Introduction to How Biodiesel Works

If you've read or watched the news lately, you've probably come across some article, snippet or sound bite related to oil and oil prices. Even in your daily routines, there's a good chance of someone mentioning it. Whether it's in automotives, economics, history, geography or politics, oil has managed to filter into almost every aspect of our daily lives. It's one of the most discussed (and controversial) commodities that consumers rely on daily.

All of this talk about oil sparks continued interest in gasoline alternatives. Things like electric cars and hydrogen fuel cells are being talked about as feasible alternatives to oil. As technology improves, these concepts could become reality. But what about now?

Lost in the mix are the biofuels, fuels made from biological ingredients instead of fossil fuels. These starting ingredients can range from corn to soybeans to animal fat, depending on the type of fuel being made and the production method.

In this article, we'll take a closer look at biodiesel, one of the major biofuels. For starters, it would be a good idea to check out How Car Engines Work and How Diesel Engines Work to get some background. After that, head back over and we'll separate biodiesel fact from fiction.

Generally speaking, biodiesel is an alternative or additive to standard diesel fuel that is made from biological ingredients instead of petroleum (or crude oil). Biodiesel is usually made from plant oils or animal fat through a series of chemical reactions. It is both non-toxic and renewable. Because biodiesel essentially comes from plants and animals, the sources can be replenished through farming and recycling.

Biodiesel is safe and can be used in diesel engines with little or no modification needed. Although biodiesel can be used in its pure form, it is usually blended with standard diesel fuel. Blends are indicated by the abbreviation Bxx, where xx is the percentage of biodiesel in the mixture. For example, the most common blend is B20, or 20 percent biodiesel to 80 percent standard. So, B100 refers to pure biodiesel.

Biofuels, such as ethanol made from corn and biodiesel made from soybeans, help support American agriculture.
Photo courtesy U.S. Department of Energy
Biofuels, such as ethanol made from corn and biodiesel made from soybeans, help support American agriculture.

Biodiesel isn't just a catch-all term, however. There is also a formal, technical definition that is recognized by ASTM International (known formerly as the American Society for Testing and Materials), the organization responsible for providing industry standards. According to the National Biodiesel Board (NBB), the technical definition of biodiesel is as follows:

    a fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, designated B100, and meeting the requirements of ASTM D 6751.

That sounds kind of rough, but it's a lot more familiar than you may think -- you encounter these fatty acids every day. We'll look at them in more detail in the next section.

Fats and Biodiesel

Soybeans can be made into biodiesel.
Photo courtesy National Biodiesel Board
Soybeans can be made into biodiesel.

Part of what makes biodiesel so appealing and interesting is that it can be made from numerous natural sources. Although animal fat can be used, plant oil is the largest source of biodiesel. You've probably used some of these in the kitchen. Scientists and engineers can use oils from familiar crops such as soybean, rapeseed, canola, palm, cottonseed, sunflower and peanut to produce biodiesel. Biodiesel can even be made from recycled cooking grease!

The common thread shared by all biodiesel sources is that they all contain fat in some form. Oils are just fats that are liquid at room temperature. These fats, or triacylglycerols (sometimes called triglycerides) are made up of carbon, hydrogen, and oxygen atoms bound together and arranged into a specific pattern. These triacylglycerols are pretty prevalent. In addition to household vegetable oils, they're also in common things like butter and lard. You may have seen a triglyceride count listed if you've been to a doctor and had some blood work done.

One way to visualize these triacylglycerols is to think of a capital "E." Forming the vertical backbone of this E is a molecule known as glycerol. Glycerol is a common ingredient used in making such things as soap, pharmaceuticals and cosmetics. Attached to this glycerol backbone and forming the horizontal elements of the E are three long chains composed of carbon, hydrogen, and oxygen. These are called fatty acids.

 H   H         H         H   H
\ / | \ /
C-----------C-----------C
| | |
O O O
\ \ \
C=O C=O C=O
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H H H

So how do these triacylglycerols end up in a car, truck or boat? Biodiesel is not pure vegetable oil. Although raw vegetable oil has been used to fuel diesel engines in the past, it has usually caused problems. The raw fat or oil must first undergo a series of chemical reactions in order to become fuel. There are a few different ways to make biodiesel, but most manufacturing facilities produce industrial biodiesel through a process called transesterification. In this process, the fat or oil is first purified and then reacted with an alcohol, usually methanol (CH3OH) or ethanol (CH3CH2OH) in the presence of a catalyst such as potassium hydroxide (KOH) or sodium hydroxide (NaOH). When this happens, the triacylglycerol is transformed to form esters and glycerol. The esters that remain are what we then call biodiesel.

Is this old news? In the next section, we'll examine some of the history and motivation behind the biofuels movement.

Biofuel History


Photo courtesy Bob Allan
Current U.S. biodiesel production is primarily from oil from soybeans such as these or from recycled restaurant cooking oil.

