Evaluation of Biosynthetic Pathways for Conversion of Natural Gas to Liquid Fuels

It has been estimated that the proven natural gas reserves in the U.S. could provide enough energy to meet the country’s transportation energy demand for the next 50 years. This, coupled with the increasing price gap between natural gas and gasoline over recent years, makes natural-gas derived fuels an attractive option for use in the transportation sector. However, the infrastructure to use natural gas directly (either as CNG or LNG) has not been developed, and so natural gas must first be converted to a liquid fuel. Chemical processes for accomplishing this suffer from high capital costs and low yields, thus there is significant interest in developing alternative processes for the high-efficiency conversion of methane to a drop-in transportation fuel. Various microorganisms have evolved enzyme systems capable of metabolizing methane, thus with the application of metabolic engineering technologies, it is conceivable that a strain capable of producing a liquid fuel from methane could be developed. Before embarking on such an undertaking, however, it is critical to establish the inherent potential and limitations of the chosen pathway, to maximize the likelihood of selecting a commercially viable process, and not just a novel scientific investigation. To that end, we present here an analysis of the various biological routes for the conversion of methane to a liquid fuel. We develop stoichiometric models for each scenario that allow calculation of the maximum potential yields, and conclude with the implication of these results in developing an organism and pathway for the biological conversion of methane to a liquid fuel.