Controlled alkali treatment in the recovery of methyl tertiary butyl ether

In the manufacture of MTBE from TBA and methanol, acidic by-products formed during the etherification reaction are removed by fractionating the etherification reaction product in a first MTBE distillation column to provide a first lower boiling distillation fraction comprising isobutylene, MTBE, methanol and acidic by-products and a first higher boiling distillation fraction comprising methanol, TBA and water, fractionating the first higher boiling distillation fraction in a recycle distillation column to provide a lower boiling TBA recycle fraction and a higher boiling water fraction, recycling the higher boiling water fraction to the MTBE distillation column at a charge point above the charge point for the etherification reaction product, and adding aqueous sodium hydroxide to the recycled higher boiling water fraction in an amount sufficient to neutralize the acidic by-products charged to the MTBE distillation column.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Invention 
This invention relates to a method for the manufacture and purification of 
methyl tertiary butyl ether prepared from tertiary butyl alcohol and 
methanol. More particularly, this invention relates to a method for 
removing acidic by-products formed during the reaction of tertiary butyl 
alcohol with methanol. 
Methyl tert-butyl ether is finding increasing use as a blending component 
in high octane gasoline as the current gasoline additives based on lead 
and manganese are phased out. 
2. Prior Art 
In U.S. Pat. No. 4,144,138 (1979) to Rao et al., there is disclosed a 
method for recovering methyl tertiary butyl ether from etherification 
reaction effluent by azeotropic distillation to recover methanol-ether 
azeotrope overhead which is water-washed to give pure ether raffinate, the 
latter being azeotropically distilled to yield ether-methanol overhead 
which is recycled to water washing. 
Kruse et al. U.S. Pat. No. 5,243,091, entitled "Method for the Manufacture 
and Recovery of Methyl Tertiary Butyl Ether", discloses a method for the 
preparation of methyl tertiary butyl ether wherein tertiary butyl alcohol 
is reacted with methanol to provide a reaction product comprising methyl 
tertiary butyl ether and by-product isobutylene and wherein the by-product 
isobutylene is reacted with methanol to provide additional methyl tertiary 
butyl ether and also a water washing method for the purification of the 
methyl tertiary butyl ether. 
Gupta U.S. Pat. No. 5,292,964 discloses a process for the manufacture of 
methyl tertiary butyl ether from tertiary butyl alcohol and methanol 
wherein tertiary butyl alcohol is reacted with methanol in a primary 
reaction zone to provide a reaction product comprising methyl tertiary 
butyl ether, unreacted tertiary butyl alcohol, unreacted methanol and 
water, wherein the reaction product is separated in a distillation zone 
into a lighter fraction comprising substantially anhydrous methanol and 
methyl tertiary butyl alcohol and a heavier fraction comprising tertiary 
butyl alcohol, methanol and water, and wherein the lighter fraction is 
charged to a finishing reactor wherein the methanol is reacted with 
isobutylene to form additional methyl tertiary butyl ether. 
The preparation of methyl tert-butyl ether from methyl and tert-butyl 
alcohols is discussed in S. V. Rozhkov et al., Prevrashch Uglevodorodov, 
Kislotno-Osnovn. Geterogennykh Katal. Tezisy Dokl., Vses. Konf., 1977, 150 
(C. A. 92:58165y). Here the TBA and methanol undergo etherification over 
KU-2 strongly acidic sulfopolystyrene cation-exchangers under mild 
conditions. This reference contains data on basic parameters of such a 
process. 
In Cassata et al. U.S. Pat. No. 5,395,982, filed Nov. 8, 1993, and entitled 
"Continuous Isobutylene-Assisted Aqueous Extraction of Methanol from 
Methyl Tertiary Butyl Ether," a process is disclosed wherein an impure 
methyl tertiary butyl ether product contaminated with isobutylene, 
methanol and water is purified by continuous counter-current contact with 
water and isobutylene in a counter-current contact extraction tower to 
provide an overhead raffinate comprising isobutylene, methyl tertiary 
butyl ether and water and an extract comprising methanol, water and a 
minor amount of methyl tertiary butyl ether, the overhead raffinate being 
separated in a methyl tertiary butyl ether purification distillation zone 
into a lighter distillation fraction comprising isobutylene and water and 
a heavier distillation fraction consisting essentially of methyl tertiary 
butyl ether, the lighter distillation fraction being decanted to remove 
water and to provide a distillate isobutylene fraction that is returned to 
the contact tower. 
