(174e) 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.