Synthesis of Polymeric Membranes to Achieve High Gas-Liquid Mass Transfer

Abstract

The world is meeting its energy requirements through fossil fuels. However, the environmental consequences caused by the utilization of fossil fuels and their expected depletion are the big concerns. These issues can be resolved by environmentally friendly utilization of coal and by exploring renewable alternatives to fossil fuels. One option is to produce biofuels such as bioethanol, biobutanol and biohydrogen by the biological conversion of syngas produced by the gasification of coal and biomass. Syngas is a mixture of CO, CO2, and H2 and can be converted into biofuels by using microorganisms. The scale up of syngas fermentation is limited by several issues, mainly the gas-liquid mass transfer (GL-MT). The GL-MT in syngas fermentation can be assessed by measuring the overall volumetric mass transfer coefficient (kLa). One of the potential ways to achieve high GL-MT in syngas fermentation is by employing membrane-bioreactors (MBRs). All the published studies on MBRs have used membranes that were synthesized for water purification. Hence, there was a need to synthesize membranes targeted for high GL-MT applications. In this study, the polyimide (P84) membranes were synthesized by varying the concentration of polymer, adding different concentrations of polyvinyl pyrrolidone (PVP), and impregnating the metal-organic framework (MOF) ZIF8 to get low pore size, high porosity, and high hydrophobicity. The highest values of porosity were achieved for membranes M-8 having 12% polyimide and 2% PVP. The GL-MT of O2 was investigated in a bubble column reactor (BCR) employing membrane spargers made of pure PI (P84), additive incorporated PI, and MOF incorporated mixed matrix membrane (MMM). The average values of the obtained kLa were 136.8 h-1 (for pure PI), 212.4 h-1 (for additive incorporated membrane), and 241.2 h-1 (for MMM). For the MOF-based membranes, 78% saturation was achieved in 60 seconds with the highest kLa at a low value of AS/VL (10.7 m-1).