Abstract
Separation and purification of butanol from Acetone-Butanol-Ethanol (ABE) fermentation broths is one of the main challenges related to the implementation of butanol biorefineries from agrofood wastes. Due to the great energy consumption of conventional solvent recovery technologies, it is essential to find more environmentally friendly and economically viable techniques. In this work, two-stage gas stripping was assessed as an ecoefficient butanol recovery technique. Firstly, in a one-stage stripping unit, three working variables (feed temperature, gas flow and refrigeration temperature) were optimized via response surface methodology (RSM) to increase simultaneously butanol selectivity (aB) and butanol recovery efficiency (?B). After one-stage simple gas stripping optimization (T feed = 60 °C, Gas flow = 1.34 L/min, T refrigeration = 5 °C and t = 4 h), values of aB = 11.08-13.95 and ?B = 59-67% were reached, with a butanol concentration in the condensate of 119 g/L (141 g/L ABE). These working conditions were applied to two-stage gas stripping, and a butanol concentration of 300-360 g/L was attained in the condensate of the second stripping, reaching a butanol selectivity (aB) of 7-8 and a butanol recovery (?B) of 70-80 %. This process could significantly reduce energy consumption in the final butanol purification process. In addition, the resistance of the ABE fermentation strain Clostridium beijerinckii CECT 508 to this technique was assessed by subjecting the microorganism to various in situ gas stripping processes under fed-batch conditions employing cheese whey as a substrate. Bacteria were negatively affected by the stripping process, due to the high T feed (60 °C) but they were able to recover and produce butanol again.
