene conversion 

rate of 10.6%. One of the problems is the recycling of the 

very expensive irilluoromclhancsulfonic acid. 

Work carried out by UO P indicates lhal relatively 

good results are obtainable with hydrogen fluoride, which 

is less expensive and easier to handle industrially than trifiuoromclhanesulfonic acid, in the presence of carbon dioxide. With 30 % hydrogen peroxide at 0"C and al a molar 

ratio of H 2 O j , toluene, H F, an d CO , of 1:10:70:10, o- and 

/--cresol are obtained in a 2:'l ratio in 67 % yield, based on 

hydrogen peroxide, in addition lo a small amount of .**-

cresol. m-Xylene gives mainly 2,4-xylenol, p-xylene mainly 

2.5-xylenol, and o-xylene mainly 2,3- and 3,4-xylenol [213]. 

The effect of the carbon dioxide is nol fully understood, bul 

this compound acts to some extent as an internal coolant. 

On titanium-modified zeolites, o-. «/-. and p-crcsols in 

a 14:11:75 ratio are formed in a yield of at least 40% , 

based on H,0 2 , when a mixture of H,0 2 , water, toluene, 

methyl isobutyl ketone, and titanium zeolite (preireated 

with HjPO J is heated under reflux in a mass ratio of 

1:7:17:10:2.6(214]. 

ICI has developed a cyclic process equivalent to the 

oxidation of toluene with peracetic acid, which gives yields 

of up to 95 % of an o-/p-cresol mixture, free of the meta 

isomer, with a cresol content of 92% . The "catalyst " in the 

reaction is iodotoluene. This is oxidized by peracetic acid lo 

iodosyltolucnc, which without isolation reacts with lolucne 

and sulfuric acid to form ditolyliodonium hydrogen sulfate. Hydrolysis is effected by diluting the reaction mixture. 

Cresol is produced; iodotoluene is simultaneously regenerated and recycled [215]. 

All processes involving nucleus hydroxylation are unsatisfactory for several reasons; for 

example, the cresols must be isolated from very 

dilute solutions, and considerable amounts of 

auxiliaries and unreacted starting materials need 

to be recycled with as little waste as possible. 

Oxidative Methylation of Toluene. In the USSR, a pilot 

plant has been operating in which toluene is oxidized adiabatically in a lube reactor at 700 750 "C and with conlact 

time of 0.2-0.5 s with oxygen in the presence of methane 

and steam (molar ratio 1:1-2:10-20:2-6) [2161. [217]. 

CeHj-CH-jCH.,-* CeHj-CH-CHj 3* 

CjHj-CH, + 0 2 + CH4—^CgHgOH + C^-Cg^-O H 

CeHe 

At a toluene conversion of ca. 45% , 0.52 t of styrene. 

0.25 t of benzene, ca. 0.11 t of phenol, and ca. 0.06 t of 

cresol are obtained per ton of toluene [218], [219]. Thus, if 

the process were to be used on the scale customary for 

petrochemical operations, it should be possible to produce 

considerable amounts of cresol by the "direct oxidation" of 

toluene. 

Hock Reaction of Toluene Derivatives. As in the 

cymene-cresol process, other toluene hydrocarbons can be 

peroxidized and cleaved to give cresol and the corresponding carbonyl compound. Particular interest has been shown 

in toluene derivatives lhal give p-cresol and are more readily accessible than p-cymene, e.g., ethylidenebis(p-methylbenzene) (coproduct: p-methylacetophcnone) [220], [221], 

4-methyl-cyclohexylbenzene (coproduct: cyclohexanone) 

[222], andp-xylcne(coproduct: formaldehyde) [223], [224]. 

Oxidation of xylene in the presence of acelic acid gives the 

corresponding cresyl acetate, which can be hydrolyzed to 

form cresol [225]. 

Hydrogenation of N,N'-Dialkylaminomethylphenols. 

The reaction of phenol with paraformaldehyde and, e.g.. 

piperidine in methanol at a 2:1:1:100 molar ratio at ca. 

10 °C gives a mixture of.piperidinomethylphenols. which 

without isolation is directly hydrogenated at 120-130°C 

and 1 MPa over a palladium-carbon catalyst: 

OH OH 

<^f> Uotlumol K^> ^ \ / Pd/C 

o and p 

1_0-130»C 

1 MP. 

OH 

'Q- C H 3 + H O 

o/ps 1 : 2 

o-Cresol and p-cresol in a 1:2 molar ratio are obtained 

in a yield of ca. 90%, based on reacted phenol, or of about 

75%, based on the formaldehyde input. In addition, some 

2,4-xylenol is formed (2-5%) without m-cresol [226]. The 

yield is lower (65-70%) if dimethylamine is substituted for 

piperidine. 

Diels-Alder Ring Closure of Isoprene and Vinyl Acetate. The Diels-Alder route leads selectively to p-crcsol in 

three reaction steps: (1) Isoprene (1 mol) reacts with vinyl 

acetate (20 mol) in the presence of 1 % hydroquinone in an 

autoclave al 180°C; (2) the reaction product, 1-mcthylcyclohcxene-4-yl acetate, is saponified; and (3) finally, the 

l-methylcyclohexen-4-ol is dehydrogenated catalytically to 

p-cresol [227]: 

.OCOCHj 

•jy 

OCOCH3 KOH^Q H 

JT 

Reflux 

1 h 

sio-c HC \ ^ 

OH 
P.57 

Vol. A8 Cresol

s and Xylenols 

41 

High yields are claimed lo be possible when ihe starling 

materials arc recycled. 

. Carbonylation. 2-Methallyl chloride, acetylene, and 

carbon monoxide in acetone as solvent give ***-cresol in 

74% yield at room temperature. 

CH, 

CH

2=C-CH2 -C

1 + HC=CH + CO 

OH 

Nl(CO),. Nil. M«0 

"'' L K 

CH3 

Fe, thiourea 

OH 6 * HCl 

The catalyst consists of tetracarbonylnickel, sodium 

iodide, iron powder, and thiourea; magnesium oxide neu-

tralizes the hydrochloric acid formed [228]. 

FromToluidincs. Under severe conditions, toluidinesin 

the presence of acidic catalysis (H

3P04

, HCl, ZnCl

2

, BFJ 

can be hydrolyzed io form the corresponding cresols [229], 

[230]. Higher yields can be achieved by boiling the diazo-

nium salts obtainable from toluidines [231], [232]. Continu-

ous operation of the process is described in [233]. 

Hydrodealkylation of Xylenols. Xylenols can be de-

methylated lo phenol and cresols with hydrogen under 

pressure, either thermally al 600 700"C [19] or on metal 

oxide catalysts at 400-500'C [234]. Simultaneous de-

oxygenation enables BTX aromatics (BTX = benzene-

toluene-xylene) to be produced at the same time. In this 

way, additional cresols can be produced, if necessary, from 

ihe xylenol fractions lhal are formed on a large scale in the 

gasification and hydrogenation of coal and other pro-

cesses. 

1.5. Separation of m- and /.-Cresol [24] 

Only o-cresol can be separated as a pure 

product by distillation from mixtures of the three 

cresol isomers. m-Cresol and p-cresol are ob-

tained as a single fraction because the difference 

between their boiling points is too small for sepa-

ration by distillation, even when carried out un-

der vacuum. 

1.5.1. Physicochemical Processes 

Crystallization. According to the melting 

point diagram for m-/p-cresol mixtures (Fig. 1), 

it is possible to obtain, at normal pressure, pure 

p-cresol from mixtures containing more than 

58% p-cresol, and pure m-cresol from mixtures 

containing more than 89 % m-crcsol. Mcta/para 

mixtures containing 42-89% of 7?i-cresol cannot 

be separated by crystallization al normal pres-

sure because m- and p-cresol exist as a molecular 

compound in a 2:1 molar ratio within this con-

centration range. 

(p-Cresol) 

20 -am 60 

Cresol fraction, % • 

80 100 

(m-Cresol) 

Figure I. Liquid-solid phase diagram of /*•- and p-cresol 

mixtures under pressure [235] 

The range within which p-cresol can be, iso-

lated by crystallization can be extended by ap-

plying pressure (Fig. 1); simultaneously the 

crystallization temperature and also the p-cresol 

yields, relative to crystallization at normal pres.; 

sure, are raised [235]. 

Crystallization is of practical importance as a 

technique for the separation of pure p-cresol 

from m-/p-cresol mixtures of high p-cresol con-

tent obtained from syntheses or other processes. 

Up lo now. this method has generally been 

carried out at normal pressure. In Japan, a high-

pressure crystallization technique known as the 

Finecry process, in which a liquid m-/p-cresol 

mixture is introduced into a high-pressure vessel 

of the piston cylinder type and crystallized 

adiabatically at 200 MPa, has been recently de-

veloped for industrial use by Kobe Steel. After 

the mother liquor has been drawn off and the 

plant decompressed, the p-cresol emerges as a 

pure crystalline product. The computer-con-

trolled crystallization-decompression cycle lasts 

2-5 min [236]. It has been reported that a plant 

for the manufacture of 500 t/a of p-cresol is to be 

constructed for Sumitomo Chemical in Japan 

[237]. 

Adsorption. Alkali metal-modified or al-

kaline earth metal-modified zeolites of type X, A 

[238], L, or ZMS5 [239], and also titanium diox-

ide [240], adsorb p-crcsol more strongjy than mcresol. Thus, one can separate m-/ps(cresol mixtures in an adsorption column and dissolve them 

again with a suitable desorbing liquid such as an 
P.58 

42 Cresols and Xylenols Vol. A 8 

aliphatic alcohol [238] or a ketone [241]. A continuous version of this process has been developed by UOP [93]. It is known as the Cresex 

process and is used industrially in the United 

States by Merichem. The separating efficiency of 

the process not only depends on ihc adsorbent, 

but is also inlluenced lo a large extent by the 

desorbent. With 1-hexanol. for example, only 

one isomer.ciher in- or p-cresol, can be isolated 

at a purity of ca. 99% in a single operation (1 

column); the purity of the other isomer obtained 

is only ca. 91%. With 1-pentanol, however, a 

mixture containing ca. 69% m-cresol and 31 % 

p-cresol can be separated into an extract containing 98.9% ofp-crcsol and a raffinatc containing 

99.2% of m-cresol in a single operation [93]. 

