GB234458A - Improvements in the method for the continuous manufacture of esters of the fatty or the aromatic series - Google Patents

Abstract

234,458. Soc. Anon. des Distilleries des Deux-SÞvres, (formerly Soc. Ricard, Allenet, et Cie). May 24, 1924, [Convention date]. Esters.-In a process for the continuous manufacture of esters of aliphatic or aromatic acids, an equimolecular mixture of the alcohol and acid is supplied continuously from a constant level tank E to a boiler A containing a quantity of one of the reacting substances (alcohol or acid) at least 50 times the quantity theoretically required for the quantity of the other reacting substance at any time present in the boiler together with a catalyst, e.g. benzene sulphonic acid, sulphuric acid or hydrochloric acid, the contents of the boiler being heated to ebullition. With esters of medium volatility, such as propyl, butyl, and amyl formates; ethyl, propyl, butyl and amyl acetates; methyl, ethyl and propyl propionates; methyl and ethyl butyrates and methyl valerianate, the water produced in the esterification forms with the ester a constant-boiling mixture which may be removed by distillation. The manufacture of ethyl acetate is given as an example, the apparatus being arranged as shown in Fig. 1. The boiler A contains 1,000 litres of commercial acetic acid and 20 kilograms of benzene sulphonic acid as a catalyst, and an equimolecular mixture of alcohol and acetic acid is supplied from the tank E at the rate of 100 litres an hour. The vapours consisting of ethyl acetate, water and traces of acetic acid pass to a column C, which returns the acid to the boiler through a conduit f. The ethyl acetate and water are condensed in a condenser Rand separate into two layers in a vessel D. A quantity of ethyl acetate corresponding to that formed by the reaction is drawn off from the upper layer and stored in a tank B. The lower layer, which consists of water with a small amount of ethyl acetate in solution, is rectified in a column C1, the water being withdrawn by a pipe g, while the ethyl acetate returns to the condenser R. Butyl acetate is manufactured in a similar manner, but the rectification of the lower layer, which consists of nearly pure water, is omitted. With the more volatile esters, such as methyl and ethyl formates, and methyl acetate, the water cannot be removed by distillation with the ester, but is withdrawn from the boiler with other products in the liquid form, the liquid being subsequently rectified. In the case of ethyl formate, Fig. 3, the boiler A contains initially alcohol, with sulphuric acid as a catalyst, an equimolecular mixture of alcohol and formic acid being continuously run in from the tank E. The vapours which consist of ethyl formate and a small quantity of alcohol pass into the column C from which the alcohol is returned to the boiler. The ethvl formate is condensed at R and drawn off into a tank B. The overflow liquid from the boiler, consisting almost exclusively of alcohol and water, passes through a conduit T into a column C1, from which the water may be withdrawn, while the alcohol passes on to a condenser R1 from which it returns to the boiler. A similar process may be used for ethyl acetate, but in this case the vapours passing from the boiler consist of a mixture of water, alcohol and ester, from which it is necessary to remove the alcohol by means of a scrubber before condensing the mixture of water and ester. In the manufacture of esters of high boiling point the method used for withdrawing the water depends on the volatility of the alcohol. In making methyl, ethyl, propyl, butyl and amyl esters, e.g. methyl oxalate, ethyl lactate, ethyl pyromucate, propyl phthalate, isobutyl phenylacetate, butyl tartrate or succinate, amyl benzoate, butyl cinnamate, or the like, the water is distilled from the boiler with the alcohol, the ester being withdrawn in the liquid state. The manufacture of butyl benzoate is described, the boiler containing butyl alcohol and hydrochloric acid as catalyst, to which an equimolecular mixture of benzoic acid and butyl alcohol is continuously added. The vapours passing from the boiler consist of butyl alcohol and water, which are condensed and separated into two layers, the upper layer, consisting of the alcohol, being returned to the boiler. The liquid overflow from the boiler consists almost exclusively of butyl alcohol and butyl benzoate, which are separated in a rectifying column. If the alcohol is not capable of removing the water, as for example in the case of esters such as benzyl benzoate, furfuryl benzoate, furfuryl pyromucate, or phenylethylphthalate, an accessory liquid such as toluene is added to the boiler. The water distils over with the toluene, while a mixture of ester, alcohol and toluene is withdrawn in the liquid state and fractionated. The manufacture of benzyl benzoate is described as an example.