In 2007, Alicia Gregory received a CASE-Kentucky Excellence Award for Feature Writing for this article.
The University of Kentucky is taking “green energy” literally. Well, if you get right down to it, it’s more like green and gold and amber and brown—plant materials, a.k.a. “biomass,” come in an array of colors.
UK is targeting our country’s oil addiction by playing up Kentucky’s agricultural strengths—the fact that we’re the largest timber producer east of the Mississippi, that our climate offers a long growing season and good annual rainfall—by turning timber waste and crop residues into fuel.
UK researchers are creating a more stable form of bio-oil, a replacement for the crude petroleum we use now to make plastics and chemicals, and targeting a new way to make ethanol with cornfield leftovers, and, eventually, with lawn clippings and cardboard. And UK scientists are designing new catalysts to produce premium biodiesel, packaging fine coal and sawdust together in a potent briquette, and looking for cheap ways to capture solar energy with devices spray painted onto rocks or tents.
By pooling the expertise of scientists in biosystems and agricultural engineering (a joint department of the College of Agriculture and the College of Engineering), chemical and materials engineering, chemistry, mining engineering, and the Center for Applied Energy Research (CAER), UK is expanding the meaning of green energy.
Biomass to bio-oil
“Biomass is just really new coal,” says Czarena Crofcheck, an assistant professor in the biosystems and agricultural engineering department who is working on bio-oil, biodiesel and ethanol projects. “It has the same stuff in it as coal and petroleum. It just hasn’t been processed for as long.
“One of the biggest problems we have with biomass is that it’s fluffy,” she laughs. “I like to call it fluffy because it’s not very dense, which makes it expensive to transport, and it’s got a lot of moisture in it.”
Crofcheck’s colleague on this bio-oil project, Mark Crocker, a chemist who has worked at CAER for three years, explains, “Our idea is to process biomass locally, on a farm or at a lumber mill, convert this biomass to a densified form, such as crude oil, and then perform some kind of stabilization step on it so it can be stored and shipped to a central biorefinery.”
Bio-oil is a renewable version of crude petroleum. While 88 percent of all petroleum extracted is processed as fuel, the other 12 percent is converted into a variety of chemical products, including solvents, fertilizers, pesticides, and plastics. And bio-oil can be refined into all of these things.
But why can’t bio-oil be stored and shipped now? First, it’s corrosive because it’s acidic. In fact, if it sits long enough it can eat through its container. Second, it’s unstable. Crofcheck says, “That’s because to create bio-oil you’re causing a chemical reaction to happen by heating it up, and, well, that reaction doesn’t want to stop.”
Crocker, a native of the U.K. who worked in Amsterdam at Shell Research for 12 years before coming to the United States, explains, “Crude bio-oils contain a lot of very reactive chemicals, which can undergo complex polymerization chemistry.” Polymerization happens when small molecules link up via a chemical reaction to form polymer chains. “You can start off with a nice, clear liquid bio-oil,” he says, “and you can end up with something that looks like tar.
“So we want to carry out a quick-and-dirty initial step to convert this crude, unstable, corrosive mixture to something that’s stable.” And the most important part of this transformation involves removing as much of the oxygen as possible. “Up to 40 percent of the oil is oxygen, in the form of carboxylic acids, aldehydes, ketones, and alcohols,” Crocker points out.
“And we do that simply by mixing the oil with a catalyst at a particular temperature,” explains Crofcheck, who came to UK as a grad student in 1994 and has been on the faculty since 2001. Catalysts are substances that accelerate a reaction, without being consumed or changed themselves. “Catalysts are a beautiful thing,” she says.
Crofcheck and Crocker are using catalysts that work based on a concept called cracking—“taking large molecules and cutting them up into smaller molecules by breaking bonds. This is a process that has been used for petroleum for a long time. Lots of catalysts are good at cracking, but many go too far—they can break all of the carbon-carbon bonds and leave you with very small molecules that aren’t very valuable,” says Crocker.
“What we want is mild cracking—just cracking the oxygen-carrying compounds and leaving the heavier compounds, which typically don’t contain so much oxygen, intact. This way you’re expelling the oxygen—present in the most reactive compounds—in the form of carbon monoxide, carbon dioxide or water.”
Czarena Crofcheck (UK biosystems and agricultural engineering) and Mark Crocker (Center for Applied Energy Research) are using catalysts to increase the efficiency of biodiesel production and convert crude, unstable bio-oil into a mixture capable of being stored, shipped and refined into plastics, solvents and fertilizers.
The type of catalyst that can achieve this “mild cracking” is a layered double hydroxide. “As the name implies these are hydroxides (hydrogen plus oxygen) that contain two or more metals. When you heat up these basic materials, they decompose to mixed oxides, which are even more basic, and, importantly, possess very high surface area.” Crocker’s hands skim across the top of the table as he explains, “All your chemistry is occurring on the surface of the catalyst, so the higher the surface area, typically the more effective the catalyst is.” In other words, the more bio-oil that can come in contact with the catalyst at one time, the faster you can process it.
