After petroleum is gone, what then?
MANAGEMENTAfter petroleum is gone, what then?Analysis of seven organic carbon sources discusses possible alternatives for transportation fuelsHarry W. Parker, PhD, PE, Texas Tech University
Recently, the Energy Information Administration projected a 2.2% annual increase in oil production through the year 2020.4 Continued improvements in exploration, drilling and production technologies provide the capability for continued oil production rate increases.5 Still, it is obvious that there is a finite amount of petroleum on planet Earth that can be produced for a reasonable price. That reasonable price is the price at which liquid fuels can be produced from sources other than petroleum. These alternative sources of U.S. liquid fuels are the topic of this presentation. All reasonable liquid fuels contain carbon; hence, a subtitle for this article could be, "Organic carbon sources for alternative transportation fuels." These alternative sources of organic carbon are numerous and far more abundant than petroleum. Technologies for conversion of alternative organic carbon sources into transportation fuels range from "proven and ready to use" to "wishful and uncertain." The price for this conversion ranges from "almost competitive today" to "outrageously high." The logic for ignoring global warming in this study and the relation of alternative carbon sources to the proposed use of hydrogen as an alternative transportation fuel are given in later discussions. Principal conclusions drawn are: 1) organic carbon is central to providing liquid transportation fuels, after petroleum is "gone"; 2) coal and lignite are abundant, environmentally benign sources of organic carbon for liquid fuels; and 3) processes for the conversion of coal to liquid fuels are proven.
Alternative Organic Carbon Sources The following alternative U.S. sources of organic carbon for transportation fuels are considered in this presentation:
These organic carbon sources are discussed here, followed by a review of the chemical processes by which organic carbon can be converted into liquid transportation fuels. Natural gas. This is the most convenient fuel for small-scale stationary uses. For this reason, there is a long-term logic for conserving natural gas for this purpose. Long-term logic and medium-term economics result in different decisions and, in a free society, medium-term economics wins. In this circumstance, gas has become an attractive fuel for large-scale generation of electricity, despite recent price surges.6 Natural gas is abundant. Its worldwide reserves approximate that of petroleum. Gas is an excellent engine fuel, but it is also very inconvenient to carry on the vehicle using it, and driving range is limited. For this reason, conversion of gas to liquid transportation fuels will be discussed later. Coal and lignite. These are the U.S.’s most abundant and usable domestic organic carbon sources. The technologies for large-scale, environmentally benign mining are already proven, since coal is still the dominant fuel for electric utilities. It is estimated that 2,800 billion tons (Bt) of coal potentially are available in the U.S.7 On a heating value basis, this is equivalent to about 9,650 Bbbl of petroleum. Western (Greenriver) oil shale. Western oil shale is abundant in Colorado, Utah and Wyoming. Considerable investment has been made in mining / processing technologies. In the period of about 1940 to 1980, oil shale was thought to be the next source of liquid transportation fuels. However, the environmental problems associated with mining and disposal of the spent shale are immense. In this circumstance, issuing permits for commercial shale utilization would be difficult and expensive. The amount of oil shale that exists is large: 2,000 Bbbl domestically and 12,000 Bbbl on our planet.8,9 Devonian shale. This is also known as eastern shale or black shale. The resource is located in Ohio, Kentucky, Tennessee and Indiana. It is exceedingly abundant, 800 Bboe have been identified just near outcrops, and the deeper resources have not been estimated.10 Utilization of this shale has not been demonstrated on a large scale, since the pyrolysis processes used for Greenriver shale do not provide an adequate yield of liquid products. Natural gas hydrates. These are a significant problem in pipelining natural gas, but a problem that has been effectively managed. Gas hydrates as found in nature, in deep permafrost and deep ocean sediments are an immense opportunity for energy production. The amount of gas contained in the hydrates is truly vast relative to conventional natural gas resources.11 But no process has been demonstrated to recover gas from these hydrates. In addition, the potential impact on the environment may be large. In this circumstance, natural gas hydrates remain a "wishful" but still vast source of fuels. Biomass residues. These are available in limited and scattered amounts. Forestry and lumber production residues are already effectively used as boiler fuel. Municipal solid waste and most agricultural residues are still not an economic source of energy; and a tipping fee is necessary for their disposal. These residues could be converted to liquid fuels, but it is more expedient to use them as a local boiler fuel, relying on existing technologies, when economic. Intentionally grown biomass. Since by-product biomass residues are not economic as bulk energy sources, it would not be expected that intentional growth of biomass for energy would be economic either. Intentionally grown biomass for energy must directly compete for land and irrigation water resources, with more profitable food and fiber crops. In addition, the potential amounts of intentionally grown biomass are small relative to transportation fuel demand.12 Converting Organic Carbon To Liquid Fuels The carbon conversion processes to be considered in this section include the following:
