By Justin Smith
2/2/2009
source: http://www.energycurrent.com/index.php?id=3&storyid=15704
The world of biofuels is as diverse as it is controversial. From being hailed as a great savior from the perils of using fossil fuels, to being a pariah that is leading to less food to go around, biofuels have, at best, a mixed reputation.
That said, not all biofuels are created equally and many different types exist, each with their own sets of pros and cons. As such, many of the negative stereotypes should not be applied to all types of biofuels.
A long history
A biofuel is defined as any fuel that is derived from raw or recently living biological material, as compared to fossil fuels, which also come from biological material, but from organisms that have been dead for a very long time. Technically biofuels have been used for millennia in the form of wood fueled fires, and in terms of liquid biofuels for transportation, those have actually been around since the inception of the automobile.
According to biofuels information Web site Biofuel.org.uk, Rudolf Diesel, the German inventor of the diesel engine, designed his engine to run on peanut oil. "Later Henry Ford designed the Model T car, which was produced from 1903 to 1926. This car was completely designed to use hemp derived biofuel as fuel," the Web site says. However, when large supplies of crude oil were discovered in Texas and Pennsylvania, the more efficient and plentiful petroleum became the cheaper fuel of choice for auto makers.
Fuel shortages in World War II led both German and British scientists to develop biofuel/gasoline blends. Biofuel.org.uk explains, "In this period, Germany was one of the countries that underwent a serious shortage of fuel. It was during this period that various other inventions took place like the use of gasoline along with alcohol that was derived from potatoes. Britain was the second country [that] came up with the concept of grain alcohol mixed with petrol."
The United States' Environmental Protection Agency (EPA) created the Energy Policy Act (EPAct) in 1992 and revised it in 2005. The U.S. Department of Energy (DOE) says the act was "passed to reduce our nation's reliance on foreign petroleum, and improve air quality."
The DOE states, "Several parts of [the] EPAct were designed to encourage [the] use of alternative fuels, which are not derived from petroleum, that could help reduce dependence on imported oil in transportation. Titles III and V employ regulatory approaches for encouraging the fundamental changes necessary to building a self-sustaining alternative fuel market."
The EPAct gave biofuels a greater platform on which to build demand. That fact, coupled with the sky-high oil prices last summer, has led to increased interest in biofuels as both a cleaner and potentially cheaper and safer supply of energy. However, the cleanliness and price of biofuels varies by what type of plant is being cultivated and converted to fuel.
Ethanol and biodiesel
The first generation of biofuels is, by far, the most common type, and they are also what incite the most passionate debates on the subject. That said, they are, in all likelihood, not the future of the biofuel industry. Ethanol and biodiesel are the most popular of this type of biofuels.
First generation biofuels are primarily derived from two types of sources: crops that have a high sugar or starch content, or using the oils of various plants. Energy giant Shell, which has a division dedicated to finding viable fuel source, states, "When choosing raw material for biofuels, people have looked first to plants that can be grown regularly in large quantities.
"Today's most widespread biofuel, ethanol, is commonly made from crops of sugar cane, corn or wheat. The second most widespread type of biofuel is often made from rapeseed, palm oil or soy beans and is known as FAME (fatty acid methyl esters)."
One downside to such fuels is that they do not provide as much power as gasoline, so more must be used to generate an equivalent amount of power. For this reason, Shell says, "today's standard vehicle engines can only use fuel with small amounts of ethanol or FAME blended in (5-10 percent)."
Engines do exist that can use much higher concentrations of ethanol. Known as flex-fuel engines, vehicles with this type of power plant can use up to 100 percent ethanol, although in the United States automobiles are currently only allowed to use up to 85 percent blends. However, some countries, such as Brazil, permit people to run vehicles on pure ethanol.
Another type of first generation biofuel, biodiesel, is quite different from ethanol. Biodiesel, as described by the National Biodiesel Board, is "made through a chemical process called transesterification whereby the glycerin is separated from the fat or vegetable oil. The process leaves behind two products -- methyl esters (the chemical name for biodiesel) and glycerin (a valuable byproduct usually sold to be used in soaps and other products)."
