An Introduction to Biodiesel

The concept of using plant matter to operate internal combustion engines is older than the gasoline and diesel fuels that are so ubiquitous in our lives today. Rudolf Diesel developed the compression ignition engine and demonstrated it at the Paris World’s Exhibition in 1900. His fuel of choice for powering the new engine: peanut oil.

Although the concept of using plant matter to operate internal combustion engines has been revisited numerous times since Diesel’s early experiments, the discovery of cheap fossil oils delayed any significant development of biofuels.

The development of the diesel engine and fuel system progressed very quickly after its first demonstrations to the public owing to its increased efficiency compared with that of the steam engine, its relative portability (paving the way for automotive, farming, and industrial uses), and access to cheap and convenient diesel fuel oil. Engine development continued for the next 80 years using low viscosity petrodiesel fuel, while the much higher viscosity plant oils were left behind on the grocer’s shelves for baking, salad dressing, and French fries.

With the first worldwide oil “shortages” in the 1970s, researchers began working in earnest in an attempt to develop the biofuel market. The many shortcomings related to the direct use of plant oils and their total incompatibility with petrodiesel fuel1 pushed researchers in the direction of chemically modified forms of plant oils and animal fats known as biodiesel.

Biodiesel is a renewable, relatively clean-burning, carbon-neutral fuel that can be obtained from a variety of oilseed plants, waste oils, and rendered animal fats. These unprocessed materials (collectively referred to as feedstock “oils”) can be converted into a petrodiesel-compatible fuel using a process known as chemical transesterification.

The properties of rendered animal fats and plant oil vary widely from those of petroleum diesel fuel, primarily in the areas of viscosity, atomization, and the coking of engine components. All plant and animal oils have essentially the same chemical structure, consisting of triglycerides, which are chemical compounds formed from one molecule of glycerol and three fatty acids. Your next Greek salad will contain an oil and vinegar dressing, which chemists refer to as a “triglyceride and acetic acid surfactant,” regardless of whether you prefer extra virgin olive oil or plain old Mazola™. Little wonder chemists are generally not invited to many dinner parties.

Glycerol (common name glycerin) is an alcohol that can combine with up to three fatty acids to form mono-, di-, and triglycerides.

Fatty acids are chains of hydrocarbons that vary in carbon length depending on the oil feedstock. If each carbon atom has 2 associated hydrogen atoms, the fatty acid is known to be saturated. If 2 carbon atoms are double bonded, having less hydrogen, the fatty acid is unsaturated. Likewise if more than 2 carbon atoms are unsaturated, the fatty acid is said to be polyunsaturated.2

Triglycerides are the main compounds or components of animal fat and vegetable oils. They have a lower density than water and will therefore float on it. If the oil is solid at room temperature the triglycerides are known as “fats;” if they are liquid they are called “oils.” As a general rule, triglycerides that are liquid at room temperature are unsaturated, which is a desirable property for engine fuels.

Plant oils have viscosities that can be as much as 20 times higher than that of fossil diesel fuel, while chicken fat, yellow grease, lard, and tallow remain stubbornly solid and unusable in their unaltered state. The problem of the high and variable viscosity of feedstock oils can be corrected by adapting the engine to the fuel or vice versa. Chapter 7.2 will debate the relative merits of the former process, while the main theme of this book focuses on the latter concept: adapting the fuel to the millions of engines that are now operating or will be produced for many years to come.

Chemical transesterification of feedstock oils is a well-known process which solves the problem of feedstock viscosity as demonstrated in Figure 3.3-3. The process was first described in 18523 when it was originally used as a means of producing high-quality soaps, and with a bit of retooling it was found to work wonders in the production of biodiesel. Simply stated, biodiesel is produced by the reaction of feedstock oils with an alcohol in the presence of a catalyst to produce fatty acid methyl esters (FAME) or biodiesel. The typical process is:

100 kg feedstock oil + 10 kg methanol k 100 kg FAME + 10 kg glycerol

The resulting FAME is known to be chemically contaminated with numerous compounds resulting from the esterification process, requiring further downstream processing to ensure a fuel quality compatible with ASTM Standard D6751 for biodiesel, a fuel comprised of “the mono-alkyl esters of fatty acids derived from vegetable oils or animal fats.” Hereinafter, FAME that is directly taken from the reaction process will be referred to as “raw FAME” and when it meets the fuel quality standard it will be referred to as FAME.

