Method for recovering resorcinol

A method for recovering resorcinol by thermally cracking high-boiling by-products contained in the acid-cleavage product of m-diisopropylbenzene dihydroperoxide, wherein the thermal cracking is effected in the presence of an aromatic ketone of the formula ##STR1## wherein R.sup.1 represents a member selected from the group consisting of hydrogen, saturated alkyl groups having 1 to 6 carbon atoms, hydroxyl, acetyl and chlorine, R.sup.2 represents a member selected from the group consisting of saturated alkyl groups having 1 to 6 carbon atoms, cyclohexyl and phenyl, and n represents 1, 2 or 3, and when there are two or more R.sup.1 groups, they are identical or different.

This invention relates to an improved method for recovering additional 
amounts of resorcinol by thermally cracking high-boiling by-products 
contained in the acid-cleavage product of m-diisopropylbenzene 
dihydroperoxide. 
More specifically, the invention relates to a method for recovering 
additional amounts of resorcinol by thermally cracking high-boiling 
by-products contained in the acid-cleavage product of m-diisopropylbenzene 
dihydroperoxide, characterized in that the thermal cracking is effected in 
the presence of an aromatic ketone of the formula 
##STR2## 
wherein R.sup.1 represents a member selected from the group consisting of 
hydrogen, saturated alkyl groups having 1 to 6 carbon atoms, hydroxyl, 
acetyl and chlorine, R.sup.2 represents a member selected from the group 
consisting of saturated alkyl groups having 1 to 6 carbon atoms, 
cyclohexyl and phenyl, and n represents 1, 2 or 3, and when there are two 
or more R.sup.1 groups, they are identical or different. 
Methods are known to produce resorcinol by acid cleavage of 
m-diisopropylbenzene dihydroperoxide (to be sometimes referred to as 
m-DHP) obtained by the oxidation of m-diisopropylbenzene (to be sometimes 
referred to as m-DIPB). The acid cleavage product is known to contain 
high-boiling by-products (by-products having a higher boiling point than 
resorcinol) in addition to resorcinol and acetone. It is assumed that 
these high-boiling by-products consist predominantly of a condensate 
between resorcinol and acetone, and condensates between resorcinol and 
olefins such as m-isopropenyl phenol. 
It is commercially advantageous therefore to recover additional amounts of 
resorcinol by thermally cracking these high-boiling by-products, and 
methods of recovery have been suggested. 
For example, British Pat. No. 739,907 discloses the recovery of additional 
amounts of resorcinol and m-isopropenylphenol from acid-cleavage 
by-products having a lower volatility than resorcinol (i.e., high-boiling 
by-products) by thermal cracking. British Pat. No. 775,813 discloses that 
the thermal cracking in the process disclosed in British Pat. No. 739,907 
is carried out while passing an inert gas such as steam, nitrogen or 
carbon dioxide. Furthermore, British Pat. No. 982,514 discloses the 
process for the recovery of resorcinol from the product of the acid 
cleavage of m-diisopropylbenzene dihydroperoxide, which comprises 
distilling the cleavage product to remove low-boiling materials, heating 
the cleavage product substantially free from low-boiling materials but 
containing the resorcinol to vaporize substantially all of the products 
other than the high-boiling condensation products, cracking the residual 
liquid mixture under reduced pressure and with the aid of steam stripping 
to vaporize further quantities of resorcinol, condensing the combined 
products of the vaporizer and the cracking process, and recovering 
resorcinol therefrom. 
In these prior techniques, cracking is performed while distilling off 
resorcinol in order to prevent recondensation of resorcinol formed by 
cracking. When the cracking proceeds and the thermally crackable 
ingredient decreases, the reaction mixture gradually becomes viscous and 
decreases in flowability. Consequently, the heat for reaction cannot be 
supplied smoothly by external heating. This not only causes a trouble to 
the cracking reaction, but also a tarry solid adheres to reactor walls, 
making it impossible to continue the reaction for long periods of time. 