The following brief reviews of these processes indicate their general nature and state of development. Conventional petroleum refining. This is mentioned as a carbon-conversion process since proven modifications of the existing refining process potentially can convert all the carbon present in petroleum into liquid transportation fuels. When petroleum prices were relatively low, refiners found that it was cost effective to produce liquid transportation fuels with coking / cracking processes. In this circumstance, the "excess" organic carbon in petroleum was rejected as coke and then gasified along with refinery wastes. The resulting synthesis gases can be burned for boiler fuel or used for production of petrochemicals and hydrogenation of petroleum products.13 Refiners even market excess electricity that results from cogeneration. Significant increases in petroleum prices serve to change this circumstance, and thus make it desirable to increase the yields of liquid transportation fuels from petroleum. This task is accomplished by using hydrogenation / hydrotreating to produce liquid transportation fuels. In addition, the potential exists for using coal or lignite as both a source of fuel and hydrogen for a petroleum refinery. By this means, it will be possible to produce more than one barrel of transportation fuel per barrel of crude petroleum processed. For this reason, conventional petroleum refining is listed as a means of converting organic carbon to transportation fuels. The proposed modification of petroleum refineries will happen on an incremental basis as the price of oil is perceived to stabilize at a moderately high level, perhaps $30/bbl. The incentives to refine heavy oil and tar will also increase as the price for conventional petroleum stabilizes at a higher level. Gasification and reforming. The objective of gasification and reforming processes is to convert organic carbon into synthesis gas, a mixture of carbon monoxide and hydrogen. This gas can then be reacted to produce a variety of liquid fuels, and also "petrochemicals." The essence of the gasification process is the reaction of carbon with water:
This reaction is written in an overly simplified form to stress the fact that the gasification reaction is "unburning" water. When hydrogen-containing fuels are burned to release energy, water is a product of combustion. When water is converted to hydrogen by gasification, about the same amount of energy must be supplied. In terms of thermochemistry, gasification is a strongly endothermic process, and this fact is a central feature in designing gasification processes. The necessary energy for the gasification reaction is frequently supplied by adding pure oxygen to the reaction mixture. The stated equation is also oversimplified because carbon dioxide is also produced and the reaction is reversible. Chemical equilibrium is reached among the species present, so the immediate yields are not 100% of the desired products. The endothermic nature of the gasification process makes the overall thermal efficiency of gasification processes to liquid fuels and petrochemical about 50%, despite energy conservation efforts. Coal gasification is commercial now, despite the above factors and the difficulty of processing solids at high pressures. Eastman Chemicals in Kingsport, Tennessee, built its initial plant in 1983, and then expanded it in 1991, proving the attractiveness of coal gasification under Eastman’s circumstances. It processes 2.1 MMt of coal per year for production of acetic anhydride. Coal gasification is also accomplished at the Great Plains Synfuel Plant in Beulah, South Dakota, where 6.3 MMt of lignite are being converted into 5.4 Bscf of synthetic natural gas. When South Africa was economically isolated due to its apartheid policies, it built the SASOL coal gasification facilities to provide an internal source of liquid transportation fuels – the facilities continue in operation today.14 Synthesis gas. Gasification of natural gas and other light hydrocarbons is termed "reforming." Natural gas is much easier to convert to synthesis gas than coal, since coal is a solid containing considerable ash. The energy required for gasification either can be supplied by partial oxidation of the natural gas, or by heating a natural gas and steam mixture in a furnace called a reformer. Production of ammonia, methanol, acetic acid, etc., is accomplished in many national and international facilities today by means of these steam