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Pervaporation and Nanofiltration with Ionic Liquids

Final Activity Report Summary - IONICMEM (Pervaporation and nanofiltration with ionic liquids)

Clostridium acetobutylicum, a gram-positive bacteria, is a well known for its ability to produce the solvents acetone and butanol. Large-scale fermentation systems based on the clostridial fermentation supplied the majority of the total requirement of these solvents until 1950. Due to the limitation of the productivity of the fermentation process by environmental conditions, e. g. toxicity of accumulated butanol, and the lower cost of petrochemical procedures the industrial fermentation was discontinued. A fermentation system developed by Bahl et al. (1982) permits now a reproducible and stable production of acetone and butanol. Cells are grown in a chemostat culture, with excess of glucose, a pH below 5 and phosphate limitation.

Using a pervaporation separation technique we were able to remove the solvents continuously out of the fermentation system leading to an increase of the growth of the bacteria as well as a higher yield of acetone and butanol. Supported ionic liquid-Polydimethylsiloxane blend membrane was used as a selective barrier in pervaporation process at 37 degrees Celsius. The ultrafiltration membrane (pore size 0.06 mm) was impregnated by 15 wt% of novel ionic liquid ([(C3H7)4N][B(CN)4]) and 85 wt% of polydimethylsiloxane. The selected supported ionic liquid membrane indicates a very high stability over six months during all measurements.

Using this membrane we were able to remove butanol and acetone from the culture supernatant more effectively as described by others (Qureshi et al. 1992, Soni et al. 1987, Liu et al. 2004). We were able to remove more butan-1-ol and acetone than the C. acetobutylicum was able to produce. Overall solvent productivity of fermentation connected with continuous product removal by pervaporation was 2.34 g/(lh). To prove the effectiveness of our set-up we ran the fermentation reaction on the limiting values of butan-1-ol concentration (15.82 g/l) to see, if the bacteria could still be alive under these conditions. We proved experimentally that this concentration was already deadly for the bacteria. Considered together, a C. acetobutylicum continuous fermentation set up used with a together with the indicated pervaporation technique would guarantee an increase in fermentation stability and higher production of BIObutanol.