title: Bioconversion of natural gas to liquid fuel: opportunities and challenges.
abstract: Natural gas is a mixture of low molecular weight hydrocarbon gases that can be generated from either fossil or anthropogenic resources. Although natural gas is used as a transportation fuel, constraints in storage, relatively low energy content (MJ/L), and delivery have limited widespread adoption. Advanced utilization of natural gas has been explored for biofuel production by microorganisms. In recent years, the aerobic bioconversion of natural gas (or primarily the methane content of natural gas) into liquid fuels (Bio-GTL) by biocatalysts (methanotrophs) has gained increasing attention as a promising alternative for drop-in biofuel production. Methanotrophic bacteria are capable of converting methane into microbial lipids, which can in turn be converted into renewable diesel via a hydrotreating process. In this paper, biodiversity, catalytic properties and key enzymes and pathways of these microbes are summarized. Bioprocess technologies are discussed based upon existing literature, including cultivation conditions, fermentation modes, bioreactor design, and lipid extraction and upgrading. This review also outlines the potential of Bio-GTL using methane as an alternative carbon source as well as the major challenges and future research needs of microbial lipid accumulation derived from methane, key performance index, and techno-economic analysis. An analysis of raw material costs suggests that methane-derived diesel fuel has the potential to be competitive with petroleum-derived diesel.
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, USA.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Fei
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, USA.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Guarnieri
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, USA.
authors.forename: Ling
authors.initials: L
authors.lastname: Tao
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, USA.
authors.forename: Lieve M L
authors.initials: LM
authors.lastname: Laurens
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, USA.
authors.forename: Nancy
authors.initials: N
authors.lastname: Dowe
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO, USA. Electronic address: Philip.Pienkos@nrel.gov.
authors.forename: Philip T
authors.initials: PT
authors.lastname: Pienkos
mesh_terms: D056804:Biofuels; D019149:Bioreactors; D007218:Industrial Microbiology; D008697:Methane; D059206:Natural Gas; D010743:Phospholipids; D020560:Proteobacteria
chemical_list: D056804:Biofuels; D059206:Natural Gas; D010743:Phospholipids; D008697:Methane
keywords: Bioconversion of natural gas into liquid fuels (Bio-GTL); Bioprocess optimization; Greenhouse gas; Hydrotreating process; Lipid extraction; Methanotrophic bacteria; Microbial lipids; Renewable diesel fuel; Techno-economic analysis