These same layered double hydroxide catalysts are the future of biodiesel processing, says Crocker.
Biodiesel is a biodegradable and renewable fuel that can be made from vegetable oils (including soy and canola), animal fats or recycled cooking oil. This light- to dark-yellow liquid has also been shown to reduce air pollutants like carbon monoxide and hydrocarbons.
Blends of 20 percent biodiesel and 80 percent petroleum diesel (B20) can be used in unmodified diesel engines, and have been shown to reduce engine wear, run quieter and produce less smoke than regular diesel. B100, or 100 percent biodiesel fuel, can be used in a regular diesel engine, but has a tendency to degrade natural rubber gaskets and hoses.
Kentucky produces 54 million bushels of soybeans each year, with 11 pounds of oil processed from each bushel. The state currently has one biodiesel refinery, Griffin Industries in Butler, Kentucky, with a 2-million-gallon-per-year capacity. Two more refineries are slated to open within the next year. Green Earth Bio Fuels, with a projected capacity of 3.2 million gallons per year, will open in Estill County. And Owensboro Grain’s 50-million-gallon refinery, advertised as the nation’s largest soy biodiesel plant, will open next to the company’s existing vegetable oil refinery.
Biodiesel is already being used in 18 vehicle fleets across the state, including the Cincinnati/Northern Kentucky Airport, East Kentucky Power Cooperative, Kentucky Public School Systems, Kentucky State Resort Parks, Murray State University, and the University of Kentucky.
Nationwide biodiesel use is increasing—70 million gallons in 2005 compared to 30 million gallons in 2004. But biodiesel is still more expensive to produce than petroleum diesel.
New catalysts are key to increasing the efficiency, and lowering the cost, of biodiesel processing. The catalysts used now are homogeneous—both the catalysts and the vegetable oil/methanol mixture are liquid. “You basically have a huge vat in which you’re processing the oil and methanol, and you have to wait for everything to convert,” Crofcheck explains. “And while you’re waiting, what was converted at the very beginning starts to convert into something else, something you don’t want. And that’s because the liquid catalyst needs to swoosh around until it comes in contact with everything.”
Crocker and Crofcheck say a heterogeneous (solid) catalyst is the necessary alternative. “If we could move the liquid through a solid catalyst, there would be less contact time and less risk of these so-called side reactions that create stuff you don’t want,” she says.
“One specific class of these layered double hydroxides has been very effective, and we’re putting a patent together on that,” says Crocker, noting that a solid catalyst allows you to separate your catalyst from the product much easier. “Right now biodiesel producers can’t reuse the catalyst,” Crofcheck says. “They wash it out and dispose of it, but with a solid catalyst, you’d be able to reuse it.
“And from where I sit, in biosystems and ag engineering, I think that’s interesting because a lot of what we do is look at the processes farmers or industry have been doing for a long time and see if we can make them better,” Crofcheck says, with an intensity that shows she clearly enjoys her work.
Rich Gates, head of the department, adds, “The exciting thing about renewable energy research in UK’s Department of Biosystems and Agricultural Engineering is that we have projects that involve the beginning of the process, harvesting and storage, the middle, microbial and thermochemical conversion, and the end processing, catalytic stabilization. We run the gamet, and that’s a strength.”
A billion tons and what do you get?
“The U.S. Department of Energy and the U.S. Department of Agriculture have a goal of using 1 billion tons of biomass annually,” says Scott Shearer, a biosystems and agricultural engineering professor who focuses on the harvesting side of the biomass equation. The DOE and USDA came up with this number in response to mandate to figure out how to replace 30 percent of U.S. petroleum consumption with biofuels by 2030.
Scott Shearer, a biosystems and agricultural engineering professor, focuses on the harvesting side of the biomass equation. He’s making low-cost equipment modifications that would allow farmers to harvest corn stover—the leaves, cobs and husks that are currently spread back on the field—a potential feedstock for ethanol.
Photo by Matt Baron
This is a daunting challenge. Biomass currently supplies just over 3 percent of the total U.S. energy consumption. However, the joint report issued in April 2005 states that, yes, 1 billion tons is doable—looking just at forestland and agricultural land, the United States has the potential for over 1.3 billion dry tons of biomass per year. This includes biomass from overgrown forest floors (dry material that needs to be cleared away to protect against forest fires), grains used for biofuels and crop residues.
The report calls for a 50 percent increase in corn, wheat and other grain yields, harvest technology capable of recovering 75 percent of crop residues, and 55 million acres of cropland, idle cropland and cropland pasture to be dedicated to the production of perennial bioenergy crops.