Biodiesel can be blended with petroleum, but diesel-powered vehicles can also run on 100 percent biodiesel, often with no modifications to their engines, especially newer versions. It is possible to use straight vegetable oil in an engine, but as it is so viscous, it must be thinned by heat so it can be atomized by the fuel injectors, according to Ghent Bio-Energy Valley, a Ghent, Belgium-based partnership focused on developing sustainable bio-energy.
The other first generation biofuels
While biodiesel may be the most common form of biofuel, there are less familiar varieties that still play a role in the industry. Biogas, syngas and solid biofuels are each other types of first generation biofuels. One upside to these fuels is that they do not always require food crops to be made.
Biogas is produced through the process anaerobic digestion, which is the break down of organic materials, including waste, by microorganisms in the absence of oxygen. According to Biofuel.org.uk, "The biogas produced is very rich in methane, which can be easily recovered through the use of mechanical biological treatment systems."
Biogas is often naturally produced in landfills and can be captured, but this method has the potential do harm as it is a greenhouse gas. "A less clean form of biogas is the landfill gas which is produced by the use of naturally occurring anaerobic digesters, but the main threat is that these gases can be a severe threat if escapes into the atmosphere," Biofuel.org.uk explains.
Syngas, which is short for synthesis gas, has a mixture of carbon monoxide and hydrogen in varying amounts. The gas is created through a combination of gasification, combustion and pyrolysis, which is a way to decompose something through the application of heat, of organic material. Having about half the energy of natural gas, syngas is useful when split into its constituent parts to perform a range of tasks, from being a fertilizer to powering up a fuel cell.
Finally, since the category includes fuels like firewood, solid biofuels are the oldest form of biofuels. A wide variety of biomass types are useful as a solid biofuel, including sawdust, dried waste and grass. To improve efficiency, solid fuel is formed into pellets and burned, however burning raw biomass releases a number of unhealthy pollutants, and it still is not very efficient. Ghent Bio-Energy Valley says, "This is not a very efficient way of using biomass and what is more it has a number of documented ill effects for the health of the people using it, such as respiratory diseases because of soot emission and negative effects of CO-emission for pregnant women."
Cellulosic ethanol, the second generation biofuel
The second generation of biofuels comes in the form of cellulosic ethanol. This form of fuel is derived from a substance called lignocellulose, which makes up the bulk of the material in plants. As such, the vast majority of plants on Earth are capable of being a source for cellulosic ethanol.
Solid biofuels and cellulosic ethanol both have similarly huge ranges of sources, but while solid biofuels are basically just burned in a raw or near-raw state, plants are refined considerably to make cellulosic ethanol. Also, first generation ethanol is produced from the parts of plants like wheat, sugar cane and corn that people use for food; however, cellulosic ethanol is made from the remaining, more fibrous plant parts that have no value as food, such as stems, leaves and wood.
It requires a lot of work to remove the sugars from lignocellulose to make cellulosic ethanol, but the resulting fuel still has more energy than is required to make it. Currently two methods are used to make the fuel, one of which strives to separate the sugars, which are then fermented into alcohol, while the other method uses heat to break down plants then uses a different fermentation process to create the fuel.
The first method, known as cellulolysis, involves pretreating the plant material with chemicals or enzymes that begin to break down the plant through hydrolysis. Once the sugars are removed, they are fermented to create alcohol using varieties of yeast, but due to the complexity of the sugars, it can take a lot of yeast to get the job done. However, new yeasts are being created that more efficiently ferment the sugars, even ones that can perform hydrolysis and fermentation at the same time.
The other method to create cellulosic ethanol is called gasification. Instead of using a pretreatment to cause hydrolysis to separate the sugars that are then fermented, gasification uses heat to break down the plant into hydrogen, carbon monoxide and carbon dioxide. After, the gas is fermented using microbes that convert it to ethanol and water. Finally, the water is removed using distillation, leaving the ethanol.
While corn and wheat and other food crops can be used to create cellulosic ethanol, just about any other non-food plant can be used. Even though the use of non-food plants does not directly take food off people's plates, it does have to contend with food crops for arable land. One possible way to help solve this problem is using hardier plants that can grow in areas where food crops cannot, thus not competing with them. One such plant that is gaining in popularity is switchgrass, but to be truly useful as a fuel, a lot of it must be grown, which still requires a lot of land.