The first reference to FAME production was in 1937 and within the next year a bus fuelled with palm oil-based biodiesel ran between Brussels and Louvain.4 However, at that point further scientific research and production ground to a halt.

Some forty years later, Professor Martin Mittelbach, Ph.D., University of Graz, Austria, and his team of researchers were producing rapeseed oil-based biodiesel and testing its feasibility as a diesel fuel substitute.

When prodded to discuss the origins of the modern biodiesel industry, Dr. Mittelbach modestly admits that he has been “involved since the beginning. We (University of Graz) were the first to produce biodiesel in Europe, more than 20 years ago, although I am not exactly sure what moved me into this program!...Because of my research on carbon-based compounds, a discussion ensued with an agricultural group in Austria that had some experience using straight vegetable oils mixed with 50% fossil fuels in tractors. The farmers found that after a period of time running on this mixture, total engine breakdowns would occur and they had to stop this practice. We looked into the problems, examined the prior research, and I guess you could say the rest is history.”

Within the next decade hundreds of research programs sprang up around the world as interest in clean and renewable fuels started to take hold.

In the United States, the demand for soybean meal (the residual husk of the bean after crushing) was greater than the demand for oil, causing an imbalance in supply and depressed soy oil prices and galvanizing the United Soybean Board into action. It voted to promote biodiesel production using soy oil, which ultimately led to the current National Biodiesel Board (NBB), headed by its executive director Joe Jobe.

The Canadian Renewable Fuels Association (CRFA), which merged with the Biodiesel Association of Canada, develops market strategy and educational data for both the ethanol and the biodiesel industries.

As a result of lobbying efforts and continued research, biodiesel has received the support of numerous federal, state, provincial, and local governments who see it as a means of reducing greenhouse gas and smog-forming emissions, supporting local agribusiness, and helping to reduce North American dependency on foreign oil.

Technical Issues

The Pros of Biodiesel

Blending

One primary advantage of biodiesel is its ability to fit almost seamlessly into the existing fuel distribution and retail sales system while other alternative “fuels” such as hydrogen6 require the complete rebuilding of distribution technology at a cost of trillions of dollars.

Biodiesel can be used in all modern diesel engines and oil-fired heating systems with minor (if any) modifications. Two notes of caution:

1. FAME may cause long-term degradation of natural rubber hoses and gaskets and some paints, and replacing natural rubber hoses, “O” rings, and gaskets with polymeric (synthetic) versions such as Viton® may be necessary. However, experience has shown that blends of 20% biodiesel or less seldom cause any problems at all, and in any event late-model vehicles seldom use natural rubber components.

2. Fossil diesel fuels may develop microbial growth that forms deposits on the walls of fuel storage tanks, pipes, and other components. The solvent abilities of FAME can cause these deposits to loosen, which can lead to fuel filter plugging and a resulting loss of engine power. Therefore, it is generally suggested that fuel filters in vehicles that have been operating on fossil diesel and switch to biodiesel be replaced a few months after the change takes place.

Biodiesel fuels are in commercial use in many European countries including Austria, the Czech Republic, Germany, France, Italy, and Spain. Biodiesel can be used in either its pure or neat form or as blends mixed with fossil diesel fuels. Neat biodiesel is designated B100, while blends are marked “BXX” where “XX” represents the percentage of biodiesel in the fuel mixture. Further, because biodiesel is stable at any concentration, users are free to choose the blending level they prefer based on availability, desired operating temperature, or price.

Biodiesel Concentration

Germany, Austria, and Sweden market neat biodiesel, although blends of 5%-20% are the preferred concentration. The “European Directive for the Promotion of the Use of Biofuels,” published in 2003, mandates that all member states ensure minimum market shares of biofuels (ethanol, ethanol derivatives, and biodiesel). Market share of biofuels is to reach 5.75% by 2010.