Shearer says candidly, “If the government puts economic incentives in place, we’re going to see more people growing dedicated energy crops, and that may be a pretty important thing for Eastern Kentucky and areas that are less intensively cropped.” Of Kentucky’s 26 million acres, less than a fourth of the state (6 million acres, primarily corn and soybeans) are intensively cropped.
“Dedicated energy crops—specially bred corn or forage crops like switchgrass and wheat straw—will only become feasible once we put an infrastructure in place to process and transport biomass. It’s a chicken-and-egg type thing,” Shearer says, smiling. “If somebody’s willing to pay for it, there will be people willing to produce it—but right now we don’t have the infrastructure for those producers to move the product.”
“If you grow soybeans or canola, you’re going to want to make biodiesel, and if you have corn, you’re going to want to make that into ethanol. So we need to use things that are not otherwise being used,” Crofcheck adds.
And Shearer, whose 20-year career at UK has focused on precision agriculture—using technology to increase crop yields—echoes her. “The feedstock that’s not being used, particularly in Kentucky, is corn residue.” And that’s where a new way to make ethanol comes into the picture.
Ethanol: it’s not about kernels anymore
“The reason we have so much ethanol production today is not necessarily as a replacement for petroleum, but rather because of the EPA restrictions on fuel-based air pollution,” Shearer says. Plants grown for ethanol production absorb carbon dioxide as they grow, and ethanol reduces pollutants (carbon monoxide, particulates and ozone) produced by gasoline combustion. “Ethanol is also added to fuel as an octane booster.”
His cohort Mike Montross, an associate professor whose expertise lies in drying, storing and processing grains, adds, “Ethanol is replacing MTBE, another octane booster, because scientists are now finding it in groundwater. They’ve discovered MTBE doesn’t break down.”
The Department of Energy reports a downside to ethanol—lower fuel economy. A 10 percent ethanol blend (which has been approved for use by every automobile manufacturer) reduces slightly the miles per gallon compared to pure gasoline. The DOE ethanol fact sheet states, “Engines are being designed that take advantage of the high-octane benefits of ethanol while increasing fuel efficiency.”
Ethanol also has its critics. Some say it takes more energy to make ethanol (from the fertilizer to grow the corn, to the fuel used to harvest and transport it, to the energy to process it) than it generates. Biosystems and agricultural engineering chairman Rich Gates says to some extent it’s a numbers game.
“It all depends on how you define inputs and outputs in this argument. For example, co-products such as the distillers grain—that can be processed into animal feed—can be valuable and aren’t included in all the balances. The latest values from the National Renewable Energy Lab assert that the energy balance is positive. Some studies gloss over energy costs of extracting, refining and distributing petrol-fuels. There is no simple answer to this, but there is definitely economic opportunity and a need for alternative fuels.”
Fifty U.S. facilities currently produce ethanol, and 16 states, including Kentucky, have their own tax incentive programs to bolster ethanol. Kentucky currently has two ethanol plants—Commonwealth Agri-Energy in Hopkinsville (with a capacity of 33 million gallons per year) and Parallel Products in Louisville (5 million gallons per year). Two more plants on the way include Bluegrass BioEnergy in Fulton County (with a proposed yearly capacity of 55 million gallons) and Agri Fuels in Brandenberg (50 million gallons per year).
In the United States, ethanol is produced primarily from starch in corn kernels, and this is not sweet corn, the kind we eat, but feed corn that is ground into animal feed. Most of the 4 billion gallons of ethanol produced in 2005 came from 13 percent of the U.S. feed corn crop.
In the field, corn kernels (i.e., grain) make up about half of the above-ground biomass, and corn stover (the stalks, leaves, cobs, and husks currently left in the field) make up the other half.
Most ethanol is made by “dry milling,” a process with six key steps. 1) Kernels are ground into a fine powder, 2) liquid is added and the temperature is increased, 3) enzymes are added to break down the long chains of starch into short chains of glucose
(sugars), 4) yeast is added for fermentation (converts glucose to ethanol and carbon dioxide), 5) the mixture is distilled (removing the ethanol from solid materials—compounds that can be processed into livestock feed—and water), and 6) the remaining water is removed to produce pure ethanol.
But converting corn stover or any other biomass material—wood, paper, grass—into ethanol is a whole other ball game. The fundamental challenge in making “cellulosic ethanol” lies in the fact that instead of breaking down starch into sugars, this conversion requires tearing apart the cell wall of the plant (the cellulose, hemicellulose and lignin) to get sugars. This so-called lignocellulose material is tough stuff. Lignin is the reason corn grows tall and wood is rigid. It has a much more complex chemical makeup than starch. Montross, who’s worked on biomass preprocessing at UK for seven years, says, “Biomass has a lot of sugar, but right now nobody really knows how to get to it. That’s where Sue Nokes comes in.”
