GB902355A - Continuous esterification process - Google Patents

Abstract

Esters are prepared by a continuous process comprising passing a mixture of a carboxylic reactant and an alcohol into a first series of zones, one reactant being in stoichiometric excess over the other, heating the mixture in this series of zones in the presence of a stream of inert permanent gas or normally gaseous hydrocarbon to produce an ester, the reactant in excess being more volatile than the ester produced, removing the water of esterification from the said series of zones by entrainment in the permanent gas or gaseous hydrocarbon, passing the esterification product consisting of the ester and unreacted reactant to a second series of heated zones through which is passed a stream of a permanent gas or gaseous hydrocarbon, recovered and freed from entrained material after passage through the first series of zones, to remove by entrainment the reactant present in the esterification product, returning all or part of the mixture of the reactant and permanent gas or gaseous hydrocarbon to the first series of zones and recovering the reactant-free ester from the second series of zones. The carboxylic reactant is an acid such as stearic, maleic, adipic, isosebacic, sebacic, phthalic, isophthalic or terephthalic acid; an anhydride such as maleic or phthalic anhydride; or a partially esterified di- or polycarboxylic acid. The alcohols may be mono-, di- or poly-hydric and are preferably not more volatile than n-butanol and include amyl, hexyl and decyl alcohols and cyclohexanol. The first series of zones are generally maintained at 105 DEG -250 DEG C., while the second series are maintained at a lower temperature. Both series may be in the form of bubble-cap towers with independent heating for each section. The gaseous entrainer may be nitrogen, hydrogen, carbon dioxide, air or butane. Unchanged reactant entrained in the gas leaving the first series of zones is recovered and recycled. Esterification is preferably effected in the presence of sulphuric acid or toluene sulphonic acid as catalyst. A suitable form of apparatus is described and is used in esterifying phthalic anhydride with an excess of n-octanol. According to the Provisional Specification, there may be used as the carboxylic reactant, an ester of a carboxylic acid with an alcohol more volatile than the alcohol to be esterified. Specifications 660,021 and 732,784 are referred to.