(613d) Esterification of Succinic and Acetic Acid Mixtures with Ethanol by Reactive Distillation

Bio-based succinic acid (SA) obtained by fermentation is considered a major platform molecule for the future chemical industry. It can be used as feedstock and intermediate in production of solvents, surfactants, biodegradable polymers, specialty chemicals and commodities. With some organisms, fermentation to produce SA also produces acetic acid (AcAc) and small amounts of pyruvic, lactic, and/or formic acid, making difficult to isolate pure SA crystals. Among proposed alternatives to economically separate and recover these carboxylic acids esterification has proven an attractive alternative. Because esterification is equilibrium limited, the ongoing removal of products during reaction is required to achieve complete reaction. In that sense, reactive distillation (RD) columns can be used not only to overcome equilibrium limitations by removing reaction products, but it also can separate succinic esters from other carboxylic acid esters formed. In this work, a pilot scale reactive distillation process is demonstrated for simultaneous succinic acid and acetic acid mixed esterification with ethanol. Experiments in an elevated pressure, pilot-scale RD column demonstrate succinic acid and acetic acid conversions greater than 99% with recovery of diethyl succinate in a purity exceeding 98%. Ethyl acetate is recovered in a mixture of water and excess ethanol, from which it can be isolated as a valuable byproduct. Using experimental phase equilibria and reaction kinetic data, AspenPlus simulations of the reactive distillation column have been performed. An equilibrium stage model with kinetically controlled reaction reasonably predicts the pilot-scale column behavior and can be used to simulate a commercial scale unit. An economic analysis of such a commercial process has been carried out. Experimental and simulation results demonstrate that reactive separations provide the opportunity to economically produce bio-based chemicals produced in the biorefinery.