(246b) Removal and Recovery of Solvents from Fermentation Broth by Pervaporation and Extractive Pervaporation Process Using Liquid Membranes

Pervaporation is attractive for separation and recovery of volatile fermentation byproducts present at low concentrations. Although polymeric or ceramic membranes are quite successful in removing most volatile organic compounds (VOCs) from their dilute aqueous solution, their selectivities for removing polar organic compounds are not very high. Previous studies indicated that liquid membranes can achieve much higher selectivity for small molecules such as acetic acid, butanol, etc. Here, we have focused on liquid membranes immobilized in novel porous hollow fiber-based membranes as a support for the pervaporation process. Volatile fermentation byproducts such as acetone, butanol and ethanol present in low concentrations have been separated by novel liquid membranes of tri-n-octylamine (TOA). We have tested the liquid membrane with model solutions (containing acetone-butanol-ethanol (ABE)) as well as a filtered solution from a fermentation broth (ABE fermentation). Very high selectivities achieved for butanol, acetone, and ethanol were 275, 220 and 80 respectively with corresponding mass fluxes of 11.0, 5.0, and 1.2 g/m2-hr at a temperature of 54 °C for a feed solution containing 1.5 wt % butanol, 0.8 wt % acetone, and 0.5 wt % ethanol. High stability of liquid membrane was also observed with virtually no contamination of the broth. This was achieved by having a nanoporous fluorosilicone coating on a porous polypropylene (PP) hollow fiber substrate. The liquid membrane was immobilized in the PP substrate. Thinner liquid membranes have also been developed in different thicknesses. When the thickness of the liquid membrane was reduced to 1/5th of the full PP substrate thickness, the membrane yielded mass fluxes of solvents 5 times higher than those through full thickness liquid membrane; for example, butanol flux was increased to 53 g/m2-hr. Thinner liquid membrane did not lead to a change in the selectivities at various temperatures. A novel extractive pervaporation technique has also been studied to enhance the performance of ethanol separation from ethanol solutions containing 5-10 % ethanol. Ethanol selectivity as high as 100 and a flux of 15.0 g/m2-hr were obtained at 54 °C in this extractive pervaporation process.