Competing with food crops for land is arguably cellulosic ethanol's biggest challenge, but not the only one. It also is still very expensive to process the plants. The microbes and enzymes it takes to break down the plants are not yet cheap to produce, and it takes a fair number of them to get the job done.
The DOE says, "To bring down costs, continued progress is needed in the development of energy crops dedicated to biofuel production, biomass-collection technologies, pretreatment methods that minimize the release of inhibitory by-products, and more efficient enzymes and microbes robust enough to withstand the stresses of industrial processing."
Also, the process of making the biofuel can have a negative impact on the environment. The chemicals that are used to pretreat plants can be harmful, and the heat used to break down plants through gasification is often generated through the use of hydrocarbons, primarily natural gas.
Biofuels: The Next Generation - Algae
The third generation of biofuels comes in the form of the water-based plants known as algae. The ability to transform algae into a biofuel is a burgeoning science, and could hold the future of the biofuel industry, although not without some hurdles to leap over first.
The DOE division of Energy Efficiency and Renewable Energy (EERE) explains, "Microalgae are single-cell, photosynthetic organisms known for their rapid growth and high energy content. Some algal strains are capable of doubling their mass several times per day. In some cases, more than half of that mass consists of lipids or triacylglycerides--the same material found in vegetable oils. These bio-oils can be used to produce such advanced biofuels as biodiesel, green diesel, green gasoline and green jet fuel."
Once algae are grown and cultivated, there are three primary methods of extracting their oil. The first and simplest method is in the form of the oil press or expeller. Algae biofuel experts at Oilgae explain, "When algae is dried it retains its oil content, which then can be 'pressed' out with an oil press. (…) While more efficient processes are emerging, a simple process is to use a press to extract a large percentage (70-75 percent) of the oils out of algae."
The second extraction technique is the hexane solvent method, which can produce up to 95 percent of the oil in algae. Oilge says, "After the oil has been extracted using an expeller, the remaining pulp can be mixed with cyclohexane to extract the remaining oil content. The oil dissolves in the cyclohexane, and the pulp is filtered out from the solution. The oil and cyclohexane are separated by means of distillation."
The algae oil specialists say that the hexane solvent method requires the use of chemicals, such as hexane, benzene and ether. The downsides to using these solvents include the hazard of an explosion, as well as the risk that benzene is classified as a carcinogen.
Finally, the supercritical fluid extraction method can draw out up to nearly 100 percent of the oils. In this process, CO2 is pressurized and heated until it is both a gas and a liquid, at which point it is mixed with algae, removing the oil. The fact that this method requires additional complex machinery to create the pressure has detracted from its popularity.
Algae have a number of upsides over other biofuels. According to EERE, microalgae can potentially produce 100 times more oil per acre of land than soybeans or any other oil-producing crop. In addition, algae do not have to compete for land with food crops as it can be cultivated in large open ponds or closed photobioreactors, which can be sited in deserts and other non-arable areas.
Another plus is that algae are not picky and EERE says, "Many species of algae thrive in seawater, water from saline aquifers, or even wastewater from treatment plants." Also, the production of algae can actually mitigate carbon dioxide. EERE clarifies, "During photosynthesis, algae use solar energy to fix carbon dioxide (CO2) into biomass, so the water used to cultivate algae must be enriched with CO2. This requirement offers an opportunity to make productive use of the CO2 from power plants, biofuel facilities, and other sources."
The primary downside to using algal biofuels is that they are not economical to produce, at least not with current technology. EERE says, "Based on conservative estimates, algal biofuels produced in large volumes with current technology would cost more than US$8 per gallon (in contrast to US$4 per gallon for soybean oil today)."
According to EERE, to lower the cost of production, research must focus on a number of sectors, including controlled mass cultivation, algae for wastewater treatment, and harvesting and oil extraction technologies. The group says, "Particular attention must be paid to the engineering of sustainable microalgal systems and to the regulatory and environmental landscape."
No comments:
Post a Comment