Of Sunlight and Science

Soybean, rapeseed and recycled vegetable oils have taken global biodiesel production to its current height. Now, research suggests that less common plant feedstocks-crop residue, algae and mustard hybrids-might hold unparalleled potential.
By Michael Briggs | July 01, 2004
Over the past few years, the biodiesel industry has grown dramatically in the United States, with production increasing from about 500,000 gallons in 1999, to over 30 million gallons in 2003. The growth of the industry has been spurred largely by the encouragement and dedication of the soybean industry, but as the industry grows, it needs to continue looking at additional feedstocks for further expansion. Unfortunately, the oil yield per acre from soybeans is not sufficient to support unfettered expansion of biodiesel production capacity.

Additionally, the volatility of soybean oil prices creates a challenge for the biodiesel sector. The total amount of soybean oil presently produced in the United States is slightly over 2 billion gallons per year, with most of that used in the food industry. The current diesel fuel market (including off-road, on-road and heating oil) is roughly 60 billion gallons per year, with potential for considerable expansion into the light-duty vehicle market after the ultra-low sulfur diesel mandate goes into effect in 2006, permitting the use of better emissions equipment that will allow passenger cars to meet the more stringent emissions standards.

Solar energy into liquid fuels
It is becoming increasingly obvious that the world is in fact nearing peak oil production, and sooner or later, worldwide demand for petroleum will surpass worldwide oil production capability. If that happens, bidding wars for the available petroleum would be the least disastrous scenario. The only thing that can prevent that from happening will be the development of transportation fuels capable of replacing a significant percentage of petroleum fuels, if not all of it.

Is it possible for biodiesel to provide a significant chunk of this market? Consider that biodiesel, like any biofuel, is essentially chemical energy made from water, atmospheric carbon dioxide, and solar energy through the process of photosynthesis. Plants use sunlight to combine water and carbon dioxide together to make carbohydrates, oils and other molecules, some of which can be readily converted into a transportation fuel. As a result, our potential to produce biofuels depends on the energy reaching the earth from the sun, and how efficiently it is converted to fuels by plants and our processing of those plants. Average photosynthetically active solar energy hitting the landmass on earth is over 25,000 terawatts, about 2,250 times current global energy consumption. So, with a fairly efficient crop for converting this solar energy into liquid fuels, it should be possible to meet our entire energy needs with biofuels-not just for the United States but the entire planet. It's just a matter of finding the most efficient (in terms of land and energy efficiency) and economical crops, and processes for doing it.

Since even the current diesel market is roughly 2,000 times greater than current biodiesel production, the potential for expansion of the biodiesel industry is enormous-far surpassing what could be supported by soybeans alone. The greatest potential for expansion of this industry will have to rely on alternative feedstocks with high yields and stable prices. For many years, researchers at several universities, a few government agencies (primarily the DOE and USDA), and a handful of small companies have been focusing on developing alternative feedstocks and alternative processes for using otherwise undesirable feedstocks. Unfortunately, this research hasn't really been put to good use yet by the industry.

While the biodiesel market is progressing nicely with the focus remaining on soybean oil and traditional transesterification, this growth rate pales in comparison to what could be achieved if the industry, farmers and researchers all worked together, bringing the research out of the lab and into the marketplace.

An issue of critical importance for new biofuels technologies and feedstocks is that they should be capable of producing significantly large quantities of fuel, or yielding high- value coproducts to lower the cost of the biofuel. Since the cost of the oil feedstock currently makes up generally 80 percent to 90 percent of the cost to make biodiesel, reducing feedstock cost can have tremendous benefits. Described below are three advancements that could make a significant impact on the biodiesel industry. The potential of each will only be realized with the involvement of the industry as a whole-farmers, producers and distributors working with researchers and bringing advancements from the lab to the market. In addition to these advancements, there are many other processes and feedstocks being investigated which could also have a very big impact. The notion of hydrogen-fueled vehicles receives considerable attention by the media, but from a scientific and engineering standpoint, it is far less feasible than these biodiesel options.

High glucosinolate mustard hybrids
Jack Brown, a plant breeder/geneticist at the University of Idaho, leads a team of researchers developing varieties of mustards (in the Brassicaceae family, like rapeseed and canola) with higher than normal levels of glucosinolates-the chemicals that give mustard its spicy flavor. These glucosinolates degrade in the presence of water and the enzyme myrosinase to form compounds such as isothiocyanates and ionic thiocyanates, which have shown pesticidal properties.

Different glucosinolate byproducts produce different effects (some make better herbicides, insecticides, etc.). When mustard seeds are crushed for oil separation, the glucosinolates remain in the seed meal, which has potential for use as a biopesticide. Planned worldwide bans on highly toxic synthetic pesticides such as methyl bromide (which depletes the ozone layer), could create an enormous market for safer biopesticide alternatives. To the biodiesel industry, the advantage is that the mustard seed meal would be far more valuable as a biopesticide than the meal from other oil bearing crops, which is used mainly as animal feed. The overall result is that mustard oil could be available in relatively large quantities at lower cost-potentially 10 cents per pound or less, resulting in biodiesel production costs around $1.10 per gallon.

