Introduction to Bioenergy
Bioenergy is energy contained in living or recently living biological organisms, a definition which specifically excludes fossil fuels. Plants get bioenergy through photosynthesis, and animals get it by consuming plants. Organic material containing bioenergy is known as biomass. Humans can use this biomass in many different ways, through something as simple as burning wood for heat, or as complex as genetically modifying bacteria to create cellulosic ethanol.
Since almost all bioenergy can be traced back to energy from sunlight, bioenergy has the major advantage of being a renewable energy source. However, it is important that bioenergy be harnessed in a sustainable fashion.
A specific plant or substance used for bioenergy is called a feedstock. Feedstocks are usually converted into a more easily usable form, usually a liquid fuel.
Liquid biofuels have attracted much attention and investment because they can be used to replace or supplement traditional petroleum-based transportation fuels and can be used in existing vehicles with little or no modification to engines and fueling systems. They can also be used for heating and electricity production. Large quantities of liquid biofuels are presently used in many countries, and the potential exists to greatly expand their use in the future. The two most common kinds of liquid biofuels are ethanol and biodiesel, but a range of other liquid fuels exist or are being developed.
Ethanol is currently produced in large quantities by fermenting the sugar or starch portions of agricultural raw materials. The feedstocks used for ethanol production vary by region, including sugar cane in Brazil, grain and corn (maize) in North America, grain and sugar beets in France, etc. The top three ethanol producers are Brazil, the US and China. Because ethanol from sugar and starch directly competes with food production, people are working to commercialize technologies to produce ethanol from cellulose, which makes up the bulk of all plants and trees and is inedible. Cellulosic ethanol is often referred to as a second-generation biofuel.
Biodiesel is typically composed of methyl (or ethyl) esters of long chain fatty acids derived from plant oils. It is produced by chemically upgrading oils obtained from the pressing of oil plants, both edible like rapeseed, soybean and the fruits of oil palms and non-edible, like jatropha and karanj. Waste cooking oil can also be converted to biodiesel.