The concept of biofuels is surprisingly old. Rudolf Diesel, whose invention now bears his name, had envisioned vegetable oil as a fuel source for his engine. In fact, much of his early work revolved around the use of biofuel. In 1900, for example, at the World Exhibition in Paris, France, Diesel demonstrated his engine by running it on peanut oil. Similarly, Henry Ford expected his Model T to run on ethanol, a corn product. Eventually, in both Diesel's and Ford's cases, petroleum entered the picture and proved to be the most logical fuel source. This was based on supply, price and efficiency, among other things. Though it wasn't common practice, vegetable oils were also used for diesel fuel during the 1930s and 1940s.

It was in the 1970s and 1980s that the idea of using biofuels was revisited in the United States. One of the most important events occurred in 1970 with the passage of the Clean Air Act by the Environmental Protection Agency (EPA). This allowed the EPA to more closely regulate emissions standards for pollutants like sulfur dioxides, carbon monoxide, ozone and nitrogen oxides (NOx). This set the stage for developing cleaner-burning fuels. This also set standards for fuel additives.

Events overseas such as the 1973-1974 Arab oil embargo and the 1978-1979 Iranian Revolution, coupled with a decrease in domestic oil production, served to drive prices up. According to the U.S. Department of Energy's Energy Information Administration, U.S. crude oil imports were cut by 30% during the embargo, and "the world price of crude oil jumped from around $14 per barrel at the beginning of 1979 to more than $35 per barrel in January 1981 before stabilizing. Prices did not drop appreciably until 1983, when the world price stabilized between $28 and $29 per barrel."

With petroleum prices increasing, researchers began to look elsewhere. In August 1982, the first International Conference on Plant and Vegetable Oils was held in Fargo, N.D. This conference dealt with matters ranging from fuel cost and the effects of vegetable oil to fuel additives and extraction methods.

In 1990, the Clean Air Act was amended and included more stringent restrictions on vehicle emissions. The amendment introduced provisions for such things as increased oxygen content in gasoline (which lowers carbon monoxide emissions) and lower sulfur content in diesel fuels.

In 1992, the EPA passed the Energy Policy Act, or EPACT. This was aimed at increasing the amount of alternative fuel used by the U.S. government transportation fleets in order to reduce dependency on foreign oil. The 1998 EPACT amendment included using biodiesel fuel in existing government diesel vehicles as an acceptable alternative to purchasing alternative fuel vehicles, or AFVs, as stipulated in the original EPACT.

With all of these rules and regulations in place, it's understandable that any viable petroleum alternative would cause a clamor. But biodiesel isn't a perfect substitute for gasoline. We'll look at its pros and cons in the next sections.

The Pros

Biodiesel has several key advantages:
  • Biodiesel is environmentally friendly.
  • It can help reduce dependency on foreign oil.
  • It helps to lubricate the engine itself, decreasing engine wear.
  • It can be used in almost any diesel with little or no engine modification.
  • It is safer than conventional diesel.
One of the major selling points of biodiesel is that it is environmentally friendly. Biodiesel has fewer emissions than standard diesel, is biodegradable, and is a renewable source of energy.

Emissions control is central to the biodiesel argument, especially in legislation matters. There are a few components of emissions that are especially harmful and cause concern among scientists, lawmakers, and consumers. Sulfur and its related compounds contribute to the formation of acid rain; carbon monoxide is a widely recognized toxin; and carbon dioxide contributes to the greenhouse effect. There are also some lesser known compounds that cause concern, such as polycyclic aromatic hydrocarbons (PAHs), ring-shaped compounds that have been linked to the formation of certain types of cancer. Particulate matter (PM) has negative health effects, and unburned hydrocarbons contribute to the formation of smog and ozone.

Biodiesel does reduce hazardous emissions. Of the current biofuels, biodiesel is the only one to have successfully completed emissions testing in accordance with the Clean Air Act.

Average Biodiesel Emissions Compared to Conventional Diesel
Emission Component B100 B20
Total Unburned Hydrocarbons -67% -20%
Carbon Monoxide -48% -12%
Particulate Matter -47% -12%
NOx +10% +2%
Sulfates -100% -20%
PAH -80% -13%
Source: National Biodiesel Board


In addition, B100 can reduce CO2 emissions by 78 percent and lower the carcinogenic properties of diesel fuel by 94 percent (National Biodiesel Board, U.S. DOE Office of Transportation Technologies).

Another feature of biodiesel is that it is biodegradable, meaning that it can decompose as the result of natural agents such as bacteria. According to the EPA, biodiesel degrades at a rate four times faster than conventional diesel fuel. This way, in the event of a spill, the cleanup would be easier and the aftermath would not be as frightening. This would also hold true for biodiesel blends.

Biodiesel could also lower U.S. dependence on imported oil and increase our energy security. Most biodiesel in the U.S. is made from soybean oil, which is a major domestic crop. With U.S. petroleum demands increasing and world supply decreasing, a renewable fuel such as biodiesel, if properly implemented, could alleviate some of the U.S. energy demands.

