(385c) Microbial Conversion of Natural Gas to Biofuel Using a Naturally Occurring Methanotroph | AIChE

(385c) Microbial Conversion of Natural Gas to Biofuel Using a Naturally Occurring Methanotroph

Methane,
the second most prominent greenhouse gas, comes from multiple sources including
the production of and refining of petroleum, domestic livestock, and landfills,
and accounts for approximately 9% of greenhouse gas emissions in the United
States according to the EPA.[1]
This research focuses on the conversion of methane to methanol, which can be
used in the process of biofuel production. The bacterium Methylosinus
trichosporium
OB3b, a naturally occurring methanotroph, is being evaluated
to promote this conversion.

M.
trichosporium
OB3b
cells, when immobilized in an alginate gel solution, maintain their metabolic
activity. This technique was used to immobilize the cells in alginate beads and
in a thin film to investigate the kinetic properties of the cells in various
reactor settings. The alginate beads were placed in a
packed column with liquid up-flow capabilities for long term experiments to
determine the viability of the culture. Immobilizing the culture in alginate
allows it to be easily used and evaluated in a packed bed column,
while maintaining mass transfer properties. A methane and oxygen saturated
solution was passed through the packed column where methane was oxidized to
methanol by the methane monooxygenase (MMO) enzyme. To stop the further
metabolism of methanol, cyclopropanol was used to inhibit the methanol
dehydrogenase (MDH) enzyme, resulting in methanol accumulation. Long and short
inhibition cycles have been evaluated at hydraulic residence times of 5-10
minutes with the overall goal of long term methanol production. Methanol
concentrations of 0.1 mmol/L have been obtained. The culture has sustained
lower levels of activity in the packed column for up to two weeks, through
cycles of inhibition and methanol accumulation, which supports long term
methanol production capabilities.

For the
further investigation of the M. trichosporium OB3b activity,
immobilization techniques and inhibition processes within the alginate gel
beads are being analyzed using a microelectrode oxygen probe. The cells are
also being immobilized in a thin alginate film on a flat surface metal slide.
The alginate film is approximately 1 mm thick and contains a cell concentration
of around 10 g/L. This slide is placed in a laminar flow bath with a media
solution flowing over the stationary film. A dissolved oxygen microelectrode
(10 µm diameter) is being used to evaluate the oxygen profile in the boundary
layer above the film and 500 µm into the film.  Estimates of the flux of
dissolved oxygen (DO) into the film will be used to calculate methane and
methanol uptake within the film. This process was repeated with concentrations
of 1 and 10 ppm methanol in the laminar flow bath. The profiles are being
created and evaluated for the various concentrations of methanol. The immobilized
cells on the slides are also being inhibited with cyclopropanol to evaluate the
inhibited oxygen uptake for comparisons. A modified system was created in batch
mode with a thick layer of alginate beads with immobilized OB3b. A DO profile
was measured with no added substrate and then methanol was added at 1 ppm and
the process was repeated in triplicates.

Future
work includes further analysis of the inhibition process using cyclopropanol,
the immobilization techniques, their effects on MMO and MDH enzyme activity,
and the oxygen and pH changes in a thin film system. These results are being
applied to the design of a thin film reactor currently in preliminary stages of
investigation for long term, high rate methanol production.




[1] EPA.
Environmental Protection Agency, 2 July 2014. Web. 9 April 2015.