ScienceWeek

SCIENCE POLICY: ON SUSTAINABLE HYDROGEN PRODUCTION

The following points are made by John A. Turner (Science 2004 305:972):

1) In his 2003 State of the Union Address, US President Bush proposed "$1.2 billion in research funding so that America can lead the world in developing clean, hydrogen-powered automobiles." Since that time, articles both pro and con have buffeted the whole concept.

2) The hydrogen economy (1) is not a new idea. In 1874, the science-fiction writer Jules Verne (1828-1905), recognizing the finite supply of coal and the possibilities of hydrogen derived from water electrolysis, made the comment that "water will be the coal of the future" (2). Rudolf Erren in the 1930s suggested using hydrogen produced from water electrolysis as a transportation fuel (3). His goal was to reduce automotive emissions and oil imports into England. Similarly, Francis Bacon (1561-1626) suggested using hydrogen as an energy storage system (4).

3) The vision of using energy from electricity and electrolysis to generate hydrogen from water for transportation and energy storage to reduce environmental emissions and provide energy security is compelling, but as yet remains unrealized. If one assumes a full build-out of a hydrogen economy, the amount of hydrogen needed just for US transportation needs would be about 150 million tons per year (5). One must question the efficacy of producing, storing, and distributing that much hydrogen. Because energy is required to extract hydrogen from either water or biomass so that it can be used as an energy carrier, if the United States chooses a hydrogen-based future it needs to think carefully about how much energy we need and where it is going to come from. In addition, sustainability must be a hallmark of any proposed future infrastructure. What energy-producing technologies can be envisioned that will last for millennia, and just how many people can they support?

4) Hydrogen can be generated from water, biomass, natural gas, or (after gasification) coal. Today, hydrogen is mainly produced from natural gas via steam methane reforming, and although this process can sustain an initial foray into the hydrogen economy, it represents only a modest reduction in vehicle emissions as compared to emissions from current hybrid vehicles, and ultimately only exchanges oil imports for natural gas imports. It is clearly not sustainable.

5) Coal gasification could produce considerable amounts of hydrogen and electricity merely because of the large size of available coal deposits. Additionally, because of its relatively low cost, it is often cited as the best resource for economically producing large quantities of hydrogen. However, the energy required for the necessary sequestration of CO2 would increase the rate at which coal reserves are depleted; converting the vehicle fleet to electric vehicles and generating that electricity from "clean coal" or making hydrogen as a possible energy carrier would accelerate that depletion. Couple that to a modest economic growth rate of 1%, and US 250-year coal reserves drop to 75 years or so, which is not at all sustainable. That leaves solar-derived, wind, nuclear, and geothermal energy as major resources for sustainable hydrogen production. The hydrogen production pathways from these resources include electrolysis of water, thermal chemical cycles using heat, and biomass processing (using a variety of technologies ranging from reforming to fermentation).

References (abridged):

1. For the purpose of this discussion, the author uses the following definition of the hydrogen economy: the production, storage, distribution, and use of hydrogen as an energy carrier.

2. Jules Verne, The Mysterious Island, 1874 http://www.literature-web.net/verne/mysteriousisland

3. P. Hoffmann, The Forever Fuel: The Story of Hydrogen (Westview Press, Boulder, CO, 1981

4. D. Gregory, Sci. Am. 228, (no. 1), 13 (January 1973)

5. Basic Research Needs for the Hydrogen Economy, available at http://www.sc.doe.gov/bes/reports/files/NHE_rpt.pdf (current U.S. production is about 9 million tons of hydrogen per year).

Science http://www.sciencemag.org

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SCIENCE POLICY: ENERGY RESOURCES AND GLOBAL DEVELOPMENT

The following points are made by J. Chow et al (Science 2003 302:1528):

1) Energy is the lifeblood of technological and economic development. The energy choices made by the US and the rest of the world have ramifications for economic growth; the local, national, and global environment; and even the shape of international political alliances and national defense commitments. Countries of varying levels of wealth also face different energy challenges (1).

2) Although estimates vary, the world's proved, economically recoverable fossil fuel reserves include almost 1 trillion metric tons of coal, more than 1 trillion barrels of petroleum, and over 150 trillion cubic meters of natural gas (2). In addition to fossil fuels, mineral resources important to energy generation include over 3 million metric tons of uranium reserves (3). To put this into context, consider that the world's annual 2000 consumption of coal was about 5 billion metric tons or 0.5% of reserves. Natural gas consumption was 1.6% of reserves, whereas oil was almost 3% of reserves, and nuclear electricity generation consumed the equivalent of 2% of uranium reserves (4).

3) Reported recoverable reserves have tended to increase over time, keeping pace with consumption, and now are at or near all-time highs. In relation to current consumption, there remain vast reserves that are adequate for continued worldwide economic development, not even accounting for reserves that will become economically recoverable through continuing discovery and technological advance (5). Thus, it seems that the world is not running out of mineral fuels.

4) Large fossil fuel reserves are concentrated in a small number of countries, with half of the low-income countries and more than a third of the middle-income countries having no fossil fuel reserves whatsoever. If energy reserves were necessary for economic development, several of the world's poorest nations would be disadvantaged. However, many energy-bereft countries (such as Japan) have become highly developed through sufficient access to international energy markets. Conversely, Nigeria possesses substantial reserves but remains one of the poorest countries, its energy production activities mired in corruption. Thus, simply possessing large fossil energy reserves is of questionable value to a country's development if there is no well-functioning and adequately equitable socioeconomic system enabling it to extract and deploy those energy resources for their full social benefit.

