A novel in situ gas stripping-pervaporation process integrated with acetone-butanol-ethanol fermentation for hyper n-butanol production

Butanol is considered as an advanced biofuel, the development of which is restricted by the intensive energy consumption of product recovery. A novel two-stage gas stripping-pervaporation process integrated with acetone-butanol-ethanol (ABE) fermentation was developed for butanol recovery, with gas stripping as the first-stage and pervaporation as the second-stage using the carbon nanotubes (CNTs) filled polydimethylsiloxane (PDMS) mixed matrix membrane (MMM). Compared to batch fermentation without butanol recovery, more ABE (27.5g/L acetone, 75.5g/L butanol, 7.0g/L ethanol vs. 7.9g/L acetone, 16.2g/L butanol, 1.4g/L ethanol) were produced in the fed-batch fermentation, with a higher butanol productivity (0.34g/Lh vs. 0.30g/Lh) due to reduced butanol inhibition by butanol recovery. The first-stage gas stripping produced a condensate containing 155.6g/L butanol (199.9g/L ABE), which after phase separation formed an organic phase containing 610.8g/L butanol (656.1g/L ABE) and an aqueous phase containing 85.6g/L butanol (129.7g/L ABE). Fed with the aqueous phase of the condensate from first-stage gas stripping, the second-stage pervaporation using the CNTs-PDMS MMM produced a condensate containing 441.7g/L butanol (593.2g/L ABE), which after mixing with the organic phase from gas stripping gave a highly concentrated product containing 521.3g/L butanol (622.9g/L ABE). The outstanding performance of CNTs-PDMS MMM can be attributed to the hydrophobic CNTs giving an alternative route for mass transport through the inner tubes or along the smooth surface of CNTs. This gas stripping-pervaporation process with less contaminated risk is thus effective in increasing butanol production and reducing energy consumption. Biotechnol. Bioeng. 2016;113: 120-129. (c) 2015 Wiley Periodicals, Inc.