Additionally, these mustards require lower energy and water inputs than many alternative crops and have excellent rotational benefits on subsequent crops. In addition, mustard biodiesel has excellent cold weather characteristics and low NOx emissions.

While two varieties of high glucosinolate mustards are already commercially available ("Ida Gold," whose meal has shown herbicidal potential, and "Pacific Gold," whose meal is more effective against insect pests), Brown and his colleagues are hoping to develop a range of "designer biofumigant" mustards whose seed meal will target specific pests. These mustards present an opportunity for farmers and the industry to work together in producing both lower cost biodiesel as well as bio-pesticides for use in intensive agricultural and horticultural situations. Approval of mustard biopesticides is currently being investigated by the EPA. If approval is granted, there could be an opportunity for farmers to grow these high glucosinolate mustard cultivars to sell to crushing plants for separation into a lower cost oil for biodiesel production and high value seed meal for sale as biopesticide.

High oil micro-algaes
The "Aquatic Species Program" (ASP) at the U.S. DOE was the first major program to investigate the growth of high-oil micro-algaes for biodiesel production. Its research began as a means of using fast-growing algaes to sequester carbon dioxide emissions from coal plants, but a shift to using high-oil algaes sparked interest in growing algae for biodiesel production. With the demise of the ASP program in the late 1990s, there were considerable technological challenges remaining, but the program had already demonstrated the potential high-oil algaes have to offer. Since then, a few other research institutions and small private companies have picked up where the DOE left off, including the biodiesel research group at the University of New Hampshire. Since micro-algaes can grow considerably more quickly than conventional crops, and some can have very high oil content, algae has the potential to yield far more oil per acre than conventional crops.

The energy efficiency for this approach can be quite high, with the cost being the main challenge to date. The group, like some of the others working in this field, have filed a provisional patent application on its approach for reducing the costs, and increasing the energy efficiency and yield, hoping to make algal biodiesel a commercially viable option in the near future. Growing algaes on waste streams presents an exciting option for more localized production of biodiesel, as well as significantly reducing cost. Growing high-oil algaes from farm animal waste can also provide a profitable means for treating the significant environmental problems posed by waste lagoons.

Micro-algaes present a more efficient option for converting solar energy into chemical energy for fuel, because of their simple cell structure and high photosynthetic efficiency compared to most other plants. They grow immersed in water, making the supply of hydrogen plentiful.

Continuing research can also yield significant improvements over the algal oil yields seen in previous studies through such methods as decreasing the number or size of chlorophyll antenna on algae via traditional breeding or genetic manipulation, in order to reduce the light saturation issue that limits growth somewhat.

The DOE's ASP program estimated that with further technological advancements, the potential yield of fuel from high oil algaes could reach one quadrillion Btu per 200,000 hectares (494,200 acres) each year, the equivalent of over 15,000 gallons of fuel per acre per year-far higher than is achievable with traditional farm crops. The challenge to the research groups that have picked up where ASP left off is to try to achieve that potential yield-or even surpass it-and do so economically. This technology is not as ready for market as some other options, such as the high glucosinolate mustards, but its potential for extremely high oil yields is promising as a means of not merely producing a boutique fuel for a small market, but potentially weaning the nation-and the world-off of dwindling supplies of petroleum.

Thermochemical processes
While transesterification is a very efficient process for making biodiesel from oils, with most crops there remains a significant amount of agricultural waste-essentially unused parts of the plants. Some of this is harvested, and some is left as crop residue on the land. Each year in the United States a few billion tons of agricultural waste is produced. It is desirable to leave a certain amount of this unharvested plant material on the farmland to prevent soil erosion or crusting, and to provide additional nutrients to the soil. However, there is still a significant amount that could be used for other purposes. This presents the potential for turning these otherwise low-value agricultural wastes into additional fuel through a few possible thermochemical conversion processes. These are less energy efficient than straight transesterification and generally more costly for the process itself, but the "feedstock" can be considerably lower in value.

Two thermochemical processes that could be used for this are thermal depolymerization or gasification followed by Fischer Tropsch (FT) synthesis. The former approach is being developed by Changing World Technologies in conjunction with ConAgra, initially focusing on using wastes from the meat processing industry as the cheap feedstock. FT synthesis is the same process Shell uses for making synthetic diesel from natural gas. The combination of gasification of biomass and FT synthesis to make a biodiesel fuel is being investigated by several companies and research groups, including a partnership between Shell and Volkswagen. The fuels produced in these processes are chemically different from the biodiesel we are most familiar with, but since they are also diesel fuels produced from biomass, it seems appropriate to refer to them as types of bio-derived diesels, perhaps as biodiesel.

Since these processes can use otherwise very low value waste biomass, they can essentially result in additional biodiesel production without additional acreage of dedicated crops. One particularly appealing characteristic of these types of biodiesel is that the resulting fuels have much better cold weather properties than biodiesel made through transesterification of oils. As a result, these biodiesels from thermochemical conversions of waste biomass could be used as a blendstock with more common biodiesel for cold weather use, eliminating the need for blending with petroleum fuels.

As these technologies continue to improve, it is worthwhile for farmers and those in the biofuels industries to keep an eye on them to see how they can be incorporated into the current state of the industry.
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