Some like it warm
“We want to get to the cellulose, but the lignin wraps around the cellulose, so it’s difficult,” says Nokes, an associate professor with expertise in producing industrial enzymes through fermentation. She is the principal investigator on a project to adapt bacteria to make cellulosic ethanol. And her UK team includes Herb Strobel in animal and food sciences, Barbara Knutson in chemical and materials engineering, and Bert Lynn in chemistry.
Strobel, who’s been at UK for 16 years and specializes in anaerobic microbiology, says, “We’re using Clostridium thermocellum—a bacterium that likes heat. It’s found in compost piles, hot springs, soil and other warm environments that contain decaying plant matter. C. thermocellum and organisms like it are critical—without their help we’d be up to our eyeballs in plant material.”
American Society for Microbiology, Edward Bayer
So why is this organism a good candidate for ethanol production? “Because it has its own enzyme system,” Nokes explains in a way that makes it clear why students have voted her an outstanding teacher more than a half-dozen times since she came to UK in 1995. “C. thermocellum naturally feeds on cellulose. With corn you have to buy and add enzymes because yeast don’t have any of their own. But this guy can do the whole thing—take the plant material, break it into sugar and ferment it. And in general, industrial processes that are warmer go faster, so the fact that they like it warm is just another way to capitalize on their natural ability.”
The first step in this project involved “growing” bacteria that could withstand increasing amounts of ethanol. “C. thermocellum can naturally tolerate ethanol at less than a 1 percent concentration,” Strobel explains. “We gradually increased the ethanol to ‘train’ the organism to adapt. This was time consuming, but with patience, and a few tricks, it was possible to select strains that tolerate 5- to 15-fold higher concentrations of ethanol than normal. One trick we used was growing the organism in slightly reduced temperatures. In some way—we’re still studying how—this helps the organism adjust to the higher ethanol levels.”
Once the team had their “super bacteria,” they began comparing them to normal bacteria. “We’re trying to find out what the organisms that have adapted do differently from those that haven’t adapted,” Nokes says. “Specifically, we’re zeroing in on the metabolic pathways and membrane fluidity.
“Metabolic pathways affect how much of the sugar coming in goes to ethanol versus acetate and lactate.” Naturally, C. thermocellum doesn’t produce much ethanol, because it also makes acetate (vinegar) and lactate (an acid used to preserve fermented foods like cheese, yogurt and sauerkraut). “We want to shift its metabolism more toward ethanol.”
Membrane fluidity has to do with the way ethanol can dissolve—break down, like a detergent—the organism’s membrane. Nokes says, “If we can strengthen the membrane, we can boost the bacteria’s resistance to ethanol.”
Sue Nokes (UK biosystems and agricultural engineering), Michael Timmons (student), Ester Dittert (student), Bert Lynn (chemistry), Anup Thakur (student) Herb Strobel (animal and food sciences), and Barbara Knuston (chemical and materials engineering).
How do you convert biomass with these bacteria? “Right now we think you’ll have to grind up the biomass—make it into small pieces of uniform size—then whether or not you have to treat it with an acid or base is still up for discussion.” Nokes explains that pretreating will separate the cellulose from the hemicellulose and lignin, the bacteria will be added to convert the cellulose into glucose, the mixture will be fermented, and then ethanol will be separated by distilling—heating it up and boiling it off.
'“If we can figure out how to produce ethanol from cellulose instead of from starch, I think everyone will go to making it from cellulose,” she says. “It’s a cheaper feedstock and there’s more of it. We’re hoping that down the road we could essentially convert the corn ethanol plants, and just replace corn with plant materials.
“Think about cities. We collect yard waste like leaves and lawn clippings, put it in our little paper bags, and it gets hauled off to the dump. Why don’t we do something else with it?” Nokes asks enthusiastically. “The conversion gets a little more complicated if it’s a mix of stuff, but that’s where we want to go.”
Shearer says that if you single out corn residue as the feedstock for cellulosic ethanol, one of the major hurdles is simply accumulation. And Crofcheck adds, “This biomass is just not valuable enough to buy a special piece of equipment to get it off the field.”
Montross and Shearer are tackling this problem headon by adjusting the combine harvester to catch the leaves, cobs and husks but leave the stalks in the field. “What comes out the back of the combine right now is everything but the grain. All of the biomass is returned to the field. We want to make modifications to the equipment the farmers already have, at a cost where the farmer derives a profit for collecting the biomass,” says Shearer.
“When you look at biomass accumulation, one of the things we’re always concerned about, especially in Kentucky, is leaving enough residue on the soil surface.” He says this is critical for two reasons. “We talk about erosion, and of course that’s vital, but there’s also the carbon content of the soil. Maintaining soil organic matter content is important to agricultural productivity in subsequent years.”