Phenolic impurities present in the cresol feed, 

e.g., o-cresol, o-ethylphenol, 2,4-, 2,5-, and 2,6-

xylenol, migrate into the m-cresol during the adsorptive separation; hence, only pure p-cresol 

can be obtained in one operation if these impurities are present in significant quantities [93]. 

Other Methods. The separation of m-/pcrcsol mixtures by azeotropic distillation with 

benzyl alcohol [242] or by countercurrent extraction with selective solvents (aqueous methanolgasoline) [243] has acquired no practical importance. This also applies to dissociative extraction 

and distillation processes that exploit Ihc higher 

dissociation constant (higher acidity) of///-cresol 

in relation to that of p-cresol. Dissociative extraction uses systems consisting of aqueous sodium hydroxide solution [244], [245], aqueous 

trisodium phosphate solution [246], or aqueous 

aminoethanol solution [244] and an organic solvent, e.g., benzene, hexane, or toluene, by which 

the p-cresol is isolated in a multistep extraction. 

In dissociative distillation, an amount of sodium 

hydroxide solution equivalent to the m-cresol 

content is added to the mixture and the p-cresol 

is distilled through a column with a large amount 

of water vapor as an azeotrope [247]. 

1.5.2. Separation via Addition Compounds 

m-Cresol and p-cresol form addition compounds with anhydrous calcium bromide; the 

compound formed with p-cresol has the higher 

thermodynamic stability. If a m-/p-cresol mixture in toluene is heated to 100 "C with 1 mol of 

calcium bromide per mole of p-cresol, the precipitate that is filtered off after ca. 8 h consists 

practically only of the adduct of p-cresol, while 

the m-cresol content of the mother liquor is correspondingly higher. If the p-cresol adduct is 

then decomposed, e.g., by heating to 200 °C, pcresol with a purity of ca. 98 % is obtained, together with reusable calcium bromide [248]. Pure 

///-cresol can be isolated from the mother liquor 

rich in m-isomer by selective adduct formation, 

e.g., with sodium acetate [249] or urea [250]. Pure 

m-cresol can also be obtained from the mother 

liquor after cooling to ca. 0 to - 5 °C and adding 

calcium bromide. Under these kinetically controlled conditions, the main product is the mcresol-calcium bromide adduct, the subsequent 

decomposition of which gives m-cresol [251]. In 

adduct formation with excess calcium bromide 

at 25-30

 CC, the m-cresol content of the mother 

liquor is directly rendered practically free of pisomer. The p-cresol from the adduct then contains correspondingly more m-cresol [252]. It is 

not known whether this process, which was developed by the Koppers Co. and has many 

variants, is being used industrially. Lithium bromide, magnesium bromide, or magnesium chloride can beaisedio.place of calcium bromide, but 

the results are less satisfactory [248]-[252]. 

Many organic nitrogen compounds react 

with in- or p-cresol to form crystalline addition 

compounds that can be separated from the reaction mixture and decomposed to regenerate the 

nitrogen compound and the respective cresol isomer [24]. Benzidine was formerly considered particularly suitable for the separation of in- and 

p-cresol by virtue of the'pos.ition of, and difference between, the melting points of its adducts; 

however, not only the carcinogenic properties of 

this compound but also other considerations 

now preclude its use. A more suitable and practical process is one in which benzylamine as the 

auxiliary substance forms with m-cresol a 1:1 

adduct, which has a melting point of 39.5 °C. The 

adduct is centrifuged and fractionated in two 

distillation columns operating at different pressures (101.3 and 11.3 kPa)in such a manner that 

the benzylamine is recovered at the top of column 1 while pure m-cresol is obtained at the top 

of column 2. The mother liquor is distilled in the 

same way, then pure p-crcsol is isolated by 

crystallization from the m-/p-cresol mixture rich 

in p-isomer obtained in this case at the top of 

column 2. The benzylamine is recycled [253]. 

CThe isolation of///-cresol via the 1:1 addition 

cbjnpound with urea is a process of some industrial importance. Formerly, the separated adduct 
P.59 

I Vol. A 8 Vol. A8 

was decomposed by healing wilh water. Now it 

is decomposed in the organic solvent in which 

the adduct has been formed. The procedure is as 

follows: 

Urea (1.25 mol per mole of m-cresol) is added to a 

mixture of m-/p-crcsol (65:35; 2 parts by weight) and 

toluene (0.5 parts by weight) at 30 "C. The mixlurc is cooled 

to - 10 "C, centrifuged, and washed wilh toluene (0.2 pans 

by weight). The product, consisting mainly of the urea 

adduct, is iniroduccd into toluene (1.5 parts by weight), 

heated at 80 °C for 10 min, and filtered hot; almost all the 

urea is thereby held back. Distillation of the filtrate gives 

toluene, while thai of the residue gives (S 98%) »i-cresol 

in 89% yield [254]. 

Advantage may be taken of adduct formation between cresols and certain other phenols 

with a view to effecting separation. For example, 

m-cresol forms with phenol an adduct with a 

melting point of 25.9 °C [255], while p-cresol 

forms an adduct with bisphenol A [isopropylidenedi(p-phenol)] [256]. Furthermore, mcresol gives with 1,4-dioxane at 20

 CC and 

110-130 MPa an addition compound that has 

been proposed for the separation of m-cresol 

from m-/p-cresol mixtures in which the content 

of m-cresol is high [257]. 

m-Cresol can be precipitated as an addition 

compound with anhydrous sodium acetate from 

m-/p-cresol mixtures (e.g., in the ratio 65:35) 

in an organic solvent (gasoline, benzene, or 

toluene) at 20-40 °C. The precipitate is removed 

from the mother liquor and decomposed in the 

same solvent by heating to 80-95 °C; the sodium 

acetate is filtered. m-Cresol is obtained from the 

organic solvent as a technically pure product 

(96-99%). The yield is ca. 70% [24]. Higher 

yields (75%) and improved m-cresol purity 

(99.5%) are said to be possible if the adduct is 

decomposed at room temperature with polar solvents such as acetone [258]. 

1.5.3. Separation via Ester or Salt 

Formation 

The mother liquor enriched with p-cresol 

(e.g., to a m-/p-ratio of 35:65) from the precipitation with sodium acetate can react with oxalic 

acid - with azeotropic dewatering - to give the 

semiester or diester, which is precipitated on 

cooling to 20 °C. The ester is separated and then 

hydrolyzed by heating with water at 85% in the 

presence of the respective nonpolar solvent. The 

oxalic acid may be precipitated on cooling and 

Cresols and Xylenols 43 

recycled. The p-crcsol dissolves in the organic 

solvent, from which it is isolated by distillation. 

The alternating use of both processes separates 

m- and p-cresol almost entirely [259]. 

Separation of the cresols via the calcium cresolates, in 

which advantage is taken either of the relatively greater 

solubility of the calcium p-cresolate or of the easier hydrolyzability of the m-crcsolale with superheated steam, is 

unsatisfactory and has no practical importance. 

1.5.4. Separation by Nuclear Substitution 

Partial separation of cresols is possible by 

taking advantage either of the lower solubility of 

p-cresolsulfonic acid in sulfuric acid [24], of the 

more rapid formation of m-cresolsulfonic acid 

during sulfonation [260], or of the fact that the 

rate of hydrolysis of m-cresolsulfonic acid is 

faster than that of p-cresolsulfonic acid [261]. 

The last-mentioned difference forms the basis of 

the Bruckner process, the continuous operation 

of which in a reaction tower is described in [262]. 

A large-scale industrial process, e.g., used by 

Sumitomo in Iapan_and Bayer in the Federal 

Republic of Germany, comprises the separation 

of m- and p-cresol via the di-ferf-butyl derivatives. In this technique, the m-/p-cresol mixture 

reacts with up to 2 mol of isobutene per mole of 

cresol in the presence of acidic catalysts (sulfuric 

acid). The resulting alkylated product consists 

mainly of 2,6-di-/er.-butyl-p-cresol (bp 147°C at 

2.67 kPa) and 2,4-di-.er.-butyl-m-cresol (bp 

167°C at 2.67 kPa), which are easily separated 

by distillation, provided that the catalyst has first 

been entirely inactivated. The process also yields 

monobutylated cresols with boiling points of 

124-129°C at 2.67 kPa which are returned to 

the alkylation reactor, and dimers, trimers, and 

possibly tetramers (bp 125 °C at 2.67 kPa) of isobutene, which are removed from the system. 

m-Cresol or p-cresol and isobutene are subsequently recovered by dealkylation of the di-/er/-

butylcresols at ca. 200 °C in the presence of such 

acidic catalysts assulfuric acid. The individual 

cresols are then further purified by distillation. 

Their purity may exceed 99% [263], [264]. Continuous operation of the butylation-debutylation process is described in [263] and [265]-[267]. 

The process is attractive not simply because it 

gives a~very high yield of pure cresol, but also 

becau^,' it enables 2,6-di-/er.-butyl-p-cresol, a 

widely used antioxidant, to be produced simultaneous]^. 
P.60 

44 Cresols and Xylenols Vol. A8 

If under suitable conditions m-/p-cresol mixtures are chlorinated with sulfuryl chloride [268], 

nitrosated with sodium nitrite [269], or condensed with formaldehyde [270], m-cresol reacts 

considerably faster, and p-cresol with a purity of 

96-98% can be isolated from the reaction mixture as a byproduct. These processes are frequently exploited in practice. 

1.6. Quality Specifications and Analysis 

Cresols and their mixtures are commercially 

available in a wide range of grades and purities. 

