In 1993, a Task Force was formed within ASTM Committee D02 on Petroleum Products and Lubricants to begin devel- opment of an industry consensus standard for biodiesel. The first step undertaken by the Task Force was the determina- tion of the philosophy to be used for the standard. Various options were considered, from adding a section to the exist- ing ASTM petrodiesel standard (D975), to development of a standard for a blend with petrodiesel, to a stand-alone stan- dard. The following was agreed on by the Biodiesel Task Force and subsequently by the membership of ASTM.
1. Develop a stand-alone specification for pure biodiesel. It was assumed the biodiesel would most likely be pro- duced by a different commercial entity than the petro- diesel refinery and then blended at terminals with petrodiesel. For such third-party blending, a trading standard for the pure biodiesel would be needed.
2. If biodiesel meets its B100 specification, it can be blended with petrodiesel in any percentage. This is simi- lar to status of No. 1 (kerosene type) diesel product being blended into No. 2 grade fuels as long as they meet the respective specifications within ASTM D975.
3. Base the development of the standard for the end prod- uct on performance tests needed for a “fit for purpose fuel” in existing diesel engines, not on the source or processing used to make the biodiesel. This is similar to how the petrodiesel specifications were developed. Use physical and chemical tests as deemed essential in defin- ing the product, or where it makes sense to use such tests in place of a performance test.
Fig. 1—Estimated US biodiesel production by fiscal year (Oct. 1–Sept. 30). (Published with permission from www.biodiesel.org.)
4. Begin with the existing D975 petrodiesel specification as the baseline for a “fit for purpose fuel” for use in con- ventional diesel engines.
5. For the biodiesel blend stock specification, eliminate items not applicable to biodiesel such as the distillation curve, cetane index, and aromatics content.
6. Extend the biodiesel specification to address biodiesel- specific quality properties not in D975 and required for acceptable performance, such as acid value, total and free glycerin, and phosphorous content.
7. Extend the biodiesel specification to new characteristics being considered for D975, and as D975 is updated add characteristics such as lubricity and conductivity.
This philosophy formed the basis used as the biodiesel standards progressed through the ASTM development and balloting process and led to the formal issuance of ASTM D6751, Standard Specification for Biodiesel Fuel Blend Stock (B100) for Middle Distillate Fuels, and incorporation of up to 5 volume percent biodiesel into ASTM D975, Standard Specification for Diesel Fuel Oils, ASTM D396, Standard Specification for Fuel Oils, and ASTM D7467, Standard Specification for Diesel Fuel Oil, Biodiesel Blend (B6 to B20).
Many references to “biofuels” and to “biodiesel” fuels can be found in the technical literature, but the definitions are not always clear. In literature outside ASTM, the term
“biodiesel” has been associated with fuel-like materials such as pure vegetable oils, mixtures of vegetable oils and petro- diesel, partially esterified natural oils, and mixtures of esters with petrodiesel. In the extreme, a case has been made for coal slurry being a “biodiesel” on the grounds that it is derived from long-decayed biomass. There has been significant negative experience with the use of
unprocessed or raw vegetable oils in existing diesel engines in the past [2]. After discussions with the engine and vehi- cle manufacturers regarding their negative experience with a variety of these materials in the past, and the generally positive experience with the methyl esters of vegetable oils in the United States and Europe, it was apparent that once the philosophy for the development of the standard was agreed on, a written description narrowing the scope of what could be called biodiesel was the next essential step.
The ASTM Biodiesel Task Force therefore adopted the following description of biodiesel:
biodiesel, n—fuel comprised of mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats, designated B100.
Discussion-biodiesel, as defined above, is registered with the U.S. Environmental Protection Agency (EPA) as a fuel and a fuel additive under Section 211(b) of the Clean Air Act. There is, however, other usage of the term
“biodiesel” in the marketplace. Due to its EPA registra- tion and the widespread commercial use of the term
“biodiesel” in the U.S. marketplace, the term “biodiesel”
will be maintained for this specification.
Discussion—Biodiesel is typically produced by a reaction of a vegetable oil or animal fat with an alcohol such as methanol or ethanol in the presence of a catalyst to yield mono-alkyl esters and glycerin, which is removed.
The finished biodiesel derives approximately 10 % of its mass from the reacted alcohol. The alcohol used in the reaction may or may not come from renewable resources.
The first key point in this definition is that biodiesel is a mono-alkyl ester. Conventionally, biodiesel is produced through a transesterification reaction of a natural oil triglyceride Fig. 2—Commercial biodiesel production plants in the United States as of September 29, 2008. (Published with permission from www.biodiesel.org.)
(animal fat or vegetable oil) with a short chain alcohol (typi- cally methanol) in the presence of a catalyst (usually sodium or potassium hydroxide). The reaction occurs stepwise, with one fatty acid chain being removed from the glycerin back- bone first (forming one mono-alkyl ester and a diglyceride), the second fatty acid removed next (forming two molecules of mono-alkyl esters and a monoglyceride), and last, reaction of the third fatty acid. The resulting products are three mono- alkyl esters (biodiesel) and glycerin. Glycerin is removed as a co-product and can be upgraded to a valuable pharmaceutical grade. The reaction is depicted in Table 1.
