Immobilization of Methylosinus trichosporium OB3b in a Biolamina Plate Reactor for the Oxidation of Methane to Methanol Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/dz010v84p

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  • Methane is a flammable gas that is the main component of natural gas. It is a highly potent greenhouse gas, and accounts for about 20% of greenhouse gas emissions. Methane is routinely flared in many industrial processes without harnessing any of its energy. The environmental impact and wasted energy potential make it highly desirable to find an economically feasible process to use this methane.One possibility is to convert methane into liquid fuels for transportation and energy generation. Current technologies to convert methane gas to liquid fuels (GTL) are complex, and the facilities are only economical at huge scales. Methane gas is very difficult to transport and store, so GTL plants must be located at the source of the methane, typically at large petroleum fields or refineries.Biological conversion of methane to liquid fuels is an attractive alternative to traditional GTL processes, as microbial oxidation of methane can produce liquid fuels (e.g. methanol) at ambient temperatures and pressures. When biological organisms are combined with microfluidic technologies, which provide enhanced mass and heat transfer along with a high degree of process control, a very efficient conversion process can be attained at much smaller scales. A further advantage of microfluidics is that the reactors are inherently modular, allowing them to be adapted to practically any required size. This enables the economical conversion of small or remote methane streams to liquid fuels.In this thesis, techniques are described for the immobilization of Methylosinus trichosporium OB3b in a biolamina-plate microreactor (BLP) for conversion of methane to methanol. Effective immobilization requires that the cells remain viable and immobile in the reactor, and that the encapsulation medium is stable and does not degrade during reactor operation. Calcium alginate gels were identified as an ideal immobilization medium, as they are inexpensive, non-toxic, and widely used for the immobilization of cells. Three main requirements must be met in immobilization of cells in the alginate: gel cohesion, gel adhesion, and cell viability. The alginate gel must remain cohesive throughout the entire reactor process, without substantial swelling, disintegration or degradation. The alginate must also adhere stably to the reactor surface, to prevent sloughing which may cause clogging and loss of biological activity. The immobilized cells also must remain metabolically active over the duration of the reactor run. Stable, thin (300-μm) calcium alginate films were achieved by combining an “internal gelation” process to uniformly cross-link the hydrogel, electrostatic adhesion of alginate gel on stainless steel reactor plates modified with aminopropyl-trimethoxysilane (APTMS), and buffering using 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) to minimize chelation of stabilizing calcium ions from the gel. The alginate-encapsulated OB3b cells retain viability and metabolic activity in these films, although their metabolism of methane to methanol appears to be slowerthan pelagic cells. Overall encapsulation of OB3b in calcium alginate films is an effective method for immobilization, although further optimization is necessary.
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