They are characterized according to the following criteria [271], [272]: 

- Content of cresols, xylenols. and oilier phenols, determined preferably by GC, e.g., according to ASTM 

3626-80 

- o-Cresol content (mixtures), determined via the crystallizing point of the cineole adduct according to [271], PC 

17-67; or m-cresol content (mixtures), determined via the 

crystallizing point of the urea adduct according to [271], 

PC 16-67 

- Crystallizing point, directly or after drying (pure isomers), e.g., according to [271], PC 10-67 

- Distillation range (mixtures), e.g., according io [271], PC 

5-67, or DIN 52137 and 52139 

- Residue on evaporation, e.g., according lo [271], PC 7-67 

- Residue on distillation, e.g., according to [271], PC 6-67 

Specific grimly, e.g., according lo [271], PC 2-67 

- Color (color number), e.g., according lo [271], PC 1-67, 

or ASTM D 3627 

• Water content, determined either hy azcolropic distillation wilh xylene according lo I)I:AN and STAKK ([271|, 

PC 3-67) or by the Karl Fischer melhod (ASTM D 

1631-80) 

- Content of neutral oils, e.g., as determined according to 

[271], PC 4-67, by distillation after addition of sodium 

hydroxide solution (cresolale formation) 

- Content of pyridine bases, determined either according to 

[271], PC 4-67, by titrating ihe distillate from the neutral 

oil determination with hydrochloric acid, or by direct 

titration with perchloric acid in glacial acetic acid [272] 

- Total sulfur content, e.g., according to [271], PC 22-67 

(reduction method) 

- Acidity or alkalinity, e.g., according lo [271], PC 9-67. by 

titration against phenol red 

- Solubitiiv in sodium hydroxide solution, e.g.. according to 

[271], PC 16-67 

Specifications laid down in British Standards are as 

follows: Hor o-cresol (crystallizing poinl, fp, grade A 

30.3-31.O--C; grade B 29.3-30.3°C; grade C 28.3-

29.3 °C), m-cresol (fp > 10.5 °C), and p-cresol {fp 

_> 34.0°C) in B.S. 522:1964; for cresylic acid of specified 

o-cresol content (45 to 90%) in B.S. 517:1964; for cresylic 

acid of specified m-cresol content (60 to 39%, grades A to 

E) in B.S. 521:1964; and for so-called refined cresylic acid 

(grades A to E with altogether 0.5, 1.0, 2.0, 3.0, or 5.0% 

water, pyridine bases, and neutral oil content) in B.S. 

524:1964. 

Maximal amounts of impurities encountered 

in commercially available cresols are usually no 

more than 0.2% water, 0.15% pyridine bases. 

0.1% neutral oils, and 0.01% sulfur. Synthetic 

cresols are practically free from pyridine bases 

and sulfur. Pure cresols are colorless but may 

have a faintly yellowish color. Their mixtures 

sometimes have a slightly stronger tinge, ranging 

from yellow to brown. 

o-Cresol is produced with a purity of 

99.2-99.9% UP Z 30.7 °C), e.g., for ECN resins 

(see p. 45). Commonly used technical grades 

have purity levels of 98.2-99% (fp % 30.3-

30.6 °C), ca. 96% (fp a 29.5 °C), and ca. 94% 

(fp a 28.5 °C) and thus correspond to grades A. 

B, and C of the British Standard. For example, 

m-cresol is sold at purities of 99% (fp 

a 11.5 °C), 98% (fp a 11 °C), and 96.5% (fp 

a 10 °C). p-Cresol usually has a purity of 99% 

(fp a 34 °C). Grades with a purity of ca. 95% 

(fp a 31 °C) and ca. 65 % are also available. The 

main impurity is m-cresol. 

Technical cresol mixtures are usually classified according to their m-cresol content, which is between 20 and 70 %. 

Within this range.-many different grades are supplied, depending on the manufacturer-ao4 the customer's requirements; there may also be substantial' differences between 

them on the basis of phenols (phenol itself, o-cresoi. pcresol, xylenols, 2-cthylphenol, and other alkylphenols) 

that arc additionally present, as well as other impurities 

(water, pyridine, neutral oils, and sulfur compounds). 

Thus, there are cresol mixtures containing up lo 50% phenol, or almost 50% xylenols and other alkylphenols. or 

which have a total cresol content of only ca. 30%; normally 

the latter lies between 60 and 90%. m-/p-Crcsol mixtures 

obtained by chlorotoluene hydrolysis or from ihe cymenecresol process are distinguished by their high m-cresol content (70% and 60%, respectively) and by their high total 

content of cresol, normally £ 99%. 

1.7. Handling, Storage, and 

Transportation 

The cresols are corrosive, and toxic if absorbed through the skin (see Chap. 4). Work 

with cresols should be carried out in closed apparatus wherever possible. The rooms must be well 

ventilated, and precautions, such as the use of 

airlocks and the gas compensation technique, 

must ensure that cresol vapor or dust cannot be 

inhaled by personnel. The fundamental criterion 

rf the effectiveness of all such precautions is the 

MAK value or TLV, which in 1984 was fixed at 

5 ppm (22 mg/m3) for all cresol isomers and 

isomer mixtures. This level corresponds to the 
P.6I 

Vol. A 8 

odor threshold. At higher concentrations, e.g., 

resulting from operational disturbances, suitable 

respirators must be worn. In addition, persons 

handling cresol must always have adequate eye 

protection and, if necessary, body protection, 

e.g., as provided by. polychloroprene or PVC 

[polyvinyl chloride)] gloves, long aprons, fully 

protective suits, etc. Further recommendations 

oh the handling of cresols and xylenols may be 

found in [273]—[276] and in the safety data sheets 

of cresol manufacturers. 

Steel vessels are suitable for storage. The discoloration that takes place on storage is promoted by elevated temperatures, light, oxygen, 

water, and catalysts, e.g., by dissolved iron or 

copper. If the product is required to remain 

colorless for as long as possible, it is best to use 

tanks of stainless steel (V4A; AISI 316Ti). If exceptional color stability is required, the product 

should also be stored under nitrogen. Access of 

moisture must be prevented, since cresols absorb 

water readily. Both o-cresol and p-cresol, which 

are solids at room temperature, have to be handled at a temperature higher than their crystallizing points. Cresol-air mixtures reach the lower 

explosive limit at ca. 76 °C in the case of o-cresol 

and at ca. 83 °C in those of m- and p-cresol; 

therefore, if the storage temperature exceeds 

70 °C or 75 °C, respectively, the gas space must 

be rendered inert with nitrogen. Storage practice 

must comply with local regulations. The storage 

coniaincrs must be tested regularly for soundness and freedom from leaks. As the cresols are 

classified as waterpollutants, measures such as 

the provision of tank basins must be taken to 

prevent cresol from entering the soil or drains. 

Cresols are transported in heatable tank cars, 

in tank trucks, or in steel drums with a capacity 

of ca. 200 L. The container must bear the appropriate hazard warnings in compliance with the 

regulations. For unloading and sampling, see 

[275]. 

Transportation is subject to the following 

regulations: 

International sea transport (IMDG Code) and international air transport (IATA-DGR) for o-, m-, and pcresol and cresol mixtures: Class 6.1, UN-no. 2076, package group II; for cresylic acids: class 6.1, UN-no. 2022, 

package group II. For transport of o-, m-, and p-cresol, 

cresol mixtures, and cresylic acids on European roads 

(ADR) and railways (RID): class 6.1, no. 14b, from January 1, 1986. As regards transportation on European waterways (ADNR), o-, m-, and p-cresol and cresol mixtures 

belong to class 6.1, no. 22n, and cresylic acid to class 6.1. 

no. 22. The ADNR classification is io be merged with ihe 

ADR/RID classification in 1986. 

Cresols and Xylenols 45 

National regulations: United States (DOT-CFR 49) for 

o-, m-, p-cresol and cresol mixtures: Corrosive material/ 

UN 2076; for cresylic acids: Poison B/UN 2810. In the 

Federal Republic of Germany class 6.1, no. 14b, is valid 

from January 1, 1986, to the transport of o-, m-, and pcresol, cresol mixtures, and cresylic acids by road (GGVS) 

and rail (GGVE). 

Cresols are liquids that are partly miscible 

with water and have flash points of 80 - 90 °C. As 

such, they are, therefore, classified in the Federal 

Republic of Germany and in West Berlin as 

belonging to group A, hazard class III, according to the regulations for the storage of flammable liquids (Verordnung iiber die Lagerung 

brennbarer Fliissigkeiten, VbF). In the United 

States, m- and p-cresol belong to Category 1 of 

the NFPA 704M fire hazard classification system. Water fog, foam, dry chemical extinguishers, and - for small fires - carbon dioxide are 

suitable for fire fighting. In the Federal Republic 

of Germany, VDE Specification 0165 places the 

cresols in Ignition Group G 1. 

1.8. Uses 

Most of the o-cresol manufactured in Europe 

is chlorinated to 4-chloro-o-cresol (PCOC), the 

starting material for the chlorophenoxyalkanoic acids 4-chloro-2-methylphenoxyacetic 

acid (MCPA), 2-(4-chloro-2-methylphenoxy)-

propionic acid (MCPP), and y-(4-chIoro-2-methylphenoxy)butyric acid (MCPB), which are important as selective herbicides. A considerably 

smaller proportion is nitrated to 4,6-dinitroo-cresol (DNCO), which has both herbicidal and 

insecticidal properties. 

Highly pure o-cresol is increasingly processed, especially in Japan, to epoxy-o-cresol 

novolak resins (ECN resins), which are used as 

sealing materials for integrated circuits (chips). 

o-Cresol (of common quality) is also used to 

modify traditional phenol-formaldehyde resins. 

o-Cresol is also important as a precursor of 

various dye intermediates, of which the most important in terms of quantity is o-cresotinic acid 

(o-hydroxymethylbenzoic acid) produced by the 

Kolbe synthesis. This acid finds further use in the 

manufacture of pharmaceuticals, whereas its 

methyl esters serve as dydftg auxiliaries. 

An appreciable amount of o-cresol is used as 

a solvent, cither directly or after hydrogenation 

to 2-methylcyclohexanol o_, 2-methylcyclohexanone. In the form of its carbonate ester, o-cresol 
46 Cresols and Xylenols Vol. A8 Vol. A 

constitutes a starting material in the synthesis 

of coumarin. The alkylation of o-cresol with 

propene gives carvacrol (3-isopropyl-6-methylphenol), which is used as an antiseptic and in 

fragrances. In addition, small amounts of ocresol are used as starting materials in the production of various.*Antioxidants. 

m-Cresol, either pure or mixed with p-cresol, 

forms a starting material for such important contact insecticides as 0,0-dimethyl-0-(3-methyl4-nitrophenyl)thionophosphoric acid (fenitrothion; Folithion, Sumithion) and 0,0-dimethyl0-(3-methyl-4-methylthiophenyl)thionophosphoric acid ester (fenthion; Baytex, Lebaycid). In 

addition, m-cresol is needed in the synthesis of 

phenyl m-tolyl ether (m-phenoxytoluene), which 

after oxidation to m-phenoxybenzaldehyde serves 

as a building block in the production of insecticides of the pyrethroid type. 