British Pat. No. 739,907 states that to avoid such troubles, the cracking 
is carried out in the presence of a high-boiling substance which is 
substantially inert to resorcinol. It describes tri-isopropylbenzene, 
methylnaphthalene, isopropylnaphthalene, chloronaphthalene, 
bromonaphthalene and 1,2,4-trichlorobenzene as examples of the inert 
high-boiling substance. However, since the tarry solid is not soluble in 
such an inert high-boiling substance, it is virtually difficult to 
satisfactorily prevent the deposition of insoluble solids within the 
reactor or the adhesion of the solids to the reactor walls. 
The present inventors made investigations in order to provide an improved 
method for thermally cracking high-boiling by-products contained in the 
acid-cleavage product, which can effect the cracking reaction efficiently, 
maintain the reaction mixture within the cracking reactor in a favorable 
flowing condition, and inhibit an undesirable coking phenomenon which 
causes, for example, the deposition of insoluble solids or the adhesion of 
solids by commercially advantageous means. These investigations led to the 
discovery that the aforesaid defects of the prior art can be 
advantageously overcome by performing the thermal cracking of the 
high-boiling by-products in the presence of the aromatic ketone of formula 
(1) given hereinabove, preferably m-hydroxyacetophenone, 
p-hydroxyacetophenone or a mixture of these. 
It is an object of this invention therefore to provide an improved method 
for recovering resorcinol by thermally cracking high-boiling by-products 
contained in the acid-cleavage product of m-diisopropylbenzene 
dihydroperoxide. 
The above and other objects and advantages of the invention will become 
more apparent from the following description. 
It is known to produce m-DHP by air oxidizing m-DIPB and/or 
m-diisopropylbenzene monohydroperoxide in the liquid phase, and the 
reaction conditions used for this process are also well known. It is of 
course known that the resulting oxidation product containing m-DHP, either 
as such or after separating m-DHP from it, is subjected to acid cleavage 
to form resorcinol and acetone as main products, and high-boiling 
by-products are formed during the acid-cleavage. 
For example, m-DHP, or the product of oxidation of m-DIPB containing m-DHP 
is sent to an acid-cleavage reactor together with a suitable acid-cleavage 
solvent, for example a ketone such as acetone, methyl ethyl ketone or 
methyl isobutyl ketone, or a hydrocarbon such as benzene, toluene, xylene 
or ethylbenzene. When the oxidation reaction product is directly used, an 
oxidizing agent such as hydrogen peroxide, tert-butyl hydroperoxide or 
peracetic acid may, if desired, be caused to act on it prior to, or 
during, the acid-cleavage reaction to convert 
2-hydroxy-2-propyl-.alpha.,.alpha.-dimethylbenzyl hydroperoxide in the 
oxidation reaction product to m-DHP so that the yield of resorcinol will 
be increased. 
As is well known, acid cleavage can be performed at a temperature of about 
20.degree. to about 120.degree. C. in the presence of an acid catalyst 
such as sulfuric acid, perchloric acid, phosphoric acid, ion exchange 
resins, clays or synthetic silica alumina. 
The acid-cleavage product contains phenols such as m-isopropylphenol and 
m-isopropenylphenol, ketones such as m-isopropenylacetophenone and 
carbinols such as m-isopropylcumyl alcohol in addition to acetone and 
resorcinol, although the types of these by-products differ depending upon 
the material to be acid-cleaved. It also contains high-boiling by-products 
which are presumably a condensate between resorcinol and acetone or 
condensates between resorcinol and olefins such as m-isopropenylphenol. 
In the process of recovering resorcinol by thermally cracking high-boiling 
by-products contained in the acid-cleavage product of m-DHP which is 
formed by known means, the invention comprises effecting the thermal 
cracking in the presence of the aromatic ketone of formula (1). 
These high-boiling by-products may be those containing resorcinol and 
low-boiling by-products (by-products having lower boiling points than 
resorcinol) which remain after removal of toluene and acetone from the 
acid-cleavage product of m-DHP, those containing resorcinol remaining 
after removal of a greater portion of the low-boiling by-products, or 
those substantially free from toluene, acetone, the low-boiling 
by-products and resorcinol. The removal can be performed by known methods 
such as distillation or extraction. When the removal is performed by 
distillation, high-boiling by-products will form. According to this 
invention, such additional high-boiling by-products formed in the 
distillation step can also be advantageously cracked. 
