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The Biodiesel Production Cycle

Source: PropelBiodiesel.


Biodiesel is a domestically produced alternative diesel fuel. It is actually an alcohol ester of vegetable oil processed from vegetable oil or animal fat by combining the oil with alcohol in a process called transestrification. Transesterification forces the feedstock 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.

Biodiesel can be used in its pure form (B100) or blended at any ratio with petroleum diesel for economy and improved cold weather performance. Most biodiesel is sold as B20, a blend that is 80 percent conventional diesel. Large trucks, buses, boats and power generation equipment require diesel engines, and B20 fuel can be used in these engines without modification. B20 is easy and inexpensive for a fueling station to sell because it can be stored in diesel tanks and pumped with diesel equipment.

Biodiesel can also be used to generate electricity, which can be used on site or transmitted through the power grid, just like electricity derived from any other source.

Environmental Benefits

Biodiesel is considered a clean fuel because it is nontoxic, biodegradable, and much less polluting than petroleum diesel. The use of biodiesel fuel results in much lower emissions of almost every pollutant: carbon dioxide, sulfur dioxide (one of the main causes of acid rain), particulates, carbon monoxide, air toxins and unburned hydrocarbons. Biodiesel is in demand for specialized uses where its air emission characteristics are a major advantage, such as in school and city buses, marine craft, and diesel engines operating in enclosed areas, such as mines.

Because biodiesel fuel is vegetable oil based, gaseous and particulate emissions are reduced with its use, since vegetation is part of the natural cycle of carbon dioxide assimilation by plants. For this reason, the use of biodiesel fuel could result in a zero net gain in oxides of carbon emissions.

Biodiesel fuel meets the registration requirements for fuels and fuel additives established by the Environmental Protection Agency (EPA) under the Clean Air Act, and it is the first alternative fuel to have a complete evaluation of emission results and potential health effects submitted to the EPA. The analysis, A Comprehensive Analysis of Biodiesel Impacts on Exhaust Emissions, reports that biodiesel significantly reduces emissions of particulate matter, carbon monoxide and hydrocarbons over petroleum diesel, based on its use in heavy duty diesel engines.

Biodiesel Feedstocks

Because the United States is the largest producer of soybeans in the world, most U.S. biodiesel is made from soybean oil or yellow grease, primarily recycled vegetable cooking oil from restaurants.

In Texas, the most common feedstocks are soybean, cottonseed, palm, and canola. Biodiesel can be made from other oils and fats as well, such as corn, mustard, coconut, peanut, olive, hemp, sesame, sunflower, and safflower oils, and oils produced from algae, fungi, bacteria, molds, and yeast.

Although Texas is the country’s largest producer of biodiesel and its climate and soil conditions are well suited for growing crops that could eventually end up in biodiesel production, Texas biodiesel producers import much of the feedstocks used in their refineries. Texas is a minor producer of soybeans, they are the preferred feedstock for most Texas biodiesel producers. As the price of soybeans continues to increase, and local access to soybeans in Texas remains limited, Texas biodiesel producers are looking to alternative feedstocks such as other oilseed crops and used cooking oil. Since most soybean supplies are shipped to Texas from the Midwest, Texas biodiesel producers are trying to cut costs by using local feedstocks that do not have to be shipped for long distances.

Currently, Texas A&M University is working with Galveston Bay Biodiesel to develop and commercialize new biodiesel feedstock technologies as options to soybean and canola feedstocks.

For more information on feedstocks and raw materials for biodiesel, refer to the Biomass Resources section of this site.

Biodiesel Infrastructure

Government incentives along with fluctuating oil prices, higher diesel fuel prices, energy security and environmental issues have made biodiesel production profitable, resulting in the rapid expansion of the industry. Biodiesel also furthers the rural farm economy by creating markets for crops such as soybeans and cottonseed. In 2004, there were 22 plants nationwide with a capacity to produce 157 million gallons of fuel. In 2008, there are 170 plants (20 in Texas) bringing production capacity to 864 million gallons of biodiesel.

Biodiesel sales are booming in Texas, the country’s largest producer of biodiesel transportation fuel. Texas has a current production capacity of over 100 million gallons per year. In addition, Texas has over 50 retail biodiesel fueling sites. Austin has the highest number of biodiesel fueling stations of any city in the nation.

As Fleet managers switch to alternative fuel vehicles (AFVs), the fueling infrastructure for biodiesel will contune to expand. The U.S. Department of Energy web site, Biodiesel Infrastructure Development Resources, provides an overview of safety issues, equipment, and standards.

Biodiesel Use


The price of feedstock and traditional diesel fuel have a direct effect on the cost of producing B20. Biodiesel can be made from local products such as used cooking oils, beef tallow and other animal fats, canola, soybean, and corn oil. Some additional feedstocks are in the development stages. With federal incentives that have been in place, the cost of biodiesel has become competitive or lower in price than traditional diesel fuel.

Smog and the Texas Low Emission Diesel (TxLED) Program

NOx is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. One common pollutant, nitrogen dioxide (NO2), often is seen as a reddish-brown smog layer over urban areas. The main component of smog is ground-level ozone which is produced by a reaction between nitrogen oxides (NOx) and volatile organic compounds (VOC) in the atmosphere. The primary manmade sources of NOx are motor vehicles, electric utilities and other industrial, commercial and residential sources that burn fuels.

According to the U.S. Department of Energy, approximately 11 percent of the weight of B100 is oxygen. This is a plus for biodiesel because oxygen improves combustion, causing a reduction in air toxins, carbon monoxide, soot, small particles, and hydrocarbon emissions by 50% or more. Air quality benefits are roughly proportional for diesel/biodiesel mixtures. However, oxygenated fuels also tend to increase NOx emissions.

