Production of Acetone Butanol Ethanol (ABE) by a Hyper-Producing Mutant Strain of Clostridium beijerinckii BA101 and Recovery by Pervaporation Nasibuddin Qureshi and Hans P. Blaschek* University of Illinois at Urbana-Champaign, Biotechnology and Bioengineering Group, Department of Food Science and Human Nutrition, 1207 W Gregory Drive, Urbana, Illinois 61801 A silicone membrane was used to study butanol separation from model butanol solutions and fermentation broth. Depending upon the butanol feed concentration in the model solution and pervaporation conditions, butanol selectivities of 20.88-68.32 and flux values of 158.7-215.4 g m -2 h -1 were achieved. Higher flux values (400 g m -2 h -1 ) were obtained at higher butanol concentrations using air as sweep gas. In an integrated process of butanol fermentation-recovery, solvent productivities were improved to 200% of the control batch fermentation productivities. In a batch reactor the hyper-butanol-producing mutant strain C. beijerinckii BA101 utilized 57.3 g/L glucose and produced 24.2 g/L total solvents, while in the integrated process it produced 51.5 g/L (culture volume) total solvents. Concentrated glucose medium was also fermented. The C. beijerinckii BA101 mutant strain was not negatively affected by the pervaporative conditions. In the integrated experiment, acids were not produced. With the active fermentation broth, butanol selectivity was reduced by a factor of 2-3. However, the membrane flux was not affected by the active fermentation broth. The butanol permeate concentration ranged from 26.4 to 95.4 g/L, depending upon butanol concentration in the fermentation broth. Since the permeate of most membranes contains acetone, butanol, and ethanol (and small concentrations of acids), it is suggested that distillation be used for further purification. Introduction Butanol is an important chemical and can be used as a feedstock for plastic industries and fuel and as an extraction solvent in the food industry. As a fuel, butanol has several advantages over other fermentatively pro- duced fuels and these include high energy content, miscibility with diesel fuel, and a low vapor pressure. Butanol is produced by fermentation using Clostridium acetobutylicum or C. beijerinckii. The other solvents produced by these cultures include acetone or 2-propanol and ethanol. C. acetobutylicum fermentation was carried out from World War I and until after World War II. In 1945 over 60% of the total butanol produced was obtained by fermentation (1). By the 1960s, efficient production of acetone and butanol by the petrochemical industry in combination with higher costs of carbohydrate substrate sources saw the virtual elimination of industrial ABE fermentation. The last butanol fermentation plant (Na- tional Chemical Products, South Africa) was closed in 1982 (2) due to the increased cost of butanol recovery. The uncertainty of petroleum supplies and the finite nature of fossil fuels has revived research efforts aimed at obtaining liquid fuels from sources other than oil. In 1989, 4.5 billion pounds of butanol was produced from petrochemical processes. During the early eighties, efficient reactor systems were developed to achieve high reactor productivities (3- 4). However, these high reactor productivities were at the expense of low butanol concentration in the effluent streams and low sugar utilization. To solve these prob- lems, product removal techniques were investigated for the in-situ/online removal of butanol. These recovery techniques include adsorption (5-8), gas stripping (5, 9-12), liquid-liquid extraction (13-21), perstraction (22-26), pervaporation (27-32), and reverse osmosis (33). The details of these methods and their application to the ABE fermentation have been detailed elsewhere (34). These developments have played an important role in achieving high reactor productivities and high sugar utilization (up to 100%) (12, 35), and hence in improving the economics of butanol production by fermentation (36). Recovery of butanol by pervaporation has received more attention than any other technique. Pervaporation results in an increased rate of solvent production, a higher rate of sugar utilization, and recovery and partial concentration of butanol and acetone. Pervaporation does not harm the culture (28, 29, 37). Although several membrane types have been studied (silicone [poly(di- methylsiloxane), PDMS], polypropylene, liquid (oleyl alcohol and polypropylene), poly(tetrafluoroethylene), and silicone membranes filled with silicalite; ref 37) for the removal of butanol from fermentation broth, silicone- based membranes are still considered to be the best available membranes. Interestingly, a superior butanol-producing C. beijer- inckii strain was developed in 1997 (38). This culture produces 23-27 g/L total solvents from 60 g/L glucose, with a yield of 0.39-0.45, compared to a yield of 0.29- 0.33 for the parental strain. Further improvements to 33 g/L total solvents have been successful under optimized conditions (39). These improvements make the ABE fermentation process more attractive for several envi- 594 Biotechnol. Prog. 1999, 15, 594-602 10.1021/bp990080e CCC: $18.00 © 1999 American Chemical Society and American Institute of Chemical Engineers Published on Web 07/14/1999