Lignocellulosic biobutanol production: Gridlocks and potential remedies

A spike in greenhouse gas emissions due to burning of fossil fuels and issues over energy security and its cost have obligated to identify the alternatives to petroleum fuels currently reigning transportation sector. Butanol, one of the substitutes, is still produced via petrochemical means but the confluence of global issues like declining oil reserves and upsurge in oil prices has compelled to identify renewable biomass resources for butanol production and commercialize the process. Biobutanol is one of the second-generation biofuels, superior to bioethanol, due to higher energy content, lower Reid vapor pressure, easy blending with gasoline at any ratio and ease in transportation. Although bioethanol, a strong competitor of biobutanol, has acquired enough attention from the transportation industry as the current commercially available liquid fuel for transportation, biobutanol possesses the potential to leapfrog various barriers and emerge as an attractive alternative biofuel. Lignocellulosic butanol production faces challenges in various frontiers such as cost of raw material, pretreatment strategies, enzymatic hydrolysis, and low butanol tolerance of the fermenting strain leading to its low yield and productivity, downstream processing of butanol, production of undesired solvents and the production cost. This review discusses these gridlocks along with the possible pertinent solutions to deal with these problems. It also sheds light on recent advancements coupled with the newer approaches for butanol production that revitalize the hopes on having a cleaner, energy-efficient commercial process.