In the shadows behind today's buzz about ethanol lurks a fundamental question: In the end, does it make environmental, economic, and just plain net energy sense to shift the nation's transportation fuel from gasoline to ethanol? Replacing imported crude oil feedstocks with U.S.-grown biomass could buy Americans some security from the chaos that comes with dependence on Middle Eastern oil, and it could ease pressure to drill in controversial and environmentally sensitive areas at home. But ethanol comes with its own baggage.
Currently, corn is the source of nearly all the 5 billion gal of ethanol the nation produced last year. Those 5 billion gal are predicted to grow to nearly 9 billion gal in a year or two, warming the hearts and filling the wallets of U.S. farmers and agricultural companies. However, the U.S. uses 140 billion gal of gasoline per year. Because ethanol has about two-thirds the energy value of gasoline, the 9 billion gal of ethanol would displace only 6 billion gal of gas, or about 4.3% of the U.S. total. Producing that much ethanol, however, would require more than 20 million acres of corn, or about one-quarter of the U.S. total corn acreage.
A ramp-up of corn production to meet ethanol feedstock demands appears to be the near-term solution, and it will require better yields, intensive farming practices, and more acres. In the future, ethanol from all sorts of biomass feedstocks might change the face of ethanol production, but for today, the choice is corn, and a lot of farmers and agricultural companies would like to see it stay that way.
More corn for ethanol is a hot topic. One of the biggest questions concerns energy balance: Is more energy needed to grow and convert corn or biomass into ethanol than the energy value present in the ethanol fuel? In other words, does it take more energy to make ethanol than ethanol is worth?
David Pimentel says "yes." One of the most consistent and oft-quoted ethanol critics, Pimentel is an entomologist and agricultural sciences professor at Cornell University. His criticisms go back to the 1960s, he says, when he was on a National Academy of Sciences panel that was examining the future of U.S. agriculture.
"I raised the issue of bioenergy, and all 11 other members said it wouldn't be a problem," he says. "I maintained I was correct and they were wrong."
He first formally raised his concerns in a paper published in 1973, he says, and has criticized ethanol for fuel ever since. He's been accused of being an antiethanol zealot and of being funded by the oil industry, which he angrily denies. Decades ago, at the urging of farm-state members of Congress, he was investigated by what was then the General Accounting Office, which, he says, concluded he was correct.
Pimentel is in a minority these days, but he is not alone in his views. He has become a sort of benchmark for ethanol supporters and opponents. Some of his objections are in part ethical—more than 2 billion of the world's people are malnourished, and corn-based ethanol takes food from them, he argues.
Joining Pimentel in this criticism is energy and agriculture guru Lester R. Brown of the Earth Policy Institute. Brown predicts corn prices will skyrocket, and the world's poor will suffer as corn-based products become more expensive.
Not much of the U.S. corn crop directly feeds humans, however. About half goes to U.S. animal feed; 20% is exported, mostly to feed foreign animals; 20% makes ethanol; and 10% is used for industrial and some food-related products, around half of which is for high-fructose corn sweeteners. Indeed, corn prices are rising due to ethanol demand, the Department of Agriculture says, and cattle, hogs, poultry, meat, milk, and cheese prices will likely follow suit.
These prices will have little effect on the developing world, and it is unclear how the corn market and farming practices will adjust to these price changes in the U.S. For instance, ethanol production from corn also generates "distillers grains," a valuable high-protein by-product used for cattle feed. USDA economists and farmers believe the production of more ethanol could provide enough distillers grains for cattle feed to offset the loss of corn for feed.
Pimentel's most cutting objection, however, concerns the fossil energy used to make ethanol. His criticism is important in two ways. First, the U.S. gains little advantage if we burn more oil to make ethanol than is replaced by the biofuel. Second, ethanol holds out the promise of reducing carbon dioxide in the atmosphere by recycling carbon from biofuels into presently growing plants; by contrast, gasoline increases today's carbon budget by burning fossil fuels that were generated millions of year ago. The greenhouse gas advantage disappears, however, if more fossil fuel is burned to make ethanol than is used to make gasoline.
Pimentel has developed an energy model with 14 inputs—electricity, natural gas, irrigation, and so forth. He argues that his proethanol opposites, who claim a net energy gain for ethanol, have played down its energy needs, particularly, the energy impact of farm machinery, labor, irrigation, and hybrid seeds.
In a recent paper, Pimentel calculates that ethanol from corn kernels requires 29% more energy than the energy value of the ethanol fuel. To use cellulosic switch grass as an ethanol feedstock, Pimentel says, would take 50% more fossil energy than the resulting fuel (Nat. Resour. Res. 2005, 14, 65).
