Patent GB-729305-A (GB)
Title: Improvements in or relating to process for the manufacture of esters
IPC: C07C69/12
Filed: 1951-10-08
Abstract: Esters of aliphatic monocarboxylic acids and aliphatic monohydric alcohols, said esters boiling below the boiling-point of the acid utilized, are obtained by continuously feeding an aliphatic monocarboxylic acid and an aliphatic monohydric alcohol to a reaction zone containing a reacting mixture of the said acid and alcohol in the presence of an acid esterification catalyst, p  feeding the vaporous reaction product containing ester, alcohol, carboxylic acid and water into an intermediate portion of a distillation column, withdrawing from the distillation column a bottoms liquid fraction consisting predominantly of the aliphatic monocarboxylic acid substantially free of the alcohol, recycling this bottoms fraction to the reaction zone and taking overhead from the distillation column a product containing ester, alcohol, and water substantially free of aliphatic monocarboxylic acid. Additional water is preferably <PICT:0729305/IV (b)/1> added to the distillation column to enable the formation of an ester, alcohol, water azeotrope therein.  The aliphatic carboxylic acid may comprise any acid which boils above the corresponding ester or ester-water azeotrope.  Specified acids are formic, acetic, propionic, butyric and valeric acids.  The aliphatic alcohols may comprise, depending on the boiling-point of the ester and the acid used, alcohols such as methyl, ethyl, isopropyl, n-propyl, sec.-butyl, isobutyl, and isoamyl alcohols.  The acid and alcohol used should preferably be as dry as possible and in starting the reaction it is preferred that the initial reacting mixture contains not more than three volumes of the acid per volume of the alcohol.  The acid catalyst used may be sulphuric or hydrochloric acid or a sulphonic acid, e.g. benzene sulphonic acid.  The description given with reference to the Figure utilizes secondary butyl alcohol and acetic acid with sulphuric acid as the esterification catalyst and the process is initiated in a reaction zone 1 containing a reacting mixture of the aliphatic acid and monohydric alcohol, the acid being preferably in excess.  The subsequent continuous feed to the reaction zone preferably contains the acid and alcohol in approximately stoichio-metric proportions, and the reaction is carried out at 109-113 DEG  C.  The resulting vaporous mixture of exter, water, unreacted alcohol and acetic acid is fed at about 109 DEG  C. by line 4 into an intermediate portion of distillation column 5, water being introduced through line 6 into line 4 in sufficient quantity to make the aqueous azeotrope compositions with the acetate and unreacted alcohol. The added water is preferably fed as liquid at about its boiling-point.  The vaporous azeotropes are removed through line 7 at about 87 DEG  C. and the mixture condensed in condenser 8 from which it flows into water separator 9 in which an upper ester layer and a bottom aqueous alcohol layer are formed.  Part of each layer is sent as reflux through lines 10 and 11 respectively to the top of the distillation column, whilst the semi-finished ester product is withdrawn from separator 9 and purified by conventional means whilst part of the water layer and of the ester layer are sent as reflux through lines 10 and 11 to the top of the distillation column.  The aqueous alcohol layer can also be returned through lines 16 and 12 in place of or supplementing fresh water entering through line 6 to the same plate as the feed in the distillation column.  Acetic acid passes through line 13 to reboiler 14 which is maintained at about 115-120 DEG  C. and recycled to the reactor either through the same line as the feed or through a different line, whereby the effective acid concentration in the reaction zone is considerably increased. Examples are given for the production of secondary butyl acetate from acetic acid and secondary butyl alcohol in the presence of sulphuric acid and the results obtained are tabulated and compared with those obtained by a prior art process in which excess acid is used and the esterification reactor is also the reboiler of a distillation column.ALSO:<PICT:0729305/III/1> Esters of aliphatic monocarboxylic acids and aliphatic monohydric alcohols, said esters boiling below the boiling point of the acid utilized, are obtained by continuously feeding an aliphatic monocarboxylic acid and an aliphatic monohydric alcohol to a reaction zone containing a reacting mixture of the said acid and alcohol in the presence of an acid esterification catalyst, and in the absence of extraneous water other than any small amounts that may be present in the acid and alcohol utilized; feeding the vaporous reaction product containing ester, alcohol, carboxylic acid and water into an intermediate portion of a distillation column, withdrawing from the distillation column a bottoms liquid fraction consisting predominantly of the aliphatic monocarboxylic acid substantially free of the alcohol, recycling this bottoms fraction to the reaction zone and taking overhead from the distillation column a product containing ester, alcohol and water substantially free of aliphatic monocarboxylic acid.  Additional water is preferably added to the distillation column to enable the formation of an ester, alcohol, water azetrope therein.  The aliphatic carboxylic acid may comprise any acid which boils above the corresponding ester or ester-water azeotrope.  Specified acids are formic, acetic, proprionic, butyric and valeric acids. The aliphatic alcohols may comprise, depending on the boiling point of the ester and the acid used, alcohols such as methyl, ethyl, isopropyl, n-propyl, sec-butyl, isobutyl and isoamyl alcohols.  The acid and alcohol used should preferably be as dry as possible and in starting the reaction it is preferred that the initial reacting mixture contains not more than three volumes of the acid per volume of the alcohol.  The said catalyst may be sulphuric or hydrochloric acid or a sulphonic acid, e.g. benzene sulphonic acid.  The description given with reference to the Figure utilizes secondary butyl alcohol and acetic acid with sulphuric acid as the esterification catalyst and the process is initiated in a reaction zone 1 containing a reacting mixture of the aliphatic acid and monohydric alcohol, the acid being preferably in excess.  The subsequent continuous feed to the reaction zone preferably contains the acid and alcohol in approximately stoichiometric proportions and the reaction is carried out at 109-113 DEG  C.  The resulting vaporous mixture of ester, water, unreacted alcohol and acetic acid is fed at about 109 DEG  C. by line 4 into an intermediate portion of distillation column 5, water being introduced through line 6 into line 4 in sufficient quantity to make the aqueous azeotrope compositions with the acetate and unreacted alcohol.  The added water is preferably fed as liquid at about its boiling point. The vaporous azeotropes are removed through line 7 at about 87 DEG C. and the mixture condensed in condenser 8 from which it flows into water separator 9 in which an upper ester layer and a bottom aqueous alcohol layer are formed.  Part of each layer is sent as reflux to the top of the distillation column whilst the semi-finished ester product is withdrawn from separator 9 and purified by conventional means.  The aqueous alcohol layer can also be returned through lines 11 and 12 to the same plate as the feed in the distillation column. Acetic acid passes through line 13 to reboiler 14 which is maintained at about 115-120 DEG  C. and is withdrawn through line 15 and recycled to the reactor either p  through the same line as the feed or through a different line whereby the effective acid concentration in the reaction zone is considerably increased.  Examples are given for the production of secondary butyl acetate from acetic acid and secondary butyl alcohol in the presence of sulphuric acid and the results obtained are tabulated and compared with those obtained by a prior art process in which excess acid is used and the esterification reactor is also the reboiler of a distillation column.