For several reasons, such as the maximum available production of biodiesel, fuel quality and stability, and the political realities of displacing fossil diesel from the market, North American industry proponents consider a blend level of B20 to be the upper limit concentration.

The question of blend concentration and related issues of politics and fuel quality are very complex; accordingly Chapter 6 in its entirety has been reserved to debate the matter further.

Biodegradability and Nontoxicity

Biodiesel is readily biodegradable and nontoxic, making it the ideal fuel choice when used in environmentally sensitive areas such as parklands or marine habitats. It is known to be less toxic than table salt and is as biodegradable as sugar.

High Cetane Value

The cetane value is a rating of the relative ignition quality of diesel and biodiesel fuels, with higher ratings offering improved ignition performance. As the cetane value increases, fuel ignition will be smoother and more complete, improving combustion and reducing emissions from unburned fuel. Virtually all biodiesel fuels have cetane values several percentage points higher than that of petroleum diesel fuel.

High Lubricity

Biodiesel has excellent lubricating properties, far in excess of those of petrodiesel, which help to reduce fuel system and engine wear. As petroleum diesel fuel sulfur levels continue to be legislated downwards, its lubricity will decline to the point where additives will be necessary. The addition of 1% biodiesel to low-sulfur petrodiesel will improve the fuel blend lubricity to within specification.

Low Emissions

As a renewable fuel source, biodiesel operates on a closed-carbon cycle, which reduces CO2 production by 2.2 kg for every liter of fossil fuel displaced.10This is because of the regenerative (biological) nature of all energy sources that absorb CO2 from the atmosphere during their growing phase, only to release the same compound during fuel combustion. Additionally, the FAME molecule contains 11% oxygen, which leads to improved combustion and significant reductions in Particulate Matter (PM) or soot.

As part of the Clean Air Act Amendments enacted by the U.S. Congress, the Environmental Protection Agency (EPA) was directed to ensure that any new commercially available motor vehicle fuel or fuel additive would not present an increased health risk to the public. Under this directive, EPA established a registration program and testing protocols which are outlined in CFR Title 40 Part 79 as part of Tier I and Tier II emissions testing.

The EPA completed a major study of the impact of various concentrations of soybean-based biodiesel in the operation of heavy-duty highway-based vehicles. The results of the study are shown in graphical form in Figure 3.3-7 and clearly demonstrate the superior emissions reductions of FAME fuels.

Nitrogen oxides (NOx) do increase as a result of high engine combustion temperatures and are discussed later in this chapter.

Renewability

Notwithstanding the findings of David Pimentel, insect specialist at Cornell University, and his associates, biodiesel has a very high net energy balance, in excess of 300%. Pimentel stirred a considerable amount of public controversy with the release of his 11-page report published in Natural Resources Research (Vol. 14:1, pp. 65-76) which concludes that soybean-based biodiesel has a negative energy balance, with an energy input 27% higher than its energy output. International media love controversy and brief, simplistic, contrary news items, thus providing Pimentel with a Warholian window of opportunity to cast doubt on the entire biofuel sector.

His comments are completely at odds with the numerous studies that have found the opposite to be true. Dr. Robert McCormick of the U.S. Department of Energy states that “the Pimentel/Patzek study uses outdated information on agricultural practices as well as unrealistic and unsubstantiated assumptions regarding energy inputs. At least eight other peer-reviewed studies have been conducted over the past 12 years and find exactly the opposite, that biodiesel has a highly positive energy balance.”

The U.S. Department of Energy (DOE) and the U.S. Department of Agriculture (USDA) in 1998 completed a thorough study of the energy balance of biodiesel and found that for every unit of fossil energy used in the entire biodiesel production cycle, 3.2 units of energy were delivered when the fuel was consumed.11

Given that Pimentel’s co-author, Ted Patzek, is a former oil company employee and is now a director of the University of California Oil Consortium, is it possible that the findings in the report could be skewed?

Readers who are interested in learning more about the life-cycle energy requirements for the production of soybean-based biodiesel are encouraged to read the entire 286 pages of analysis completed by the U.S. Departments of Energy and Agriculture (versus 1.5 pages of analysis completed by Pimentel) at www.biodiesel.org.