Most other economists and researchers disagree. They say Pimentel has overestimated the impact of many inputs, in particular, the cost of farm equipment, maintenance, and crop irrigation. Among critics are USDA economists, who said in a 2002 study that the net energy value of corn ethanol may have been negative once but now shows a 34% energy gain due to technological advances. Other researchers have turned up similar numbers. They particularly challenge Pimentel's energy calculation for cellulosic ethanol, which would require fewer farming inputs than ethanol.
Bruce E. Dale, a chemical engineering professor at Michigan State University, backs the USDA numbers and has applied Pimentel's methodology to making gasoline. He found gasoline production has a 45% net energy loss, worse even than Pimentel's charges for ethanol. He also looked at generating electricity from coal and found a net energy loss of a whopping 240%.
He asks rhetorically: Does that mean coal shouldn't be used to make electricity? Dale says the debate over net energy loss or gain is "irrelevant."
Liquid fuel—gasoline or ethanol—is far more valuable than an untapped oil reserve or a corn field. Considering electricity, he calculates that it has 12 times the market value of coal, and it makes sense that it is much more expensive. Try plugging your computer into a lump of coal or dumping crude oil or corn cobs in your gas tank.
Dale, an ethanol supporter, adds that ethanol offers a modest 13% advantage over gasoline in terms of greenhouse gas emissions, a result similar to other researchers'.
Pimentel tells C&EN that he recently applied his model to gasoline production and found it takes about 1.2 gal of oil to produce a gallon of gasoline. He also acknowledges that electricity requires about three times more energy to make than it provides.
Consequently, he admits that the net energy losses for corn ethanol and gasoline are "close," but, he stresses, corn has many other negative environmental impacts: It erodes more soil, uses more nitrogen fertilizer, and uses more water than any other crop. "Corn is the prime cause of the dead zone in the Gulf of Mexico, which is the size of New Jersey," he says, referring to an area off the coast of Louisiana that is depleted of oxygen due to high levels of nutrient-rich agricultural runoff from the Mississippi River. "These are serious problems," he says.
So, should corn be the ethanol feedstock of the future?
Big agricultural interests—Archer Daniels Midland and Monsanto—are pushing for corn. ADM produces 20% of today's ethanol and is building refineries to increase production by 50% within a year or two. Monsanto executives recently announced plans to increase corn yield from 150 to 300 bushels per acre through hybrid seeds and intensive farming practices. They have also predicted increased acreage and the use of stalks and waste (stover) to increase ethanol's market share (C&EN, Dec. 4, 2006, page 57).
All this would have a huge impact on U.S. farming practices and the environment. However, other equally large companies—DuPont and BP among them—are pressing for other biofuels, not ethanol, and other feedstocks, not corn. Biofuels are a busy marketplace today with many competing players.
Consequently, what is now and what might be are likely to be far different. Ten years from now, ethanol's feedstock is likely to be cellulose, processed in a completely different way from what is done today.
The Department of Energy is funding $250 million in research to develop enzymes to break down cellulose from plants whose biomass volume exceeds corn's to avoid corn's need for intensive farming. Recently, researchers at the University of Minnesota found that a mix of native prairie grasses could provide more biomass per acre than corn or cellulosic energy crops without displacing food products, ripping up animal habitat, or increasing fertilizer use (Science 2006, 314, 1598).
Through the millennia, says Jason Hill, one of the paper's authors and a research associate at Minnesota's department of applied economics, complementary plant species have thrived in indigenous soils with no anthropogenic inputs. Capturing and obtaining biofuels from their biomass could provide a cheap feedstock with little energy input and good carbon removal (C&EN, Dec. 18, 2006, page 40).
Also, a recent industry report says using corn stover as well as corn kernels could significantly increase ethanol production without greatly affecting current corn uses or increasing corn acreage (C&EN, Nov. 20, 2006, page 58).
Meanwhile, today's fuel-use patterns could be overhauled through vehicle efficiency. A 3% increase in efficiency would displace more gasoline than was saved through last year's record ethanol production. The current vehicle efficiency standard was set in the 1970s and was required to be met in 1985, more than 20 years ago. In the future, a drive for better efficiency could force ethanol to compete with electric cars and fuel cells, as well as gasoline.
What's clear is that corn-based feedstock is likely to be the start of a biofuels market, not its end. Innovation and science in this new marketplace have the power to transform biomass-based transportation fuels in the same way they transformed the petrochemical industry in the past century. The future may be cloudy, but it is exciting, and for chemists, it doesn't get much better than that.