Pure m-cresol has considerable importance in 

the production of fragrance and flavor substances: its isopropylation gives thymol, from 

which (-)-menthol is obtained by hydrogenation and separation of the isomers. 6-tertButyl-m-cresol, obtained by alkylation of mcresol with isobutene, is the starting material 

for the perfume fixative musk ambrette. The 

condensation of 6-rerf-butyl-m-cresol with sulfur dichloride gives 4,4'-thiobis(6-rerf-butyl-mcresol), an important antioxidant for polyethylene and polypropylene. Further antioxidants arc produced from 6-fMV-bulyl-m-crcsol 

by condensation with butyraldehyde or crotonaldehyde. In Japan, m-toluidine is produced, on 

demand, by amination of m-cresol. 

The 4-chloro-m-cresol obtained by selective 

chlorination of m-/p-cresol mixtures finds use as 

a disinfectant and preservative. 2,4,6-Trinitrom-cresol can be used as an explosive. 

p-Cresol, pure or mixed with m-cresol (see 

p. 43), is used mainly to produce 2,6-di-ferfbutyl-p-cresol (BHT), a nonstaining and lightresistant antioxidant with a wide range of applications. 2-Alkyl-p-cresols obtained by the 

monoalkylation of p-cresol in the ortho position, 

e.g., tert-butyl-, cyclohexyl-, methylcyclohexyl-, 

a-methylbenzyl-, or nonyl-p-cresol, can be condensed with formaldehyde or sulfur dichloride to 

give 2,2'-methylene- or 2,2'-thiodiphenols, which 

are also important as antioxidants. 2,6-Dicyclopentyl-p-cresol, obtainable by dicyclopentylation of p-cresol, is a very effective antioxidant. 

Coupling of 2--er.-butyl-p-crcsol with diazotized 

4-chloro-2-nitroaniline yields Tinuvin 326, an 

absorber of UV light, which finds use, e.g., for 

polyethylene and polypropylene films and coatings. In the fragrance industry, p-cresol is used to 

obtain p-cresolcarboxylic acid esters and, particularly, p-cresol methyl ether, most of which is 

used in the production of anisaldehyde. Like ocresol, m- and p-cresol are used as components of 

various dyes. 

An important field of application for technical cresol mixtures is the production of modified phenolic resins by condensation with formaldehyde. The suitability and price of cresol 

mixtures for this purpose depends on their content of m-cresol, the most reactive of the three 

isomers. Cresol mixture'*, are highly important 

as solvents for synthetic resin coatings (wire 

enamels). 

m-/p-Cresol mixtures free of the o-isomer are 

used to produce neutral phosphoric acid esters 

(tricresyl phosphate, diphenyl cresyl phosphate), 

which find use as fire-resistant hydraulic fluids, 

as additives in lubricants, as air filter oils, and as 

flame-retardant plasticizers for PVC and other 

plastics. 

The bactericidal and fungicidal properties of 

cresols enable them to be used as disinfectants in 

soap. Synthetic tanning agents of commercial 

importance are obtained by the condensation of 

formaldehyde with cresolsulfonic acids and by 

the sulfonation of novolaks obtained from cresols. Crude cresols are used as wood preservatives. Cresol mixtures arc also used in ore flotation and fiber treatment, as metal degreasing and 

cutting oils, as extracting solvents, and as agents 

for removing carbonization deposits from internal combustion engines. Methylcyciohexanol 

and methylcyclohexanone produced by hydrogenation of cresols are used in the paint and textile 

industries. 

1.9. Economic Aspects 

The combined total output of cresol of the 

United States, Western Europe, and Japan in 

1984 was estimated to be 2200001: 

Synthetic cresol ca. 1400001 

Cresol from coal Ur ca. 55 0001 

Cresol from spent refinery caustics ca. 25 0001 

Total £ ca. 2200001 

About 650001 was ^produced in the United 

Stales, about 95 0001 in. Western Europe, and 

about 600001 in Japan. Approximately half of 

f 

si 

;_ 

3 

the tot; 

the pur 

About 

manufi 

The 

spent r 

content 

tained 

which : 

were cr 

tars pre 

cresols 

in Sou 

accpun 

cresols. 

The 

over the 

especial 

shutdo\ 

noco, K 

thus, to 

[43]. Ne 

eration 

General 

ducing c 

scale tha 

capacity 

(Genera 

and GE: 

2. XvL 

OH 

60 CH. 

OK 3r 
P.63 

Vol. A8 

finds use, e.g., for 

me films and coat-

, p-cresol is used to 

; esters and, particmost of which is 

saldehyde. Like o-

_ as components of 

plication for techoduction of modinsation with formid price of cresol 

I ends on their conactive of the three 

highly important 

.in coatings (wire 

of the o-isomer are 

.phoric acid esters 

cresyl phosphate), 

it hydraulic fluids, 

ir filter oils, and as 

_r PVC and other 

| cidal properties of 

as disinfectants in 

us of commercial 

ie condensation of 

onic acids and by 

.btained from creas wood preserva-

> used in ore flota-

•tal degreasing and 

[ ents, and as agents 

J deposits from incthylcyclohcxanol 

duced by hydrogele paint and textile 

|ut of cresol of the 

•pe, and Japan in 

! 000 t: 

ca. 140000 t 

ca. 55O0Ot 

ca. 25 000 t 

ca. 220 000 t 

ced in the United 

;tern Europe, and 

| roximately half of 

r 

m 

I 

Vol. A 8 

the total cresol output is processed in the form of 

the pure isomers, and the rest as isomer mixtures. 

About 30% of the total output is used by the 

manufacturers themselves. 

The above figures for cresol from coal tar and 

spent refinary caustics refer only to the cresol 

content. They do not include the xylenols contained in the raw material (30000-400001), 

which to some extent are sold as though they 

were cresol. The tar cresols are obtained from 

tars produced in Eastern Europe and from crude 

cresols resulting from the gasification of coal 

in South Africa. This proportion probably 

accounts for ca. 25% of the total output of tar 

cresols. 

The total output of cresol has not increased 

over the last ten years. Substantial overcapacity, 

especially for o-cresol, has led to the (temporary) 

shutdown of plants in the United States (Conoco, Koppers, and Diamond Shamrock) and, 

thus, to a decrease in capacity of ca. 50 000 t/a 

[43]. Nevertheless, the capacity remaining in operation is not being used fully, partly because 

General Electric in the United States is now producing o-cresol in place of 2,6-xylenol on a larger 

scale than before and partly because new o-cresol 

capacity has been installed in the Netherlands 

(General Electric) and in Japan (Nippon Crenol 

and GEM-Polymer). 

2. Xylenols [i]-[3] 

Xylenol, dimethylphenol, C8H10O, M, 

122.166, occurs in six isomeric forms: 

OH OH OH 

CH, 

2.3-Xj**l«nol 2.4-X7lw_ol 2,S-Xyl<aol 

2.3-<___-ot_*7'p_.«nol 2,4-d-____tbylpl_*nol 2.5-<___nth*-lph«aol 

[528-33-0] [103-87-9] [98-87-4] 

OH OH OH 

> ^ T^ S HsC^^CH , 

CH, 

2,a-X*f_«nol 3.4-Xj*i«__ol 3,5-Xjrl«_ol 

2,8-d___Mt__7ip_t«__ol 3.4-dimtUijrlp-iaaol 3.S-<_i_o»t_i*riphe_*ol 

[878-28-1] [83-83-8] [108-88-9] 

The numbering of the substituents normally 

and correctly begins from the OH group; but is 

Cresols and Xylenols 47 

occasionally (erroneously) started from the 

methyl group: 2,4-xylenol can be referred to as 

1,3,4-xylenol, 4-hydroxy-m-xylene, or 4-hydroxy-1,3-dimethylbenzene. 

Xylenols are present, e.g., in the essential oils 

of various conifers, in tea, in tobacco and tobacco smoke, in roasted coffee, and in various 

smoked foods. In many cases, they contribute to 

the flavor of these products. 

From the standpoint of economics, the most 

important isomer is now 2,6-xylenol, of which 

coal tar contains only a relatively small amount 

and which is produced, therefore, almost entirely 

by synthetic means. 

2.1. Properties [l]-[3] 

The xylenols are colorless crystallizing compounds that are soluble in alcohol, acetone, and 

in many other organic solvents. They are less 

soluble in water than the cresols. Except for 

3,5-xylenoI, their acidity is likewise lower than 

that of the cresols. They are soluble in aqueous 

sodium hydroxide, but to different extents, depending on the structure. Their chemical behavior is similar to that of the cresols. Physical data 

are presented in Table 4. For dependence of the 

thermodynamic data on temperature, see [8], 

[277]-[279]. 

2.2. Isolation 

With regard to the formation of xylenols in 

various thermal cracking processes, see Section 

1.3. 

Xylenols, with the cresols and other phenols, 

are isolated from high-temperature, low-temperature, and Lurgi pressure gasifier coal tars 

(see Section 1.3.1) and from spent refinery caustics (see Section 1.3.2). The resulting crude phenols (cresylic acids) contain all six xylenols in 

amounts that differ greatly according to the raw 

material and conditions of formation (see Table 

3). Moreover, the ratio of the xylenols themselves differs. In xylenols from spent refinery 

caustics, 2,4-xylenol generally predominates; besides this, the content of 2,5-xylenol is high, 

whereas that of$,5-xylenol is relatively small 

[280]. Xylenols from bituminous coal tar are 

characterized by their high content of 3,5-

xylenol. The average isomer ratio of bituminous 

coal tar xylenols is given in [281]; for example, as 
keley 

KIRK-OTHMER 

York 

York 

RCER 

ENCYCLOPEDIA OF 

CHEMICAL TECHNOLOGY 

THIRD EDITION 

A WILEY-INTERSCIENCE PUBLICATION 

John Wiley & Sons 

NEW YORK • CHICHESTER • BRISBANE • TORONTO 
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Copyright © 1978 bv John Wiley & Sons, Inc. 

