Bioconversion of synthesis gas to second generation biofuels: A review

The ever increasing concerns over fluctuating price of oil and the possible future supply constrains have reinforced the need for alternative fuel resources. Use of synthesis gas (syngas) to generate fuels through a microbial route would likely be an option to address part of this challenge. Syngas fermentation offers a pathway for sustainable synthesis of fuels and chemicals with lots of advantages over catalytic syngas conversion. This work reviews the available literature on production of second generation biofuels from syngas using various biocatalysts. The potential of syngas fermentation using acetogenic, hydrogenogenic and methanogenic organisms have been surveyed. A vast variety of biofuels and biochemicals including ethanol, acetate, hydrogen, butanol, butyrate, methane and etc. have been produced from gaseous substrates using microbial catalysts. The role of various parameters including medium composition, fermentation pH, trace elements, reducing agents and mass transfer limitations on bioconversion process has been extensively discussed. From this survey of literature it has been deduced that despite years of research and endeavors, fermentation of syngas to biofuels is still a relatively immature technology and long-term view for this potential conversion should be undertaken for future commercial deployments.