5) In summary: In order to address the economic and environmental consequences of our global energy system, the authors consider the availability and consumption of energy resources. Problems arise from our dependence on combustible fuels, the environmental risks associated with their extraction, and the environmental damage caused by their emissions. Yet no primary energy source, be it renewable or nonrenewable, is free of environmental or economic limitations. As developed and developing economies continue to grow, conversion to and adoption of environmentally benign energy technology will depend on political and economic realities.

References (abridged):

1. The authors analyzed year 2000 data from 211 countries, using the World Bank's method of distinguishing between low-, middle-, and high-income countries according to GNI/pop. The authors refer to low- and middle-income countries jointly as "developing countries", and high-income countries are considered "industrialized or developed countries". Of the countries considered in this analysis, approximately 75% fall into the former category. Countries are low-income if GNI/pop is less than US $750 (69 countries, including the Congo, India, and Indonesia); middle-income if GNI/pop is between US $750 and $9250 (85 countries, including Argentina, Mexico, and Turkey); or high-income if GNI/pop is greater than US $9250 (57 countries, including the United States, Japan, and Western Europe). The authors have also identified those countries comprising the poorest 10% (such as Cambodia, Chad, and Tajikistan) and the richest 10% (such as the United States, Singapore, and the United Kingdom). The developing-country group is heterogeneous in resource endowments and development conditions, whereas classification as a developed country does not imply a preferred or final stage of development. GNI/pop is a convenient criterion among many metrics for levels of development and does not necessarily reflect development status. GNI, GDP, and population data for 2000 are drawn from the World Development Indicators 2002, published by the World Bank. Population, GNI/pop. 2. These numbers are based on year 2001 data. Reserves include only resources that are identified as economically and technically recoverable with current technologies and prices. Other resources with foreseeable or unknown potential for recovery exist but are not included in this report, because estimates are often highly speculative and unreliable, particularly estimates of resources in developing countries. Reserve estimates tend to expand overall with time, as technology increases the number of economically recoverable reserves.

3. These numbers are based on year 2001 data. This estimate includes reasonably assured resources (RARs) identified by the IAEA and does not include other potential resources and secondary supplies from reprocessed uranium, reenriched uranium, and highly enriched uranium from the dismantlement of nuclear weapons.

4. However, 42% of uranium used for nuclear electricity generation is currently supplied by secondary sources, so the actual consumption of uranium reserves is less than this estimate suggests.

5. It should be noted that the three major fossil fuels are not perfect substitutes for each other, particularly in the short term. Petroleum derivatives offer versatility in use and ease of transport that make them ideal for the transportation sector. Coal is the most abundant fossil fuel but generates the most airborne pollutants. Hence, coal-fired electricity generation plants are gradually giving way to gas-fired plants. Natural gas is the cleanest-burning and most energy-efficient fossil fuel, but supply is currently hindered by insufficient extraction and transport infrastructure, such as regasification and storage facilities for importing liquefied natural gas from overseas.

Science http://www.sciencemag.org

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ON HYDROGEN AS AN ENERGY SOURCE

The following points are made by R.D. Cortwright et al (Nature 2002 418:964):

1) Concerns about the depletion of fossil fuel reserves and the pollution caused by continuously increasing energy demands make hydrogen an attractive alternative energy source. Hydrogen is currently derived from nonrenewable natural gas and petroleum(1), but could in principle be generated from renewable resources such as biomass or water. However, efficient hydrogen production from water remains difficult and technologies for generating hydrogen from biomass, such as enzymatic decomposition of sugars(2-5), steam-reforming of bio-oils, and gasification, suffer from low hydrogen production rates and/or complex processing requirements.

2) The authors report a demonstration that hydrogen can be produced from sugars and alcohols at temperatures near 500 K in a single-reactor aqueous-phase reforming process using a platinum-based catalyst. The authors report they are able to convert glucose -- which makes up the major energy reserves in plants and animals -- to hydrogen and gaseous alkanes, with hydrogen constituting 50% of the products. The authors find that the selectivity for hydrogen production increases when they use molecules that are more reduced than sugars, with ethylene glycol and methanol being almost completely converted into hydrogen and carbon dioxide. The authors suggest these findings indicate that catalytic aqueous-phase reforming might prove useful for the generation of hydrogen-rich fuel gas from carbohydrates extracted from renewable biomass and biomass waste streams.

References (abridged):

1. Rostrup-Nielsen, J. Conversion of hydrocarbons and alcohols for fuel cells. Phys. Chem. Chem. Phys. 3, 283-288 (2001)

2. Kumar, N. & Das, D. Enhancement of hydrogen production by enterobacter cloacae IIT-BT 08. Process Biochem. 35, 589-593 (2000)

3. Woodward, J. et al. Enzymatic hydrogen production: Conversion of renewable resources for energy production. Energy Fuels 14, 197-201 (2000)

4. Yokoi, H. et al. Microbial hydrogen production from sweet potato starch residue. J. Biosci. Bioeng. 91, 58-63 (2001)

5. Woodward, J., Orr, M., Cordray, K. & Greenbaum, E. Enzymatic production of biohydrogen. Nature 405, 1014 (2000)

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