“Biodiesel” – diesel fuel made from animal or vegetable materials – is an alternative fuel that has been used in motor vehicles since the beginnings of the automobile industry. It can be substituted for petroleum-based diesel fuel (“petrodiesel”) in diesel engines. Vehicles using biodiesel emit fewer pollutants than petrodiesel, although they also generally get slightly fewer miles per gallon.
The basic process for making fuel from organic matter has not changed since it was invented in the nineteenth century. The process, called transesterification, forces vegetable oil or animal fat to react with a catalyst (usually sodium hydroxide) and methanol or ethanol to produce glycerol and fatty acid esters, the latter being the actual chemical name for biodiesel. Transesterification originally was used to obtain glycerol for soap; what we now call biodiesel was a byproduct of the soap-making process.
Many products, including peanut oil, hemp oil, corn oil and tallow (beef fat) have been used as feedstocks for the transesterification process. Today, the most common sources for biodiesel are:
- plants: soybeans, peanuts, rapeseed, palm, corn, sorghum, canola, sunflower and cottonseed;
- animal fats: tallow, white grease, poultry fats and fish oils; and
- recycled greases: used cooking oils and restaurant frying oils.
As the nation’s largest producer of biodiesel, Texas could benefit from any future expansion in its production or use. The biodiesel industry can affect the economy through investments in construction, spending on related goods and services and jobs.
When German engineer Rudolph Diesel first demonstrated his compression ignition engine at the 1898 World Exhibition in Paris, he used peanut oil for fuel. At the time, Diesel thought that biofueled engines were a good alternative to the steam engine. In fact, diesel engines generally ran on vegetable oils until the 1920s, when the engines were first altered to allow them to use petroleum products for fuel.
Diesel was not alone in his faith in biofuels. Henry Ford designed his automobiles, beginning with the 1908 Model T, to use ethanol, a fuel distilled from corn. Ford even built an ethanol plant in the Midwest and formed a partnership with Standard Oil to sell it in the company’s fuel stations.
Despite the financial support of these leaders of industry, the biofuels industry did not last. Extremely low prices for petroleum products in the 1920s led to their eventual domination of the vehicle industry. Today’s sharp increase in oil prices, however, has spurred renewed interest in biofuels.
Most biodiesel used in the U.S. fuels fleet vehicles. Hundreds of big and small fleets run on biodiesel, including those operated by the U. S. Postal Service (USPS) and the military as well as vehicles belonging to various metropolitan transit systems, agricultural concerns and school districts. USPS states that its fleet of 43,000 alternative-fuel vehicles is the world’s largest. San Francisco’s city fleet of diesel vehicles, which includes fire trucks, ambulances and buses, also runs on biodiesel.
Biodiesel can be used alone or mixed with petroleum-based diesel fuel. The most common blend in current use, “B20,” is 20 percent biodiesel and 80 percent petroleum diesel. B100 is pure biodiesel.
Biodiesel contains residual alcohol from the esterification process that can remove deposits from fuel tanks and lines, causing filter plugging when it is used initially. Fuel systems should be flushed before using biodiesel, and fuel filters may need more frequent replacement when it is first used in older vehicles.
Low temperatures can affect B100 biodiesel during storage and operation, causing it to begin to solidify. At such temperatures, the fuel may need to be stored in a heated building or storage tank, and the engine itself may require heated fuel lines, filters and tanks.
Petrodiesel also may solidify in cold weather, but petroleum companies and distributors manage the fuel inventory and additive treatments based on the history of the fuel’s performance in each geographical region throughout each season, so the right blend of diesel fuel is available at the right time of year, allowing consumers to avoid cold flow problems. Biodiesel distributors hope to develop the same system for biodiesel once the market becomes more established across the country.
Biodiesel has a flash point – the temperature at which it will ignite when exposed to a spark or flame – of 150° C. This means that it is safer to store and handle than petrodiesel fuel, which has a flash point of 70° C.
Biodiesel has a tendency to absorb and attract water, so it must be stored in tanks that are free of water and do not absorb it. Above-ground tanks are preferable, since they are not readily contaminated by groundwater. Otherwise, biodiesel stores nearly as well as petrodiesel. Biodiesel may be stored (in the dark and at a cool temperature) for up to eight months before it begins to degrade. Petrodiesel has a longer shelf life; it can be stored for up to one year before it begins to degrade.
Since biodiesel can be stored in tanks currently used to store petrodiesel, little or no additional storage cost is involved in converting from one fuel to the other. The same regulations and monitoring are required for both fuels.
One potential problem is that biodiesel can react chemically with the rubber seals in vehicle fuel systems. This is a slow process, however, and one that usually can be avoided by adhering to normal maintenance schedules. Also, many engine manufacturers now use silicone rather than rubber seals to avoid any problems with biofuels.