Process for purification of alkyl alkanoate

Details Process for purification of alkyl alkanoate Process for purification of alkyl alkanoate

2001-06-05

2003-10-14

Manoharan, Virginia (Department: 1764)

Distillation: processes, separatory

With chemical reaction

Including step of adding catalyst or reacting material

C203S018000, C203S075000, C203S055000, C203S056000, C203S057000, C203S077000, C203S078000, C203S064000, C203S080000, C203S038000, C560S248000

Reexamination Certificate

active

06632330

ABSTRACT:

This invention relates to a process for purification of an impure feedstock containing an alkyl alkanoate which contains up to 12 carbon atoms as well as at least one impurity selected from an aldehyde and a ketone and containing the same number of carbon atoms as the alkyl alkanoate.
Alkyl alkanoates can be produced by esterification of an alkaroic acid with an alkanol. An example is the esterification of acetic acid with ethanol according to equation (1):
CH
3
.CO.OH+CH
3
CH
2
OH=CH
3
.CO.O.CH
2
.CH
3
+H
2
O  (1)
Because the esterification reaction does not tend to lead to formation of by-products which have boiling points close to that of the alkyl alkanoate, recovery of substantially pure alkyl alkanoate from the esterification product mixture is usually not complicated by the presence of by-products of the esterification reaction.
Alkyl alkanoates can alternatively be produced using the Tischenko reaction. For example ethyl acetate can be produced from acetaldehyde according to the Tischenko reaction given in equation (2):
2CH
3
.CHO=CH
3
.CO.O.CH
2
.CH
3
  (2).
It is also possible to produce alkyl alkanoates from alkanols by dehydrogenation. For example ethyl acetate can be made from ethanol by dehydrogenation according to equation (3):
2CH
3
.CH
2
.OH=CH
3
.CO.O.CH
2
.CH
3
+2H
2
  (3).
Catalytic dehydrogenation of alcohols with reduced copper under ultra violet light was described by S. Nakamura et al, in
Bulletin of the Chemical Society of Japan
(1971), Vol. 44, pages 1072 to 1078.
K. Takeshita et al described reduced copper catalysed conversion of primary alcohols into esters and ketones in
Bulletin of the Chemrical Society of Japan
, (1978) Vol. 51(9), pages 2622 to 2627. These authors mention that the mechanism for ester formation has been described in the literature as the Tischenko reaction. That is to say that dehydrogenation of ethanol yields acetaldehyde as an intermediate which combines according to the Tischenko reaction to produce ethyl acetate. Alternatively, or as well, 1 mole of ethanol may combine with 1 mole of acetaldehyde to yield 1 mole of ethyl acetate and 1 mole of hydrogen according to equation (4):
CH
3
CH
2
OH+CH
3
.CHO=CH
3
.CO.O.CH
2
.CH
3
+H
2
  (4).
Production of esters from primary alcohols by dehydrogenation using bromous acid or a salt thereof in acid medium is described in JP-A-59/025334.
In SU-A-362814 there is described a process for production of ethyl acetate by dehydrogenation of ethanol at 180° C. to 300° C. in the presence of a copper catalyst containing zinc as an activator with an ethanol feed rate of 250 to 700 liters per liter of catalyst per hour.
The dehydrogenation of ethanol to form ethyl acetate is described in GB-A-287846. This proposes use of a dehydrogenating agent, such as a copper catalyst, a temperature of from 250° C. to 500° C., and a pressure of more than 10 atmospheres (1.013×10
6
Pa)
Vapour phase contact of ethanol at a temperature above its critical temperature with a catalyst comprising copper and a difficultly reducible oxide, such as zinc oxide or manganese oxide, is proposed in GB-A-312345 for the production of ethyl acetate, use of a temperature of 375° C. and a pressure of 4000 psi (27.58 Mpa) being suggested.
GB-A-470773 teaches a process for conversion of ethanol to ethyl acetate by dehydrogenating ethanol over a catalyst consisting of a reduced metal, for example, copper on infusorial earth with 10% uranium oxide as promoter, maintained at a temperature of 220° C. to 260° C. , removing by condensation some of the gas-vapour product rich in hydrogen resulting from the reaction, and returning the gaseous remainder rich in hydrogen to the catalysing zone.
EP-A-0151886 describes a process for the preparation of C
2+
