Biomass and Green Energy

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The question as to what constitutes biomass has at least two responses; the short answer is, all living things are biomass. All animals, plants, and we humans are the organic matter that characterizes biomass. The more specific, industrial response defines biomass as the organic matter produced by crops, roots, stems, seeds, and stalks, along with animal metabolic wastes, and refers to materials that do not go into food products, but do have alternative commercial uses. Again, the concern is for energy, bioenergy, the energy inherent in the carbohydrates, fats, and proteins that constitute all organic matter.

Biomass has been used for energy since fire was discovered and people used wood to cook food and keep warm. Although wood remains the largest biomass energy source today, other sources include food crops; grassy and woody plants; residues from agriculture such as cornstalks, straw, sugarcane, bagasse, nutshells, and dung (manure from cattle, poultry, and hogs); yard clippings; and the organic components of municipal and industrial wastes. Even the methane emanating from landfills can be used as a bioenergy source. The fact is, the entire surface of the earth is covered with biomass—and because it is renewable, its potential for energy is nothing less than tremendous—at least 10 times the total amount of energy consumed worldwide annually from all sources. Think about that!

Biomass can be used for fuel, power production, and commercial and consumer products that would otherwise be made from fossil fuels, providing an array of benefits. For example, bioenergy has the real potential to reduce greenhouse gas emissions. Burning biomass releases about the same amount of carbon dioxide as burning coal or oil. But—and this cannot be taken lightly—fossil fuels released CO2 captured by photosynthesis millions of years ago—an essentially "new" greenhouse gas. Burning biomass, on the other hand, releases the CO2 balanced by the CO2 used in the photosynthetic process that more recently created it. Furthermore, use of biofuels, as we shall see, can reduce our dependence on imported oil. Since the US economy is so closely linked with petroleum (importing over 60% of its oil), small fluctuations in oil prices or disruptions in supplies can have an enormous impact on our economy. Consequently biomass offers an alternative to foreign oil, providing national energy security, economic growth, and environmental benefits. Yet another benefit is its renewability. Utilizing sunlight energy in photosynthesis, plants metabolize atmospheric CO2 to create new biomass, producing an estimated 140 billion metric tons annually. Combustion of biomass forms CO., which plants use to form more biomass. The overall process is referred to as the carbon cycle. From an energy viewpoint the net effect of the carbon cycle is to convert solar energy into thermal energy that can be converted to more useful forms such as electricity and fuels. Recall, too, that coal and oil were originally created from biomass deep in the earth over millions of years ago, and, because of the long periods needed for their formation, they are not considered renewable. Even though coal and oil replaced biomass fuels because of their higher energy content and ease of handling, with oil production peaking and for the reasons noted above, biomass is once again in ascendance.

Biomass is a complex mixture of carbohydrates, fats, and proteins, along with small amounts of sodium, iron, calcium, and phosphorus. However, the main components of biomass are the carbohydrates—some 75% dry weight, and lignin, the remaining 25%, but these do vary by plant type. The carbohydrates are primarily the long- chain cellulose and hemicellulose fibers that impart structural strength, and lignin, which holds the fibers together. Plants also store starch, another long-chain polymer, and fats as sources of energy. Starch and cellulose are polysaccharides, long, repeating chains of a single sugar, glucose, used by living systems as their source of biochemical energy. Hemicellulose, in the cell walls of plant tissue, is composed of the sugars, xylose, arabinose, mannose, and glucose. Lignan, another cell-wall polymer, combines with hemicellulose to bind cells together and direct water flow [24]. Fats are triglycerides, three long-chain fatty acids attached to a molecule of glycerol. The major part of the fat molecule are the fatty acids which have a chemical structure similar to that of hydrocarbons—petroleum. Hydrocarbons, composed solely of carbon and hydrogen, release water, CO2, and heat when burned in air. The more oxygen involved, the more energy released.

The composition of biomass leads directly to its use as a biofuel, but given the renewability of biomass, a brief diversion is in order to reacquaint ourselves with photosynthesis. In a word, photosynthesis is the biological conversion of light energy into chemical energy. Sunlight is absorbed by chlorophyll in the chloroplasts of green plant cells, which produce carbohydrates from water and CO2 taken from the atmosphere. In its most simplified form, the process can be represented by the formula

6CO2 + 6H2O chlorophyll ^ CeH^Oe + 6O2 sunlight in which six molecules of carbon dioxide and six of water combine to produce one molecule of glucose and six molecules of oxygen. Globally, this process produces about 220 billion dry tons of biomass annually. Of course, it is the photosynthetic process that provides the oxygen that allows all living things, including us humans, to breathe.

