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4 Interface Challenges and Opportunities in Energy and Transportation James R. Katzer, ExxonMobil INTRODUCTION Future challenges in energy and transportation depend on the projected costs for energy options. These options are dependent on world energy demand, renew- able energy availability (particularly photovoltaic refining), hydrogen availability as an energy resource, and light-duty vehicle power train changes. In general, as the world's economies grow, the world energy demand also will grow. The magnitude of this growth is expected to be large from about 200 million barrels of oil equivalent a day to over 300 million barrels per day in 2020. Given the expected rates of economic growth, energy demand is expected to con- tinue to grow through 2050. Fossil energy sources will continue to dominate through at least the first half of the 21st century because they are plentiful, readily available, and fundamen- tally inexpensive. Currently, 75 million barrels of oil are consumed every day. By 2020 it is anticipated that 112 million to 114 million barrels of oil will be con- sumed daily. Availability of oil will not be a problem outside of geopolitical issues that may appear. In fact, in the last 20 years, the proven reserves of crude oil have increased by over 50 percent from a little over 600 billion barrels to about 1 trillion barrels of oil. RENEWABLE ENERGY Renewable energy technologies are expected to grow significantly. How- ever, over the next 20 years even with this rapid growth, renewable wind and solar energy will contribute only about 1 million barrels of oil equivalent per day 23
24 ENERGY AND TRANSPORTATION of energy out of 300 million in 2020. Beyond 2020, growth of renewable energy technologies could be very rapid, but it is projected that this technology will produce less than 3 percent of the total energy demand. The main forms of renewable energy have a significant hurtle in terms of cost. While there appears to be a consensus for increased use of renewables for electricity generation the largest user of primary energy at present the cost of renewables must be addressed if this is to take place. Significant progress has been made in reducing the cost of renewables, but they are still limited in applicability by cost. Costs can be expected to decrease in the future, but the rate and extent will be critical to the rate of growth of renewables. Photovoltaics and New Materials Although the costs of generating electricity using most sources of renewable energy are still very high, they have been decreasing over the past 20 years and should continue to decrease. Wind is currently cost competitive for electricity generation, and while photovoltaic solar technology is improving, it is still an order of magnitude too expensive to be competitive. Module efficiency is a key parameter for photovoltaics because cost per watt generally decreases as module efficiency increases. Module material costs and manufacturing costs per unit are fairly fixed. Thus, power costs decrease as module efficiency increases. Advanced materials such as polymers that can reduce module and manu- facturing costs may help photovoltaic technology become more competitive. Crystalline silicon module costs have decreased in the past 20 years but remain too high to be broadly competitive. Even the use of glass is too expensive compared to other low-cost power-generating technologies. Improvements in manufacturing processes also are needed to reduce costs and increase reliability. Power electronics must be improved, but there is additional cost related to energy storage. Major reductions in every component associated with the system are necessary to make photovoltaics a viable method of energy capture and storage. This will require research at the interfaces between the various chemical sciences as well as at the interfaces with theoretical physics, solid-state physics, materials science, electrical engineering, and manufacturing technologies. Fuels for Transportation The main source of energy for transportation is crude oil. In 1980, world oil demand was 65 million barrels per day. For the year 2000, actual world oil demand was 75 million barrels per day, essentially in line with projections made by Exxon in 1980. Proven reserves increased significantly between 1980 and 2000, due mainly to the impact of advanced technologies and increased exploration.
INTERFACE CHALLENGES AND OPPORTUNITIES 25 Crude oil refining is a key factor in keeping energy costs down using oil. Refining today is a sophisticated process that uses advanced technology to con- vert crude oil into a range of products, including transportation fuels, lubricants, petrochemicals, and lower-value so-called black products. Depending on its configuration, the energy efficiency of a typical refinery is between 87 and 92 percent. Most of the energy in the crude is consumed in sepa- rations in the refinery; more than 90 percent of this energy is used in distillation. Over 80 percent of the products from a refinery are transportation fuels and on-road fuels that are being driven to be more chemically specific through both regulation and the needs of vehicle power trains. Many other products are by nature chemical specific. Tightening of tailpipe emission standards is driving sulfur in gasoline and diesel fuel to ever lower levels. This is to allow after- treatment technologies that are focused on reducing nitrogen oxide and hydro- carbons to extremely low levels. Concerns over air toxins will also impact the chemical composition of gasoline in the future. Automakers' search for more efficient power trains will consequently pro- duce changes in the fuel that is needed to operate those power trains. This, too, will require chemical specificity, in the form of composition-based refining. The keys to molecular specificity in the refinery are accurate, chemically specific measurements; analysis; chemically specific processes; and real-time optimiza- tion of the integrated refinery. Today, the petroleum industry's ability to accom- plish this is rapidly improving. For example, high-detail hydrocarbon analysis allows measurement of composition in great detail and structure-oriented lump- ing enables modeling of reactions with high precision. With these capabilities and with process models that now can predict product composition and properties from the crude to the end products, the foundation exists to do real-time optimiza- tion on the activities of the integrated refinery. Despite of improvements and new technologies, there are related needs that can be met by research in applied physics, materials science, chemical sciences, chemical engineering, and applied math. THE REFINERY OF THE FUTURE The refinery of the future will be more technology focused than today. It will make only high-value products, with one of those products being power. The refinery will be a clean, smart, high-value, energy-efficient installation "clean" in that it will be environmentally benign, and "smart" in that it will be highly integrated, with operations managed around quantitative chemical reaction engi- neering models. Chemical specificity will be achieved in the refinery of the future through the use of new catalysts. Catalysts are clearly a tool for creating and managing the desired chemical specificity. Shape-selective zeolite catalysts have been very effective in managing molecular composition based on size and shape. High-
