Sustainable Hydrogen, Gasoline, and Diesel Biofuels From Grasses and Crop Residues

Today world is facing two critical problems: (1) high fuel prices, and (2) climatic changes. Both of these are linked to the overdependence on the fossil fuels: petroleum, natural gas, and coal.  The transport is almost totally dependent on fossil particularly petroleum based fuels such as gasoline, diesel fuel, liquefied petroleum gas, and natural gas. Of the special concerns are the liquid fuels for use in the automobiles. Hence, there is a widespread recent interest in obtaining liquid fuels from non-fossil sources. The combination of rising oil prices, issues of security, climate instability and pollution, and deepening poverty in rural and agricultural areas, is propelling governments to enact powerful incentives for the use of biomass-based fuels, which is in turn sparking investment.

Production of grain-based ethanol and vegetable-oil-based bio-diesel are being practiced today with difficulties due to the competition with the food supply. Now the industry is looking toward using biomass which does not compete with the food or fiber supplies; however it is facing unsolved technological/scientific difficulties. Cellulosic ethanol involves the use of expensive cellulase enzymes.  Biomass can be gasified to produce synthesis gas which can be converted into liquid fuels by Fischer-Tropsch technology.  Another exciting technology is hydrothermal process in which biomass components (cellulose, hemi-celluloses, and lignin) are first depolymerized to their respective monomers, followed by hydrogenation to produce liquid fuels.  The process is carried out in sub- or supercritical water, which can utilize wet biomass without any need for drying.  Since the carbon dioxide released upon burning of the biomass-based fuels is captured-back in producing new biomass, there is no net emission of CO₂. The technology can significantly address both fuel and climatic challenges as today’s world has a large surplus of biomass or biomass-producing capacity.

Biomass can also be used to produce hydrogen, which can be directly used as a clean fuel or combined with heavy crude in the upgradation step. The former use can produce petroleum which has part of the energy from biomass, suitable for near term sustainability.