esters of alkyl carboxylic acids from C
2+
primary alcohols which comprises contacting a vaporous mixture containing a primary C
2+
alkanol and hydrogen in an alkanol:hydrogen molar ratio of from 1:10 to about 1000:1 at a combined partial pressure of alkanol and hydrogen of from about 0.1 bar (10
3
Pa) up to about 40 bar (4×10
6
Pa) and at a temperature in the range of from about 180° C. to about 300° C. in a catalytic reaction zone with a catalyst consisting essentially of a reduced mixture or copper oxide and zinc oxide, and recovering a reaction product mixture containing a primary C
2+
alkyl ester of an alkyl carboxylic acid which ester contains twice as many carbon atoms as the primary C
2+
alkanol.
In EP-A-0201105 there is described a method for converting primary alcohols, such as ethanol, to their corresponding alkanoate esters which involves the regulation of the mole feed ratio of hydrogen gas to alkanol in the reaction zone of a copper chromite containing catalyst.
Separation of ethyl acetate from a composition comprising ethyl acetate, ethanol and water is disclosed in JP-A-05/186392 by feeding the composition to a distillation column to obtain a quasi-azeotropic mixture comprising ethyl acetate, ethanol and water, condensing it, separating the condensate into an organic layer and an aqueous layer, returning the organic layer to the column, and recovering ethyl acetate as a bottom product from the column.
EP-A-0331021 describes how carbonylation of olefins to produce monocarboxylate esters causes formation of aldehydes and acetals as byproducts. Monocarboxylate esters produced in this way are subjected to a three step purification process involving treatment with a strongly acidic agent, followed by hydrogenation and distillation. The initial treatment with a strongly acidic agent is intended to convert acetals to vinyl ethers and aldehydes and acetals to aldols. The subsequent hydrogenation step then converts these compounds to byproducts which are more easily separated from the desired monocarboxylate ester.
EP-A-0101910 contains a similar disclosure regarding carbonylation of olefins to give monocarboxylate esters. It proposes treatment of the monocarboxylate ester with hydrogen at elevated temperature in the presence of an acidic ion exchanger or zeolite doped with one or more metals of Group VIII of the Periodic Table, followed by hydrogenation. It is stated that acetals present as byproducts are converted to vinyl ethers which are converted by hydrogenation to low boiling esters or the aldehydes and acetals are converted to high boilers by an aldol reaction. Unsaturated ketones are converted to saturated ketones.
One particular problem in production of alkyl alkanoates by dehydrogenation of an alkanol is that the reaction product mixture tends to be a complex mixture including esters, alcohols, aldehydes and ketones. The reaction product mixtures contain components with boiling points close to that of the desired alkyl alkanoate or alkanoates. In some cases such components can form azeotropes, including azeotropes with the desired alkyl alkanoate or alkanoates whose boiling points are close to that of the alkyl alkanoate or alkanoates. This is a particular problem when a high purity alkyl alkanoate, such as ethyl acetate, is desired.
The present invention accordingly seeks to provide a novel process for recovery of a substantially pure alkyl alkanoate from an impure feedstock, for example a crude product produced by dehydrogenation of an alkanol which contains by-products whose boiling point is close to that of the desired alkyl alkanoate or alkanoates and which, in some cases at least, from azeotropes with the alkyl alkanoate or alkanoates whose boiling points are close to that of the desired alkyl alkanoate or alkanoates. It further seeks to provide a process for purification of an impure feedstock containing an alkyl alkanoate containing up to 12 carbon atoms which further contains as an impurity at least one aldehyde and/or ketone which contains the same number of carbon atoms as the alkyl alkanoate so as to result in production of a substantially pure alkyl alkanoate product. In addition the invention seeks to provide an improved p

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