And in their study, Shearer says, the stalks were the best field protectors. “The high lignin content in the stalks is valuable for erosion control because the stalks degrade slowly, while leaves and husks break down very quickly.”
Montross adds, “Until we’ve figured out an economical way to process biomass into ethanol, and until there’s someone who actually wants it and is willing to pay for it, cellulosic ethanol isn’t going to happen. But that’s the direction we’re headed.” Speaking of new markets for green energy, Shearer, Montross and Darrell Taulbee, a chemist at the Center for Applied Energy Research (CAER), are partners on a project to turn biomass into briquettes. These briquettes offer an alternative to the huge quantities of fossil energy, primarily natural gas and coal, which are currently used in ethanol and biodiesel production. They could also be used to produce green power at existing utility plants. And while some of these nuggets are 100 percent biomass, others are an innovative mix of mill and coal waste.
Packaging green energy: the fine coal/sawdust briquette
“There’s a growing demand for green energy, but there are a lot of problems getting green energy into the market—transportation, low density,” says Taulbee, who has worked at CAER since 1980. “So the question becomes,
how do you overcome these problems?”
The answer: Briquettes.
Mining Engineering Professor Rick Honaker points out that any powder that is compressed into a solid nugget is a briquette. “We use briquettes all the time. Charcoal, medicinal pills, dog food, cat food—it’s all briquetted.”
Taulbee, Honaker and B.K. Parekh, a coal expert from CAER, are partners on a project that began in 2002 to create a premium fuel, for use in industrial boilers like those at utility companies, by taking two waste materials—fine coal and sawdust—and packaging them as a briquette. “It just simply made sense,” says Taulbee, whose words are measured and tinged with an accent that hints at his Eastern Kentucky roots. “This is a way that you can put two waste materials together and address all of the problems that you had trying to market them individually.”
In the process of mining, 20 to 30 percent of the coal generated is “fine coal”—tiny particles with the consistency of flour. Typically this fine coal material is disposed of in sludge-like ponds called slurry impoundments. These impoundments hold wastewater and impurities that result from coal washing and processing. A bulkhead or embankment is made of coarse coal refuse and acts as a dam. The sizes of the ponds and bulkheads vary, but impoundments are often hundreds of feet deep and hold millions of gallons of slurry. Parekh notes that these waste ponds are under increasing scrutiny because of potential safety and environmental risks. And Taulbee recites a staggering statistic: “There’s 2 to 5 billion tons of waste coal material in the United States.”
“And Kentucky has 500 million tons of fine coal in slurry impoundments,” says Parekh. Taulbee interjects, “To put that in perspective, Kentucky only mines 100 million tons of coal each year. We throw away enough each year to run a small industrial country of 10 to 20 million people.”
Parekh, who earned a master’s in physical chemistry from Vikram University in his native India before pursuing a master’s degree and doctorate in minerals processing at Penn State, continues, “We used to throw away 20 percent of the fine coal we produced, but now we’re down in the 5 to 10 percent range.” That’s due in part to Parekh’s research that started back in 1985. His device, the Ken-Flote column, allows coal-preparation plants to clean and recover these tiny coal particles. With a number of competing “column flotation” companies selling their units, he says, “this process is becoming very popular in the coal industry.”
So what’s the problem with using this fine coal? First, it’s wet.
“The product that comes out of these machines is 20 percent solids and 80 percent water,” Parekh explains. Through a process called dewatering, the coal company can reduce the moisture content to about 35 percent, and then can mix the fine coal with larger, coarser coal and sell it to utility companies. But industry regulations limit the amount of fine material coal companies can mix in with regular coal. “And if you want to make briquettes, 35 percent moisture won’t cut it.
“The numbers we want are 20 percent water and 80 percent solid. That’s not easy,” Parekh says. “So the main emphasis of my work has been going after these ultra-fine particles, recovering them, and then producing a very low-moisture product.”
And there’s a second problem, says Taulbee. You can’t transport fine coal by itself. “If you ship this fine coal out of Kentucky by train, even though it’s wet when it starts out, the surface layer will be dry before it gets to Florida. It’s going to be blowing out the back of the railcar.”
The same goes for sawdust. Because it’s so lightweight, it’s not economical to transport more than 40 miles, says Honaker, who has been at UK since 2000 and earned his Ph.D. in mining and minerals engineering at Virginia Polytechnic Institute & State University.
Taulbee, who has a Ph.D. in analytical chemistry from UK, says, “In 2002 one of the first things we discovered was that Kentucky is the largest timber producer east of the Mississippi. At that time we were producing three-quarters of a million tons of sawdust in Eastern Kentucky alone. The utilization rate of sawdust statewide was 35 percent, but it was lower in Eastern Kentucky.”