Both the EPA and the National Renewable Energy Laboratory (NREL) conducted comprehensive studies to determine if B20 raises NOx levels. The tests found that biodiesel did not contribute to higher NOx emissions.

Because NOx is a serious problem in certain areas of Texas, the Texas Commission on Environmental Quality (TCEQ) created the TxLED (Texas Low Emission Diesel) Program to regulate diesel fuel NOx and VOC levels. 110 counties and several major cities are covered under TxLED, including Austin, Dallas, Houston and San Antonio. Pure biodiesel (B100) is not regulated by TxLED because it is not defined by TxLED as a diesel fuel. However, most biodiesel is sold as B20, and because B20 is a blend of 80% diesel and only 20% pure biodiesel, it meets the TxLED definition of diesel fuel.

The federal Renewable Fuel Standard program (RFS-2) has mandated significant use of “biomass-based” diesel in the United States. The Texas Commission on Environmental Quality (TCEQ) has concluded that the volumes of biodiesel blended in the Texas Low Emission Diesel (TxLED) market to meet these requirements will have no measurable negative impact on Texas’ air quality. Consequently, effective December 16, 2011, TCEQ allows biodiesel to be added to any TxLED compliant fuel, at any ratio, without additional additization. This will enable Texas to be a significant market for biodiesel.

Fuel Quality

ASTM International, one of the largest standards development organizations in the world, has approved a new specification for diesel fuel blends containing 6%-20% biodiesel. According to the National Biodiesel Board (NBB), ASTM standards for the 20% biodiesel blends, or B20, are a crucial hurdle for the full acceptance of the use of such blends in diesel vehicles. With the new specification in place, automakers and engine manufacturers can test B20 in their diesel engines and know that consumers will be fueling their vehicle with a fuel of the same quality. While setting the new B20 standard, ASTM International also made changes to its specifications for B5 and for 100% biodiesel, or B100.

Like all fuels, biodiesel and biodiesel blends have a shelf life and should be used within one year to ensure that the quality of the fuel is maintained.

For fuel-grade biodiesel to be a legally registered fuel and fuel additive with the U.S. Environmental Protection Agency (EPA), it must meet the strict industry specifications of this standard prior to blending in order to insure proper and consistent performance. The specification for pure unblended biodiesel (B100) is ASTM D6751-03. This specification is intended to insure the quality of biodiesel to be used as a blend stock at 20% and lower blend levels.

The Energy Independence and Security Act of 2007 requires the Federal Trade Commission (FTC) to set labeling requirements that address the blending of biodiesel and other types of biomass-based diesel fuels into diesel fuel. Some companies are converting biomass such as animal fats directly into a liquid with the properties of diesel fuel, a product that blurs the lines between biodiesel and diesel fuel. At first, the FTC proposed to treat all renewable diesel fuels the same, but the NBB warned that not all biomass-based diesel fuels would necessarily meet the ASTM standards required by automakers for diesel fuels. On the other hand, biomass-based diesel fuels that meet ASTM standards could be used in much higher concentrations than biodiesel, which is usually limited to 20% biodiesel blends for standard diesel vehicles. Considering those comments, the FTC decided to set separate labeling requirements for biodiesel blends and biomass-based diesel fuel blends.

BQ-9000 helps companies improve their fuel testing procedures and reduces the chances of producing or distributing out-of-spec fuel. The BQ-9000 National Biodiesel Board Accreditation Program is a cooperative and voluntary program developed by the biodiesel industry for the accreditation of producers and marketers of biodiesel fuel. The program is a combination of the ASTM standard for biodiesel, ASTM D 6751, and a quality systems program that includes storage, sampling, testing, blending, shipping, distribution, and fuel management practices.

The program includes accredited producers and certified distributors. The fuel supplied by either an accredited producer or a certified distributor meets all applicable standards for sale and use in the United States.

Additional Resources

For more information on Biodiesel in Texas, go to the “Biodiesel” chapter in the Texas Comptroller’s 2008 Energy Report.


  • The National Biodiesel Board (NBB) is the national trade association representing the biodiesel industry as the coordinating body for research and development in the United States.
  • ASTM International is a consensus based standards group comprised of engine and fuel injection equipment companies, fuel producers and fuel users whose standards are recognized in the United States by most government entities with the responsibility of insuring fuel quality.
  • Biodiesel Coalition of Texas (BCOT) is a Texas non-profit corporation formed by biodiesel producers, distributors, and retailers, as well as agricultural interests that provide biodiesel producers feedstock for their fuel.
  • BQ-9000: National Biodiesel Accreditation Program is a voluntary program for the accreditation of producers and marketers of biodiesel fuel.


  • ASTM Biodiesel Portal provides access to all ASTM standards that cover biodiesel.
  • Just Ask Ben is a site sponsored by the National Biodiesel Board and the Petroleum Marketers Association of America.
  • is a portal specifically for truckers. In addition to road, traffic and weather conditions, a searchable database for biodiesel providers, frequently asked questions and other information a trucker would need, there’s also the Biodiesel Hotline, (866)-BIODIESEL or (866) 246-3437. The hotline is staffed 24 hours a day, 7 days a week and is available to all drivers of diesel vehicles, including cars and pick-up trucks.
  • Alternative Fueling Station Locator part of the Alternative Fuels and Advanced Vehicles Data Center, contains fueling stations for the following alternative fuels: compressed natural gas (CNG), 85% ethanol (E85), liquefied petroleum gas/propane (LPG), biodiesel (BD), electric, hydrogen, and liquefied natural gas (LNG).
  • The Biodiesel Fuel Education Program by the University of Idaho.

Other Publications available from NBB:

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