26 ENERGY AND TRANSPORTATION activity, site-specific, supported catalysts also play a critical role in refining molecular management. However, much fundamental science needs to be devel- oped to allow catalysts to become more effective in operations. Today, most multistep reactions are carried out a single step at a time followed by separations, resulting in high-energy consumption and byproduct formation. Better approaches to chemical reactions are required, including catalysts with the appropriate balance of activity in multifunctional capabilities that lead to successful execu- tion of multi-step reactions either with a single catalyst or in a single reactor. For these capabilities it may be instructive to learn from nature, which per- forms mulitstep reactions very efficiently. Enzymes and biological systems under a wide range of conditions carry out a very sophisticated array of reactions with high selectivity and essentially no undesired byproducts. Biocatalysts and pro-
INTERFACE CHALLENGES AND OPPORTUNITIES 27 cesses could be adapted for use in a refinery, where bioproduced fuels could also be a feed- or blend stock. More futuristic ideas include adaptive catalysts that respond to changes in feedstock, impurities, and the product needs of a refinery and that can be driven by some outside signal, such as microwaves and electronic or magnetic radiation. For all of these developments, interfaces are needed between the chemical sciences and materials science, physics, and the biological sciences. Membranes play a more important role in the refinery today and will do so to an even greater extent in the future. They promise energy efficiency and chemical specificity, two of the most critical issues for the refinery of the future. Approxi- mately 10 percent of the energy in crude oil is used or consumed in the refining process. Membranes have the potential to markedly reduce this energy consump- tion, increase refinery efficiency, and decrease the emissions associated with refining. For example, membrane separations could reduce capital and operations costs for the separation of propane and propylene by 50 to 70 percent. Savings due to reduced energy costs could be between $0.6 and $0.9 per pound, which is roughly half the cost of the propylene.
28 ENERGY AND TRANSPORTATION Combining membranes with catalytic reactions offers new opportunities for increased specificity and lower selectivity reactions as well as reduced costs. Such a combination could be applied to air separation, gasification, and large down- stream separations. The challenges are to find membranes with high fluxes that are highly selective and durable under the conditions in which they operate in the refinery, field, or reservoir. These are significant challenges with possible sig- nificant results, especially if they affect hydrogen sulfide and carbon dioxide sepa- rations, which consume significant amounts of energy. Membrane development requires work across many chemical science interfaces, with much to learn from the biosciences. The future of research is at critical interfaces among the manu- facturing sciences, device development sciences, and engineering. There are still many needs required for improvements to refineries. One is a wide array of sensors, which will help to provide the foundation for real-time optimization of the integrated refinery and help to manage every point in the refinery. To help meet these needs, a key interface must be developed between chemical engineering and applied mathematics. IMPROVING VEHICLE FUEL EFFICIENCY Changes in automotive light-duty vehicle power trains are being driven by the need to increase energy efficiency and reduce carbon dioxide emissions. Conventional gasoline today is highly efficient and has very good emissions per- formance. To increase energy efficiency, additional technologies are being inves- tigated very aggressively by the auto industry. Technologies also need to be developed to meet increasingly tough emissions standards that require reductions in nitrogen oxide from gas-powered engines. Nitrogen oxide reductions have been made continually over the past 30 years. The newest regulations, federal Tier 2 standards that go into effect in 2004, effectively target other cold start pollutants such as nonmethane organic gas emissions without affecting nitrogen oxide control. Extremely high levels of simultaneous reduction of NOX, carbon monoxide, and hydrocarbons have been possible because of the stoiciometric nature of engine-out exhaust of the internal combustion gasoline engine and the development of three-way catalyst technology. To meet current or future emis- sions reduction legislation, there is a push toward more sophisticated models of engine operation with predictive capabilities and real-time optimization. Meeting even higher levels of emissions controls will require further techno- logical advances. Catalysts with lower thermal mass and light-off temperature that can be coupled to the exhaust manifold will be required. Catalysts are needed to very efficiently adsorb emissions during cold-start operations. Catalysts are also need that can convert these adsorbed materials when they desorb. Sophisti- cated models of energy operation, including predicting emissions when going from transient cold-start to full-throttle operation, coupled with a catalyst after treatment operating mode that can deliver precise individual-cylinder air/fuel con-
INTERFACE CHALLENGES AND OPPORTUNITIES 29 trot must be developed. Technological advances such as these should allow for further emissions reduction by a factor of 2 to 10. Lean-Burn Technologies Lean-burn engine technologies such as gasoline direct injection and diesel engines can provide significant improvements in fuel efficiency and performance.
