Currently, biodiesel and ethanol are the two major forms of biofuels being sold and distributed around the world. However, these fuels only represent a fraction of renewable fuels necessary to make an impact on the global energy crisis. Multiple obstacles still need to be overcome in order for these biofuels to become a mainstream energy source.
A major challenge originates from issues dealing with international trade and the transportation of biofuels. These issues range from feedstock costs and availability to fuel quality and the international compatibility of biofuel testing standards. Both biodiesel and ethanol face similar problems, and steps are being taken toward resolving these issues. ASTM International recently published new specifications for a broader range of biodiesel blends. Advancements in other biobased or alternative energy technology have widened the scope of what are seen as feasible solutions to the world's energy problems. These developments and advances are a positive sign for the alternative fuels industry and could result in a more timely solution to this global problem.
Feedstock Challenges
The usability of vegetable oil is of utmost importance. Currently, the cost of the feedstock is high because it can be used for many things besides being an energy source. Its primary use is food for human nutritional needs. Only a fraction of vegetable oil production is available for nonfood use, which creates the dilemma better known as "food versus fuel." To simply grow and produce more vegetable oil and use it for fuel would not work. There is a finite amount of land and other natural limitations that make this notion unfeasible. "New agriculture" such as algae does not compete with food crops for land use. A public policy initiative would act as a catalyst and push the thinking in this direction.
This should be a performance-based policy that pays according to performance, not production. Ultimately, a system of development and sustainability must be in effect for the growth of biodiesel to be successful.
Quality Challenges
Quality control is another challenge facing the biodiesel industry. One major difference that separates biodiesel from petroleum-based diesel is how biodiesel behaves under extreme temperature conditions. Cold-flow properties in the winter and oxidation stability in both summer and winter are major issues in quality control. These properties differ slightly based on the feedstock in which the fuel was produced. For example, biodiesel derived from palm oil, tallow or used cooking oils generally has worse cold-flow properties than biodiesel derived from soybean or canola oil, while the oxidative stability of biodiesel differs greatly from that of petroleum-based diesel. The rate at which this oxidation occurs increases with higher temperatures. Therefore, storage during the summer months will cause biodiesel to deteriorate rapidly. The chemical composition of biodiesel also contributes to its oxidation. Again, the composition depends on the feedstock from which the biodiesel was produced. Biodiesel composed of unsaturated fatty-acid alkyl-ester-like linoleic and linolenic acid esters is more susceptible to oxidation than saturated fatty-acid esters.
The diversity among existing biodiesel testing standards is a result of a number of factors. The first factor is that some existing specifications have been formulated mainly around locally available feedstocks. This feedstock diversity is then translated into significant divergences in the specification properties of the derived fuels. Another factor contributing to the discrepancies in the specification properties is that some specifications, such as those in the U.S. and Brazil, are based on the use of biodiesel as a blend stock or extender for fossil-based diesel fuel. Others, such as the European specification, are based on the use of biodiesel as a 100 percent fuel for engines and as a blending component in hydrocarbon-based fuel. Furthermore, biodiesel standards in Brazil and the U.S. are applicable for both fatty-acid methyl esters (FAME) and fatty acid ethyl esters, whereas the current European biodiesel standard is only applicable for FAME. Another reason for the differences in the biodiesel specifications from region to region is the predominance of the types of diesel engines most common in that region. For example, the most prominent diesel engine in Europe is found in passenger cars. This engine is fairly different than the heavy-duty diesel engines found in the U.S. and Brazil. The different engines amount to differences in the emissions regulations that govern these engines, which then contribute to differences in the diesel specifications in the regions. Because the biodiesel specifications in each country were based upon their corresponding diesel specifications, the regional differences were therefore carried over to the biodiesel specifications.
As previously mentioned, ASTM International recently published new and revised biodiesel standards. Revisions to the diesel fuel oil (D 975) and fuel oil (D 396) specifications now allow for up to 5 percent biodiesel. ASTM D 6751, the specification for biodiesel fuel blend stock (B100) for middle distillate fuels, was also revised to include a requirement that controls minor compounds using a new cold soak filtration test. A new specification for diesel fuel oil and biodiesel blends (B6 to B20) was designated D 7467. This spec covers finished fuel blends for on- and off-road diesel engine use.
Various institutions such as petroleum corporations, biodiesel manufacturers, engine companies, military representatives, government representatives, researchers and academics assisted in the development of these standards. "We have engine interests, petroleum interests, biodiesel interests and third parties," said Steve Howell, chairman of the ASTM Biodiesel Task Force. "It took cooperation, and a lot of data and information sharing, between all those parties to reach consensus on these specifications." The new specs ultimately represent the next step to making biodiesel a mainstream energy source.
