The recent emphasis on finding alternative energy sources to fuel the energy needs of the United States and the world is leading to an accelerated search for new fuels or new sources of fuel. Producing a liquid fuel from biomass, or biofuel, is an important focus of many alternative energy strategies. Ethanol production from plant biomass is one example of this. Another example of a newer fuel is biodiesel. Refined vegetable oils have been the typical starting materials for the production of biodiesel. Biodiesel can be produced from the oils of many plants. Biodiesel is an alternative, non-toxic, biodegradable and renewable diesel fuel. These characteristics of biodiesel reduce the emission of carbon monoxide, hydrocarbons, and particulate matter in the exhaust gas compared to diesel fuel.
Biodiesel is commonly referred to as fatty acid methyl esters (FAMEs) which are usually obtained from oils extracted from soybean, sunflower, rapeseed or even waste cooking oil. Biodiesel production relies on a chemical reaction called transesterification that transforms esters such as triglycerides into mono alkyl esters. Conventionally, this reaction requires a large excess of methanol, or in some cases ethanol, and an acid or a base catalyst under heated conditions.
In practice, the commercial production of biodiesel from plant feedstocks involves a multi-step process that is time-consuming and not necessarily economically attractive. Triglycerides in oils have been esterified in a multi-step process using acidic or alkaline catalysts. The amount and type of catalyst necessary has varied widely depending upon free triglyceride content of the oil. Initially, the oil feedstock must be extracted. The oil extraction step is typically done in a variety of ways. Oil from plant material may be extracted by lysing and separating, crushing, and centrifuging. The oil may be expressed with rollers, then separating the oil and discarding the residual organic material. Oil can be extracted using chemicals. Benzene, ether and hexane have been used, with the downside to using such solvents being the dangers involved in working with the chemicals. Enzymatic extraction and osmotic shock are other methods that may be used. The oil is blended with an alcohol such as methanol, an acidic or alkaline catalyst is added, and the blend is then heated and cooled. In the transesterification, an acidic or alkaline catalyst is added to the oil with anhydrous methanol to carry out the reaction. This multi-step process is required because a feedstock having a free fatty acid concentration, when exposed to an alkaline catalyst, produces a high concentration of soap. Additional steps are typically required to remove the catalyst residue and strip off the lower alcohols.