Recovery of Butanol From ABE Mixture Using Pervaporation Hollow Fiber Contained-Liquid Membrane

Pervaporation is an energy-efficient and cost effective  process that can be used in the recovery of  volatile organic compounds (VOCs) from fermentation broth. Pervaporation is considered to be the best among various methods for the recovery of butanol.  A new technology in pervaporation was demonstrated by using  hollow fiber contained-liquid membrane which can achieve high selectivity, increased rate of permeate flux and high recovery of butanol. Mixture of acetone, butanol and ethanol (ABE) in the ratio of 3:6:1 was used in the pervaporation experiments. The pervaporation module with polypropylene hollow fibers coated with nanofluorosilicone was  purchased from Applied Membrane Technology, Inc. (AMT, Minnetonka, MN).  The performance of the pervaporation  module was  investigated at high butanol feed concentration. Two glass tubes were used to simultaneously collect permeate using a vacuum pump operated  at 29.9 inches of water (Figure 1). Over the high butanol feed concentration  range  (~30 to 120 g/L) the butanol mass flux was shown to increase proportionally (60 to 592 g/m²-h) with an increase in the feed concentration (Figure 2). The values of ABE selectivity in water for butanol feed concentration of 30, 50, 85  and 120 g/L varied from 28, 17, 47, and 12, respectively. The pervaporation permeate collected formed two layers – organic and aqueous  –which was ~ 50 %wt butanol. The recovery of butanol from the mixture was dependent on the initial feed concentration. The recovery of butanol in 120 g/L ABE mixture was ~61 %wt, which represented the highest yield of butanol. The permeate mixture obtained was ~50 %wt  butanol. An increase in butanol feed concentration increased both the butanol and water fluxes, however, the increase in butanol flux was more pronounced than water flux, resulting in higher butanol recovery. The membrane selectivity initially increased and then started to decrease when the butanol concentration was as high as 85 g/L. These results are especially important for potential application of  hollow fiber pervaporation membrane  in  integrated process for butanol  extraction from fermentation.

        

Figure 1. Schematic diagram of hollow fiber              Figure 2. Effect of butanol feed concentration in

               pervaporation membrane                                             permeate mass flux