30 ENERGY AND TRANSPORTATION In these engines, fuel is injected directly into the combustion chamber, forming fuel-rich and fuel-lean regions. The overall combustion mixture is typically lean. These engines operated over a wide range of in-cylinder combustion regimes. Diesel engines, however, are well known for soot particle production, and both diesel and gasoline direct injection engines produce large amounts of nitro- gen oxide. Furthermore, when operated lean, these engines present enormous challenges in nitrogen oxide removal because the exhaust is strongly oxidizing, and three-way catalysts developed for conventional gasoline engines are not applicable. To use these lean-burn engine technologies, entirely new after- treatment technologies will be required. Resolution of these challenges will require an approach that integrates key chemical sciences disciplines. Included are fuel science and combustion chemis- try, thermodynamics, and kinetics to understand the combustion process and the formation of particulates and nitrogen oxide. Computational fluid dynamics is needed throughout the entire system. This must be coupled with combustion kinetics to predict the course of the combustion process and to identify strategies for controlling nitrogen oxide and particulate formation. Engine design and control skills are required to convert theoretical understanding into real-world performance. Catalysts and reactor design and development are necessary for after-treatment systems to trap or reduce nitrogen oxide and particulates to very low levels. Finally, all of these needs must be predictive, not in the steady state but in the highly transient operation that the system continuously performs. Fuel Cells Current interest in fuel cell vehicles is focused on increased fuel efficiency, reduced or zero emissions, and enhanced performance to meet consumer needs and expectations. Fuel cell vehicles offer great opportunities and challenges. Current proton exchange membrane fuel cells require hydrogen to produce elec- tricity. This raises a myriad of challenges regarding the source, production, and storage of hydrogen. The classical model of fuel supply would favor off-board hydrogen genera- tion and refueling at stations, much the way gasoline is managed today. However, there is no hydrogen fueling infrastructure today, and infrastructure development is costly. Onboard hydrogen generation from available fuels such as gasoline avoids infrastructure challenges but has vehicle technology and cost challenges. The experience of the process industry is that, as the scale of a process is increased, the cost of the product per unit is reduced. For hydrogen generation at very large scales, production from natural gas is possible for slightly more than the cost of gasoline. However, as plant size decreases to the range of a station servicing an average of 150 fuel cell vehicles, the cost of hydrogen fuel is higher because of the capital cost associated with the facility and the higher cost of
INTERFACE CHALLENGES AND OPPORTUNITIES hydrogen production. The challenge to break this paradigm requires major devel- opment and breakthrough. The method of off-board hydrogen generation greatly affects its cost. Hydro- gen produced in large-scale refineries is estimated to cost $0.85 per gallon, while small-scale hydrogen generation at a vehicle refueling station is expected to cost $6 to $8 per gallon.1 These added costs result mainly from distribution, which involves compressing hydrogen to high pressure of 6,000 to 7,000 pounds and storing it in cylinders at the station. The associated capital cost is more than double the cost of fuel delivered to the vehicle. Energy storage density is a major issue because the low energy density of hydrogen makes it expensive to transport and store. Automobile companies and energy companies have the same storage problem. Breakthroughs in understand- ing system integration modeling are needed. A major breakthrough in hydrogen storage will be required through innovation and new technologies from all the chemical, materials, and engineering sciences, solid-state physics, and all the interfaces associated with these fields. The challenge for onboard generation of hydrogen is no less monumental. To be competitive with the internal combustion engine, the fuel cell engine must cost approximately $3,000. This means that for a 100 kW power source the onboard iDonald Hubert, President, Shell Hydrogen, presentation to the National Hydrogen Association.
32 ENERGY AND TRANSPORTATION fuel processor needs to cost approximately $15 per kilowatt. This is less than one- tenth the cost of a large-scale, highly efficient, steady-state methane reformer for hydrogen production. In addition, the onboard fuel processor must operate in a highly transient mode. Innovation will be essential in almost every aspect of the fuel processor to achieve this goal. Innovation in materials, including both catalysts and mem- branes, separations and hydrogen storage, systems integration, and manufactur- ing will all be necessary. A potential solution to these challenges may be the generation of hydrogen from renewable sources, such as sunlight. However, until photovoltaic electricity costs decrease, there will be no solar hydrogen generation at a competitive cost. Again, innovation in materials and manufacturing will be necessary. CONCLUSIONS For energy and transportation in the next 20 years the chemical sciences are positioned to be the key sciences involved in resolving the issues and moving society forward. Fundamental innovations will be required, particularly in the area of materials chemistry. The challenges are becoming increasingly complex and interdisciplinary, which will require working across all of these interfaces to have progress. The concern will not be a lack of innovations, since an innovation does not denote a successful application. The challenges for the chemical sciences com- munity will be to sift through those innovations, repeatedly refocus them, drive them through development as a multidisciplinary team, and diffuse them out into the entire economy. This is the biggest challenge that the community will have in the future.
