(38d) Reactive Distillation for the Biorefinery : Pilot Plant Synthesis of Succinic Acid Esters

Reactive distillation is a multifunctional process where chemical reaction and distillation occur simultaneously in a single integrated vessel. The numerous advantages arising from the synergistic interaction of unit operations in a single unit over conventional, sequential operation of a reactor followed by a distillation column include overcoming thermodynamic limitations of chemical reaction, improving selectivity via rapid removal of products from the reaction zone to limit secondary reactions, reacting away azeotropes, utilizing exothermic heat of reaction for vaporization, and avoiding hot spot formation.

Organic acid esters, produced by reaction of organic acids and alcohols, can be classified as biorenewable or green chemicals that replace petroleum-based solvents. Succinic acid esters have low toxicity and vapor pressure at the same time exhibit exceptional solvent properties and find commercial applications in solvents and paint strippers. In addition succinate esters are intermediates in the synthesis of polybutylene polymers which finds broad applications in automobiles and consumer goods.

Dilute aqueous solutions of organic acids are produced through fermentation routes. Many of these fermentation processes yield a mixture of products based on the metabolic pathways and the conditions within the bioreactor. Succinic acid synthesis from fermentation route typically contain a mixture of acids such as acetic acid and lactic acid as fermentate byproducts.

In this work, a pilot scale reactive distillation process is demonstrated for succinic acid esterification and for mixed succinic acid and acetic acid esterification. The products of the mixed acid reactive distillation process are separated from each other in the reactive distilation column. The pilot scale experiments are performed at pressures from 4 to 80 psig and experimental conversions of >99% has been experimentally demonstrated. Recovery of diethyl succinate in purities exceeding 98% has been experimentally achieved.

Aspen Plus simulation software has been used for modeling the reactive distillation system. Simulation of a commercial 25 million lb/annum column shows that reactive distillation can cut the cost of ethyl succincate production and provide a significant non fuel revenue stream for ethanol plants.