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7 Challenges for the Chemical Sciences in the gist Century Ralph P. Overend, National Renewable Energy Laboratory Predictions indicate that in the future energy usage will grow exponentially. In response to this growing need, it is also expected that new energy sources will be developed. The plot in Figure 7.1 depicts shares of the different energy forms. Basically, society has moved from a renewable, biomass, and wood economy in 1850 to a coal, oil, and gas economy by the late 1960s. Key to the trend in increased future energy consumption is the anticipated growth of new energy sources: hydra, nuclear, intermittents that are a combina- tion of solar and photovoltaic, and deep thermal sources. The most important message from Figure 7.1 is that somewhere between the years 2025 and 2050, there will be multiple sources of primary energy. Development of the various of energy sources is the first challenge to chemists and chemical engineers. There is no single solution. In addition to this challenge, the possibilities of carbon capture, geological sequestration, viable hydrogen systems, energy storage systems (these are crucial), and commercial biomass energy must all be considered. Often, the use of biomass is considered a cycle in which the sun shines on a custom-grown plantation of biomass material for energy. This energy is then con- sumed in a convergence system, with residual carbon dioxide and water vapor escaping into the atmosphere only to be fixed back into the same plantation by photosynthesis. The truth is that the biomass renewable carbon system in the world's economy is very large. We eat bread. We wear cotton shirts. We live in wooden buildings. The fiber component in the United States alone represents between 5 to 7 percent of the total energy input to the U.S. economy. Crops and animals are not grown specifically for energy but instead are part of a sensible cycle using residues. Under those circumstances, biomass has an extremely large component contribution to this future energy supply. 45
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46 1 500 1 000 500 ENERGY AND TRANSPORTATION u 1860 1900 1940 1980 2020 Surprise Geothermal Solar Biomass Wind Nuclear Hydro Gas Oil &NGL _ Coal Traditional Biological 2060 FIGURE 7.1 Shell's sustained growth scenario. The breakdown in growth of various energy forms is expressed in exajoules versus year. Source: The Evolution of the World's Energy Systems, 1995, Shell International Ltd. London. Per capita power available in the United States has risen dramatically, from 200 to 300 watts per person in 1850, to close to 100 kilowatts per person today. Most is due to automobiles, which use between 60 and 130 kW. During the time period around World War I, the percentage of total energy from coal, oil, and gas was nearing 80 percent, concurrent with the mass use of the internal combustion engine during the war. Over the years a virtually unidimensional system has been created into which very diverse energy resources must be fit. That is a major challenge to scientists today. The mechanical sciences have been the lubrication and the friction in a sym- biosis between the petroleum industry and the transportation industry. On one side, refiners make different fuel, which have created the discipline of chemical engineering. On the other side, fuels conversion specialists have worked to make more efficient engines. In the 1970s this unidimensional energy system was causing significant prob- lems. Urban smog became the predominant feature of the West Coast, lead in gasoline was identified as a public health problem, and the first oil crisis occurred. However, these factors did not serve to hold public interest in fuel economy. Fuel economy became a popular topic because of clean air actions. In the early 1990s the Partnership for a New Generation of Vehicles attempted to put together a vehicle that had high fuel economy, high emissions control, and very good environmental performance while safety and affordability were still maintained. These initiatives are beginning to have an impact. In its energy predictions for 2030, the Finnish National Research Council shows that despite environmental issues the internal combustion engine has been actually saved from obsolescence by changes to the engine itself. These changes include exhaust gas recirculation, multipoint fuel injection, closed-loop air ratio
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CHALLENGES FOR THE CHEMICAL SCIENCES IN THE 21ST CENTURY 47 control, direct injection spark ignition, and small diesel engines. Other improve- ments were made simultaneously: three-way catalytic converters, unleaded gaso- line, detergent additives, oxygenated gasolines, and reformulated fuels. These scientific advances were made by multidisciplinary teams, including chemists and chemical engineers. The development of catalysts in the engine system has evolved and has shown a significant impact. The 1970 engine had massive production of carbon monoxide, hydrocarbons, and nitrogen oxide. The way to control emissions was the three- way catalyst, but the overall energy efficiency was only 20 percent. Diesel engines reduced the levels of emissions and increased efficiency to 25 percent, but they have high particulate emissions. Oxycatalysts with a filtration system increases efficiency to 32 percent, but high nitrogen oxide emissions are still present. This trend involves not just engines and the catalyst systems but also the fuels. When scientists talk about getting 80 miles per gallon, what is actually meant is 0.5 MJ per passenger-kilometer. Presently, the overall transportation system, not just autos, is actually running around 2 to 3 MJ per passenger- kilometer. There are many ways to improve efficiency besides working on the automobile. The first way to improve efficiency is to use electricity. However, an electric system that can act like the gasoline or natural gas distribution system does not yet exist. Another problem with electricity is that batteries are still insufficient to run a vehicle for a day. Hydrogen is a solution but, like electricity, does not have the infrastructure required for mass production and use. Finally, many resources such as corn and forest residues can be converted through syngas into methanol. The question then becomes how the methanol is used: directly, through fuel cells, or as oxygenates in the traditional combustion system. The diversity of possibili- ties is part of the challenge. Many of the needed engineering and science tools exist, but there is a lack of focus.
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48 ENERGY AND TRANSPORTATION There are many predictions for the future. They range from the fuel cell electric drive vehicle by 2015 to the fall of pure petroleum fuels by 2030. A vision for the future based on the leaf may be considered. A leaf accumulates carbon dioxide, water, and photons; stores energy; and releases energy for its needs when it is wanted. Perhaps someday the personal automobile will, similar to the leaf, require no fuel other than sunlight. The skin would receive all the energy, be recyclable, be the energy storage medium, and use regenerable systems so that the solar energy received each day into the vehicle would be enough to provide for personal transportation needs. There are certainly some disadvantages to such a system, but these are merely challenges that must be overcome by chemists and chemical engineers.) There are no single solutions to future energy needs, so chemists, chemical engineers, and other scientists must have a robust and diverse strategy to meet this need. The future will be varied with respect to energy. Energy supply and demand, and therefore infrastructure, may even be regionally different. Chal- lenges lie in these many different production systems. iOne of the challenges is the amount of power possible from such a system. If a large car has an incident area of 7.5 m2, this equates to about an available solar power of 10 kW. The current power requirement for an automobile to cruise at about 60 mph is approximately 40 HP. This is about 50 kW, which is where the design target is for most fuel cell systems. During this drive, even at 100% efficiency, the solar flux is insufficient for driving. In this case, an additional charging source will be necessary.