Binder specialist Darrell Taulbee (left), coal expert B.K. Parekh and mining engineer Rick Honaker are partners on a project to create a premium fuel, for use in industrial boilers like those at utility companies, by taking two waste materials—fine coal and sawdust—and packaging them as a briquette.
“And that simply has to do with the lack of industrial development in the region,” Honaker points out. “We recognized a unique situation in Eastern Kentucky. Here were slurry impoundments right next to mountains of wood waste. Why not link up these coal plants and lumber mills?”
So with funds from the U.S. Department of Energy, the team set out to find the least expensive means to produce briquettes, and they determined that if you located a 50-ton-per-hour briquetting operation at an active coal-preparation plant, you could make briquettes valued at $17 per ton. Honaker says, “We looked at all of the costs—equipment, sawdust transportation, labor, etc.—and came up with $17 per ton.”
“Compared to $40 to $45 per ton for coal, you can’t beat it,” says Parekh. And with the fine coal’s BTU (heating energy value) at 13,000 to 14,000 per pound,and the sawdust’s BTU at 6,000 per pound, this briquette is a premium fuel source.
The team’s scenario involved taking the fine coal directly from the column flotation unit, dewatering it, mixing it with the sawdust, adding the binder, and pressing it into a briquette. The binder—the most expensive item in the briquetting process (they budgeted $8 per ton for the binder alone)—is the “glue” that holds the sawdust and fine coal together. “We’ve identified several multi-component formulations that work well, but we haven’t released the names of those yet,” says Taulbee with a smile, alluding to the fact that his competition would love to know the make-up of his binders.
Honaker adds, “Darrell had over 50 different chemicals that he tried. He went through the list, crossing out those that exceeded the $8-per-ton target price, that didn’t measure up with compressive strength, and that couldn’t endure drop-shatter tests. This was our biggest achievement in the whole project—finding the binders that make economic sense.”
Holding the smooth, nearly two-inch by a half-inch briquette, Taulbee explains that the binder reduces the amount of energy you have to exert to form the briquette. “So you mix the fine coal and sawdust and add the binder, then you feed it through a machine that compresses the powder under high pressure for less than 2 seconds. The briquette comes out shiny and hot,” Taulbee says. “The two-inch size was simply the size of the die on the briquettor we rented to start this project. The die size is going to correlate with the amount of pressure you need and how much power the process will consume. For example, producing wood pellets takes 10 to 15 tons of force. We only need 1 to 2 tons because we’re using a binder.”
But before they tested which compounds performed best as binders, they needed to find out what kind of sawdust worked best and what mix of sawdust and fine coal was optimal.
“The harder woods, like hickory, beech and oak, yield higher density sawdust than trees like poplar, maple or willow. And higher-density sawdust gives us a higher compressive strength briquette,” says Taulbee.
And it turns out that 10 percent sawdust, 90 percent coal is the right combination. “The sawdust actually reduces the strength of the briquette. Initially, the wood absorbs some of the moisture in the coal and it swells,” explains Honaker. But as the briquette cures (or dries) the wood shrinks, which weakens the briquette.
With new funding from the Kentucky Office of Energy Policy, the team will tackle the two biggest obstacles to commercialization they’ve found so far.
Obstacle #1: Straight out of the machine, these briquettes are fragile. Taulbee says, “They tend to have a low compressive strength when they’re first produced, and that prevents you from immediately handling them and loading them onto railcars.” They need to cure—sit in a dry place for a few days up to a week or go through some type of drying process.
Obstacle #2: The more significant problem, says Taulbee, is that the moisture in the coal prevents consistent feed rates to the briquette machine. “If you can’t get consistent feed rates, you can’t get a consistent product.” The team will test four different methods to see which is best for making the tiny coal particles flow better.
And what they find may soon make its way to a commercial operation. Leaning back and crossing his arms, Taulbee says, “We need to demonstrate this on a larger scale in the field.”
“We’ve had several meetings with potential investors and utility companies who are interested in this because of their need to respond to CO2 emission concerns,” explains Honaker. The United States currently has no cap on CO2 emissions, but limits are in the works.
Kunlei Liu, who joined CAER last year and has expertise in clean combustion technology and emissions control research, says, “A Congressional proposal, the Climate Stewardship Act of 2005, introduced by Senator John McCain, would mandate CO2 emission
reductions in the United States for facilities emitting 10,000 metric tons of greenhouse gas per year. As now proposed, this legislation would apply to all coal-fired power generation units in Kentucky. From what I see, the legislation on CO2 emissions isn’t a question of yes or no, it’s about how soon.”
So coal power plants are eager to mix in as much green energy as they can. And they’re investigating all kinds of renewable biomass. Taulbee explains, “If you look at agricultural waste, seasonal availability is a problem. A utility company can’t just run in the summer. People want electricity year-round. There are storage problems with biomass. You have to keep it dry, and you have to invest additional capital to transport and process it.
