Overcoming Biodiesel Problems

The energy picture in the United States and worldwide is changing. Higher oil prices and environmental concerns are causing consumers to look to alternative sources of fuel. As they do this, biodiesel is gaining increasing prominence in the nation’s energy usage landscape. The name biodiesel refers to a ratio of treated vegetable oil or animal fat to diesel or heating fuel. For this article, it will be referred to as vegetable oil. Soybean oil and rapeseed oil are the most common vegetable oils used to produce biodiesel.

The major advantages of biodiesel are that the vegetable oil portion is a renewable energy source, that it will reduce our dependence on foreign oil sources, and, most importantly, will reduce emissions. EPA testing confirms that, depending on the percentage of vegetable oil in the fuel blend, biodiesel lowers carbon monoxide emissions by up to 48% and particulate matter emissions by up to 47%. In addition, sulfate emissions (from which sulfur dioxide and sulfuric acid can result) can be reduced by up to 100% from regular diesel fuel.

Major reasons for the increasing popularity of biodiesel include the implementation of a federal tax credit for fuel consumers using renewable fuels like biodiesel, and movement on the state level to turn to renewable fuels which reduce emissions and improve the air quality of urban areas within the state that are in regular violation of the EPA’s air quality standards (such as many areas of Texas). In a possible reflection of future trends, in late 2005, the State of Minnesota enacted a law that all diesel fuel sold in the state would be required to contain no less than 2% soy or vegetable oil (commonly known as a B2 blend). If more states follow Minnesota’s lead, the use of biodiesel will surely continue to expand.

The most common blends of biodiesel are B2, B5, and B20, which correspond to 2%, 5% and 20% vegetable oil concentration, respectively. The vegetable oil for use in biodiesel is produced by a process called esterification through a batch-to-batch process, and each batch can vary in terms of quality. The oil from crushed soy beans, for example, is filtered and then reacted with sodium hydroxide (common lye). The product is then rinsed with alcohol, and a finished product is produced, which can be blended with #2 diesel fuel to produce biodiesel.

In spite of the higher price for biodiesel, almost everyone is touting its use. However, it is wise to consider that there are many documented and reported problems with the use of biodiesel that you should be aware of. We will summarize the most common issues from this point on.

Energy Value and Water Problems

Most concerning for the consumer concerned about fuel costs is that biodiesel, specifically B20, has only 117,000 BTU per gallon of fuel compared to 131,000 BTU per gallon of #2 diesel fuel. Less energy value in the fuel means less mileage and less power. In over-the-road operation, there can be both a loss of power (meaning the driver has to shift more often) and a decrease in miles per gallon of between 0.5 to 1.0 miles per gallon. For a truck that might get 7-8 miles per gallon on #2 diesel fuel, this loss of mileage is significant.

Water contamination is a significant problem for biodiesel users. Biodiesel fuel wants to absorb water and hold on to it, either in free form or in the form of a milky emulsion. In cold weather, this water can form ice and cause operating problems. In emulsion form, the water can negatively affect the auto-ignition properties of the diesel fuel. In either form, it can promote the growth of bacteria and microbes. The bio- (vegetable oil) portion of the fuel is an excellent nutrient for slime and bacterial growth. Bacterial growths in biodiesel blossom very quickly and, if not controlled, can cause massive filter plugging.

Cold Flow Problems

The most common form of biodiesel, B20, does not flow very well in cold weather; at temperatures below 50 degrees, it can form a thick and cloudy bio-mass. According to the National Biodiesel Board, B20 blends can raise the cold filter plug point value of the fuel by 10 degrees F. Due to this, some biodiesel suppliers do not recommend its use during the winter months. To compound the problem, most existing cold flow and anti-gel additives do not improve the flow of B20 because they are designed to act upon paraffin wax crystals, which exist naturally in petroleum; they are not designed to be effective on the components within the vegetable oil phase, which cause gelling.

Quality Control Issues

Ease of manufacture has been both a blessing and a curse for the biodiesel industry – almost anyone with the proper equipment can manufacture the fuel, but not everyone can or is willing to monitor their processes to ensure that the fuel produced meets specifications. As a result, there have been problems with out-of-spec biodiesel fuels reaching the market (a 2006 survey by the National Biodiesel Board of 200 different fuel batches found that 50% of them did not meet minimum specifications for quality). This specification, ASTM D-6571, gives guidelines for important biodiesel fuel parameters such as alcohol content and glycerin content, both of which can be met with proper quality controls in the manufacturing process. It is important to have fuel that meets these particular specifications in order to eliminate potential fuel-related issues. It is not uncommon to see cloudy product and oil that drops out of the biodiesel mixture (doesn’t stay blended); when this happens, the oil will only re-dissolve when heated above 100 degrees (how will you do that?). Excessive alcohol content (from the methanol wash) is another common problem in out-of-spec biodiesel; excessive alcohol affects the auto-ignition temperature of the fuel and causes rough running in diesel engines. As a biodiesel user, it is important to ensure that the fuel you use is certified to meet the ASTM specification for biodiesel fuel.

Other Problems

Biodiesel is known to act as a detergent when first introduced into existing storage tanks. It will disperse any old sludge that has settled to the bottom of the tank, leading to massive filter plugging problems if the user is unprepared. This problem occurs during the first few loads of switching to biodiesel. Therefore, it is advisable to have extra filters on hand during the initial introduction of biodiesel to a new system.

Biodiesel degrades about four times faster than diesel fuel or heating oil. In the presence of even small amounts of water, pure biodiesel degrades 80-85% faster than pure diesel fuel alone. Blending biodiesel with other fuels accelerates its bio-degradability; blending 20% oil with 80% diesel or home heating fuel creates a blend that breaks down twice as fast as #2 diesel alone. This aging can be predicted by having an ASTM aging test performed on the fuel. Destabilized biodiesel fuel turns thick, darkens in color, and plugs fuel filters. Having seen this problem repeatedly, Bell Performance has developed a Fuel Storage Stabilizer that greatly reduces the aging of biofuels and biodiesel.

The compatibility of biodiesel with various seal and hose materials is another issue of concern. Some o-rings, seals, and gasket materials can be affected by biodiesel, while various hose materials used to dispense biodiesel are softened and have failed when in contact with the fuels. Natural or nitrile rubber compounds, polypropylene, polyvinyl, and Tygon materials are particularly vulnerable. On the bright side, many elastomers produced after 1993, including Teflon, Viton, and Nylon, have very little reaction to biodiesel.

Finally, many Biodiesel users have problems when they do their own blending of vegetable oil and diesel fuel. Users have found that the bio portion that they are adding to a tank of #2 diesel or home heating oil must be added on top of the regular fuel to assure good mixing. This type of “splash blending” takes advantage of the difference in the weight per gallon, as vegetable oil weighs more than diesel fuel.

As with anything new, we tend to hear all of the good things about a newer product – why it is good for the economy, the environmental benefits, etc. We at Bell Performance feel that if we take the experience of our customers and combine it with laboratory and field experiences to make you aware of potential problems, everyone can be better prepared.