Preferred high-boiling by-products to be cracked by the method of this 
invention are those containing up to about 60% by weight, based on the 
starting material to be cracked, of resorcinol and low-boiling by-products 
which remain after the removal of the acid catalyst from the acid-cleavage 
product by neutralization or filtration, and preferably after further 
removal of acetone and low-boiling substances such as the solvent used in 
the acid-cleavage reaction; or those containing more than 60% by weight, 
especially more than 70%, based on the material to be cracked, of 
high-boiling by-products and not more than 40% by weight, especially not 
more than 30% by weight, of low-boiling by-products and resorcinol which 
remain after further removal of a greater portion of the low-boiling 
by-products and resorcinol. 
The thermal cracking in accordance with this invention can be performed in 
the presence or absence of a catalyst. The catalyst may, for example, be 
sulfuric acid and activated terra alba which are known catalysts. 
Investigations of the present inventors have shown that a metal selected 
from tin and zinc or its oxide can also be used as the catalyst. Compounds 
of such metals capable of being converted to the corresponding metals or 
metal oxides may be used. An especially preferred catalyst is metallic 
tin, and next comes metallic zinc or tin oxide. The form of the catalyst 
is optional, and it is generally used in the form of a powder, granules or 
a plate. Depending upon the reaction temperatures, the metallic tin is 
used in liquid form. The amount of the catalyst is not particularly 
restricted. Usually, the suitable amount is 0.01 to 5 parts by weight per 
100 parts by weight of the material to be thermally cracked, although it 
may vary depending upon whether the thermal cracking is performed 
batchwise or continuously. 
As stated hereinabove, the thermal cracking of high-boiling by-products is 
carried out in the presence of the aromatic ketone of formula (1). 
Specific examples of the aromatic ketone are acetophenone, phenyl ethyl 
ketone, phenyl propyl ketone, phenyl butyl ketone, phenyl cyclohexyl 
ketone, benzophenone, tolymethyl ketone, m- and p-isopropyl acetophenones, 
m- and p-hydroxyacetophenones, o- and p-hydroxybenzophenones, diacetyl 
benzene, and o- and p-chloroacetophenones. These aromatic ketones may be 
used singly or as a mixture of two or more. Especially preferred aromatic 
ketones are m- and p-hydroxyacetophenones. 
The amount of the aromatic ketone of formula (1) is preferably at least 7 
parts by weight, more preferably at least 12 parts by weight, especially 
preferably at least 14 parts by weight, per 100 parts by weight of the 
high-boiling by-products. The use of a large amount of the aromatic ketone 
does not cause any appreciable trouble, but usually, it is used in an 
amount of up to 150 parts by weight per 100 parts by weight of the 
high-boiling by-products. 
In the present invention, the aromatic ketone may be added to the cracking 
by-product system at the time of cracking. If desired, it may be caused to 
be present in the step of oxidizing m-DIPB, or in the step of acid 
cleaving m-DHP. 
The temperature (the tower bottom temperature) of the thermal cracking is 
preferably about 170.degree. to about 400.degree. C., more preferably 
about 200.degree. to about 330.degree. C. The reaction time, which varies 
according to the thermal cracking temperature, is suitably about 0.1 to 
about 10 hours. When the thermal cracking temperature is too low, the rate 
of thermal cracking is too slow, and the process is inefficient. On the 
other hand, the use of excessively high thermal cracking temperature tends 
to induce coking, and will undesirably cause the clogging of the apparatus 
and accessory devices. 
The mode of thermal cracking can be selected as required. For example, it 
is possible to perform the thermal cracking by using a thermal cracking 
reactor of the closed type, and isolating resorcinol, etc. from the 
thermally cracked product by extraction, distillation, etc. Preferably, 
however, resorcinol and other distillable components formed by the thermal 
cracking should be distilled out of the system rapidly so as to prevent 
their consumption by secondary reactions. For example, there can be 
employed a method in which the starting high-boiling by-products are 
continuously or batchwise fed into a thermal cracking apparatus and 
thermally cracked, and resorcinol and other distillable components are 
recovered by distillation at a pressure of about 5 to 70 mm Hg; and a 
method to which superheated steam or an inert gas is blown from the bottom 
of the distillation tower, and resorcinol, etc. is recovered from the 
tower top while entraining them by this gas. 