All rights reserved. Published simultaneously in Canada. 

No part of this book may be reproduced by any means, 

nor transmitted, nor translated into a machine language 

without the written permission of the publisher. 

Library of Congress Cataloging in Publication Data: 

Main entry under title: 

Encyclopedia of chemical technology. 

At head of title: Kirk-Othmer. 

"A Wiley-lnterscience publication." 

Includes bibliographies. 1. Chemistry, Technical—Dictionaries

. I. Kirk, 

Raymond Eller, 1890-1957. II. Othmer, Donald Frederick, 

1904- III. Grayson, Martin. IV. Eckroth, David. 

V. Title: Kirk-Othmer encyclopedia of chemical tech-

nology. 

€ 

TP9.E685 1978 66O*.03 

ISBN 0-471-02037-0 

77-15820 

Vii I IX 

XXI 

XXVI 

XXVIII 

XXIX 

120 

120 

120 

120 

120 

j 120 

120 

- 120 1

 623 I 323 ! 624 | 753 ! 932 ! 962 

12 from 

13 

2 3 fro

m b 

3 from fc 

6 

Table 3ft 

Table 3d 

Table 3(t 

Table 3d 

Table 3d 

Table 3d 

Table 3d 

Table 3d 

ref 3 

bot 

3 14 

1 

1 

Page 17 

Printed in the United States of America 
P.66 

CurVSjuHTED 

Vol. 22 TAR AND PITCH 593 

Cresylic Acids. The higher boiling cresylic acids are mixtures of cresols or xylenols 

With higher boiling phenols (see Phenol; Alkylphenols). Their main uses are in phenol-formaldehyde resins, solvents for wire-coating enamels, as metal-degreasing 

agents, froth-flotation agents, and synthetic tanning agents (see Table 16). Statistics 

do not distinguish between the various grades or between cresylic acids derived from 

coal tar or petroleum or made synthetically (see Phenolic resins). 

Naphthalene. Until the 1960s, the principal outlet for naphthalene was the production of phthalic anhydride; however, more recently, o-xylene has replaced naphthalene as the preferred feedstock (see Phthalic acids). Today, only ca 21.3% of the 

phthalic anhydride made in the United States is derived from naphthalene; in Western 

Europe, ca 10%; and in Japan, ca 30%. 

In Europe, the main uses for naphthalene are for the manufacture of/3-naphthol 

and for dyestuff intermediates (see Dyes and dye intermediates). 

Creosote. In coal-tar refining, the recovery of tar chemicals leaves residual oils, 

including heavy naphtha, dephenolated carbolic oil, naphthalene drain oil, wash oil, 

strained anthracene oil, and heavy oil. These are blended to give creosotes conforming 

to particular specifications. 

Creosote oils are by far the most widely used timber preservatives (see Wood). 

This use dates back to 1850. The 1981 U.S. consumption is estimated at <500,000 

t. 

For the treatment of railway ties and marine pilings, the Bethell or Full-cell 

process is preferred. The timber to be treated is charged to a pressure cylinder, which 

is evacuated to extract the air from the wood cells. The cylinder is then filled with hot 

creosote and the pressure increased to 0.8-1 MPa (ca 8-10 atm) to force the oil into 

the cells. When uptake of the oil has ceased, residual creosote is drained from the 

cylinder and the treated timber is briefly subjected to a vacuum before discharge. 

For the treatment of telegraph and transmission poles, fence posts, and farm 

buildings, where a clean outer surface is desired, the empty-cell process is generally 

used. The Rueping process employs an impregnation cycle in which the timber is first 

subjected to a moderate air pressure to compress the air in the cells before the cylinder 

is charged with hot creosote. The pressure in the cylinder is increased to force the oil 

into the wood cells. When no more oil is absorbed, the pressure is released, allowing 

the air inside the timber to expand and force the creosote out; a protective film remains 

on the cell wall. After discharging surplus creosote, the treated timber is evacuated 

Table 16. 

Use 

U.S. Distribution of Cresol and Cresylic Acids Uses, 1976-* 

% 

phosphate esters 

solvents 

wire-coating enamels 

antioxidants 

phenolic resins 

cleaning compounds 

froth-flotation agents 

miscellaneous 

export 

" Kef. 72. 

20 

15 

15 
•AIR 

npany 

souri 

Encyclopedia of 

Chemical Processing 

and Design 

EXECUTIVE EDITOR 

ASSOCIATE EDITOR 

John J. McKetta 

William A. Cunningham 

. LUDWIG 

suiting Engineers. Inc 

c. Louisiana 

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MARCEL DEKKER, INC. " NEW YORK AND BASEL 
COPYRIGHT© 1976 by MARCEL DEKKER. INC. ALL RIGHTS RESERVED. 

Neither this book nor any part may be reproduced or transmitted in any form or by any 

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iterna 

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\ ALLAWAl 

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-in. -*aki*t_n 

MED H.A M 

*.i; Supervi 

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• • 4.Pt 

.'.MTHON' 

•r Depart* 

c ; !_•_. • 

.*. M L'r. 

M.H*...--.. I 

; -*'fl*.'.••'MM 

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ALU L :; 

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P.69 

2.12 Cracking, Thermal Cresol 

Nelson, W. L., Oil Gas J., 55(15), 139 (April 15, 1957). 

Nelson, W. L., Petroleum Refinery Engineering, 4th ed., McGraw-Hill, New York, 1958. 

"Nelson Cost Indexes," Oil Gas J., 73(H), 134 (April 7. 1975). 

Sachanen, A. N., Conversion of Petroleum, 2nd ed., Reinhold, New York, 1948. 

Staff, Hydrocarbon Process. Pet. Refiner, 41(9), 172 (1962). 

Staff, Hydrocarbon Process., 47(9), 153 (1968). 

Staff, Hydrocarbon Process., 53(9), 123 (1974). 

Stephens, M. M., Petroleum Refining, Vol. 2, Pennsylvania State College, State College, 

Pennsylvania, 1941. 

W. P. BALLARD 

G. I. COTTINGTON 

T. A. COOPER 

Cr->, V/ -, 

Cresols and Cresylic Acids 

•Jf£D 

Cresols are monomethyl derivatives of phenol. There are three cresol isomers 

which differ by position of the methyl substituent as ortho, meta, or para 

relative to the phenolic-OH group. All three isomers are known and each is 

commercially important. 

The terms cresylic acid and tar acids historically have been applied to the 

mixture of phenol homologs recovered from coal tar and/or petroleum. Such 

mixtures typically contain phenol, the three cresols, the six xylenols (dimethyl 

phenols) along with minor amounts of ethyl phenols, and C3- and C4-

substituted phenols (trimethyl, ethyl-methyl, propyl, butyl, diethyl, methylpropyl, etc.). 

In modern usage the term cresylic acid has generally evolved to designate 

mixtures containing significant amounts of two or more of the alkyl-substituent 

homologs of phenol. It is most commonly applied to mixtures derived from 

recovery of natural origin (coal or petroleum). Cresylic acid has been defined in 

one instance [1] as "mixtures of phenol and alkyl-substituted, mono-hydric 

phenols, but limited to phenolic constituents whose normal boiling points are 

230°C or less." However, it is not uncommon to exclude phenol from the 

cresylic acid designation in which case a crude mixture might be considered as a 

mixture of phenol and cresylic acid. This practice is followed by the U.S. Tariff 

Commission in its reports [2]. 

The dominant commercial sources of cresols and cresylic acids are natural 

sources; coal tar and petroleum. These sources, supplemented by direct 

synthesis of various isomers, comprise all of the currently significant commercial supply. Commercial production of synthetic cresols began in the late 

1950s and has shown significant growth. 

Substantial increase in supply from a "new" natural soprce may be coming 

in the 1980s. With diminishing domestic crude petroleum reserves and a 

government policy of avoiding excessive dependence on foreign crude pe-
P.70 

Cresols and Cresylic Acids 213 

troleum, emerging technologies are aimed at conversion of enormous coal 

reserves to liquid and gaseous fuels [9]. The recovery of substantial commercial 

quantities of phenol and cresylic acids from these "new" coal-based operations 

olTers the promise of adding major increments to current supplies. If these coalbased operations materialize and couple with the separations technology as 

currently practiced in the coal-tar and petroleum-based cresylic acid industry, 

they will tend to limit the manufacture of specific isomers via synthesis to those 

inadequately supplied by natural sources. 

D 

N 

R Properties 

rs 

ra 

is 

ie 

:h 

yl 

• 4 * 

ALte 

nt 

>m 

in 

ric 

ire 

he 

sa 

-iff 

ral 

eet 

relate 

ing 

I a 

peThe chemical properties of cresols, xylenols, and higher homologs are 

substantially extensions of the parent homolog, phenol. Similarly, the physical 

properties form a logical extension from the parent. Selected values for cresylic 

acid constituents are given in Table l, in which the values shown were taken 

(except where otherwise noted) from the critically reviewed tabulation prepared 

by the Manufacturing Chemists Association research project [8]. 

Historical Evolution of Coke, Coke Chemicals, and 

Cresylic Acid 

The discovery and commercial evolution of phenol and cresylic acids has 

followed man's quest for deriving energy from fossil fuels. Recovery of "tar 

acids" from coal tar comprised the earliest commercial source of phenol, 

cresols, and xylenols. 

The practice of producing coke by carbonization of coal originated in 

Europe in the 1600s for the purpose of producing a clean, convenient solid fuel 

[3]. Coke was first successfully used in a blast furnace by Abraham Darby in 

Shropshire, England, in 1707. About the time beehive ovens were developed, 

the usefulness of the volatile products evolved upon heating coal began to be 

recognized. In 1792 a young mechanical engineer, William Murdock, was 

convinced that these volatile products could be utilized for illumination. With 

this conviction he commenced 5 years of experimentation and succeeded in 

carbonizing coal in iron retorts and piping the evolved gases into his home and 

workshop for illumination. Having demonstrated the practicality of coal gas 

illumination, he convinced his employer, the Boulton and Watt steam engine 

factory in Birmingham. England, to install the system injliat factory. In 1802 

the first commercial tise of manufactured gas was undertaken when the Soho 

plant of Boulton and Watt was illuminated by gas lights fueled by a process of 

Murdock's design. Murdock ultimately rose to be works superintendent and 

became known as "the Father of the Gas Industry." 

