Prospecting Biofuels
by Nick Sutcliffe and Alan Mencin '79

If you heat wood to approximately 500 degrees Celsius in the absence of oxygen, you get pyrolysis oil—a flammable liquid that can be used to make liquid fuels or a variety of chemicals. If you heat wood to greater than 700o and include a small amount of oxygen and steam, you get synthesis gas, or syngas, which, among other things, will run a combustion engine, generate electricity, or yield a variety of liquid fuels. All this from wood—or switchgrass, or straw, or just about any dried cellulosic biomass.  And there are many other ways to convert biomass to useable forms of energy.

However, despite such potential, much of the science surrounding biofuels is poorly understood, and most technologies for industrial-scale production are in their infancy. To help advance understanding, Colorado School of Mines has entered into a partnership with three Front Range research institutions and several private corporations to form the Colorado Center for Biorefining and Biofuels, also known as C2B2. The collaboration includes the University of Colorado at Boulder (CU); Colorado State University (CSU); the National Renewable Energy Laboratory (NREL); Mines; and more than 10 private corporations including Chevron, ConocoPhillips, Dow Chemical and Shell Global Solutions.

Interest in industrial-scale production of biofuels has been growing for some time, driven by various arguments from diverse political and ideological points of view. For example, many believe that reducing the country’s dependence on foreign oil increases national security. Others point out that the diminished use of fossil fuels will slow the accumulation of greenhouse gases in the atmosphere. And still others point to the economic boost biofuels would give to American agriculture.

To explore how much energy America could generate from domestically produced biomass, the U.S. Department of Energy and the Department of Agriculture completed a joint research project in 2005 known as the “Billion Ton Study.” They concluded that by making relatively moderate changes to agricultural and forestry practices, the U.S. could sustainably provide sufficient biomass for one-third of its transportation fuel needs using existing conversion technologies.

While the potential is evident on paper, if the U.S. is going to get anywhere near such a lofty goal in practice, the science must be better understood and complex new systems engineered. Therein lies the mission of C2B2, which is the
first major initiative of the recently established Colorado Renewable Energy Collaboratory signed in Feb. (see story p. 6).

Chemical Engineering Professor John Dorgan, who is the C2B2 site director for the Mines campus, points out that there are three primary pathways—biochemical, chemical and thermochemical—for converting biomass into electrical power or useable fuels. The biochemical platform, currently the most widespread, involves breaking biomass down into simple sugars that can be fermented into ethanol. An example of chemical conversion is biodiesel, which involves growing crops rich in triglycerides (such as soybeans), extracting their oils and chemically converting them into liquid fuel. There are a variety of thermochemical conversion methods, most of which involve heating biomass to produce either syngas or pyrolysis oil.

Biochemical Conversion
By far the most popular biofuel in the U.S. is ethanol, and production has skyrocketed in recent years. At current rates, we’ll produce in excess of 5 billion gallons during 2007, up from 3.7 billion gallons in 2005. Almost all of this is produced through the biochemical conversion of sugars, with starch from corn grain serving as the primary feedstock.

Corn is a particularly convenient feedstock because it is so easily broken down into fermentable sugars such as glucose. Under the right conditions, glucose is metabolized by specific microbes, commonly called yeast, to produce ethanol. When ethanol concentrations reach about 14 percent by volume, the microbes die and the fermentation liquid, or “beer,” is distilled to obtain pure ethanol.

Although this approach is successfully yielding large quantities of ethanol, it is expensive and the industry is propped up by a 51-cents-per-gallon subsidy. The use of corn grain as the feedstock inflates the price considerably, and switching to a production process that utilizes cellulosic feedstocks (for example, wood, grasses and corn stover) is viewed by many as the key to lower costs.

Cellulose, the most abundant organic compound on earth, is a complex polysaccharide composed entirely of glucose. However, unlike starch, it is hard to break down. A triumph of evolutionary design, it is the biological equivalent of armor plate and has become the fundamental building block of the plant kingdom. In searching for a chink in the armor that would allow cellulose to be easily and inexpensively hydrolyzed into simple sugars, researchers have developed an innovative new process. This approach employs heat, sulphuric acid and enzymes to convert cellulose into its constituent sugars, and it is expected to be economically feasible in the not-too-distant future.

Fermentation has some similarly promising technologies on the horizon. Along with glucose, hydrolysis of cellulosic feedstocks yields additional five- and six-carbon sugars which cannot be fermented into ethanol by naturally occurring yeast. Genetically engineered yeasts are currently available that can metabolize these sugars, thereby increasing the efficiency of the overall conversion process, but their use is not yet cost competitive.