Biodiesel also contributes to an engine's lubricity, or its ease of movement. Biodiesel acts as a solvent, which helps to loosen deposits and other gunk from the insides of an engine that could potentially cause clogs. Since pure biodiesel leaves no deposits of its own, this results in increased engine life. It is estimated that a biodiesel blend of just 1 percent could increase fuel lubricity by as much as 65 percent (U.S. DOE Office of Transportation Technology).

Biodiesel is also safer. It is non-toxic (about 10 times less toxic than table salt) and has a higher flashpoint than conventional diesel. Because it burns at a higher temperature, it is less likely to accidentally combust. This makes movement and storage regulations easier to accommodate. Next, we'll look at the cons and the future of biodiesel.

The Cons

Microalgae, organisms from which a diesel-like fuel can be derived: Cultured in the American southwestern deserts, NREL-developed microalgae may one day produce large amounts of lipids for conversion to biodiesel fuel.
Photo courtesy Paul Roessler
Microalgae, organisms from which a diesel-like fuel can be derived: Cultured in the American southwestern deserts, NREL-developed microalgae may one day produce large amounts of lipids for conversion to biodiesel fuel.

Of course, nothing is without penalty, and biodiesel does have its drawbacks. Some have to do with the fuel itself, and many have to do with the bigger picture.

One of the problems with the fuel itself is the increase in NOx in biodiesel emissions. Often, in diesel fuel manufacturing, when you decrease the amount of particulate matter in the emissions, there is a corresponding increase in nitrogen oxides, which contribute to smog formation. Though some of this can be addressed by adjusting the engine itself, that's not always feasible. There are technologies being researched to reduce NOx amounts in biodiesel emissions.

Another problem is biodiesel's behavior as a solvent. Though this property is helpful, it's kind of a double-edged sword. Some older diesel vehicles (such as cars made before 1992) may experience clogging with higher concentrations of biodiesel. Because of its ability to loosen deposits built up in the engine (which may be there from old diesel fuel), biodiesel can cause the fuel filter to become jammed with the newly freed deposits. Biodiesel manufacturers suggest changing the fuel pump shortly after switching to high-concentration biodiesel blends. Components within these older fuel systems may also become degraded. In addition to deposits within the fuel system, biodiesel also breaks down rubber components. Some parts in the older systems, such as fuel lines and fuel pump seals, may become broken down due to their rubber or rubber-like composition. This is usually remedied by replacing such components. Though many manufacturers have included biodiesel in their warranties, potential for problems could still exist. For more information on biodiesel and vehicle warranties, check out The Biodiesel Standard.

Also, in some engines, there can be slight decrease in fuel economy and power. On average, there is about a 10 percent reduction in power. In other words, it takes about 1.1 gallons of biodiesel to equal 1 gallon of standard diesel.

The major drawbacks to biodiesel are connected to the bigger picture, namely the market and associated logistics. Of these, the most important is cost. According to the EPA, pure biodiesel (B100) can cost anywhere from $1.95 to $3.00 per gallon, while B20 blends average about 30 to 40 cents more per gallon than standard diesel. This all depends on variables such as the feedstock used and market conditions.

The other, perhaps more important issue is that of amount and availability. Though biodiesel isn't necessarily produced in all 50 states, it can be made available in all of them. There are three major ways to get biodiesel, with each particular method better suited for certain types of customers. Biodiesel can be purchased directly from the supplier, from a petroleum distributor, or from public pumps. There are currently 19 NBB-members producing and marketing biodiesel in the United States. To find out how to get biodiesel, contact the National Biodiesel Board. Also, the Alternative Fuels Data Center has a search feature that allows you to locate refueling stations by city or state.

For information on locating biodiesel stations outside the U.S., contact your local biofuels agency.

So how much do we make? Given the number of different producers (i.e., federal, private, industrial) and crop sources, it's hard to attach a neat figure. Right now, the U.S. produces approximately 75 million gallons of biodiesel per year (National Biodiesel Board). This production is flexible and can be increased or decreased as needed.

Whether or not it grabs the spotlight occupied by flashier technologies, biodiesel will certainly be a constant work in progress.

Currently, the largest biodiesel market is fleet vehicles. According to the National Biodiesel Board, there are over 100 such fleets using biodiesel in the United States. These include federal and public organizations such as the U.S. Postal Service, the U.S. Air Force, U.S. Army, NASA, the U.S. Department of Energy, Duke Energy, and Florida Power & Light. Many public transportation services are also looking to biodiesel in order to complement petroleum usage. City buses such as Cincinnati Metro are also using biodiesel. Potential future targets include areas such as marine and agricultural applications and home heating.

As public awareness grows, biodiesel and biofuels in general could easily find their way into dinner conversations. Political support is also on the rise and, in the wake of legislation such as the 1998 EPACT amendment, alternative fuel sources will be a necessity in the not-so-distant future.

For more information on biodiesel, biofuels and related topics, check out the links on the next page.

Lots More Information

Related Articles

More Great Links