Low Sulfur

In order for petroleum diesel fuel to be given a rating of “low” or “ultra-low” sulfur content, it is necessary to subject the fuel to an energy-intensive refining process that generates additional carbon dioxide emissions. The resulting fuel will have reduced lubricity levels that must be supplemented with lubricating additives.

Biodiesel by contrast retains its excellent lubricity while being intrinsically free of sulfur. Having a virtually zero-sulfur level allows the optimum use of oxidation catalytic converters in the exhaust system.

The Cons of Biodiesel

So far, biodiesel sounds like the perfect fuel. Unfortunately, there are a number of issues which must be considered on the negative side of the balance sheet.

Oxidation and Bacteriological Stability

Biodiesel is biodegradable, which is an excellent environmental benefit, but it creates long-term storage and fuel stability issues. When it is exposed to high temperatures, oxygen, or sunlight or placed in contact with non-ferrous metals, FAME will deteriorate, resulting in polymerisation (fuel thickening) which leads to plugged filters and “glazing” within the fuel injection system. To prevent storage degradation, anti-oxidant additives may be added to extend storage life. Of course, the simplest corrective action may be to simply limit the storage time of FAME fuels through rapid consumption and rotation.

Water content can destabilize FAME as well as create an active growing medium for microorganisms. Biodiesel manufacturers produce fuels that have very low water content, but biodiesel is hygroscopic and actually attracts water much more readily than petrodiesel does. (Although according to one German report, the hydroscopic nature of biodiesel may prevent the growth of bacteria, by denying a water saturated growing media12).

Biodiesel will become saturated at water levels above approximately 1,000 ppm, and if water ingress continues unchecked, water no longer remains bonded and collects at the bottom of the storage tank, leading to the very condition that promotes microbial growth. To test this theory, I placed two samples of FAME and rain water (simulating a rain-induced leakage into a fuel storage unit) in small beakers which were placed in a darkened area for a period of 90 days. One of the samples was treated with Kathon® FP1.5 diesel fuel biocide. At the end of this period, a black, slimy growth had formed at the water/oil interface of the untreated sample, indicating the presence of bacteria. The second sample was bacteria free.

Howard Chesneau is President of Fuel Quality Services Inc., the North American distributor of Kathon® biocide and LTSA-35A fuel stabilizer as well as a complete series of microbial test kits. According to Mr. Chesneau: “Conditions with excessive wetting of the fuel can occur where storage tank plumbing or access seals are damaged or if partially filled steel tanks are subjected to repeated thermal excursions, causing condensation of atmospheric moisture. The effects of microbial contamination include product spoilage, corrosion on fuel-wetted surfaces, filter plugging, and engine failure. Microbes are not selective about the type of fuel product they consume and will contaminate all types of petroleum-based products, fuels, feedstock, and especially biodiesel. Microbes require only droplets of condensation or a single millimeter film of water to initiate the fuel system degradation process.”

Mr. Chesneau continues by explaining that biodiesel manufacturers are taking excessive risks by pushing biodiesel into markets that are not accustomed to the issues of this fuel type. “In the industry’s zest to get product into the marketplace, fuel quality standards are lacking in the United States and Canada. There is no requirement for storage, oxidation, or thermal stability as is required by the European Union. This will, and already has, led to trouble in the market.”

Edward English II, Vice President and Technical Director of Fuel Quality Services, concurs: “Biodiesel is a very different product from fossil diesel fuel and there needs to be better education surrounding handling and storage of these fuels. B100 may well leave the factory meeting ASTM standards, but each time it is pumped, transferred, stored, blended and dispensed, it will pick up ever-increasing amounts of water. This stuff is like a sponge, and the only way neat or blended biodiesel will remain stable and microbial free is through proper handling, monitoring and remedial procedures.”

“Our detection kits allow fuel handlers and retailers a very quick ‘pregnancy test’ to determine if the fuel is contaminated with microbial growth,” interjects Mr. Chesneau. “Unlike the food industry, we are not concerned about what type or quantity of bacteria is present in biodiesel, simply whether they are there or not. A positive result will then require remedial treatment with biocide additive and investigation as to where the water contamination entered the fuel chain, to prevent repeat problems.”