Ethanol Challenges
The challenges facing the ethanol industry are similar to those of the biodiesel industry. Ethanol is also subject to the "food-versus-fuel" dilemma and the speculation that it raises food prices. Cellulosic ethanol, a biofuel produced from nonedible parts of plants, could be the solution to this dilemma. The transportation of ethanol yields yet another challenge.
It can't be shipped through existing gasoline pipeline systems because it's easily contaminated by water and may corrode the pipeline. Therefore, it needs to be shipped by truck or rail, both of which are expensive and slower than pipeline transport and, in turn, add to the product's cost. In order for ethanol to become a mainstream energy source, transport vehicles will have to be retrofitted to run on ethanol, or governments will have to build or fund pipelines explicitly for ethanol.
Ethanol specifications are more closely aligned between the U.S., Brazil and Europe than the biodiesel specifications (see Table 1). This is based on a number of factors. Starting at the molecular level, ethanol is a single chemical compound. Conversely, biodiesel is derived from several types of feedstocks, which can translate to variations in the performance characteristics of the finished fuel. Similarities in the three regional ethanol specifications are also largely due to the fact that they all originate from a single (Brazilian) specification. However, differences have arisen due to market developments, climatic conditions in each country and feedstock variances. The ethanol specifications are so similar that the Tripartite Task Force concluded there is no technical specification that constitutes an impediment to trade given the current situation. Water content is a specification that yields a problem, however. The water content level is set at significantly different levels within the three specifications. The European Union specification has the lowest limit, thus requiring additional drying and testing by Brazil and U.S. exporters wishing to supply the EU market.
Recently, the U.S. denatured ethanol standard was converted to an undenatured basis in order to make the U.S. specification more comparable with the Brazil and EU specifications.
The unit of measure in the three specifications has also been converted to a common basis. Some key standards that the task force is considering universalizing are the inorganic chloride content, electrolytic conductivity and water content. Water content is the most difficult parameter to agree upon because it's based on the ethanol content of the gasoline-ethanol blend that the individual countries use, and the amount of ethanol used in gasoline is tied to each country's regulatory framework, making negotiated changes to this parameter difficult. Furthermore, a phosphorous content parameter is only found in the European Union specification. In an attempt to universalize this parameter, the U.S. and Brazil have agreed to collect data in order to determine the phosphorous levels in their products, and from this data determine whether a phosphorous level specification should be adopted. For inorganic chloride content, the U.S. and EU have agreed to review the specification in an attempt to lower the limit, bringing it closer to the Brazil limit. In addition, the U.S. recently updated its specification to include two new ion chromatography test methods that identify inorganic chlorides and sulfates.
Second-Generation Biofuels
Advancement in second-generation biofuel production technology has attracted significant attention. It's becoming more feasible for fuels such as biobutanol, cellulosic ethanol and synthesized higher-chain alcohols to aid in solving the world's energy problems. These technologies are increasingly more efficient, and will ultimately complement or replace ethanol altogether. The technology for cellulosic ethanol is getting closer to commercialization and seems to be a direct replacement for corn-based ethanol. Cellulosic ethanol does not compete much with food production, and it has a better carbon emissions profile.
Biobutanol also has great potential to replace ethanol. Butanol's properties make it a much more attractive biofuel than ethanol with respect to gasoline blending, distribution and refueling, and use in existing vehicles (see Table 2). Biobutanol can also be produced commercially today unlike other advanced biofuels such as cellulosic ethanol, fermentation hydrocarbons and algae-based biodiesel. The challenge is to improve the commercial process enough to produce large volumes while remaining economically competitive.
Biobutanol has also been found to be more toxic to humans and animals in the short term than ethanol or gasoline, and it is not clear whether butanol will degrade the materials commonly used in automobiles that come into contact with motor fuels.
Higher-chain alcohols may also replace ethanol, due to recent advances in metabolic engineering techniques. Metabolic engineering is a field that merges genetic engineering, physiology and systems engineering. Metabolic engineers have made significant progress in the production of fuel-grade compounds due to rapidly expanding genomic information, molecular biology techniques and high-throughput tools. These compounds have higher energy densities, lower vapor pressures and are not corrosive, resulting in a fuel that can circumvent or alleviate many problems associated with ethanol.
To cover all the areas discussed, a variety of agencies must be involved, making a universal solution to biofuels as a mainstream energy source more complicated. The food-versus-fuel dilemma involves organizations such as the USDA and U.S. DOE in the United States alone. Alignment of the international biofuels standards will require a large investment of time and effort in testing and research by specialists in laboratories, test facilities and private companies around the world. However, emerging new technologies, the refining of existing techniques, and ongoing development and alignment of testing standards will make for a quick and balanced solution to the global energy crisis.
Raj Shah is a director with Koehler Instrument Co. Inc. Reach him at rshah@koehlerinstrument.com. Vincent Colantuoni is a sales application engineer with Koehler Instrument Co. Inc. Reach him at vcolantuoni@koehlerinstrument.com or (631) 589-3800.