“Briquetting addresses all of those issues. You can simply transport these coal-sawdust briquettes by train, just like you would a chunk of coal. And if you build the proper briquette, it can resist water so you can store it outside. People want to use biomass. Utilities are willing to pay for it, and they sell their electricity at a premium. There’s money to be made in a green way.”
And speaking of green, the greenest energy of them all—sunlight—may soon be producing electricity for your home and car.
Solar cells on the cheap
John Anthony and Rodney Andrews see the future of solar energy as a can of spray paint. It’s a far cry from the solar panels you see on houses today. Andrews, CAER carbon materials group manager, proudly says the heavy, brittle and expensive silicon panels (which run about $12,000 for three kilowatts, including wiring) are old news.
“We’re on the opposite end of the spectrum,” says Anthony, who holds the Gill Professorship in Chemistry. “Our goal is to make cheap solar cells.” These solar cells, a.k.a. photovoltaic cells, are tiny semiconductors that convert solar light into electricity. “We want to bring the price down to about $1 per watt—the mark at which consumers will start adopting solar cells because they are essentially disposable.”
What’s the bright idea? Cheap solar cells. John Anthony (left), who holds the Gill Professorship in Chemistry, and Rodney Andrews, Center for Applied Energy Research carbon materials group manager, are creating plastic solar cells with nanotubes.
Why do we need a new kind of solar cell? Current silicon panels are 17 percent efficient (and, of course, that’s related to the fact that solar cells produce energy only while the sun is shining). Anthony’s early-stage test cells are about 1 percent efficient. And while they’re working on improving efficiency, he says, efficiency isn’t everything.
“The cost is going to be significantly lower than silicon,” says Anthony, whose previous research on the same kind of molecules he’s using in the solar cells was geared toward flexible flat-panel displays. This work led to Outrider Technologies, a company located on campus at the UK Advanced Science and Technology Commercialization Center. “Our organic, i.e., plastic, solar cells are going to be flexible, portable and disposable, and those are the qualities our military partners are interested in.”
The UK researchers, with scientists at Cornell and Northwestern, are working on three different solar energy projects funded by the Army, the Navy, and the Defense Advanced Research Projects Agency (DARPA). The Army project utilizes a UK strength—the Advanced Carbon Nanotechnology Program (ACNP). Headed by Janet Lumpp in electrical and computer engineering, ACNP includes a subgroup on energy conversion, led by Anthony. And Andrews, a chemical engineer whose work covers several parts of this program, quips, “I’m everybody’s nanotube dealer.
“We can make about two-and-a-half kilograms of nanotubes each day, which means, as far as we know, we have the largest
academic capacity in the world. A couple companies beat us, but nobody in academia.”
And what do nanotubes have to do with solar cells? Nanotubes—cylindrical carbon molecules that are efficient conductors of heat and exhibit extraordinary strength and unique electrical properties—are a cutting-edge replacement for the metal needed for conductivity. “Compared to metal,” says Andrews, “nanotubes are great because they’re flexible, they’re durable, they don’t break over time, and they don’t rust.”
Anthony, a semiconductor expert, explains, “What you have with a plastic solar cell is two electrodes—one made of nanotubes and the other a transparent conducting polymer or very thin aluminum—and sandwiched between those two electrodes is what we call the active layer. It’s where all the business happens.”
And that “business” can be summed up as: “When strong light pulls an electron away from the material, it leaves a positive charge behind, called a hole. The whole impetus for the work that the electrons do, in any electronic device, is that the electrons are screaming around trying to find another hole to recombine with,” says Anthony.
Andrews says, with a laugh, “There are a whole bunch of physicists that are going to give you a hard time about that explanation.”
Nodding, Anthony says, “I know. It’s not exactly right. But electrons and holes—that’s what it’s all about. Pulling them apart and letting them recombine. You’ve got to love that fundamental balance of nature.”
Taking advantage of what happens in biology, specifically a phenomenon called self-assembly, is the team’s goal. “Self-assembly is a process whereby molecules are designed so that they find each other and arrange themselves in a particular fashion,” Anthony explains. “This process is why there is life. DNA, the double helix, is formed by self-assembly.
“Applying this to an electronic system, we stick little bits and bobs onto the molecules—it’s like Tinker Toys—so that when you dissolve them in a solution and you spray that out, the solution evaporates, the molecules start getting closer and closer until they recognize, ‘Hey, this is the part I want to interact with,’ and they stick together.”
Andrews adds, “Where self-assembly really comes in handy is when you’re working at the nano scale. You can set up these molecules to arrange themselves in the shape you need.”
The active layer of one of these solar cells is less than 100 nanometers thick—“that’s one-6,000th of a human hair,” Andrews says. “You can’t get in there with a pair of tweezers to push stuff around, so self-assembly does the work for you. We use this process to grow an array of nanotubes that all line up the same way—like a piece of carpet—with ‘fingers’ that stick up.”