In copending Peters et al. U.S. patent application Ser. No. 08/299,391, 
filed Sep. 1, 1994, and entitled "Preparation of Methyl Tertiary Butyl 
Ether with Recycle" (D#81,148-D1), there is disclosed a process for the 
manufacture of methyl tertiary butyl ether from tertiary butyl alcohol and 
methanol and to the purification of a methanol-contaminated methyl 
tertiary butyl ether intermediate product formed during the process; the 
intermediate product being purified by counter-current contact with water 
in an extraction tower, wherein isobutylene is added to the extraction 
tower to assist in the formation of an extract composed of methyl tertiary 
butyl ether, isobutylene and water and in the formation of a raffinate 
comprising methanol, isobutylene, residual methyl tertiary butyl alcohol 
and water. 
SUMMARY OF THE INVENTION 
This invention is directed to an improved method for the manufacture of 
methyl tertiary butyl ether from tertiary butyl alcohol and methanol and 
to the removal of acidic by-products formed during the reaction of 
tertiary butyl alcohol with methanol by charging the etherification 
reaction product to a first MTBE distillation column and fractionating it 
therein to provide a first lower boiling distillation fraction comprising 
isobutylene, methyl tertiary butyl ether, and methanol and also to provide 
a first higher boiling distillation fraction comprising methanol, tertiary 
butyl alcohol and water, by charging the first higher boiling distillation 
fraction to a recycle distillation column and fractionating it therein to 
provide a lower boiling recycle fraction comprising tertiary butyl alcohol 
and a higher boiling fraction comprising water and acidic by-products, by 
recycling the higher boiling water fraction to the MTBE distillation 
column at a charge point above the charge point for the etherification 
reaction product, and by adding aqueous sodium hydroxide to the recycled 
higher boiling fraction water in an amount sufficient to neutralize the 
acidic by-products charged to the MTBE distillation column. 
The etherification reaction product obtained by reacting tertiary butyl 
alcohol with methanol will comprise methyl tertiary butyl ether, methanol, 
tertiary butyl alcohol, water, isobutylene, and acidic by-products 
including organic acids and esters such as methyl formate isobutyl 
formate, t-butyl acetate, etc. It is difficult to remove methyl formate 
from methyl tertiary butyl ether. 
In accordance with a preferred embodiment of the present invention, the 
alkalinity of the recycled higher boiling fraction water is monitored and 
the amount of sodium hydroxide added to the recycled higher boiling 
fraction water is modified to compensate for a deviation in the alkalinity 
from a desired value. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
I 
In accordance with a preferred embodiment of the present invention, a 
method for the continuous preparation of methyl tertiary butyl ether from 
tertiary butyl alcohol, and methanol is provided which comprises: 
a) continuously reacting methanol with tertiary butyl alcohol in a primary 
reactor to form an etherification reaction product comprising methanol, 
tertiary butyl alcohol, water, isobutylene, acidic by-products and methyl 
tertiary butyl ether; 
b) continuously charging the etherification reaction product to a first 
methyl tertiary butyl ether distillation zone and separating it therein 
into a first lower boiling distillation fraction comprising methyl 
tertiary butyl ether, isobutylene, methanol and water and a first higher 
boiling distillation fraction comprising tertiary butyl alcohol, methanol 
acidic by-products and water; 
c) charging the first higher boiling distillation fraction to a recycle 
distillation column and fractionating it therein to provide a lower 
boiling recycle fraction comprising tertiary butyl alcohol and a higher 
boiling fraction comprising acidic by-products and water; 
d) recycling higher boiling water fraction to the first MTBE distillation 
column at a charge point above the charge point for the etherification 
reaction product; and 
e) adding aqueous sodium hydroxide to the recycled higher boiling water 
fraction in an amount sufficient to neutralize the acidic by-products 
charged to the MTBE distillation column. 