The discussion continues to include bio-heat products (biodiesel blended with home heating oil), discussed in further detail in Chapter 9. “Oxidation of biodiesel can begin through contact with various non-ferrous metals such as brass, copper, lead and plumbing solders,” states Mr. English. “The majority of oil-fired home heating systems contain fuel lines plumbed with copper and this will definitely create sediment and sludge, especially when fuel sits during the six-month period after the heating season. For this reason, we recommend twice-yearly treatments of oil storage tanks to prevent expensive fuel-related problems from occurring.”

“As much as we would love to sell lots of biocide and fuel stabilizers, the fact of the matter is that careful handling and attention to storage environments will go a long way toward ensuring quality biodiesel,” Mr. Chesneau concludes.

Nitrogen Oxide Emissions

Numerous studies have confirmed that overall emissions from the combustion of biodiesel are low but show slightly elevated levels of nitrogen oxides (NOx). This increase is regarded as a problem related to higher combustion cylinder temperatures and is not inherently a fuel-related issue. Manufacturers believe that improvements in engine sensor and management technology as well as NOx catalytic reduction are just around the corner.

Unfortunately, this issue of NOx emissions is placing a damper on the entire diesel engine industry. Diesel proponents believe that gasoline-based exhaust emission strategies are strangling the potential of the diesel market and that each engine technology should receive its own emission profile in light of the considerable fuel and greenhouse gas emissions savings of diesel engines.

Not every automotive manufacturer is worried. Mercedes-Benz is well known for its innovative, quality automobiles featuring state-of-the-art engineering. The company marked the epitome of its technological prowess by showcasing its leading edge BLUETEC technology, launching the diesel power train of the future. “Vision has therefore become reality as the extremely economical Mercedes-Benz CDI models are the cleanest diesel in the world in every category and consume between 20 and 40 percent less fuel than the gasoline counterparts,” states a January 2006 corporate press release. Mercedes-Benz certainly recognizes the importance of emissions reduction technology, as over 50% of their total production volume is now captured by diesel engines.

Courtesy Mercedes-Benz

The release of the BLUETEC technology coincided with the US release of low-sulfur diesel fuel in the autumn of 2006. Sulfur occurs naturally in mineral diesel fuel (see Chapter 3.1) in varying amounts, resulting in corrosive action which damages NOx reduction technology. Restricting sulfur content to a maximum of 15 ppm permits the use of particulate filters and efficient nitrogen oxide exhaust treatment. But the question remains: will the vehicles using BLUETEC technology be certified for use with biodiesel fuels?

Cold Flow Issues

No. 2 diesel fuel suffers from a thickening condition known as “waxing” or “gelling” when temperatures drop below the cloud point of the fuel. Should this occur within the fuel system of a vehicle, expensive cleaning becomes necessary.

By contrast, biodiesel suffers from a similar but reversible problem. Should low-temperature fuel gelling occur, causing loss of engine power or complete fuel starvation, the problem can be remedied by simply moving the vehicle to a warm location such as a parking garage until fuel temperatures moderate.

Both No. 2 diesel fuel and biodiesel can be “winterized” by the addition of so called “pour point enhancers,” which may be as simple as blending No.1-D into the fuel blend.

No. 2 diesel fuel is treated by fuel refineries to meet the expected minimum temperatures within a given geographical location. To a retail consumer, the transition from “summer” to “winter” diesel fuel is completely transparent. However, adding any amount of biodiesel fuel into an already winterized diesel fuel mix will degrade the minimum operating temperature by raising the cloud and pour points. This occurs because all biodiesel fuels are known to have cloud point temperatures greater than No.2-D; therefore adding biodiesel to an already winter-treated fuel dilutes the total amount of pour point enhancer present in the fuel mixture, reducing cold weather performance.

Although the addition of No.1-D will greatly improve the minimum working temperature of fuel, there is a resultant loss of approximately 3,000 BTU of energy per gallon (790 BTU per liter), resulting in higher fuel consumption and higher operating costs. In addition, the lubricity and viscosity of the No.1-D and No. 2-D fuel mixture will be reduced, which may have a detrimental effect on engine wear and engine life as well as requiring increased lubricating oil changes as a result of low-viscosity fuel leakage past piston rings.