Chemical Conversion
Ethanol is only one of several biofuels the energy industry is taking seriously—another is biodiesel. Made from vegetable oil, this organic liquid fuel can be manufactured at room temperature using a rather simple chemical conversion process. In the presence of a catalyst and an alcohol, the triglyceride (fat) molecule is converted into fatty acid esters and glycerin. Once the glycerin has been removed, the resulting fatty acid esters provide an adequate substitute for petroleum-based diesel in almost every application. The drawback is cost: Production is expensive and the industry’s growth is currently supported with subsidies ranging from 50 cents to $1 per gallon.

A more economical feedstock would reduce prices, and one promising alternative is oil from algae, which can be produced much more intensively than traditional crops. While soybeans typically yield about 48 gallons of oil per acre annually, algae, grown in carefully monitored shallow, open ponds or clear plastic tubes, have the longer term potential of producing yields upwards of 10,000 gallons of oil per acre. Although the process is capital intensive and requires large quantities of water, carbon dioxide and nutrients, its potential has captured the interest of capital investment markets and the energy industry.

A synthetic diesel fuel can also be made by introducing heated animal or vegetable oils into a hydrogen-rich environment in the presence of a catalyst. Called renewable or “green” diesel, it is nearly indistinguishable from the petroleum-based product and is the focus of a recently announced joint venture between ConocoPhillips and Tyson Foods.

Thermochemical Conversion
Turning biomass into a useable fuel source via a thermochemical conversion process can take a variety of paths, all of which involve heating biomass in either low- or no-oxygen environments. When cellulosic biomass is heated in the absence of oxygen (a process known as fast pyrolysis), the main product is bio-oil, which can be burned as a substitute for petroleum-based fuel oil in boilers. Alternatively, when cellulosic biomass is heated with a limited amount of oxygen and steam (a process known as gasification), the main product is synthesis gas, or syngas. Among other uses, this flammable combination of carbon monoxide and hydrogen can be burned in a turbine, fed into a solid oxide fuel cell to produce electricity, or converted into a variety of liquid fuels using Fisher-Tropsch processes.

Before these processes can be applied on a commercial scale, however, numerous problems must be solved and the chemistry better understood. Syngas made from biomass contains ash and tars, which can damage turbines and degrade catalysts in solid oxide fuel cells. Understanding how to deliver a clean supply-stream of biomass-produced syngas has researchers busy around the world, including Professor Andy Herring, in the Chemical Engineering Department. Understanding how to engineer solid oxide fuel cells so they tolerate supply streams of unscrubbed syngas is a research focus of Tony Dean, the William K. Coors Distinguished Professor in Chemical Engineering.

The C2B2 Partnership
C2B2 brings together four diverse research institutions that encompass the full spectrum of biofuel- and biorefining-relevant expertise: CSU has world-class capabilities in the agricultural sciences, as well as the internationally recognized Engines and Energy Conversions Laboratory; CU-Boulder is well known for its expertise in biological and chemical engineering, molecular and cellular biology, and biochemistry; NREL has highly specialized laboratory facilities and decades of experience researching biomass energy conversion technologies; and Mines brings a wealth of knowledge in refining, chemical engineering, materials engineering and fuel cell technologies.

The goal of C2B2 is to develop new technologies and advance them into the private sector as quickly as possible. Companies participate in C2B2 with payment of a membership fee that funds shared research initiatives. In so doing, they gain access to this rich pool of expertise, as well as the research and development resources of sponsoring industrial partners.

The partnership has received strong political support at the state level. The formation of the Renewable Energy Collaboratory can be traced back to the 2006 Renewable Energy Summit sponsored by Sen. Ken Salazar’s office. His staff has remained actively involved by facilitating negotiations and helping to frame the final C2B2 agreement. After campaigning on a strong renewable energy platform, Gov. Bill Ritter has embraced C2B2. And on the Mines campus, President Bill Scoggins is enthusiastic, seeing it as “substantive and timely progress toward finding solutions to [our energy] challenges.” On the front lines of C2B2 research, Tony Dean is particularly upbeat about the School’s role: “We are a key player on a big-league team. We’ve got a lot to offer and we have a lot to gain in terms of sharing knowledge and sharing facilities. Having NREL so close is a major advantage.” With the partnership barely two months old, it’s impossible to predict where C2B2 will lead, but with four multinational corporations on board, exceptional research capacity at hand and worldwide interest in biofuels at an all-time high, the future looks bright.