Biomass can be converted into gaseous and liquid fuels through thermochemical and biochemical routes. Some of the common gaseous biofuels are:
1. Biogas. This is the gas mixture produced by anaerobic digestion of biodegradable materials such as cow manure, sewage, municipal wastes, and plant materials. The major component in biogas is methane (CH4), which is about 60%, the remainder is carbon dioxide.
In addition to this, small amounts of hydrogen sulfide and nitrogen are also found in this gaseous biofuel.
2. Biosynthetic gas or biomass-derived syngas. Gasification of lignocellulosic biomass under controlled conditions is used to produce syngas. This gaseous biofuel is a mixture of carbon monoxide, hydrogen and carbon dioxide. The syngas produced from biomass can be used directly as a fuel in gas turbines for electricity generation or as a transport fuel in internal combustion engines. Biomass-derived syngas can also be converted to ethanol by chemical and biochemical methods as well. Production of syngas and upgrading of syngas to bioethanol is described in Part 3 of this book.
3. Biohydrogen. This is the hydrogen produced from biomass resources. Several routes are currently under study for production of hydrogen, which include dark/photo fermentations [11, 12] and steam reforming of bio-oil .