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Research Opportunities and Challenges in the Energy Sector Alexis T. Bell, University of California, Berkeley Energy usage in the United States presently is largely from fossil fuels- petroleum, natural gas, and coal. Petroleum is used to produce transportation and heating fuels and to a smaller degree it is a source of chemicals and lubricants. Natural gas is used to produce electricity along with domestic and industrial heat- ing. Coal is largely used to produce electricity. In the 21st century this pattern of energy usage probably will not change significantly. The main reason is that carbon-based fuels will remain plentiful and low in cost. Examination of the reserve supply of fossil fuels indicates a substantial amount of petroleum still in the ground and accessible. At present consumption rates, and analyzing only proven reserves for fossil fuels, it is antici- pated that oil reserves will last for at least another 40 years, supplies of gas another 70 years, and coal supplies 200 years. If likely reserves that have not yet been discovered are included, fossil fuels will be plentiful for decades to come. In light of the supply predictions, what are the drivers for changing the nation's primary fuel sources? The first is a desire to reduce the nation's depen- dence on imported petroleum. The second driver is the need for clean-burning fuels, including gasoline containing less sulfur and diesel fuels that produce less soot, which would reduce the impact of vehicle emissions and other combustion sources on human health. A third and very significant motivator is the increasing concern about man-made carbon dioxide emissions being released into the atmosphere. The extent to which man-made carbon dioxide emissions contribute to global warming is still an issue of considerable debate. Analysis indicates that while the contribution to the total amount of this gas in the atmosphere from anthropogenic sources amounts to 3 to 4 percent, the problem is that carbon dioxide remains in 13
4 ENERGY AND TRANSPORTATION the atmosphere for a very long time and thus accumulates. If currently projected rates of fuel consumption continue, a doubling of carbon dioxide in the atmo- sphere is anticipated by the end of this century. Even though the question of whether man-made carbon dioxide emissions are responsible for global warming is still unresolved, there is a growing global consensus that these man-made carbon dioxide emissions must be reduced. Options for reducing man-made carbon dioxide emissions include improve- ments in the efficient use of carbon-based fuels. This goal could be achieved by moving to lighter-weight vehicles that consume less fuel and also by switching from gasoline to diesel fuel. With a threefold increase in efficiency, it is esti- mated that a two and one-half to threefold decrease in the amount of carbon emitted per mile driven would result. Another means to reduce man-made carbon dioxide emissions is sequestra- tion in the land or the ocean. When carbon dioxide is produced locally it may be possible to efficiently separate it from other gases, concentrate it, and dispose of it. A number of complex scenarios may be envisioned to accomplish this dis- posal, from pumping it into the ocean, to displacing methane in coal mines, to storage in depleted hydrocarbon reservoirs. FUELS WITH HIGHER HYDROGEN CONTENT One of the most promising means to mitigate carbon dioxide emissions is to either reduce the use of carbon-based fuels and/or increase the hydrogen content of the fuels that are used. Looked at historically, it is clear the trend in fuel use over the past 150 years has been toward fuels with progressively higher hydrogen- to-carbon content, starting with wood, moving to coal and petroleum, then to methane. If this trend continues, we will eventually move toward a nonfossil- based hydrogen economy. Over the past decade, natural gas usage increased by 20 percent, petroleum utilization increased by 12 percent, and coal use decreased by 6 percent. This trend indicates that for the near term at least there is already a noticeable increase in the use of more hydrogen-rich fuels. Natural Gas Natural gas has a high hydrogen-to-carbon content and is plentiful world- wide. It can be brought to market in four different ways pipelines, liquefied natural gas, conversion to electricity, or conversion to liquid products that can be pipelined. It is also possible to envision in the near future a natural gas refinery for which natural gas will serve as the principal feedstock. This type of facility would provide an effective means to use natural gas to produce electricity and liquid fuels while also allowing for the recovery of carbon dioxide on site that then could be sequestered.