In the fifty years between 1800 and 1850, a significant industry evolved 
___ 

4^ 

TABLE 1 Properties of Cresylic Acid Constituents (from Ref. 8 unless otherwise noted) 

Boiling point: 

CC at 760 mmHg 

CC at 300 mmHg 

°C at IOO mmHg 

'C at 20 mmHg 

Freezing point, °C 

Liquid density at 

20C , g/mlJ 

Specific heat, cal/g at O'C 

Latent heat, fusion. 

cal/g • mol 

Latent h£at,*vSJJ«**j;ization, 

cal/g • mol at 760 mmHg 

'Densities of subcooled liquid 

Phenol 

181.839 

150.95 

120.70 

85.32 

40.90 

1.0767 

0.548 

2752 

10.920 

o-Cresol 

191.004 

158.62 

127.06 

90.21 

30.944 

1.0460 

0.4955 [II] 

3095 

10,801 

.-.-Cresol 

202.232 

169.91 

138.23 

101.13 

12.22 

1.03409 

0.4727 [II] 

2169 

11,329 

/.-Cresol 

201.940 

169.79 

138.32 

101.55 

34.739 

1.0348 

0.4685 [11] 

2067 

11,365 

2,6 

201.030 

166.88 

133.54 

94.68 

45.62 

3633 

10,641 

2.5 

211.132 

177.43 

144.57 

106.30 

74.85 

1.024 

3323 

11.219 

Xylenol 

2.4 

210.931 

177.40 

I44.6S 

106.57 

24.54 

1.02017 

3069 

11.268 

2,3 

216.871 

182.68 

149.34 

110.49 

72.57 

4750 

11,310 

3,5 

221.692 

188.22 

155.47 

117.19 

63.27 

1.022 

4342 

11,785 

3,4 

226.948 

193.07 

159.98 

121.38 

65.11 

1.035 

3140 

11,871 

O 

1 

CD 

o 

(/I 

CD 

_} 

a. 

_-_ Iresyli

c Acids 

o 

- I 

CD 

IA 

O 

*•>! 
P.72 

Cresols and Cresylic Acids 215 

around carbonizing coal to produce manufactured gas for gas lighting and coke 

for a growing steel industry. Little or no commercial attention was given to 

utilizing tar and liquids. In fact, many coke producers gathered these troublesome problems into barrels and dumped them at sea. However, considerable 

attention was paid to these coal tar liquids by chemists during the period, 

particularly in Germany, centering around the work of Justus von Liebig at 

Giessen. In 1834, Friedlieb Ferdinand Runge, a chemist with the Prussian 

Marine Service in Berlin, discovered in coal tar oil an acidic substance he called 

carbolic acid [6]. Five years later the French chemist, August Laurent, 

succeeded in recovering pure phenol from coal tar, and was first to nitrate it to 

picric acid. 

Around 1840 a German chemist and student of Liebig at Giessen, A. W. 

Hofmann, became interested in the volatile products obtained by heating coal. 

Hc came to England in 1845 to become professor at the ncwly-formcd Royal 

College of Chemistry where he remained for 20 years. He pursued his ideas 

about coal tar at the college and assigned some of his students the task of 

identifying its constituents. One of Hofmann's students was Charles Mansfield, 

who studied at the college from 1847 to 1850 and is regarded as the founder of 

coal tar chemistry. Mansfield had a strong desire to convert his research into a 

business, and in this was encouraged by his teacher and friend, Hofmann. He 

had examined in detail the light naphtha fraction from tar distillation and, by 

repeated distillations and successive washes with sulfuric acid and caustic soda, 

was able to obtain benzene, toluene, and xylene. Mansfield was granted a patent 

on his purification process in 1848, and this process was the forerunner to the 

coal tar chemicals business. He promoted the use of benzene as a dry-cleaning 

solvent and, with Hofmann, progressed to the manufacture of nitrobenzene 

and thence to aniline, which was to prove important later in the development of 

dyestuffs. Mansfield died tragically in a laboratory fire in 1855, but in a few 

short years he made an indelible mark on the early history of coal tar chemistry 

[4]. 

Another of Hofmann's students was W. H. Perkin who in 1856 was 

attempting to synthesize quinine by oxidation of impure aniline. Instead, he 

discovered an aniline dyestuff with a brilliant purple color which he named 

mauveine. This discovery prompted Perkin to abandon his research at Royal 

College and to enter commercial production al Green ford. 

In the early 1860s, commercial exploitation of Perkin's process brought an 

acute shortage of benzene. It was recognized that more benzene was present in 

coal gas than in coal tar. Dr. Caro of the Badische Co. in Germany developed a 

process for benzene recovery from coal gas by oil scrubbing and was granted a 

patent thereon in 1869. This process enabled benzene production to expand to 

meet demand as new chemical uses for it were developed. 

During this inauguration of commerce in benzene recovered from coal tar, 

the recovery of "carbolic acid" as a by-product of benzene vafs begun. J. Fairlie 

had discovered cresol in coal tar creosote at University College (London) in 

1855 [7]. However, the first commercial use of "tar acid" did hot arise until after 

the I869 discovery of its antiseptic properties by Joseph L. lister, an English 

surgeon. 

As a result of the efforts of Mansfield, Perkin, Lister, Hofmann, and many 
P.73 

216 Cresols and Cresylic Acids Cresols an 

others, there was by 1875 a significant industry established around recovery of 

chemicals from coal tar. However, the requirements for coke, particularly in 

England, were so great that the needs for coal lar were adequately served by 

incremental recovery ofcoal tar. The first true by-product coke ovens, designed 

especially to facilitate recovery of coke by-products, were constructed by Albert 

Hussner at Gelsenkirchen, Germany, in 1881. These ovens supplied the rising 

German chemical industry which was largely based on coal-tar derivatives. It 

was not until 1893 that any by-product ovens were erected in the United States 

when a battery of 12 ovens was designed :\nd built hy Louis Semel for the 

Solvay Process Co., Syracuse, New York, largely to obtain ammonia for use in 

the ammonia-soda process. By 1900 the value of the volatile products had been 

established and the combined economics and quality of by-product coke 

became entrenched as preferred fuel for blast furnaces by the growing steel 

industry in the United States. 

From 1880 until 1899 the uses of antiseptic phenol were adequately supplied 

from coal tar, even though it had been known for some time that phenol could 

TABLE 2 History of Coking in the United States* 

Year . 

1880 

1893 

1895 

1900 

1905 

1910 

1915 

1920 

1925 

1930 

1935 

1937 

1939 

1941 

1943 

1945 

1946 

1948 

1950 

1955 

I960 

1965 

1970 

1973 

Ovens in E 

By-product 

0 

12 

72 

1,085 

3.159 

4.078 

6.268 

10,881 

11,290 

12,831 

12,860 

12,194 

13.010 

13.016 

14,253 

14,510 

14,494 

15,139 

14,982 

16,039 

15,323 

14.357 

— 

— 

ustence 

Behive 

12.372 

44.000 

45,493 

57,399 

84,405 

100,362 

93,110 

75,298 

57,587 

23,907 

13,674 

12.194 

10,934 

18,699 

17,666 

12,179 

12,864 

14,078 

17,708 

10,104 

7,583 

3,433 

— 

— 

Coke Produced (M tons) 

By-product 

0 

13 

19 

1,076 

3,462 

7,139 

14.073 

30,834 

39,912 

45,196 

34,224 

49,211 

42.882 

58,048 

63,743 

62,094 

53,929 

68,300 

66,900 

73,600 

56,219 

65,197 

65,654 

63,496 

Behive 

3.300 

9.465 

13.315 

19,458 

26,769 

34,570 

27.508 

20,511 

11,355 

2,776 

917 

3.165 

1.444 

6.704 

7,933 

5,214 

4,568 

6,600 

5,800 

5,200 

1,009 

1,656 

871 

829 

Total 

3.300 

9,478 

13,334 

20,531 

30,231 

41,709 

41.581 

51,345 

51,267 

47,972 

35,141 

53.376 

44.326 

64,752 

71,676 

67,308 

58,498 

74,900 

72,700 

78,800 

57,228 

66,854 

66,525 

64,325 

Blast Furnace Rate (lb 

coke per ton pig iron-f 

ferro alloys) 

— 

— 

— 

— 

2,170 

— 

2,120 

— 

— 

— 

1.930 

. . „ 

— 

— 

— 

— 

1,937 

1,865 

$ 1 6 

l;-330 

1.^7 

I.2J22 

'From Minerals Yearbook, U.S. Bureau of Mines. 
P.74 

ds Cresols and Cresylic Acids 217 

of 

in 

by 

ed 

crt 

ng 

. It 

tes 

:he 

: in 

.•cn 

^ke 

eel 

ied 

uld 

TABLE 3 History of Production and Refining of Coke-Oven Tar and Production of 

Light Oil" 

Year 

I9I0 

I9I4 

I9I8 

1923 

1929 

1933 

1937 

194I 

1943 

1945 

1950 

1956 

1965 

1973 

Tar Produced 

(M gal) 

66.303 

109.901 

263,299 

440.907 

680.864 

363.299 

603,053 

704.149 

738,167 

696.307 

739.868 

832.800 

802.737 

732,455 

Coal T. 

M Gallons 

— 

— 

— 

328.087 

215,550 

378.935 

458,334 

532,683 

562,446 

607,248 

702.091 

678,307 

562,143 

ir Relined 

Percent of 

Production 

— 

— 

— 

48.1 

59.3 

62.9 

65.1 

72.2 

80.8 

82.1 

84.3 

84.5 

76.7 

Light Oil Produced 

(M g.il) 

— 

87.220 

101.438 

164,488 

96.632 

187.103 

234.026 

264,321 

260.237 

260.858 

290.900 

262.700 

214,201 

"From Minerals Yearbook, U.S. Bureau of Mines. 

be synthesized from benzene by sulfonation and fusion. Despite the discovery 

by Turpin in 1885 of the explosive natureofpicricacid.it was not until the Boer 

War created a large demand for explosives that it became practical to make 

phenol synthetically. In 1899, Read Holliday & Co. initiated commercial 

production via benzene sulfonation/fusion, the same year as the discovery in 

Germany of the analgesic properties of a phenol derivative, acctyl-salicylic acid, 

whose discovery proved a major impetus to sustaining the commercial future of 

synthetic phenol. 

