Abstract
BackgroundButanol is regarded as an advanced biofuel that can be derived from renewable biomass. However, the main challenge for microbial butanol production is low butanol titer, yield and productivity, leading to intensive energy consumption in product recovery. Various alternative separation technologies such as extraction, adsorption and gas stripping, etc., could be integrated with acetone–butanol–ethanol (ABE) fermentation with improving butanol productivity, but their butanol selectivities are not satisfactory. The membrane-based pervaporation technology is recently attracting increasing attention since it has potentially desirable butanol selectivity.ResultsThe performance of the zeolite-mixed polydimethylsiloxane (PDMS) membranes were evaluated to recover butanol from butanol/water binary solution as well as fermentation broth in the integrated ABE fermentation system. The separation factor and butanol titer in permeate of the zeolite-mixed PDMS membrane were up to 33.0 and 334.6 g/L at 80°C, respectively, which increased with increasing zeolite loading weight in the membrane as well as feed temperature. The enhanced butanol separation factor was attributed to the hydrophobic zeolites with large pore size providing selective routes preferable for butanol permeation. In fed-batch fermentation incorporated with pervaporation, 54.9 g/L ABE (34.5 g/L butanol, 17.0 g/L acetone and 3.4 g/L ethanol) were produced from 172.3 g/L glucose. The overall butanol productivity and yield increased by 16.0 and 11.1%, respectively, which was attributed to the alleviated butanol inhibition by pervaporation and reassimilation of acids for ABE production. The zeolite-mixed membrane produced a highly concentrated condensate containing 169.6 g/L butanol or 253.3 g/L ABE, which after phase separation easily gave the final product containing >600 g/L butanol.ConclusionsZeolite loading in the PDMS matrix was attributed to improving the pervaporative performance of the membrane, showing great potential to recover butanol with high purity. Therefore, this zeolite-mixed PDMS membrane had the potential to improve biobutanol production when integrating with ABE fermentation.
Highlights
Butanol is regarded as an advanced biofuel that can be derived from renewable biomass
Butanol is considered as an advanced biofuel that can be derived from renewable biomass by ABE fermentation [1, 2]
The dispersion of zeolite particles could be uniformly in the PDMS membrane matrix. This can be attributed to the hydrophobic nature of the zeolite particles, their favorable association with the prior dispersed silicone elastomeric base. Due to this structural integrity, the mixed matrix membrane can be observed as single composite matrix, and the performance of the membrane can be evaluated by changing loading weights of the zeolites in the membrane matrix
Summary
Butanol is regarded as an advanced biofuel that can be derived from renewable biomass. The membrane-based pervaporation technology is recently attracting increasing attention since it has potentially desirable butanol selectivity. Butanol is considered as an advanced biofuel that can be derived from renewable biomass by ABE fermentation [1, 2]. In addition to the energy consumption from vacuum pump to create driving force for permeation, the phase change requires additional energy which should be at least equal to the heat of evaporation of the permeate It would be very energy-efficient if the membrane could permeate the target products with high selectivity. The zeolite-mixed PDMS membranes were once selected for product removal from ethanol/water, butanol/2,3-butanediol binary mixture due to their excellent hydrophobic nature and stability [15, 16]. There is little study about the zeolite-mixed PDMS membrane, especially ZSM-5 type of zeolite, for butanol or ABE recovery integrated with ABE fermentation
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