Pervaporative recovery of ABE during continuous cultivation: Enhancement of performance

Acetone, butanol and ethanol were produced in a continuous two-stage fermentation integrated with pervaporation using freely suspended cells of C. acetobutylicum ATCC 824. PDMS composite pervaporation membranes were directly coupled to the second fermentor which lead to decreased solvent titers. Overall productivity was increased from 0.45 g L−1 h−1 to 0.88 g L−1 h−1 when increasing the carbohydrate concentration in the feed from 60 to 120 g L−1. The highest overall productivity of 1.13 g L−1 h−1 was achieved when increasing the carbohydrate concentration further to 150 g L−1 even though productivity decreased significantly in the first fermentor due to substrate inhibition. In this phase that lasted 200 h, the average flux reached 0.621 kg m−2 h−1 and the total solvent concentration in the permeate was 202 g L−1. High solvent titers in the second fermentor were beneficial for the performance of the pervaporation unit leading to higher fluxes and total solvent concentrations in the permeate.