In 1906 a large battery of by-product ovens designed by Heinrich Koppers 

was installed at Joliet, Illinois, for the Illinois Steel Co. During the following 

years the development of by-product coking evolved steadily until it received an 

enormous boost in 1914-1918, spurred on by major expansion of the steel 

industry and by surges in demand for toluene and other coal chemicals during 

World War I. In 1914 the H. Koppers organization was acquired by the Mellon 

interests and under aggressive new management secured a dominant position in 

by-product coking with respect to number and size of installations. 

The evolution of coal carbonization in the United States can be seen in the 

statistics of coking (Table 2) and the production and refining of coke oven tar 

(Table 3). £ 

In 1909, Leo H. Baekeland successfully developed Impractical, thermosetting plastic resin based on condensation of phenol-formaldehyde [5]. The early 

products of General Bakelite Corp., which Baekeland organized in 1910, found 

success in molded parts, insulating varnishes, and laminated sheets for the 

growing electric and automalivc industries. 
P.75 

218 Cresols and Cresylic Acids Cresols ant 

The emerging phenolic plastics business increased demands for the recovery 

of phenols and cresylic acid from coal tar. From the early 1920s this use of tar 

acids comprised their major market, and it has remained a substantial end-use 

of cresylic acids to the present time. 

By the end of World War II the number of coke ovens in existence in the 

United States was in excess of 27,000, 14,494 of which were by-product ovens. 

Of these by-product ovens, 11,069 were of Koppers or Koppers-Becker design. 

Aggregate coal tar production had reached almost 800,000,000 gal/yr, of which 

80.8% was being refined, and the aggregate production of cresols and cresylic 

acid was approximately 50 MM lb/yr in addition to approximately 20 MM 

lb/yr of natural phenol. 

In the early 1940s, Dr. H. L. Lochte, a professor at the University of Texas, 

isolated and identified many constituents in the cracked naphtha produced in 

petroleum refining [10]. In 1946, John T. Files, a student of Lochte's, was 

convinced that cresylic acid could be recovered economically from the spent 

caustic generated in the treatment of cracked naphtha. By 1951 he was 

instrumental in constructing and operating a Houston plant (Merichem Co.) 

based on the spent caustic acquired from Gulf Coast refineries. By 1956, others 

had followed suit: Productol Co. in Santa Fe Springs, California; Pitt-Consol 

Co. in Newark, New Jersey; and Northwest Petrochem Co. in Anacortcs, 

Washington. In 1956 these companies were producing a total of 35 MM lb/yr of 

cresylic acid from petroleum sources'. Coal tar cresylic acid production in 1956 

was about 90 MM lb/yr. 

During the period from 1956 to 1974, technology improvements in coke 

elliciency by blast furnaces resulted in diminishing coke production in the 

United States. During the same time, a vast increase in catalytic-cracking 

capacity was made by the petroleum refining industry in response to increased 

demand in quantity and quality of motor fuels. These changes caused a shift in 

the sources of cresylic acids. By 1974, petroleum had displaced coal tar as the 

dominant source of cresylic acid. 

Also, during this same period, commercial production of certain isomers by 

synthesis was begun, largely in response to specific requirements. 

Processes 

In all processes for producing phenols the personnel safety and environmental 

hazards associated with phenols must be taken into account in operating and 

design practices. Essential information for safe handling of phenol and cresols 

is given in appropriate chemical Safety Data Sheets SD-4 and SD-48, published 

by the Manufacturing Chemists Association [13]. An immediate personnel 

hazard associated with the handling of these materials stems fromrthe fact that 

painful burns can result from iheir contact with skin or mucous membranes. 

The hazards associated with handling solutions of the sodium salts of cresols 

and cresylic acid are substantially equivalent to those for handling caustic soda 

solutions. 
P.76 

Cresols and Cresylic Acids 219 

Coal Tar Acids 

The manufacture of coke in by-product coke ovens typically results in the 

production of 10 to 16 gal of tar and light oil per ton of coal. The crude coal tar 

is subjected to distillation to yield light oil (5%), middle oil (17%), heavy oil or 

creosote oil (17%), and pitch (61%). 

The cresylic acid typically represents about 2 to 3% of the original tar and is 

primarily present in the light oil (up to 200°C) and the middle oil (200 to 250°C) 

fractions. The classical process for recovering cresylic acid from these tar 

distillates stems all the way back to Charles Mansfield's pioneering work in 

1848. The appropriate tar fraction containing tar acids is washed with a caustic 

soda solution, resulting in the formation of their sodium salts which are called 

sodium cresylates. After the sodium hydroxide has become 70 to 75% utilized, 

the cresylate is withdrawn from the washer. Neutral oils and pyridine bases 

which are present in this cresylate solution are removed by steam distillation 

under vacuum where these impurities arc removed with the aqueous condensate. 

The phenols are recovered by "springing'* the stripped cresylate with C02-

rich gas. as from a lime kiln, and removing the liberated cresylic acid by 

decantation. The resulting sodium carbonate solution is then causticized with 

lime to regenerate caustic soda solution for the washers. 

In washing the middle oil fraction of tar distillate which is typically rich in 

naphthalene, it is normally necessary to operate the washer at elevated 

temperature (~75°C) to avoid naphthalene crystal deposits in the washer. 

The crude cresylic acid from the decanter after springing is normally 

dehydrated by distillation and fractionated into various isomers or mixtures of 

isomers. The cresylic acid recovered from coal tar typically contains 45% 

phenol. 35% cresols. 15",, xylenols. and 5% other phenolic homologs. 

Refinery Spent Caustic 

In many refineries, thermal and catalytic cracked distillates are caustic 

sweetened to remove mcrcaptans; coincident components of the spent caustic 

are phenolic materials which are contained in the form of sodium cresylates. A 

typical spent caustic contains 15% hydroxide. 20",, cresylic acids. 10",, sulfur 

compounds, and the balance water and other impurities. 

The cresylic acid can be removed from the spent caustic by neutralization 

with acid. Sulfur impurities may be removed before neutralization by oxidation 

to disulfide oils and/or after neutralization by extraction. The extraction route 

utilizes more complex equipment and involves solvent recovery by distillation. 

The neutralization can be achieved by acid gases such as C02, S02 or H2S, 

or by mineral acids. By-products of C02, S02, and H2S neutralization are 

sodium carbonate, sodium sulfite, and sodium sulfide. After neutralization and 

removal of oil. water, and sulfur, the acid can be fractionated into'a variety of 

phenolic homolog fractions. j 

The approximate isomer distribution in natural cresylic acids from 

pciroleum sources is phenol 20%, ..-cresol 18%, /;;,/;-cresol 30%, xylenols 22",,. 
T 

P.77 

220 Cresols and Cresylic Acids Cresols a> 

and C3 and higher alkyl phenols 6%, with the balance being trimethyl phenols 

and ethyl phenols. A residue stream equal to about 3% of the total fractionated 

phenolics listed above is also produced which may be used in creosote treatment 

of lumber or for fuel. 

The processing of refinery spent caustic solutions for recovery of cresylic 

acid requires a substantially integrated, rather complex plant facility. The 

largest and most integrated operation of this type in the world is found in the 

Merichem Co. plant in Houston, Texas. The basic processes used in this 

operation include many ecological innovations, including foul air incineration 

and an extensive water management system, necessitated by the nature of the 

spent caustic raw material. These are shown on the block process flow sheet in 

Fig. 1. 

Spent caustic, collected from many refineries and admixed with recycle 

water, is first sweetened in reactors in which air is dispersed into the alkaline 

liquid. The exit air, befouled with traces of noxious components and denuded of 

oxygen, is incinerated prior to release lo Ihe atmosphere. The spent caustic is 

then extracted with an immiscible solvent for removal of sulfur compounds. 

PHENOL -

CRESOLS • 

XYLENOLS -

CRESYLIC ACIDS -

FRACTIONAL 

DISTILLATION 

SULFUR __ _ 

COMPOUNDS "*-] 

£ 

SOLVENT 

REGENERATION 

SWEETENING 

REACTORS 

SOLVENT 

EXTRACTION 

WATER MANAGEMENT SYSTEM ' 

lll l REOCLE ' 

' ' ' r WATER 

W4IE R IMPOUNDMENT 

(R_IN RUNOFF: QUIP SYSTEM! 

COOLING TOWERS 

PROCESS 

SIEAM 

B0ILEP 0R&W00WN 

IPfAlMfNI 

STEAM 

f\ AN 1 

SODIUM SULFIDE 

CONCENTRATE 

n 

CRUDE 

DISTILLATION 

NEUTRALIZATION 

PHENOLS 

EXTRACTION 

SOLVEN U T 

REGENERATION 

MULTIPLE 

EFFECT 

EVAPORATION 

€ 

FIG. 1. Cresylic acid recovery from refinery spent caustic. 
P.78 

ds Cresols and Cresylic Acids 221 

ols 

ted 

.nt 

•li e 

"he 

the 

his 

on 

the 

. in 

cle 

ine 

lof 

: is 

ds. 

The purified spent caustic is "sprung" or neutralized with a suitable acid, 

normally hydrogen sulfide, in a reactor system and separated into the primary 

phases of crude cresylic acid and aqueous sodium sulfide. The sodium sulfide 

liquor, after extraction for removal of phenols, is fed to a multiple effect 

evaporator and subsequently withdrawn for marketing as a sodium 

sulfide/hydrosulfide concentrate. Condensate water from the evaporators is 

diverted into a water management system for balanced reuse and disposition as 

described elsewhere [12]. Tight water management and extensive water reuse 

are practiced in cresylic acid recovery operations to insure that no phenols 

escape to surface water estuaries. 

After the primary phase separation from neutralization, the crude cresylic 

acid is subjected to distillation to remove the tarlike residue. Finally, the cresylic 

acid enters a fractionation train where it is separated into its constituents and/or 

trade mixtures. 