The mono-alkyl ester definition, therefore, eliminates pure vegetable oils as well as monoglycerides and diglycerides from consideration as biodiesel. During the 1970s and 1980s, research was conducted with pure vegetable oils and partially esterified oils in their neat (or pure) form as well as with blends of petrodiesel. The use of these pure or partially esteri- fied oils caused a variety of engine and injector problems and should not be confused with biodiesel meeting today’s ASTM specification for B100 blend stock, ASTM D6751.
The second key point is that biodiesel is produced from a vegetable oil or animal fat. This eliminates some of the confu- sion over other materials referenced as “biodiesel” in the past.
Another key point is biodiesel’s intended use in compression ignition (diesel) engines. Biodiesel is not suitable for use in gas- oline engines—it is strictly intended for use in diesel engines.
The ASTM Biodiesel Task Force determined that the critical items in the determination of biodiesel quality are as follows:
1. Complete reaction to the mono-alkyl esters 2. The removal of free glycerin
3. The removal of residual processing catalyst 4. The removal of reactant alcohol
5. The absence of free fatty acids
The B100 standard was developed to address each of these quality assurance needs.
While the initial proposal for the biodiesel specification at ASTM was focused on B100 as a stand-alone fuel, experi- ence of the fuel in use with blends above B20 was insuffi- cient to provide the technical data needed to secure approval from the ASTM members for B100 as a stand-alone fuel.
Based on this, efforts after 1994 were focused on defining the properties for pure biodiesel needed to provide a “fit for purpose” fuel for use in existing diesel engines at a B20 or lower level blend.
The biodiesel industry was extremely small in the United States during the 1993–1998 period, and efforts focused on securing the technical data on the use of biodiesel, primarily in bus fleets, as well as emissions and health effects informa- tion needed for EPA registration as a legal fuel or fuel addi- tive in the United States. Over $50 million in research and development investments occurred to secure this informa- tion, with the majority of that funding coming from Ameri- can soybean farmers through the soybean check-off program. One-half of 1 % of the purchase price of a bushel
of soybeans is provided by each soybean farmer into the soy- bean check-off fund each year.
Representatives are elected from the farmers inputting into the check-off program, and they invest the funds in research, marketing, new uses, and promotion of soybeans as a means to increase the profitability of soybean farming.
Soybeans are 80 % high protein meal, primarily used as feed for hogs (pigs) and poultry, and 20 % oil. Because the demand for meal was increasing faster than the demand for oil, large excess supplies of soybean oil were a consistent problem for the soybean industry over the years. Farmers viewed this excess supply of oil as an increasing threat to profitability in the future, because demand for meal would likely increase even more as countries like China and India gradually include more meat, especially hogs and poultry, in their diet, which today is mostly grain based.
As interest in cleaner burning fuels increased in the late 1990s, biodiesel volumes began to grow and there was increas- ing interest in finalizing ASTM specifications for biodiesel. A provisional specification, ASTM PS121, for B100 as a blend stock was approved by ASTM in 1999. The primary reason for the provisional specification was to secure a formal ASTM test method for the GC method for measurement of the total and free glycerin—one of the most critical specifications for biodiesel—because it was necessary to include the test method in a mandatory appendix for PS121. After securing an ASTM test method for total and free glycerin, ASTM D6584, the first full specification was developed and approved in 2001 and released for use in 2002 as ASTM D6751, Standard Specification for Bio- diesel Fuel Blend Stock (B100) for Middle Distillate Fuels.
The philosophy used to approve D6751 as a blend stock was the same as that used for the blending of kerosene-type fuel, No. 1 grade, into a No. 2 grade of fuel within the con- ventional specification, ASTM D975. If the parent fuels meet their respective specifications, then the two can be blended in any percentage and used in conventional diesel engines.
These same conditions hold true for biodiesel; if biodiesel meets ASTM D6751 and conventional diesel meets ASTM D975, the two can be blended and used in conventional engines. Users should note there may be OEM warranty and usage recommendations, which usually include an upper limit of biodiesel content in the finished fuel (i.e., B5 or B20) with either no restrictions or some minor service modi- fications such as limits on oil drain intervals.
The most important aspect of successful use of B20 and lower blends over the past 5 years has been to ensure B100 meets D6751 prior to blending. While this philosophy of meeting a base stock specification for blending has served the U.S. market well, there has been substantial effort since 2003 to develop and formally approve specifications for the fin- ished blends of biodiesel and conventional diesel fuel. In addi- tion, several improvements and changes to D6751 were also undertaken, some as a result of changes needed to secure approval of the finished blended biodiesel specifications.
TABLE 1—Typical Biodiesel Reaction
Catalyst
100 pounds þ 10 pounds = 10 pounds þ 100 pounds
Triglyceride Alcohol Glycerin Mono-alkyl esters
(Soybean oil) (Methanol) (Biodiesel)