Biofuels: Good, But How Good?
by Thomas W. Kerlin (ISA Interchange) …Plants convert carbon dioxide and water into sugar via photosynthesis using energy from the sun. The sugar undergoes further transformations within the plant. Carbohydrates, compounds composed entirely of carbon, hydrogen and oxygen, are produced. They are large molecular chains made up of sugar links. Carbohydrates produced include starch, cellulose and hemicellulose. Lignin, a high molecular weight polymer is also produced.
To make biofuels, the idea is to rearrange the components of the biomass to yield a new compound that can serve as a fuel. Enzymes, proteins that catalyze biochemical reactions, are capable of facilitating the desired reactions in carbohydrates. Common and inexpensive enzymes exist for converting starch into ethanol. Practical enzymatic conversion of cellulose and hemicellulose is not yet available, but it is expected that genetic engineering will yield suitable new enzymes. Chemical and thermochemical processes for converting biomass (including lignin) into liquid biofuel also exist.
But ethanol is not the only fuel that can be made from biomass. For example, butanol, a fuel with more desirable properties than ethanol can be produced enzymatically and hydrocarbons can be produced thermochemically. Processes such as these are well known, but are not currently competitive with enzymatic ethanol production from carbohydrates. Also, some plants produce triglycerides that can be used as fuel, either directly or after chemical processing by transesterification. READ MORE