(425e) Reactive Distillation in a Mixed Acid Esterification Process for Biobased Chemicals Production

Diluted aqueous solutions of organic acids are generated in different fermentation processes as the valuable product or byproduct. Many of those fermentation systems yield a mixture of products depending on the intended metabolic pathways and conditions within the bioreactor. The recovery and purification of individual species from fermentor effluents can be costly, contributing more than 50% of the overall production cost in some cases. Several alternatives have been proposed to overcome this problem. Among others, reactive distillation (RD) has proved success in the recovery of different acids through esterification with a variety of alcohols.

Taking this into account, this work is focused on the process to recover and esterify mixed acids produced by fermentation. Initially it is presented a new and simple method to recover carboxylic acids from diluted aqueous solutions prior esterification reaction. After recovery, and based upon a previous work involving lactate and citrate esters, it was developed a process to simultaneously esterify and separate individual products from solutions of mixed organic acids by RD. General concepts and limitations of applying simultaneous reaction and separation to mixed acid systems are discussed, and specific results from mixed succinic acid and acetic acid esterification with ethanol as a prototypical system are presented. Experiments in an elevated pressure, pilot-scale RD column, demonstrate succinic acid conversions greater than 99%, with recovery of diethyl succinate as a pure product stream.

In order to exploit and optimize this technology by computer simulation, lab scale and bench studies have focused on characterization of physical properties and phase equilibria of key species in the acetate/succinate system, and a non-ideal kinetic model for esterification of the acids has been developed. These physical properties and reaction kinetics have been incorporated into a model of the RD system using Aspen Plus simulation software, facilitating characterization of the pilot-scale results and scale-up to a commercial esterification facility.

Experimental and simulated results demonstrate that reactive separations provide opportunity for lower capital costs and greater energy efficiencies than traditional reaction and separation approaches.