Continuous Isobutanol Production in a Bioreactor for Incompatible Gases

Continuous Isobutanol Production in a Bioreactor for Incompatible Gases

For presentation at 2013 Annual American Institute of Chemical Engineers Conference, November 3-8, 2013

Yangmu C. Liu¹, Soumen K. Maiti¹, Anthony Sinskey², and R. Mark Worden¹

¹ Department of Chemical Engineering and Materials Science, Michigan State University

² Department of Biology, Massachusetts Institute of Technology

Fermentations that use H₂ to reduce CO₂ to electrofuels present significant challenges for bioreactor development. First, these fermentations have unusually high demands for gas mass transfer. Second, the need to simultaneously deliver H₂ and O₂ creates safety issues, because these gases are incompatible, forming a flammable mixture over the range 4 to 94% H₂. Third, electrofuels are typically inhibitory to the microbial biocatalysts, making in-situ removal desirable for continuous bioreactor operation. This paper describes use of a novel Bioreactor for Incompatible Gases (BIG) to address these challenges. The BIG features a hollow fiber configuration, in which the microbial biocatalysts are immobilized in the porous fiber walls. A liquid phase containing microbubbles of one gaseous reactant is pumped through the fiber lumens, while a gas phase containing the gaseous reactant(s) incompatible with the first is pumped through the space outside the fibers. In this way, rapid mass transfer of both gaseous reactants is achieved, either via microbubbles or direct contact between the gaseous reactant and the immobilized cell layer. Safe operation is achieved by maintaining the incompatible gaseous reactants on opposite sides of the membrane, and in-situ product removal is achieved through the liquid stream (nonvolatile product) and/or the gas stream (volatile product). The bench-scale BIG was integrated with an Opto22-based control system that monitored and controlled the composition of the gas phase, dissolved oxygen concentration in the liquid phase, and temperature. The control system was programmed to make intelligent operational decisions in response to process contingencies. The BIG system was inoculated with an IBT-producing strain of R. eutropha and operated stably for up to 19 days. Performance properties of the BIG system during continuous IBT production under both heterotrophic and autotrophic conditions will be presented.