In a more specific embodiment of the present invention: 
a) methanol is continuously reacted with tertiary butyl alcohol in a 
primary reactor under reaction conditions including a pressure of about 30 
to about 500 psia, and more preferably from about 200 to about 300 psia, a 
temperature of about 30.degree. to about 200.degree. C., and more 
preferably from about 80.degree. to about 140.degree. C., and still more 
preferably from about 90.degree. to about 130.degree. C., to form an 
etherification reaction product comprising methanol, tertiary butyl 
alcohol, water, isobutylene, acidic by-products including methyl formate, 
and methyl tertiary butyl ether; 
b) the etherification reaction product is charged to a first MTBE 
distillation zone and fractionated therein under distillation conditions 
including a liquid reflux temperature of about 30.degree. to about 
100.degree. C., and more preferably about 40.degree. to about 80.degree. 
C., a reboiler temperature of about 80.degree. to about 115.degree. C., 
and more preferably from about 95.degree. to about 105.degree. C., and a 
pressure of about 15 to about 60 psia to provide a first lower boiling 
distillation fraction comprising isobutylene, methyl tertiary butyl ether, 
methanol and acidic by-products and a first higher boiling distillation 
fraction comprising methanol, tertiary butyl alcohol and water, the 
distillation condition being selected such that substantially all of the 
MTBE in the etherification reaction product is taken with the first lower 
boiling distillation fraction; 
c) the first higher boiling distillation fraction is charged to a recycle 
distillation column and fractionated therein under distillation conditions 
including a liquid reflux temperature of about 35.degree. to about 
170.degree. C., and more preferably about 140.degree. to about 150.degree. 
C. and a reboiler temperature of about 100.degree. to about 190.degree. 
C., more preferably about 170.degree. to about 180.degree. C., and at a 
pressure of about 15 to about 190 psia, and more preferably about 110 to 
about 160 psia, to provide a lower boiling tertiary butyl alcohol recycle 
fraction and a higher boiling water fraction; 
d) an alkaline solution of a sodium hydroxide is prepared by mixing aqueous 
sodium hydroxide with a portion of the higher boiling water fraction; 
e) the alkaline recycle water fraction is recycled to the first MTBE 
distillation column at a charge point above the charge point for the 
etherification reaction product, in an amount sufficient to neutralize the 
acidic by-products charged to the MTBE distillation column; and 
f) the lower boiling recycle tertiary butyl alcohol fraction is recycled to 
the primary MTBE reactor. 
In accordance with this embodiment, a measurement is made of the alkalinity 
of the alkaline recycle water fraction is made by measuring a property of 
the alkaline recycle water fraction (e.g., specific gravity) that is 
indicative of the alkalinity of the fraction and the amount of sodium 
hydroxide added to the recycle water fraction is adjusted in response to 
the measurement. 
DETAILED DESCRIPTION OF THE PRESENT INVENTION 
The Etherification Reaction Catalyst 
In accordance with the MTBE manufacture and purification method of the 
present invention, an etherification reaction zone containing a bed of 
etherification catalyst is utilized. A wide variety of etherification 
catalysts can be used for this purpose, such as supported phosphorus 
acid-type catalysts. A preferred catalyst is a sulfonic acid resin 
etherification catalyst such as a sulfonated polystyrene resin 
cross-linked with divinyl benzene. 
Any suitable solid resin etherification catalyst may be used for this 
purpose, such as a strongly acidic ion exchange resin consisting 
essentially of sulfonated polystyrene, such as a divinyl benzene crosslink 
polystyrene matrix containing from about 0.5 to about 20% of copolymerized 
divinyl benzene. Resins of this nature are manufactured and sold 
commercially under various trade names such as "Dowex 50", "Nalcite HCR" 
and "Amberlyst 15". The use of catalyst of this nature is disclosed, for 
example, in Rao U.S. Pat. No. 4,144,138. 
Also, Kieselguhr impregnated with phosphoric acid as disclosed in Frolich 
U.S. Pat. No. 2,282,469, titania having phosphoric acid impregnated 
thereon as disclosed in Knifton U.S. Pat. No. 4,822,921, a hetero polyacid 
such as 12-tungstophosphoric acid or 12-molybdophosphoric acid supported 
on titania, etc., may be used. 
Zeolites as disclosed in Japanese Patent 0007432 or aluminosilicate 
zeolites as disclosed in Chang et al. U.S. Pat. No. 4,058,576 may also be 
used. 