Curiously enough, how plants obtain the nutrients needed for growth is as much a mystery today—for too many people—as it was before Johannes

Baptiste Van Helmont (1579-1644), a Dutch alchemist performed his enlightening experiment. Van Helmont placed a willow tree weighing 5 pounds (lb) in a clay pot in which he also placed 200 lb of soil. Five years later, after watering the willow as needed, it weighed about 169 lb, even though the soil in the pot lost only 2 ounces (oz). Clearly, the tree had gained weight from the water, not the soil—although the role of sunlight and carbon dioxide were not yet known [25].

In the photosynthetic process, sunlight stimulates the pigment chlorophyll found in the chloroplsasts, where sunlight also reacts with the CO2 the plant breathes in via the stomata—microscopic holes in the leaves—and with water the plant absorbs from its roots. During a series of light and dark reactions the water molecules are split into hydrogen and oxygen; the hydrogen combines with carbon dioxide to produce glucose, which will become the building blocks for starch and other long- chain, complex carbohydrates. The excess oxygen is released to the atmosphere during the process of respiration.

It is the carbohydrates that are of interest today, as they can be used directly as fuel, burning wood, or converted into liquids and gases—ethanol and/or methane.

Two types of alcohol can be produced from biomass: (1) ethanol, C2H5OH, grain alcohol, which can be made by the microbial fermentation of sugarcane, sweet sorghum, cassava, sweet potatoes; and, of course, (2) maize or corn, which provide the hexose sugars that are metabolized by yeast cells to alcohol. Methanol, methylalcohol, CH3OH, wood alcohol, originally made by the distillation of wood chips, is now made from natural gas. Most current interest however is in fuel ethanol production involving the use of cornstarch—in the United States (and sugarcane in Brazil, where, as we shall see, straight gasoline is no longer used to power motor vehicles), which is a two-step process in which starch is converted to glucose and the glucose is then microbioally metabolized to alcohol. In 2003, corn-produced ethanol reached 2.81 billion gallons—not all that much given our enormous usage.

In addition to ethanol, biodiesel fuel is a domestically produced, renewable fuel for diesel engines derived from soybean oils. The typical soybean oil methylester contains a number of fatty acids as shown in Table 7.3, and contains no petroleum.

TABLE 7.3.

Typical Soybean Oil Methylester Profile



Fatty Acid























CH3 (CH2CH=CH)3 (CH2)7CO2CH3

Biodiesel is made by the process of transesterification, in which glycerine is separated from the fat or vegetable oil. The process byproducts are methylesters, the chemical designation of biodiesel. (Esters, by the way, are a class of organic compounds formed by the reaction of organic acids and alcohols.) It is worth recalling that when, the German engineer Rudolph Diesel unveiled his prototype engine that bears his name, he fueled his engine with peanut oil, an idea that never took off because gasoline became so plentiful and so cheap. The smell of biodiesel fuel is another selling point, smelling as it does like a kitchen, not a garage.

As for the kitchen, northern Biodiesel, in Ontario, NY, is opening a plant to turn cooking oils and agricultural waste into biodiesel fuel. Brent Baker's 1989 International Blue Bird School Bus smells like a barbecue now that he uses only leftover cooking grease from french fries, fried chicken, and fish. Baker has logged thousands of miles driving his highly visible bus around the country, highlighting the relative ease of shifting away from gasoline. The ride is smooth and quiet, and when the gas gauge so indicates, he simply pulls into a roadside diner and empties out the grease in their dumpsters—with permission, of course. Baker is not alone in believing that vegetable oil could be a valuable source of fuel. Cars and trucks of more than 40 federal and state agencies across the country, including the U.S. Postal Service and the EPA, run on a blend of vegetable oil and diesel fuel [26].

