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What is biodiesel?
Biodiesel is a renewable fuel for diesel engines. Biodiesel, defined by ASTM International D6751 consists of long-chain fatty acid alkyl esters and is made from renewable vegetable oils, recycled cooking oils, or animal fats. It can be used at full strength, but is typically blended with petroleum diesel. A blend of 2% biodiesel and 98% diesel is referred to as B2. Other typical blends include B5, B10, and B20; pure biodiesel is sometimes referred to as B100. 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. 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. 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. 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. Biodiesel has several key advantages: * Biodiesel is environmentally friendly. * 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. 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 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. 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. 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. Diesel Engines vs. Gasoline Engines In theory, diesel engines and gasoline engines are quite similar. They are both internal combustion engines designed to convert the chemical energy available in fuel into mechanical energy. This mechanical energy moves pistons up and down inside cylinders. The pistons are connected to a crankshaft, and the up-and-down motion of the pistons, known as linear motion, creates the rotary motion needed to turn the wheels of a car forward. Both diesel engines and gasoline engines covert fuel into energy through a series of small explosions or combustions. The major difference between diesel and gasoline is the way these explosions happen. In a gasoline engine, fuel is mixed with air, compressed by pistons and ignited by sparks from spark plugs. In a diesel engine, however, the air is compressed first, and then the fuel is injected. Because air heats up when it's compressed, the fuel ignites. Why should I consider using biodiesel? Biodiesel is a renewable, biodegradable, cleaner burning alternative to petroleum fuels. It has a slightly higher cetane rating which can promote easier cold starting and lower idle noise. With tax incentives and rising petroleum prices, biodiesel is becoming more economically competitive. Is all biodiesel the same? Because biodiesel can be made from a number of different raw materials and with a number of different processes, there can be some subtle variations in chemical and physical properties. ASTM has established standards for testing diesel fuels to insure some uniformity in performance. In most applications, if the biodiesel conforms to ASTM standards it can be used in the same equipment as other diesel fuels. Verify with your supplier that the biodiesel conforms to ASTM standards. Will I have to modify anything mechanically in my engine to use biodiesel? Not if you are using blends of B20 or less. The specifications for biodiesel have been established so that it can be used in any diesel engine. Some modifications may be desirable with higher biodiesel concentrations. Consult your equipment manufacturer before using higher biodiesel blends. Will biodiesel hurt the mechanical parts of my engine? No. In fact biodiesel can be good for an engine for two reasons. First, biodiesel has more lubricating properties than petroleum diesel. Loss of lubricity is one of the drawbacks of newer low sulphur diesel fuels. Adding just 1% biodiesel increases the lubricity to an acceptable level, so any biodiesel blend will have the required lubricity without sulfur or other additives. The second advantage is that biodiesel will actually help clean the fuel system. Because it is a good solvent, it can remove deposits and buildup from tanks, lines, pumps and other fuel system components. Be aware, though, that since it is such a good solvent, it has the potential to damage certain paints and finishes, so always clean up spills immediately. Will biodiesel hurt seals and other components? Biodiesel blends higher than B20 can cause problems with natural rubber engine components, such as seals and hoses. Biodiesel will degrade rubber, so any seals or hoses in the fuel system that are made of rubber will be susceptible to damage. Biodiesel blends of B20 or below should not cause problems with rubber components, but users should periodically check rubber components when using any biodiesel blend to make sure they are not degrading or getting hard. As the use of biodiesel increases, most equipment manufacturers are increasing the use Viton-based materials in seals and hoses. Viton is a synthetic rubber substitute that will not be damaged by biodiesel. Some manufacturers do caution users about potential problems with the lubricating oil in an engine. If biodiesel gets mixed with the lubricating oil, it can react with the oils to create “sludge” that might accumulate in the sump or in oil passages. Check manufacturer recommendations about oil change frequency as some suggest changing oil more often when using biodiesel. Will biodiesel cause fuel filter problems? The most common fuel filter problems occur when switching older machinery from petroleum diesel to biodiesel. Petroleum diesel has a tendency to leave paraffin-based buildup on the insides of tanks and other fuel system components. Biodiesel will loosen this buildup, which will be trapped in the fuel filter. Users can expect to replace fuel filters several times after switching older equipment to biodiesel. After the fuel system gets cleaned out, filter usage should return to normal. Another less common cause of filter problems comes from the use of higher biodiesel blends that have been stored for extended periods of time. Biodiesel will degrade with age (see storage question below), producing some gums and sediments, which can cause filter plugging. Will I get as much power from my engine with biodiesel? Pure biodiesel contains 5-8% less energy per gallon than petroleum diesel. Blended fuels obviously will have less of an energy loss. Some literature does indicate that other factors such as more efficient burning and better injection efficiency due to higher viscosities may counteract this energy loss. In any event, users might notice a slight power loss with biodiesel fuels. Will I void the manufacturer’s warranty if I use biodiesel? Warranties vary significantly from manufacturer to manufacturer, but most will not categorically void a warranty if you use biodiesel. However, most warranties will not cover damage that was caused by the fuel (be it biodiesel or any other fuel) because those damages were not caused by a defect in the machine. For instance, if you damage a diesel engine by accidentally putting gasoline in the tank, the manufacturer probably will not repair the engine under warranty. Therefore, it may be more difficult to get warranty coverage for problems that may have been caused by biodiesel. Furthermore, many manufacturers are reluctant to recommend use of blends higher than B5 in engines. Check carefully with the individual manufacturer to verify what is covered and/or recommended. Can I use biodiesel in cold weather? Pure biodiesel is more susceptible to cold temperature problems than petroleum diesel, but when blended, this effect is moderated. A B2 biodiesel blend, for example, has the same cold flow properties as petroleum-based diesel. However, B20 will have a higher gel point, from 3 to 5 °F higher. The bottom line is that as with petroleum diesel, you will need to use a kerosene blend or other anti-gelling additive in colder temperatures. Consult your fuel supplier to make sure you will be protected in your climate. Is biodiesel more susceptible to water contamination? Biodiesel is more susceptible to water contamination than petroleum diesel. The presence of water in biodiesel or any fuel can promote corrosion of fuel system components and growth of microorganisms. The following are some common sense techniques useful for preventing water contamination in any fuel system. * Make sure all tank caps are in place and in good condition. * Store machinery with tanks full to minimize condensation inside the tank. Get in the habit of filling the tanks at the end of the day so there is no room for condensation to form when the temperatures cools overnight. * Large temperature swings can promote moisture condensation on the inside of storage tanks. Underground storage tanks are best at preventing condensation since fuel is kept at a relatively constant temperature, but underground storage introduces many other potential problems such as leakage and liability. Above ground storage tanks should be insulated (double wall) and shaded if possible to moderate temperature swings thereby reducing the possibility of condensation formation. * Drain a small amount of fuel from the bottom of storage tanks every 6 months to remove any water that might have accumulated in the tank. * Avoid prolonged exposure of fuel to light, which can induce algae growth. Fiberglass tanks should be painted and/or placed in shaded areas. * If biological growth is a problem, the same products that are used with petroleum diesel can be used in biodiesel to “dry” the fuel and clean up biological contaminants. How long can I store biodiesel? Fuel aging and oxidation can lead to heightened acid content, high viscosity and the formation of gums and sediments that clog filters. It is recommended that biodiesel be stored for no more than six months without an anti-oxidant additive. Will biodiesel totally replace diesel someday? There are no specific efforts at this point to make biodiesel a requirement. Because it is a cleaner burning, renewable fuel source, though, availability and usage will continue to increase. |