(661a) Removal And Recovery Of Solvents From Fermentation Broth By Pervaporation Using Liquid Membrane

Pervaporation is an attractive technique for separation and recovery of volatile fermentation byproducts present at low concentrations due to its lower energy cost compared with distillation. Although polymeric rubbery membranes or ceramic membranes are quite successful in removing most volatile organic compounds (VOCs) from their dilute solutions in water, their selecitivies for removing polar organic compounds are not very high. Previous studies indicated that liquid membranes can achieve much higher selectivity for some small molecules such as acetic acid, ethanol, butanol, etc. In the current work, we have focused on liquid membranes immobilized in novel porous hollow fiber-based membranes as a support for the pervaporation process to increase the VOC selectivity and membrane stability. Volatile fermentation byproducts such as acetone, butanol and ethanol present in low concentrations in synthetic aqueous solutions have been separated by novel liquid membranes. We have tested the liquid membrane with model solutions (containing acetone-butanol-ethanol (ABE)) as well as a filtered solution from a fermentation broth (from ABE fermentation) by the pervaporation process. Very high selectivities for the solvents were obtained in the permeate especially at higher feed temperatures (> 50°C). The selectivities of butanol, acetone, and ethanol achieved were 275, 220, and 80 respectively with 11.0, 5.0, and 1.2 g/m2-hr for the mass fluxes of butanol, acetone and ethanol respectively 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. Fluxes and selectivities of solvents were studied over a range of temperatures; higher temperatures yielded much higher selectivities. Thinner membranes have been developed in different thicknesses. The thickness of liquid membrane was reduced to 5 times thinner than the full substrate thickness, which yielded mass fluxes of solvents 5 times higher than those through full thickness liquid membrane. Thinner liquid membranes did not lead to a change in the selectivities at various temperatures. The thinner liquid membranes have been tested with model solutions and filtered fermentation broth from ABE fermentation at various temperatures.