More importantly, perhaps, Willie Nelson, my rock idol, drives a Mercedes, but the exhaust of his diesel-powered vehicle smells like french fries or peanuts, depending on the alternative fuel that happens to be in his tank—no longer a "gas" tank, just a tank; a fuel tank, filled with "biowillie," which, as Nelson sees it, is a domestic product that can profit farmers and help the environment. Biodiesel is picking up around the country: Cincinnati began using B30, 70% conventional diesel and 30% vegetable oil. The state of Minnesota now requires all diesel fuel sold in the state to be 2% biodiesel. In the Seattle area, B20, 20% vegetable and 80% diesel, is being used. Willie Nelson's company, Willie Nelson Biodiesel-B20-at Carl's Corner, Hillsboro, Texas, is aimed at truckers. His biodiesel is currently being sold in four states, and is fueling buses and trucks for his tours. Willie doesn't expect to get rich on his biodiesel as there just isn't enough used grease or vegetable oil to go around [27].

Since fatty acids from plant fats and petroleum hydrocarbons have similar chemical structures, plant-based fats can be coverted into a liquid fuel similar to diesel fuel. Fatty acids obtained from soybeans or other oil-rich vegetation are reacted with methanol to form fatty methylesters, or monoalkylesters of long-chain fatty acids. As these methylesters have nearly equivalent energy content and chemical structures similar to those of petrochemical diesel fuels, they have been dubbed "biodiesel fuels." They not only work well in diesel engines but also have lower particulate emissions than does gasoline.

Ethanol and biodiesel can be blended with or directly substituted for gasoline or diesel fuel. Use of these biofuels reduces toxic air emissions, greenhouse gas buildup, and dependence on imported oil, while supporting agriculture and rural economies. Unlike gasoline and diesel, biofuels contain oxygen—ergo, adding biofuels to petroleum products allows the fuel to combust more completely, reducing air pollution.

Because the vast bulk of biomass consists of cellulose, hemicellulose, and lignin, compared to starch and sugar, the U.S. Department of Energy (DOE) is spear-heading a national effort to develop methods to break down cellulose and hemicellulose into their component sugars. Doing so will allow biorefiner-ies to biologically process the monosaccharide sugars to ethanol. The ability to use cellulosic materials in addition to sugar will open the way for far greater production of ethanol. Lack of available agricultural acreage to grown corn is a current bottleneck for expanded use of ethanol. So, in October 2005, the DOE awarded $92 million for six genomic projects that seek solutions to more efficient microbial metabolism of the long-chain polysaccharides that currently resist breakdown. To develop solutions, it is essential to know the details of microbial biochemical pathways under normal and environmentally modified conditions. It is anticipated, and rightly so, that these newly funded projects will develop this much needed information [28].

In his State of the Union address to the nation in February 2006, President Bush touted switchgrass, Panicum virgatum, a cereal grain and member of the millet family, currently used as fodder for cattle, horses, sheep, and goats, as another crop useful for ethanol production. This perennial grows in great abundance on the prairies of the Great Plains. Considering that there is so much of it, and that it is easy to grow, it can be a valuable addition to corn.

The substitution of ethanol for gasoline in passenger cars and light vehicles is only in its infancy in the Unite States. South of the border, ethanol is well into its adulthood. In Brazil, the world's largest commercial biomass-to-energy program is in full bloom. Would anyone have imagined that engines that run only on gasoline would be banned in Brazil, or anywhere else, for that matter? Brazil has decreed that automobiles and light trucks must use either all ethanol, or gasohol, a blend of 78% gasoline and 22% ethanol. Although ethanol from sugarcane has been used as engine fuel in Brazil since 1903, it was the institution of the "Pro-alcool" program in 1973, that Brazil's addiction to imported oil was abruptly halted. For years the government feared disruption of supplies from foreign countries. When the world oil crisis struck in 1987, Brazil was financially wrecked, as they had been importing 80% of their oil. Faced with an economic crisis, not unlike what is happening in the United States today, the decision was taken to substitute alcohol for oil. The "Pro-alcool" program went into effect and the outcome was a new sugarcane—alcohol industry. Over the ensuing decades, the "Pro-alcool" initiative has served as a model for other countries; led to the creation of high quality jobs, cleared the air, became an effective tool for managed energy costs, and the country learned to integrate new fuels into existing commercial end-use systems [29] . The United States has much to learn from Brazil. We need only shore up our political will. Of course, the oil companies are not going to be happy, but the United States does not exist to please oil companies. Certainly not now with oil prices bouncing between $60 and $70 per barrel. In fact, governments and sugar producers around the world have beaten a path to Brazil looking for help in developing their own ethanol industries. India, the world's number 2 sugar producer after Brazil, is rushing to spread the use of ethanol as it also seeks to reduce dependence on imported oil, as automobile ownership rises sharply.

