Diethyl succinate is valuable as a solvent and as an intermediate feedstock. In this project, we considered production of diethyl succinate from hydrolysis broth that may contain small amounts of acetic acid in addition to succinic acid. We considered esterification with ethanol.
We developed and patented a separation procedure to remove the succinic acid from the fermentation solids by esterification. The partially-reacted succinate is fed into a prereactor go further raise concentration, and then fed to a reactive distllation.
A combination of literature parameters and our own work was used for process modeling. The green cells show binary parameters that were obtained in this work. As part of the work, we synthesized and purified monoethyl succinate so that binary parameters for the monoester could be obtained. Becasue traces of other components were present in the monoethyl succinate, we obtained binary parameters from multicomponent mixtures for monoethyl succinate.
Phase equilibria measurements were modeled with both UNIQUAC + Hayden-O'Connell and NRTL + Hayden-O'Connell. AcAc - acetic acid, DES - diethyl succinate, EtAc - ethyl acetate.
Using parameters obtained from phase equilibria, We represented the reversible reactions. The solid lines are concentration-based kinetics and the dased lines are activity-based kinetics.
The reactive separation was designed using our models and verified in our pilot facility. The flow rates for the pilot facility are shown in the figure. The process simulation agrees extremely well with the pilot plant data.
We performed process economics to show that recovery of the ethyl acetate adds significantly to the cost. Without recovery of ethyl acetate, the price to provide a 30% ROI is about $1.25/kg when the feedstock is 100 g/L and production is 100 million lbs/year.