The aromatic ketone used in the thermal cracking can be recovered for reuse 
by conventional means such as extraction or distillation. 
The following examples illustrate the present invention more specifically.

EXAMPLES 1 TO 11 AND COMATIVE EXAMPLES 1 TO 4 
From the reaction mixture obtained by the acid cleavage of the product of 
oxidation of m-DIPB, the solvent, resorcinol and by-products having lower 
boiling points than resorcinol were removed by distillation to separate 
resinous high-boiling by-products. Each of the aromatic ketones shown in 
Table 1 in the amounts indicated was added to 100 g of the high-boiling 
by-products, and the viscosity of the mixture was measured by using a 
Bismetron viscometer. The results are shown in Table 1. 
Table 1 
__________________________________________________________________________ 
Measuring 
Aromatic ketone temper- 
Viscosity 
Amount 
ature (centi- 
Example 
Type (g) (.degree.C.) 
poises) 
__________________________________________________________________________ 
1 m-Hydroxyacetophenone 
5 250 4900 
2 " 10 " 1050 
3 " 15 " 660 
4 " 25 " 135 
5 " 5 300 2700 
6 " 15 " 550 
7 p-Hydroxyacetophenone 
" 250 690 
8 " 5 300 3200 
9 p-Chloroacetophenone 
15 250 725 
10 m-Tolyl methyl ketone 
" " 900 
11 Benzophenone 20 " 920 
Comp. 
Ex. 
1 None -- 250 16000 
2 " -- 300 6400 
3 .beta.-methylnaphthalene 
40 250 11000 
4 .beta.-chloronaphthalene 
30 " 9200 
__________________________________________________________________________ 
EXAMPLE 12 
The product of oxidation of m-DIPB was acid-cleaved in a toluene/acetone 
mixed solvent, and from the reaction mixture, toluene and acetone were 
distilled off to afford a composition (A) of the following composition. 
______________________________________ 
Low-boiling by-products 
22.5% by weight 
Resorcinol 33.6% by weight 
High-boiling by-products 
43.9% by weight 
______________________________________ 
A preheater having an inside diameter of 5 mm and a length of 400 mm was 
mounted onto the third tray from the bottom of a 10-sieve tray 
distillation tower having an inside diameter of 35 mm with a distance 
between adjacent trays being 30 mm. To the composition (A) was added 
m-hydroxyacetophenone in an amount of 14% by weight based on the 
high-boiling by-products. The pre-heated was maintained at 280.degree. C. 
and the bottom of the tower was heated to 290.degree. C. The starting 
material prepared was then thermally cracked under a pressure of 8 to 14 
mmHg while adjusting the rate of feeding the starting material to 320 
ml/hr. During the distillation, the low-boiling by-products, resorcinol 
and 30%, based on the amount initially fed, of m-hydroxyacetophenone were 
continuously withdrawn from the top of the tower, and tarry components and 
70%, based on the amount initially fed, of m-hydroxyacetophenone were 
withdrawn continuously from the bottom of the tower. After the thermal 
cracking was continued for 50 hours, there was hardly any adhesion of 
insoluble matter to the inner walls of the preheater and to the withdrawn 
line from the bottom of the tower. 
EXAMPLE 13 
The composition (A) of Example 12 was heated to 220.degree. C., and 
distilled at 4 mmHg to afford composition (B) of the following 
composition. 
______________________________________ 
Low-boiling by-products 
2.0% by weight 
Resorcinol 11.5% by weight 
High-boiling by-products 
86.5% by weight 
______________________________________ 
To the composition (B) was added m-hydroxyacetophenone in an amount of 14% 
by weight based on the high-boiling by-products. The resulting starting 
material was thermally cracked in the same apparatus as used in Example 12 
for 50 hours. There was hardly any adhesion of insoluble matter to the 
inner walls of the preheater and to the withdrawing line from the bottom 
of the tower. 
COMATIVE EXAMPLE 5 
The procedure of Example 12 was repeated except that 30% by weight, based 
on the high-boiling by-products, of .beta.-chloronaphthalene was used 
instead of the m-hydroxyacetophenone. After a lapse of 9 hours, insoluble 
matter adhered to the walls of the preheater and to the withdrawing line 
from the bottom of the tower. Thus, the thermal cracking could not be 
continued further.