(761a) Achieving Mass-Transfer Requirements in Methane Gas-to-Liquid Bioreactors

Advances in methanotrophic biocatalysis combined with inexpensive waste methane feedstock are opening avenues for commercial production of liquid fuel in gas-to-liquid bioreactors. Methanotrophs utilize the enzyme methane monooxygenase (MMO) to activate methane to methanol, which is then further metabolized to various end products. Broths of these methanotrophs are demonstrated to grow with biomass doubling time of 7 to 20 hours and cell densities up to 62 g / L dry weight [Adegbola 2008; Reisenberg and Guthke 1999]. Enzyme turnover of 6 / s and activities near 100 umol product / g enzyme / min have been measured [Colby et al. 1977; Smith and Dalton 2004]. Further development of the biocatalyst is needed to improve conversion energy efficiency, intensify the biocatalyst activity, and allow higher bioreactor cell loading [Conrado & Gonzales 2014], ultimately to intensify production intensity toward 50 g fuel / L / hr with energy efficiency above ~65%.  While improving the biocatalyst performance is critical to enable liquid fuels from waste gas, ancillary research must also be performed to improve bioreactor gas transport to the microbes [Adegbola 2008; Fei et al. 2014; Conrado and Gonzales 2014].

Producing liquid fuel commercially requires CAPEX well under $100,000 / BPD, which places strict limitations on the size of bioreactor system components such as pumps, compressors, and balance of plant.

Other size limitations exist due to footprint requirements in the facilities that produce the waste gas feedstock. These facts set the target production rate of 50 g fuel / L / hr, which requires reactor kla of at least

10,000 / hr at vessel pressures that don't require high CAPEX/OPEX.

Control of the dissolved gas substrate during this fast reaction is important, as high concentrations are damaging to the cells and low concentrations produce byproducts [Adegbola 2008; Fei et al. 2014]. State of the art reactors must meet the high kla requirement maintain the disolved gas substrate in an optimal range. These facts highlight the need for intensification and improved control of bioreactor gas-liquid mass transfer to support future developments in biocatalysis.

This talk reviews the known gas-to-liquid transfer performance in bioreactors in terms of kla and power density. The rate-limiting gas transfer step is explored and strategy toward improved efficiency and reduced variability of kla are suggested. Our recent efforts toward achieving these targets in test reactors in our laboratory are presented.

Adegbola, O. (2008, August 21). High cell density methanol cultivation of Methylosinus trichosporium OB3b. Queen's University.

Colby, J., Stirling, D. I., & Dalton, H. (1977). The soluble methane mono-oxygenase of Methylococcus capsulatus (Bath). Its ability to oxygenate n-alkanes, n-alkenes, ethers, and alicyclic, aromatic and heterocyclic compounds. Biochemical Journal, 165(2), 395–402.

Conrado, R. J., & Gonzalez, R. (2014). Envisioning the Bioconversion of Methane to Liquid Fuels. Science, 343(6171), 620–621.

Fei, Q., Guarnieri, M. T., Tao, L., Laurens, L. M. L., Dowe, N., & Pienkos, P. T. (2014). Biotechnology Advances. Biotechnology Advances, 32(3), 596–614.

Riesenberg, D., & Guthke, R. (1999). High-cell-density cultivation of microorganisms. Applied Microbiology and Biotechnology, 51(4), 422–430.

Smith, T. J., & Dalton, H. (2004). Biocatalysis by methane monooxygenase and its implications for the petroleum industry. In Petroleum Biotechnology: Developments and Perspectives, pp. 1–31