Bio-methanol as a renewable fuel from waste biomass: Current trends and future perspective

•Higher grade fuels can be obtained from biomass.•Methanol is obtained through thermochemical and biochemical conversion of biomass.•Thermochemical processes employed are gasification, pyrolysis and liquefaction.•Methanotrophs produce methanol by the virtue of methane monooxygenase enzyme. Use of abundantly available virgin and waste biomasses as feed-stock for producing gaseous (bio-gas) and liquid fuels (bio-methanol, bio-ethanol and bio-butanol) is being considered as the sustainable and viable alternative to fossil fuels (coal, natural gas and petro-fuels like gasoline and diesel). Out of these bio-methanol is being considered as an attractive liquid fuel as well as feed-stock for the synthesis of enumerable valuable organic compounds currently being produced from coal, natural gas, and petroleum feed stocks. This review presents an overview of various thermo-chemical and biochemical routes that are being explored for the sustainable production of bio-methanol from waste biomass. The advantages and limitations of both the routes are discussed to provide a brief account of their basic principles and also indicate the issues to be addressed through further technological up-gradations for satiating the future energy demand. It focuses specially on the biochemical conversion route which utilizes microbes as biocatalysts for methanol production under normal temperature and pressure conditions. Available information on various process parameters affecting microbial production of bio-methanol have been critically reviewed. To make the process cost effective certain improvements like utilization of raw biogas instead of natural gas for methanol production and development of methane-utilizing microbes through genetic engineering as the subject for future research are discussed. The gap existing in the current knowledge that needs to be bridged to facilitate development of technology for large scale production of bio-methanol at an economical rate to meet the future demands are also pointed out.