Dartmouth Engineer - The Magazine of Thayer School of EngineeringDartmouth Engineer - The Magazine of Thayer School of Engineering

Power Plants

In the drive for alternative fuels, Professors Lee Lynd and Charles Wyman explain the growing role of ethanol.

By Genevieve Chan

The latest spikes in gasoline prices have reawakened the public to the need for viable alternatives to finite and vulnerable supplies of oil. The ideal alternative fuel would be both economically and environmentally sound. It would be renewable, plentiful, sustainable, and clean. And, for widespread use in motor vehicles, it would be easily stored and distributed.

This is a tall order — and an increasingly urgent one. The U.S. transportation sector alone consumes a staggering 130 billion gallons of gasoline each year. Beyond draining a decreasing resource, motor vehicles produce 32 percent of the nation’s carbon dioxide emissions that contribute to global climate change.

Scientists and engineers are driving down several promising but challenging paths to break the transportation sectors’ thirst for gasoline. One is electric batteries, used in today’s hybrid cars. At this point, hybrids still require gasoline, and current battery technology cannot support all-electric long-distance travel. Another is hydrogen, a potentially clean-burning energy source, with water vapor as its only byproduct. Substantial technical challenges must be overcome to economically produce, store, and transport hydrogen. Hydrogen fuel cells, the most promising way to efficiently utilize hydrogen, are still in early stages of development and require a radical departure from the internal combustion engine.

Another alternative is ethanol.

Photograph courtesy of Paul Antonin/Getty Images.
Photograph courtesy of Paul Antonin/Getty Images.

Ethanol — including ethanol produced from corn and from cellulosic biomass — offers both immediate and long-term benefits, according to Thayer Professor Lee Lynd and adjunct professor Charles Wyman, until recently the school’s Paul E. and Joan H. Queneau Distinguished Professor in Environmental Engineering Design. Because ethanol is made from plants that are continually regenerated, it is renewable and potentially sustainable. It also has the potential to be carbon-dioxide neutral. And as a liquid, ethanol can be readily phased into the current infrastructure without much change to cars or fuel distribution systems.

“Ethanol is already widely used and accepted for blending with gasoline,” says Wyman, a former director of the National Renewable Energy Laboratory’s alternative fuels division.

In fact, more than four billion gallons of ethanol made from corn and other grain starch are added to gasoline in the United States annually to increase octane and help reduce tailpipe emissions. Brazil makes a similar amount of ethanol from cane sugar and uses it in gasoline blends and as a pure fuel. Several models of “flexible fuel vehicles” already on the road can run on any combination of gasoline and ethanol. The blend E85, consisting of 85-percent ethanol, is available at several hundred refueling stations in 30 American states.

Ethanol isn’t an exact match for gasoline. It has a lower energy density. One gallon of ethanol contains the energy equivalency of 2/3 gallon of gasoline — 76,000 BTUs compared to gasoline’s 112,000. But Lynd doesn’t see this as a big problem. “At most, vehicles could have larger fuel tanks to compensate for the difference,” he says.

Fields and Yields

The ethanol used now is mainly produced from edible crops such as corn in the United States and sugar in Brazil. Current ethanol production methods use simple enzymes to break down starches to simple sugars, which are then fermented into ethanol.

Lynd and Wyman are working to make it feasible to produce ethanol out of lignocellulosic materials­ — grass, wood, and various agricultural and forestry wastes. “Cellulosic biomass at $40 per ton is competitive with oil at $13 per barrel”, says Lynd, “hence we have a cost-competitive raw material. The challenge is to reduce the cost of processing.” To that end, Lynd and Wyman are using genetically engineered bacteria and bioengineered enzymes to help break down the plant cellulose into sugars quickly and at high yield.

ECONOMIC CATALYSTS:  Lynd, right, and Wyman believe that genetically engineered bacteria and bioengineered enzymes will reduce the cost of converting cellulosic biomass to ethanol.  Photograph by Joe Mehling ’69.
ECONOMIC CATALYSTS: Lynd, right, and Wyman believe that genetically engineered bacteria and bioengineered enzymes will reduce the cost of converting cellulosic biomass to ethanol. Photograph by Joe Mehling ’69.

Biomass comes in a wide variety of forms, including agricultural residues such as corn stover (the stalks and leaves left over from corn production), sugarcane bagasse (the cellulosic fiber residue left after extracting sugar from the cane), and wheat straw; forestry wastes such as bark and wood chips; and dedicated energy crops such as willows, eucalyptus, and switchgrass, a tall perennial grass that requires minimal irrigation, tilling, and herbicides to produce high yields.

Raising fast-growing plants and utilizing stover and other forms of biomass are keys to maximizing energy yields per acre. According to Wyman, an acre of land can produce greater amounts of biomass than corn. Moreover, low-grade land that may be unsuitable for producing corn may still be viable for producing biomass.

Wyman and Lynd are working on several fronts in the biomass energy field. Wyman leads the Consortium for Applied Fundamentals and Innovation, a collaboration between five universities, Genencor International, and the National Renewable Energy Laboratory. The consortium’s goal is to compare and improve pretreatment technologies vital for maximizing yields of ethanol from cellulosic biomass.