Significant Product Fractions of Natural Cresylic Acids 

The fractions of recovered phenolic isomers which arc significant commercially 

are 

99 + % Phenol 

99 + % o-Cresol 

96 + %/;7,/7-Cresol 

85 + %/;;,/>-Crcsol 

Mixed xylenols 

Mixed xylenols and ethyl phenols 

Alkyl phenols (C3 and C4) 

Various blended cresylic acid mixtures 

The recovered phenol competes directly with synthetic phenol, is a small 

portion of the total phenol market, and is competitively priced with synthetic 

phenol. Other cresylic isomers also have prices influenced by the market price of 

phenol, benzene, and toluene. Certain isomers in high purity have values of two 

to three times phenol market value due to complexity of synthesis and/or the 

complexity of separations processes to recover them from natural cresylic acid 

streams. 

Use s 

f 

\ 

Some major uses of o-cresol are as an intermediate in herbicides, in dye carriers, 

and in the formulation of additives for lubricants. 

Three herbicides prepared from o-cresol are 2-methyl-4-chlorophenoxy 
222 Cresols and Cresylic Acids 

acetic acid (MCPA), 2-methyl-4-chlorophenoxy proprionate (MCPP), and 2.4-

dinitro-o-cresol (DNOC). These are widely used in Europe and their use in the 

United States is continuing to grow. 

The major uses of mixed m,/;-cresols are in the manufacture of phosphate 

esters and industrial phenolic resins and as solvents. High purity p-cresol is used 

as an intermediate in the manufacture of the antioxidant 2,6-diterbutyl-/>-

cresol. 

Xylenols and cresylic acid mixtures are used in phosphate ester functional 

fluids- industrial phenolic resins, and wire enamel solvents, in addition to many 

minor uses. 

An approximate profile of uses for cresols and cresylic acid in the United 

States is 

Phosphate esters 

Wire enamel solvents 

Antioxidants and additives 

Resins and adhesives 

Miscellaneous 

25 

17 

16 

17 

25 

Synthetic Cresols 

Synthetic routes to cresol manufacture have the advantage over recovery 

processes in allowing manufacture of high purity isomers with less by-product 

of low demand isomers than is contained in natural cresol sources. However, 

the raw material cost is much higher since the building blocks are phenol or 

toluene which have high market values relative to finished cresol prices. There 

are four processes used in the commercial synthesis of cresols: (1) alkylation of 

phenol with methanol, (2) toluene sulfonation, (3) cymene cleavage to cresol 

and acetone, and (4)chlorination of toluene. These arc discussed in bricfbclow. 

Alkylation 

Alkylation of phenol with methanol is a commercially important source of 

synthetic o-cresol and 2,6-xylenoL The major commercial use of 2,6-xylenol is 

as a raw material for polyphcnylencoxidc polymers developed by General 

Electric Co. Reaction between phenol and methanol over catalyst favors 

formation of ortho-substituted cresols and xylenols wittipesser activity at the 

para site and very little attack on the meta site. CatalysPsclcction is critical in 

controlling the relative proportion of alkylation between orrtho and para sites, 

with more acidic catalysts leading to increased para-site Activity. 

Methanation at the meta site ranges from virtually nil to a minor 

contamination depending on reaction conditions. The meta-site methanation 
P.80 

Cresols and Cresylic Acids 223 

which does occur is presumably formed by isomerization of other isomers 

rather than activity of the meta site during alkylation. 

Reaction temperature can have a great effect on selectivity of the alkylation 

for ortho substitution. Low temperatures (below 200°) result in production of 

anisole as the major product. Other side reactions form small amounts of 

dimethyl ether and diphenol oxide. 

Alkylation may take place in a liquid or vapor reaction, but catalyst cost 

and unfavorable increases in production of ni,/.-cresol as a side product have 

reduced the commercial value of the liquid-phase process. 

Subsequent to the alkylation reaction, removal of side products (water, 

anisole, dimethyl ether, mixed xylenols, in,p-cresol, trimethyl phenols, unreacted phenols, and methanol) is required. Pure o-cresol can be recovered 

through fractionation, but 2,6-xylenol will contain m,p-cresol unless an 

extractive step follows distillation. 

Production of pure isomers by this route is economic due to a shortage of 

petroleum and coal tar production of these isomers, but raw material costs 

make the product more expensive to produce than material recovered from byproduct streams. 

Vapor phase reaction over alumina catalyst is used to produce roughly 100 

MM lb/yr o-cresol and 2.6-xylenol in the United States. Worldwide production 

of an additional 50 MM lb/yr is reported. 

Sulfonation 

y 

;t 

Cresol manufacture by sulfonation of toluene is an analogous process to phenol 

manufacture by benzene sulfonation. except that the reaction rate is greater. 

The reaction takes place in four steps, as follows: 

>r 

e 

)f 

jl 

v. 

Sulfonation 

I. CftHsCH, + H:S 0 4 -- ChH4(CH.,)(SO,OH) + H : 0 

Neutralization 

jf 

is 

al 

rs 

ie 

in 

:s. 

or 

311 

2. 2C„H4(CH.,)(SO,OH) + Na2SO;i-> 

2C„H4(CH.,)(S02ONa) + SO, + HX) + Na 2S04 

Caustic fusion 

3. ChH4(CH3)(S02ONa) + 2NaOH - Cf,H5(CH3)ONa + Na 2S03 + H, 0 

Acidification 

i 

4. C(,H3(CH3)0Ha + SO, + H2 0 + H,S04 - } 

C„H5(CH.,)OH + Na,S03 + Na 2S04 
P.81 

224 Cresols and Cresylic Acids Cresol 

1. Toluene sulfonic acid is formed by reaction of toluene in the vapor phase 

with concentrated sulfuric acid. Water is removed azeotropically during 

reaction. 

2. Sodium toluenesulfonate is formed by neutralizing with sodium sulfite. 

S02 is boiled oil'and sodium sulfate is filtered oui. 

3. Sodium cresylate is formed by fusion of the sulfonate with sodium 

hydroxide. 

4. Free cresol is formed by acidifying the cresylate with SO'. Cresol is 

removed by phase separation and decanting. The product is then distilled 

for removal of cresylic impurities. 

The product of sulfonization is generally above 80%/;-cresol with in- and oisomcrs forming the bulk of the impurities. Some phenol and xylenol are 

present. The isomer distribution is altered by temperature and acid strength in 

sulfonation. 

Cymene Cleavage 

Cymene cleavage processes are used commercially to produce m,/;-cresols with 

relative quantities of approximately 60% meta and 40% para. o-Cresol is nearly 

absent due to difficulty of conversion of o-cymene to cresol. This makes the 

cymene process for in.p-cresol attractive to end uses in which o-cresol is an 

undesirable impurity. 

The cymene process for synthetic m.p-cresols begins with production of 

cymene from toluene and propylene over a Friedel-Crafts catalyst (e.g., 

aluminum chloride); in- and p-cymene are prevalent. Toluene and polyisopropyl toluene are removed by distillation after neutralization. Cymene is then air 

oxidized to hydroperoxycymene over a noble catalyst (palladium). Unreacted 

cymene is removed by distillation leaving a concentrated hydroperoxycymene 

which is cleaved into acetone and cresol in an acid-catalyzed reaction. Finally, 

acetone, unreacted cymene, cresols, and by-products are separated by distillation. The yield of toluene eventually converted to in,p-cresol ranges from 80 

to 95%. This process is utilized to produce synthetic m,p-cresol in Japan. 

Toluene Chlorination 

Following the same mechanism as for the manufacture of phenol by the 

chlorobenzene route, cresols have been manufactured in Europe by chlorination of toluene followed by hydrolysis with sodium hydroxide at elevated 

temperature and pressure. The resultant sodium cresylate is acidified to yield 

mixed cresols and sodium chloride. vThe mixed cresols formed contain approximately 60^, w-crcsol with the 

balance being o- and p-cresol. In order to be eeonomical,-the process requires 

salt electrolysis to regenerate the chlorine and caustic consumed. 

The yield of this process is approximately 70% conversion of toluene lo 

cresol. 
P.82 

ids 

ase 

ing 

ilc. 

um 

I is 

led 

.1 »-

are 

1 in 

Cresols and Cresylic Acids 225 

*-* 

•ith 

irly 

the 

an 

or 

.g.. 

•roair 

ted 

ene 

ny. 

ail-

. 80 

the 

ori-

.ted 

ield 

the 

ires 

: to 

TABLE 4 U.S. Marketers and Production Capacity (captive production not included) 

Producer Capacity (MM lb/yr) 

Coal tar: 

Koppers 

U.S. Steel 

Petroleum: 

Merichem Co. 

Productol Division, 

Northwest Petroche 

Ferro Corp. 

mical Division. 

Stimson Lumber Co. 

Alabama Western 

Synthetic: 

Conoco Chemicals 

Koppers 

Sherwin-Williams 

30 

20 

50 

100 

30 

30 

10 

170 

50 

10 

40 

100 

Process: 

Alkylation 

Alkylation 

Sulfonation 

Production 

See Table 4. 

Bibliography 

Patents 

U.S. 2.042.331 (1936). T. S. Carswcll (to Monsanto Chcmieal Co.). 

U.S. 2,225,564 (1940). J. W. LcMaistre et al. (lo Theo. Swann). 

U.S. 2,362,612 (1944), W. B. Brown (to Allied Chemical and Dye). 

U.S. 2,438,125 (1948), E. J. Lorand et al. (to Hercules Powder). 

British 600,837 (1948), N. M. Cullinane and W. C. Davis (to Peter Spence & Sons). 

U.S. 2,551,628 (1951), J. E. Nickels (to Koppers Co.). 

U.S. 2,632,774 (1953), J. C. Conner et al. (to Hercules Powder). 

German 889,443 (1953), E. Bruening ct al. (to Bayer). 

U.S. 2,728,797 (1955), L. J. Filar (to Hercules Powder). 

U.S. 2,751,418 (1956), H. J. Enos (to Hercules Powder). 

British 754,872 (1956). Hercules Powder. 

U.S. 2,744.143 (1956), L. J. Filar (to Hercules Powder). 

U.S. 2.767,220 (1956), M. B. Neuworth (to Pitt-Consol).