To counter these problems, fuel-additive companies have developed a range of products to improve the cold-weather performance of petrodiesel and biodiesel fuels. Primrose Oil Company Inc. offers the Flow-Master® winter diesel fuel treatment product it claims to be more cost effective than using No.1-D blended fuels.

The reason fuel gels at cold temperatures is that waxes inherent in the fuel begin to form microscopic crystals. If untreated, these crystals will immediately agglomerate (combine) with one another to form a gel and eventually solidify, blocking fuel lines and filters. Pour point enhancers limit the ability of wax crystals to grow large enough to agglomerate. Primrose indicates that its product will improve the cold flow rating of any untreated fuel by a minimum of 20°F to 30°F (11°C to 17°C).

It is virtually impossible to determine the exact blend ratio or concentration of biodiesel that can be used at a given geographical location without knowledge of the fuel’s cloud point temperature.13 There is considerable variability in biodiesel cloud point temperature resulting from the inconsistency of the feedstock oil saturation level, with long-chain compounds displaying poor cold weather properties. Tallow, lard, palm oil, and yellow greases may remain solid or semisolid at room temperature, requiring great care in blending and storage.

Some researchers have taken a different approach to the problem by attempting to modify the FAME chemical structure through the use of alternate alcohols which have shown improved cold weather performance. Unfortunately, these alcohols have a higher cost and this process is of limited value in the current marketplace.14

Repeated cooling and filtration of crystal growth within the FAME has also been attempted with varying rates of effectiveness. However, this process requires considerable amounts of energy and removes valuable esters that are lost during the filtration process, lowering overall biodiesel yields.15

As a result of biodiesel demand growth in the northern United States and Canada, including a Minnesota bill that requires all on-highway diesel fuels to contain at least 2% biodiesel, the National Biodiesel Board commissioned the Cold Flow Blending Consortium. It studied ways to improve blending techniques in order to limit problems associated with lower temperature blending without the use of pour point enhancers.16 The Consortium developed a test rig to simulate proportional and splash blending at a terminal, using No.1 and No. 2 diesel fuels as well as three biodiesel samples with a range of cold flow properties.

Key test results indicate that biodiesel must be at least 10°F (5.5°C) above its cloud point to successfully blend with diesel fuels in cold climates.

Chapter 8.3 will provide a direct test method that may be used to determine the cloud and pour points of any petro/biodiesel mixture.

Lower Energy Content

Biodiesel has a lower energy density or “energy content” than No. 2 diesel fuel: approximately 12.5% by weight and 8% by volume. As fuel injection systems operate on a volumetric basis, the theoretical energy loss will be the lower value. Experience has shown that actual energy losses are lower than this as a result of the slightly higher viscosity of the fuel, preventing blow past the fuel injector components and reducing leakage into the engine cylinder.

In most fleet applications, biodiesel consumption rates were between 0% and 5% higher than those of petrodiesel.

In fact, the minor change in “real world” energy content will go largely unnoticed, and if you have any ability to moderate your driving speed a mere 2 miles per hour (3.2 kph) slower at highway speeds will more than compensate for the difference.

OEM Warranty Issues

One of the popular misconceptions about biodiesel is that it will not affect engine and fuel system warranties provided the fuel meets applicable specifications.17 Statements such as these are not only misleading; they are simply wrong.

All major engine, vehicle, and fuel injection equipment manufacturers have clearly stated guidelines regarding the use of biodiesel fuels. Without hesitation, all manufacturers state that biodiesel that is used within the blend limits of their warranty statements must meet the appropriate national and/or international fuel standards.

Volkswagen of America sums up the general OEM equipment position regarding biodiesel with the following statement:

“Volkswagen of America Inc. is proud to be the automobile industry’s leader in diesel technology for passenger cars and light-duty trucks. Many customers have expressed interest to us in operating their Volkswagen TDI vehicles on ‘biodiesel’ fuel….Volkswagen has determined that diesel fuel containing up to 5% biodiesel meets the technical specifications for Volkswagen vehicles equipped with TDI engines imported into the United States. While this historic decision by Volkswagen is a first step in a renewable fuel strategy for ou