RESEARCH OPPORTUNITIES AND CHALLENGES IN THE ENERGY SECTOR 15 One of the ways in which natural gas could be converted to liquid products is by Fischer-Tropsch synthesis. In this process, methane is reformed with steam and oxygen to produce a synthesis gas that is a mixture of carbon monoxide and hydrogen. The synthesis gas is then reacted over a catalyst to produce a variety of fuels. However, recently the most emphasis has been on the production of high- cetane, sulfur-free diesel fuel. Fischer-Tropsch fuels can be produced at the equivalent of $14 to $20 a barrel of oil, and plants with capacities of 10 to 100,000 barrels a day have either been built or designed.) Another liquid fuel that can be produced in a natural gas refinery is methanol. Methanol is itself a high-octane fuel used in racecars, and it is sulfur free. It can be reformed readily to hydrogen and carbon dioxide, and the hydrogen can be used for fuel cells. Direct methanol fuel cells convert methanol into protons, free electrons, and carbon dioxide, thus providing a safe and simple-to-use energy source.2 The byproducts of this type of fuel cell steam and carbon dioxide- are produced in such small amounts that these fuel cells are particularly environ- mentally friendly. However, methanol, while readily degradable, presents prob- lems. It has half the energy content of gasoline on a per-volume basis and has a much higher acute toxicity than gasoline. To use methanol as a common fuel would require modifications in the storage and delivery infrastructure. An alternative to methanol that possibly may be more attractive is dimethyl ether, which is produced by coupling two methanol molecules. Dimethyl ether provides a good substitute for liquefied petroleum gas. It burns very cleanly, it is a high-cetane sulfur-free smokeless diesel fuel, it can be easily reformulated to hydrogen and carbon dioxide, and it can readily be converted to gasoline using zeolites. Balanced against these benefits is the fact that dimethyl ether is very volatile and, similar to methanol, would require a new storage and delivery infrastructure. Biomass presents another option for mitigation of carbon dioxide in the atmosphere. The basic concept is to grow plants to provide cellulose that can be converted to ethanol with known technology and then concentrate the ethanol produced up to 100 percent and use it as a fuel. It is estimated that use of biomass could be a carbon dioxide-neutral technology, meaning that as much carbon dioxide is consumed as is returned to the atmosphere. It has been estimated that there is sufficient land mass available in the United States to replace the 1.3 x 10~i gallons per year of gasoline used in 20003 without substantially impacting land other- iG.N. Choi, S.J. Kramer, S.S. Tram, J.M. Fox III. July 9-11, 1996. "Economics of a Natural Gas Based Fischer-Tropsch Plant." First Joint Power and Fuel Systems Contractors' Conference. Pitts- burgh, PA. 2One issue to consider with direct methanol fuel cells is their relative efficiency compared to indi- rect methanol fuel cells. Direct methanol fuel cell anode catalysis is currently poor and requires a high overpotential. When comparing an indirect methanol fuel cell (reforming of methanol to hydrogen and carbon dioxide, feeding the hydrogen to a fuel cell) and a direct methanol fuel cell, the efficiency on an indirect methanol fuel cell system is much higher, thus the carbon dioxide emissions are lower. 3"Worried Drivers," ExxonMobil Corporation, Houston, TX, 2001.