“Rodney’s nanotube fingers stick up, and my active layer fingers stick down. This maximizes the surface area, the interaction between the conductive bit and the semiconductive bit,” says Anthony.
Andrews gives a little more detail: you’ve got two types of semiconductors, n-type and p-type. “We’re tailoring the nanotubes so they better match, and accentuate, the electronic properties of the active layer.”
“N-doped nanotubes like to hang out with electrons, and p-doped tubes like to hang out with the holes, the positive charge,” Anthony says, laughing at this oversimplification and adding that the technical term for this is “work function.” “It’s nice because work function gives you a definite number, and the whole point is to get Rodney’s nanotubes’ energy, the work function for the n-doped and p-doped tubes, to line up with the energy level in the n-type and p-type molecules I make.”
John Anthony sprays a blue semiconductor mixture onto paper coated with silver cathode dots to demonstrate the ease with which solar cells can be fabricated in the field. Connect the cells with a few wire electrodes, and a solar cell array is born.
And what has all of this electronic fiddling accomplished? “The first-ever demonstration of a spray-painted solar cell,” Anthony says with a smile. “DARPA wanted us to show spray painting was possible, but we took it one step further. One of the postdocs on the project took a rock out of his garden, and we spray painted a working solar cell onto it.” Now, why would the military be interested in a spray-painted rock?
“Special forces soldiers carry about 14 pounds of batteries. Since they don’t have the capability of recharging them in the field, they have to carry replacements,” Anthony says. “We’re trying to replace that 14 pounds with a couple little cans of spray paint. These guys bed down during the day and operate at night. They could spray out their solar cell during the day, plug their batteries into it, go to sleep, and when they wake up they can pick up their charged batteries and they’re off and running. And when they’re done with the solar cell, they just kick it into the sand and it’s gone.”
Anthony and Andrews list a number of surfaces solar cells could be spray painted onto—the sides of a tent, a panel on the back of a soldier’s uniform, an inflatable structure, and, beyond military use, your driveway, the roof or your car.
Anthony says, “Right now we’re trying to increase the efficiency of these cells, but we’re also trying to create a device with a lifetime of about a week. The idea being that these could be used for emergency disaster relief or short military operations.”
Andrews adds, “The Department of Defense has been very generous and very helpful because they have immediate demands and very specific needs, but through these projects we’re making materials that could eventually be put into everybody’s house and everybody’s car.”
“A friend of mine said what he envisions is a roller system that goes across the roof of your house. It’s automatic. Every week the thing just rolls out a new segment of solar cells,” Anthony says. “And if you can spray paint the roof of your car for a few cents and that’s going to generate some power for you, why not?’”
The “why not?” is driving the UK team to explore the possibility of capturing UV to produce electricity. Anthony says, “We just submitted a proposal to the Navy on down-conversion—taking really powerful ultraviolet light and converting its energy down to something that’s more useful for solar cells.”
Andrews adds, “In Kentucky, the problem with using solar for large-scale energy production is it’s too cloudy. But when it’s cloudy you still get substantial UV.”
“That’s why you sunburn on a cloudy day,” Anthony says. “You know how people put these films on their windows to keep out the UV rays? Why not actually absorb the UV and do something useful with it by turning it into electricity? If we can adapt our technology, a whole new range of possibilities will open up.”
Green starts at home
Green energy means different things to different people, and most view it as a way to wean our country off foreign oil. But University of Kentucky researchers understand that the potential of green energy is based in the combined power of ethanol, bio-oil, biodiesel, briquettes, clean-coal technologies, solar cells, and more.
As Rich Gates puts it: “It’s hard to predict which combination of technological innovation, market and consumer forces, and government incentives will link up to be successful, so a broad-based examination of the technical roadblocks is critical to improving our knowledge.
“Some of the problems we’re addressing won’t have solutions for years, and that is why investment in higher education is so important. We are working for future generations, not only for the fuel we pump into our cars this week.”
Scott Shearer adds, “We’ve forgotten the lessons we learned back in the ’70s. Look at the number of SUVs and pickups on the road if there’s any question in your mind about that. We need to focus more on our individual energy use.”
To underscore this point, Burt Davis, director of the clean fuels and chemicals group at CAER (whose research on making liquids from coal, along with other projects on hydrogen and catalyst advances, will be covered in part two of this article in the Fall 2007 issue), gives a staggering analogy.
“Every man, woman and child in the United States uses the equivalent of 16 six-packs of energy every day. Now students like a six-pack of cola, but they can’t handle 16,” he says with a chuckle. “It’s an enormous amount of energy. It’s stupid not to look at every resource we can—biomass, ethanol, biodiesel, hydrogen, and coal. We can’t afford to look at one thing to the exclusion of