The reaction conditions to be utilized when reacting methanol with tertiary 
butyl alcohol in the presence of a sulfonic acid resin etherification 
catalyst of the type disclosed in the prior art include a reaction 
temperature of about 90.degree. to about 140.degree. C., a pressure of 
about 30 to about 500 psia and a space velocity of about 0.5 to about 20 
volumes of feed per volume of etherification catalyst per hour.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to the Figure, there is shown a schematic flow sheet 
illustrating a preferred method for the practice of the process of the 
present invention. In the figure, conventional parts, such as valves, 
pumps, temperature control sensors, pressure sensors, heaters, coolers, 
flow control regulation apparatus, reflux condensers, reboilers, etc., 
have been omitted. 
In accordance with the present invention, there is provided an 
etherification reaction zone 10 containing a bed of solid etherification 
catalyst. Any suitable etherification catalyst may be used such as, for 
example, a solid resin etherification catalyst of the type described 
above, such as a strongly acidic ion exchange resin consisting essentially 
of sulfonated polystyrene cross-linked with divinyl benzene (e.g., Dowex 
50, Nalcite HCR, Amberlyst 15, etc.). As another example, the catalyst may 
be a fluorophosphoric acid-on-titania catalyst of the type disclosed in 
Knifton et al. U.S. Pat. No. 4,822,921 or a heteropoly acid such as 
12-tungstophosphoric acid or 12-molybdophosphoric acid supported on an 
inert support such as titania. 
Substantially peroxides-free tertiary butyl alcohol is continuously charged 
by a line 17 leading to a manifold 12. Methanol is continuously charged to 
the manifold 12 by a line 15. The flow of methanol and tertiary butyl 
alcohol to the manifold 12 through the lines 15 and 17 is regulated so 
that a molar excess of methanol is present in the line 15 leading to the 
etherification reaction zone 10, such as, for example, a molar ratio of 
about 1.1 to about 3 moles of methanol per mol of tertiary butyl alcohol. 
Within the etherification reaction zone 10, the feed mixture is brought 
into contact with a bed of etherification catalyst, such as a sulfonic 
acid resin etherification catalyst under reaction conditions including a 
pressure of about 30 to about 500 psia, and more preferably from about 200 
to about 300 psia, a temperature of about 30.degree. to about 200.degree. 
C., and more preferably from about 80.degree. to about 140.degree. C., and 
still more preferably from about 90.degree. to about 130.degree. C. When 
the catalyst is a supported phosphorus acid-type catalyst, the reaction 
temperature may suitably be in the range of about 150.degree. to about 
190.degree. C. 
Contact time within the etherification reaction zone is suitably such that 
about 0.5 to about 20 volumes of feed mixture per volume of etherification 
catalyst per hour are fed to the etherification reaction zone 10 and, more 
preferably from about 1 to about 4 volumes of feed mixture per volume of 
etherification catalyst per hour. 
Within the etherification reaction zone 10, methanol will react with the 
tertiary butyl alcohol to form methyl tertiary butyl ether which will be 
contained in a reaction product discharged from the etherification 
reaction zone 10 by way of a line 20 leading to a first methyl tertiary 
butyl ether (MTBE) distillation column 30. 
As a specific example, when the solid etherification catalyst is a sulfonic 
acid resin such as Amberlyst 15 and when the molar ratio of methanol to 
tertiary butyl alcohol in the feed mixture charged to the etherification 
reaction zone 10 by the line 14 is within the ratio of about 2.0 moles of 
methanol per mole of tertiary butyl alcohol, and the reaction is conducted 
at a temperature of about 110.degree. C. at a feed rate of about 2.0 
volumes of feed mixture per volume of catalyst per hour, the 
etherification reaction product may have the composition in part shown by 
the following table: 
______________________________________ 
ETHERIFICATION REACTION PRODUCT 
wt. % 
Component (Approx.) 
______________________________________ 
Water 14.0 
Methanol 27.6 
Isobutylene 3.0 
TBA.sup.1 14.1 
MTBE.sup.2 34.5 
Other.sup.3 6.8 
______________________________________ 
.sup.1 Tertiary butyl alcohol 
.sup.2 Methyl tertiary butyl ether 
.sup.3 Includes the acetone, propanol, ditertiary butyl peroxide, methyl 
formate, tertiary butyl formate, etc. 