16 ENERGY AND TRANSPORTATION wise used for agriculture. As with other fuels, ethanol would require change in the fuel infrastructure. Hydrogen Hydrogen in many respects may be the ultimate fuel. It is completely carbon free and sulfur free. It can be used for spark injection engines and can be com- bined with natural gas and burned in such engines as well. It is an ideal fuel for fuel cells, although problems with storage and distribution would require an entirely new infrastructure. There are a number of significant issues regarding hydrogen production and bringing it to market. Current technology requires a high water-to-methane ratio to avoid carbon deposition on the catalyst used for the reforming of methane. Electrolysis of water is an alternative, but if carbon-based fuels are used for elec- tricity generation, double the amount of carbon dioxide is produced per mile when compared to gasoline. Photovoltaic generation of hydrogen is attractive, but the silicon technology required for making energy through electrolyzed water is at present prohibitively expensive. The use of fuel cells running on hydrogen produced by the reforming of a liquid fuel has been much discussed as a fuel-efficient means of powering auto- mobiles. While this technology has been demonstrated, approximately 100 to 150 grams of noble metal principally platinum would be required per car using present technology. For reference, this is two orders of magnitude more precious metal per car than is required for the catalytic converter. Since at present roughly one half to one third of the world's supply of precious metals is being put into automobiles for use in automotive conversion technologies, it is hard to envision fuel cells as a widespread alternative for automobiles unless the requirements for precious metals can be reduced by one to two orders of magnitude, or other cata- lytic approaches are developed that do not require the use of precious metals. An additional challenge to the use of fuel cells for automobiles is response time. Currently, fuel cells have a response time of 15 seconds from 10 percent power to 90 percent. In order to be viable, this response time must drop to 1 sec- ond. Because they require liquid water to operate, a further challenge is to operate fuel cells in subfreezing temperatures. In addition, the current cost per kilowatt- hour for fuel cells must be reduced from $300 down to $45. OPPORTUNITIES FOR THE CHEMICAL SCIENCES To meet the challenges discussed above, research opportunities for the chemi- cal sciences may be envisioned in four areas. First, in carbon dioxide sequestra- tion, an understanding is required regarding how molecular carbon dioxide inter- acts with various species present in coal mines or other geological formations where carbon dioxide might be stored. It is particularly important to understand
RESEARCH OPPORTUNITIES AND CHALLENGES IN THE ENERGY SECTOR 17 carbon dioxide flow in permeable underground formations, as well as the geology and geochemistry of these formations, to ensure that large amounts of carbon dioxide do not escape back into the atmosphere. In order for methane to be used for energy, a number of developments must take place. New catalysts for the conversion of methane to oxygenated products are needed, particularly for transformation of methane to formaldehyde or methanol without first converting methane to syngas. Highly effective catalysts are also required to lower the reaction temperature and increase overall efficiency. Photovoltaics also require significant research activity in the chemical sciences. Low-cost methods are required for producing solar-grade silicon for photovoltaic cells. Better solar cell materials are needed than the presently uti- lized amorphous silicon. These materials must be more efficient without the use of heavy metals such as cadmium, tellurium, indium, and lead, which present significant environmental issues. An understanding of the degradation process of photovoltaic cells is needed, as is an answer to why these materials lose their effectiveness after prolonged exposure to the sun. Finally, there is a need to develop catalysts for the efficient photochemical conversion of water. A fourth area for research opportunities is in the development of fuel cells. There is a need to develop electrode materials for methanol-based fuel cells. This would allow for the use of liquid fuel directly without a reformer. Less expensive alternatives to Nation are required for fuel cell membranes. Rapid-response onboard reformers are also needed for potential use in conjunction with the fuel cell to convert liquid fuel to hydrogen. Requirements to Achieve these Goals In order for the chemical sciences to take advantage of the research opportu- nities outlined above and to achieve the goals set, two major requirements must be met. First, public policies must be set that signal the need for development and deployment of new technologies in the energy sector that meet four criteria: and 1. Technologies that are carbon efficient; 2. Technologies that enable carbon dioxide sequestration; 3. Technologies that enable the use of natural gas to produce liquid fuels; 4. In the longer term, technologies that enable the use of biomass, solar energy, and renewable sources of energy in general. A second major requirement is a major commitment toward federal support for energy-related research. In the 13-year period from 1985 to 1998, real dollar U.S. investment in energy research dropped 36 percent. Worldwide there was a 33 percent drop. This commitment should not be a short-term one lasting 1 to 2 years but rather a sustained investment over several decades.
