(328e) Isolation of Biobased Chemicals By Combination of Reactive Distillation and Pervaporation; Process Modeling

Wastewater from pulping contains several acids, mainly acetic acid and formic acid. The ternary mixture acetic acid, formic acid and water forms a binary high boiling azeotrope between formic acid and water and a ternary saddle point azeotrope. The separation step of azeotropic mixtures is energy intensive, especially when water is present as low boiling component with high excess. By changing the substance properties via esterification, reaction products with lower boiling points and low enthalpy of evaporation compared to water as well as the acids are produced.

Reactive distillation is perfectly suited for the separation of acetic acid, formic acid and water by esterification with methanol or ethanol. Therefore low boiling esters are produced which are continuously removed via the distillate. Elevated temperature in the reboiler and simultaneous esterification of both acids enhances the reaction rates. High conversion of the acids is achieved. The distillate contains the esters and excess alcohol. This mixture can further be separated via pervaporation by removing the alcohol with hydrophilic membranes. Chemical conversion of the carboxylic acids simplifies the separation step and produces esters with a higher market value.

Minimization of energy consumption and maximum acid conversion of reactive distillation was optimized by simulation and validated experimentally. Diffusivity of membranes in pervaporation of binary and ternary mixtures was determined experimentally and was modeled with an activity based approach.