Biodiesel is a clean burning alternative fuel produced from domestic, renewable resources. The fuel is a mixture of fatty acid alkyl esters made from vegetable oils, animal fats or recycled greases. Where available, biodiesel can be used in compression-ignition (diesel) engines in its pure form with little or no modifications.
Biodiesel is simple to use, biodegradable, nontoxic, and essentially free of sulphur and aromatics. It is usually used as a petroleum diesel additive to reduce levels of particulates, carbon monoxide, hydrocarbons and air toxics from diesel-powered vehicles. When used as an additive, the resulting diesel fuel may be called B5, B10 or B20, representing the percentage of the biodiesel that is blended with petroleum diesel.
Biodiesel is produced through a process in which organically derived oils are combined with alcohol (ethanol or methanol) in the presence of a catalyst to form ethyl or methyl ester. The biomass-derived ethyl or methyl esters can be blended with conventional diesel fuel or used as a neat fuel (100% biodiesel). Biodiesel can be made from any vegetable oil, animal fats, waste vegetable oils, or microalgae oils. There are three basic routes to biodiesel production from oils and fats:
- Base catalyzed trans-esterification of the oil.
- Direct acid catalyzed trans-esterification of the oil.
- Conversion of the oil to its fatty acids and then to biodiesel.
There are a variety of oils that are used to produce biodiesel, the most common ones being soybean, rapeseed, and palm oil which make up the majority of worldwide biodiesel production. Other feedstock can come from waste vegetable oil, jatropha, mustard, flax, sunflower, palm oil or hemp. Animal fats including tallow, lard, yellow grease, chicken fat and fish oil by-products may contribute a small percentage to biodiesel production in the future, but it is limited in supply and inefficient to raise animals for their fat. Jatropha is a small pest and drought resistant shrub that is capable of being grown on marginal land that produces seeds that yield more than four times as much oil per acre than Soybeans
Among alternative feedstocks, algae holds enormous potential to provide a non-food, high-yield, non-arable land use source of biodiesel, ethanol and hydrogen fuels. Microalgae have been grabbing biofuel attention because on an acre-by-acre basis, microalgae can produce 100 to 300 times the oil yield of soybeans on marginal land and with salt water. Microalgae is the fastest growing photosynthesizing organism and is capable of completing an entire growing cycle every few days.
The potential for commercial algae production is expected to come from growth in translucent tubes or containers called photo bioreactors or open ocean algae bloom harvesting. The other advantages of algal systems include:
- carbon capture from smokestacks to increase algae growth rates
- processing of algae biomass through gasification to create syngas
- growing carbohydrate rich algae strains for cellulosic ethanol
- using waste streams from municipalities as water sources