E85 is the new kid on the fuel "block" in the United States. As extensive as our communication system is, most people are unaware that over four million american cars are in fact flex-fuel cars, designed to run on E85, a blend of 85% corn-based ethanol and 15% gasoline. The next time you fill up with gas, take a hard look at the gas flap; there may just be a sticker the size of a business card announcing the fact that this is a flex-fuel car that can run on E85. Unfortunately E85 is unavailable at most of the 180,000 gas stations in the United States. Only about 500 carry it, and they' ve mostly where the corn grows [30]. When, not if, ethanol becomes cellulose-based, there could easily be a hefty shift from gasoline to ethanol. Glucose-based ethanol simply cannot provide the multibillion gallons required for the many millions of American vehicles, and even when cellulose bares its biochemical secrets, biofuels will be unable to replace oil/gasoline completely because sufficient agricultural area is simply unavailable. But together with other renewables, we will become far less dependent on the vagaries of foreign oil. However, it does take two-thirds of a gallon of oil to make a gallon equivalent of ethanol from corn. Therefore, one gallon of ethanol used in gasahol displaces about one-third of a gallon of oil or less. Not that much of a savings. If one were to bet on a technology that could displace foreign oil/gasoline, the difficult-to-digest celluloses and hemicelluloses could do it, once new enzymes become available.

Corn is a many splended thing—beyond ethanol. Polylactides are yet another of its gems. Polylactides, or polylactic acid, is a corn-based transparent plastic without a whiff of petrochemicals. Refining corn can yield a plastic that is readily maleable into cups, containers, candy wrappers, cutlery, and medical sutures.

Polylactide, an alternative plastic, is Cargill/Dow' s latest attempt to wean us off oil. At their new plant in Blair, Nebraska, cornstarch is hydrolyzed to glucose, which is then microbially fermented to lactic acid. Squeezing out water from lactic acid yields lactide molecules that form into long chains that can be spun into fiber for clothing and bedding, or molded and shaped into clear, glossy, rigid cups, bottles, knives, forks, and spoons. Wal-Mart, Del Monte, Wild Oats, and Newman's Own Organics have already opted for these "green" plastics. The next time you're in a supermarket, check the molded vegetable containers for the Nature Works trademark, which is beginning to make a welcome appearance. Sales at Nature Works, the Cargill subsidiary that produces the plastic, grew 200% in the first half of 2005, over the same period in 2004 [31]. These environmentally friendly plastics take less than 2 months to degrade in a landfill, compared to petroleum-based plastics, which can take ages to decompose. These yellow nibblets on a cob surely look like corn, but actually they're all-chemical—waiting for creative minds to unleash their bounty—in addition to tickling our palates.

Creativity is what the DuPont Company of Wilmington, Delaware, is using in its quest to switch us from a hydrocarbon to a carbohydrate economy, which has much to recommend it, as carbohydrate is infinately sustainable, and of course, hydrocarbon is not. DuPont believes that biology can solve problems that chemistry can't.. So, for example, they will be marketing Sorona (propane diol) made from glucose, a product used in carpet fibers that offers greater dye absorbtion and stain resistance than does the petrochemical version that they've been selling. They are also developing plant-based hair dyes and nail polishes that will not adhere to skin, surgical glues that can stop bleeding, and a textile fiber made from sugar that will act and feel like cotton—cotton candy? Industrial biotechnology is DuPont's new direction. Perhaps it will take the country along with it [32]. Another way is via BioButanol, a crop-based fuel that may just jump to the head of the biofuels line. Developed by DuPont in conjunction with BP (British Petroleum), biobutanol is inherently better than ethanol because it has as much energy per gallon as gasoline. Although called biobutanol because it' s produced from biomass, it is no less butanol, C4H10O, a four carbon alcohol. The fermentation of biomass via the bacterium Clostridium acetobutylicum- is relatively simple and inexpensive. Cl. aceto-butylicum is the same microbe that Prof. Chaim Weizmann used to obtain acetone from horse chestnuts for explosives for the British military during the first World War. Given appropriate nutrients microbes can be induced to produce almost any substance.

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