Lynd leads a team of students and research associates at Thayer School that is collaborating with Advanced Bioconversion Technologies of Lebanon, New Hampshire, to develop a strain of Clostridium thermocellum, a rapid cellulose-fermenting microorganism that can produce ethanol at high yields and concentrations from pretreated substrates.

Lynd is also a leader in a 10-institution project called the Role of Biomass in America’s Energy Future (RBAEF). Sponsored by the U.S. Department of Energy, the Energy Foundation, and the National Commission on Energy Policy, the project focuses on identifying and evaluating paths by which biomass can make a large contribution to energy services and determining what can be done to accelerate biomass energy use and the timeframe in which associated benefits can be realized.

Conversion Factors

The economics of ethanol production are growing clearer. A study by David Pimentel of Cornell and Tad Patzek of UC Berkeley argues that corn-to-ethanol production requires more energy to produce than it provides. However, numerous other studies, such as one led by Hosein Shapouri of the U.S. Department of Agriculture’s Office of the Chief Economist, show that corn-to-ethanol processes provide a net energy gain of at least 67 percent. And according to new research by Argonne National Laboratory researcher and RBAEF member Michael Wang, improved technology has reduced energy use and operating costs in corn ethanol production.

Cellulosic biomass requires more intense processing than corn because the sugars in cellulose are more tightly bound. But cellulose processing also yields lignin, and, says, Wyman, “Hypothetically, after you break down the cellulose and hemicellulose to release the sugars for fermentation to ethanol, you can then burn the lignin to provide all the heat and electricity needed to operate the factory with some excess left for sale.”

“Thus,” adds Lynd, “there is widespread consensus that the energy balance for cellulosic ethanol is decidedly positive.”

Another concern about biomass energy production is that it would divert agricultural resources away from food crops. Some people wonder if there is enough land to grow sufficient quantities of biomass. Would the environmental footprint be too big?

Wyman doesn’t see land use as an either-or situation. “With most biofuels, you remove the energy and are still left with the protein for food — or feed for livestock,” he says. “The dried grain byproduct resulting from processing corn into ethanol contains more protein than the original unprocessed grain.”

According to Lynd, the very fact that cellulosic biomass can be grown makes it a leading replacement for fossil fuels — and a source of global social and economic benefits. “There is no question that the ability to grow biomass is much, much more widely distributed than oil,” he says. “As a locally produced, renewable fuel, ethanol has the potential to diversify energy portfolios as well as lower dependence on foreign oil.” He points out that some of the world’s most attractive areas for biomass production are also among the poorest. “Which regions would be the big biomass producers? Africa and South America are way high, and Asia also has significant biomass potential,” he says.

As Indiana Senator Richard Lugar and former CIA director R. James Woolsey put it in an article in Foreign Affairs, growing biomass to produce cellulosic ethanol has the potential to “democratize the world’s fuel market.”

Moving Forward

The last two years have seen a huge upswing of support for biomass as a viable sustainable replacement for petroleum, not just an interim transition strategy. Lynd attributes this significantly to RBAEF’s efforts to articulate future scenarios. In fact, RBAEF has detailed more than 20 mature process technology scenarios for producing a broad range of fuels and electrical power from cellulosic biomass. “The economics for many of these scenarios are highly competitive with established processes based on fossil fuels,” says Lynd. And he notes, “By a combination of approaches — incorporating biomass energy feedstock production into currently managed lands, high end-use efficiency, and use of high-productivity cellulosic crops — it is projected that a large fraction of U.S. mobility requirements could be met with little or no additional land beyond that already allocated to agriculture.”

“The RBAEF study has redefined the debate about the viability of biomass as a large-scale energy source,” says Tom Foust of the National Renewable Energy Laboratory. “The kind of long-term thinking the RBAEF project embodies is crucial but in short supply.”

“Industry is often constrained to taking a relatively short-term view by cash-flow expectations and other factors,” says Lynd. “Government should take a long-term view with the public interest in mind, but often does not. As an academic, I am trying to look to the future in part because I do not see others doing this.”

There are signs, however, that industry is taking some steps forward. The three major U.S. automobile manufacturers already make flexible fuel vehicles. Royal Dutch/Shell Oil has invested in Iogen, a Canadian-based cellulosic ethanol company. During the next five years, Lynd predicts, agricultural groups, fuel deliverers, and distributors will jointly establish a vertically-integrated biomass fuel supply chain that does not now exist.

Both Lynd and Wyman stress the importance such partnerships will have in developing alternative fuels — and in producing policies and technologies that deliberately promote energy efficiency and sustainability. “Efficiency leverages the other two goals: low environmental impact and a sustainable replacement for oil,” says Lynd. “If we continue to make decisions as if sustainability were unimportant, will it happen anyway? I think the answer’s no. But if we decide it’s important to plan for, then we can make great things happen.”

—Genevieve Chan is a freelance writer based in Norwich, Vermont.

For more photos, visit our Energy Technologies set on Flickr.

Categories: Features

Tags: climate change, energy, entrepreneurship, environment, faculty, research

comments powered by Disqus