Wednesday, May 6, 2009 - 10:00 AM
9-04
Reactive separations for esterification and purification of individual organic acids from mixed solutions
Aspi K. Kolah, Alvaro Orjuela, Carl T. Lira, and Dennis J. Miller. Chemical Engineering and Materials Science, Michigan State University, 2527 Engineering Building, East Lansing, MI 48824
Many 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 fermenter effluents can be costly, contributing more than 50% of the overall production cost in some cases. We present here the results of reactive separation studies, building on prior work involving lactate and citrate esters, to simultaneously esterify and recover individual products from aqueous solutions of mixed organic acids. 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 as a prototypical system are presented. Experiments in an elevated pressure, pilot-scale reactive distillation column in our laboratories demonstrate succinic acid conversions greater than 99%, with recovery of diethyl succinate as a pure product stream. 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 simultaneous esterification of the acids has been developed. These physical properties and reaction kinetics have been incorporated into a rigorous simulation of the reactive distillation system using AspenPlus simulation software, facilitating characterization of the pilot-scale results and scale-up to a commercial esterification facility. Reactive separations are thus emerging as versatile, economical, and “green” technologies for the biorefinery, providing opportunity for lower capital costs and greater energy efficiencies than traditional reaction and separation approaches.