Plants have the ability to capture solar energy and use carbon dioxide and water to photosynthesise carbohydrate during their growth. This carbohydrate can be converted into starch or oils for longer-term energy storage.

Lignocellulose

Plants have also evolved cell walls, which are complex and difficult to break down, protecting them against biological attack. The lignocelluloses material contained in plant cell walls represents the most abundant form of organic carbon on our planet. Lignocellulose is the major structural component of plant material and is used in a range of industrial sectors as a building material, for paper and pulp production, textiles and polymers manufacture.

Plant biomass for production of biofuels and biochemicals

Plant biomass is of interest to the renewable chemical and bioenergy sectors as the sugars contained in lignocellulose could be used for the production of biofuels and biochemical building blocks (platform chemicals) to make alternative products to those produced in the petrochemical industry today. Plant biomass is an abundant resource and it is estimated that between 10 and 100 billion tonnes of plant biomass is degraded in nature every year.
If all the energy stored in plant biomass could be converted into renewable energy, it would be equivalent to approximately 680 billion barrels of oil, close to the global annual energy consumption.

Different processes are available to release energy from plants:

• Combustion: Provide heat or electrical power
• Fermentation: Manufacture ethanol as a petroleum substitute
• Trans-esterification: Manufacture biodiesel as a diesel substitute
• Gasification and Fischer-Tropsch: Manufacture syn-diesel as a diesel substitute
• Anaerobic Digestion: Bacteria break down biomass to produce methane (biogas).

Commercial biofuel production is  focussed on "first-generation" technologies. Currently, crops that have high yields of sucrose (e.g. sugar-cane, sugar beet) are used to produce bioethanol. Starch crops such as maize, wheat and cassava are also used for production of bioethanol.

Research centres around the world are also focussing on "second-generation" technologies to make cellulosic bioethanol production a commercial reality, with projects being established to demonstrate the technology at pilot-scale in North America and Europe.

A wide range of feedstocks are available globally for biofuel production, including energy crops (e.g. Miscanthus, Jatropha, short-rotation willow/poplar), wastes (e.g. waste oils, food processing wastes, etc), agricultural residues (straw, corn stover, etc), forestry residues and novel feedstocks, such as algae.

The following links provide relevant examples of some of UK activities on this subject:

• Algal Bioenergy Special interest Group
• BBSRC Sustainable Bioenergy  Centre
• EPSRC's SUPERGEN Initiative: SUPERGEN Biomass and Bioenergy Consortium
• Carbon Trust: The Pyrolysis Challenge and The Algae Biofuels Challenge