The etherification reaction product charged to the first MTBE distillation 
column 30 by way of the charge line 20 is fractionated therein under 
distillation conditions including a liquid reflux temperature of about 
30.degree. to about 100.degree. C., and more preferably about 40.degree. 
to about 80.degree. C. a reboiler temperature of about 80.degree. to about 
115.degree. C., and more preferably from about 95.degree. to about 
105.degree. C., and a pressure of about 15 to about 60 psia, the 
distillation condition being selected such that substantially all of the 
MTBE in the etherification reaction product 20 is taken overhead from the 
first distillation column 30 by a line 32. As a consequence, the first 
lower boiling distillation fraction 32 taken overhead from the 
distillation zone 30 will comprise substantially all of the isobutylene, 
substantially all of the methyl tertiary butyl ether and some of the 
methanol charged to the first distillation zone 30. The acidic by-products 
that would normally be present in the lower boiling distillation fraction 
32 are neutralized in the first distillation zone 30 in a manner to be 
described and the neutralized acids, including sodium formate, exit the 
distillation column 30 with the higher boiling fraction 34. 
The methyl tertiary butyl ether in the line 32 is separated from the 
isobutylene and methanol by any suitable method (not shown) such as the 
method shown and described in Kruse et al. U.S. Pat. No. 5,243,091. 
The first heavier distillation fraction 34 discharged from the first MTBE 
distillation zone 30 will comprise methanol, tertiary butyl alcohol 
neutralized acidic by-products and water. 
The first heavier distillation fraction 34 is charged to a recycle 
distillation column 100 and fractionated therein under distillation 
conditions including a liquid reflux temperature of about 35.degree. to 
about 170.degree. C., and more preferably about 140.degree. to about 
150.degree. C., and a reboiler temperature of about 100.degree. to about 
190.degree. C., more preferably about 170.degree. to about 180.degree. C., 
and at a pressure of about 15 to about 190 psia, and more preferably about 
110 to about 160 psia, to provide a lower boiling tertiary butyl alcohol 
recycle fraction 102 and a higher boiling water fraction 104. 
The lower boiling tertiary butyl alcohol recycle fraction 102, comprising 
tertiary butyl alcohol and methanol is suitably recycled to the manifold 
12 and thence by feed line 14 to the etherification reaction zone 10. 
The higher boiling water fraction 104 is charged to a manifold 106 from 
which a part of the fraction 104 is recycled to the first MTBE 
distillation column 30 at a charge point above the charge point for the 
etherification reaction product 20. The remainder of the fraction 104 is 
discharged from the system through discard line 108 to prevent an 
undesired build-up of by-products in the system. 
An aqueous solution of sodium hydroxide is prepared having a desired 
alkalinity (i.e., sodium hydroxide content), such as an aqueous solution 
containing about 15 to about 20 wt. % of sodium hydroxide. Such a solution 
will have a predeterminable specific gravity that can be changed by 
changing the amount of sodium hydroxide that is added to the aqueous 
solution of sodium hydroxide. The thus-prepared specific gravity-adjusted 
aqueous solution of sodium hydroxide of predetermined alkalinity is added 
to the recycle line 110 through a branch line 120 containing a control 
valve 122. 
The aqueous solution of sodium hydroxide of predetermined alkalinity is 
added to the recycle line 110 through the branch line 120 in an amount 
sufficient to provide an alkaline recycle fraction 110 containing an 
amount of sodium hydroxide sufficient to neutralize the acidic by-products 
present in the MTBE distillation column 30, and to thereby form 
neutralized acidic by-products, including sodium formate, that descend the 
MTBE distillation column 30 for withdrawal with higher boiling water 
fraction 104. As indicated, a portion of the higher boiling water fraction 
104 is discarded by the line 108 in order to prevent a build-up of 
neutralized acidic by-products in the system. 
In accordance with this embodiment, a sample of the alkaline recycle 
fraction 110 is withdrawn by a sample line 130 and charged to a suitable 
device, such as a specific gravity meter 140, for measuring a physical 
property of the alkaline recycle fraction 110, such as specific gravity, 
which correlates with the alkalinity of the alkaline recycle fraction 110. 
A signal responsive to the measurement (e.g., a signal responsive to a 
determination of specific gravity in the specific gravity meter 140) is 
transmitted by a line 144 to the control 124 for the control valve 122 so 
that the setting of the control valve 122 can be changed in response to a 
measurement of the specific gravity of a sample supplied to the specific 
gravity meter 140.