(601g) An Alternative Method for Mono, Di and Tri Esters of Citric Acid Separation

Citric acid triesters are well known green plasticizers that are preferred over phthalates on medical devices and children products applications. Its production is accomplished by batch esterification using large excess of alcohol and long reaction times. During esterification of citric acid a broad distribution of products is formed: mono, di and triesters together with dimmers and oligomers produced by self esterification of hydroxyl and acid moieties of the acid. This distribution is in general inevitable due to the reversible nature of the esterification reaction.

In order to enhance esterification of citric acid, a simultaneous reaction and separation process such as reactive distillation (RD) can be applied. By using this technology, chemical equilibrium limitations can be overcome and selectivity can be improved due to rapid separation of products. However there is poor or none characterization of intermediate products of reaction. In order to develop a RD process for citric acid esterification it is required to know phase equilibria an properties of intermediate compounds (mono and di esters). In this direction preparative chromatography is a highly efficient method for separation of chemicals with similar structures and moieties. This process is suitable for separation of thermolabile, heat sensitive, non volatile components.

In this work a semi-continuous preparative chromatography process was developed for separation of ethyl citrate esters. Initially, partial esterification reaction was carried out using a stirred glass reactor using Amberlyst 70 as catalyst. An especially developed polymeric packing was used as stationary phase and the reactive mixture was used as mobile phase with and without solvent.      

A high purity mono ethyl, di ethyl and tri ethyl citrate fractions were obtained, and they were analyzed by High Performance Liquid Chromatography (HPLC) and Nuclear Magnetic Resonance (NMR) to confirm the chemical identity of obtained substances. Some physicochemical properties of pure intermediate esters useful for RD modeling are reported.