reformers producing synthesis gas. Synthesis gas can be processed into a wide variety of liquid fuels. Shell is producing premium diesel in Malaysia from natural gas liquids. FT synthesis is also employed in South Africa SASOL facilities. Methanol is produced directly from synthesis gas today. In theory, methanol is a very good SI engine fuel, but it is not widely used. Methanol can be converted directly to high-octane gasoline by the Mobil M-gasoline process. This process was to be commercialized in New Zealand, but low petroleum prices have confused the situation. Synthesis gas can be converted into dimethyl ether, which is a good diesel fuel, whereas methanol is not.15 Currently, announcements for new natural-gas-to-liquid fuel plants are frequent. One example is the 75,000-bpd plant for Egypt, to begin operation in 2005, using Shell’s middle distillate synthesis process.16 It should be noted that wood and other organic materials can be gasified, and the synthesis gas used to produce liquid fuels that are, incidentally, environmentally friendly and renewable. It is noted that in WWII, civilian vehicles were operated directly with gas generated by wood gasifiers mounted on the car. This use of solid fuel to operate a vehicle was very inconvenient, and the on-car gasifiers were rapidly abandoned when WWII was over, again illustrating the need for convenient liquid transportation fuel. In summary, gasification can convert both coal and natural gas to good liquid transportation fuels by commercially proven processes. Long-term projections of petroleum prices and uncertainties associated with these price projections are crucial concerns with regard to the construction of synthetic liquid fuel facilities using gasification technologies. Pyrolysis. Also termed "destructive distillation," pyrolysis is, superficially, a very simple process. Heat any material containing organic carbon in the absence of oxygen, and it will be converted into three products: liquid oils, combustible gases and char. Manufacture of metallurgical coke, and production of charcoal are examples of commercial pyrolysis processes. Coal tar from the pyrolysis of coal for coke was the major source of simple organic chemicals known as "petrochemicals," before petrochemicals existed. Pyrolysis of Greenriver oil shale, termed "retorting," is the process of choice for production of shale oil. At least two oil shale processes have been demonstrated in a reasonably large-scale: the Union (now Unocal) retort and the gas-combustion retort. Unocal closed its commercial, but still federally subsidized, 10,000 bpd oil shale plant near Parachute Creek, Colorado, in June 1991.17 It is expected that the economics of oil shale retorting will be less attractive than coal gasification, although some individuals might question that point. The environmental impact of mining oil shale and then disposing of the spent shale ash containing such toxic residues as arsenic is considerable. In addition, significant amounts of water are required for the overall retorting process. Pyrolysis can also be applied to coal, prior to burning the remaining char in electric power plants. By this means, organic hydrogen and carbon will be conserved for liquid fuels, and only the remaining carbon would be burned for electric power production. Superficially, this is an attractive concept, and it has received minimal testing. The author attempted to facilitate further development of this process without success in the 1980s.18 Coal pyrolysis may become more attractive as petroleum reserves decrease. The economics of coal pyrolysis vs. coal gasification for liquid fuels are not obvious at this time. Hydrogenation. This is inherently an expensive process, requiring hydrogen at high pressures and special catalysts. It is basically a known process, and is applied to petroleum products as needed, particularly to remove unwanted constituents such as sulfur and aromatics. Hydrogenation has been considered for direct liquefaction of coal. It has been tested on a small-scale to get increased yields of oil from the eastern, Devonian oil shale – the HYTORT process. Process developers estimated that 400 Bbbl oil could be made available from Devonian shale using the process.19 For large-scale production of liquid fuels from alternative carbon sources, hydrogenation is not considered economically attractive. The author is not aware of HYTORT being reconsidered in recent years. Fermentation. Ethanol is a good fuel for SI engines. Producing ethanol via fermentation makes it a renewable and environmentally friendly fuel. It is also perceived as supporting the rural economy, when the fermentation feed stock is starch or sugar – it is doubtful that a statistical analysis of corn price and volume would verify that this perception is true. The costs for ethanol are rather high relative to gasoline, and food-quality materials are being used for their fuel value. Despite these inherent disadvantages, tax incentives have been provided for use of ethanol in gasoline. Commercially, ethanol for solvent and industrial usage is produced as an ordinary petrochemical, i.e., the hydration of ethylene directly with water. In another proposed fermentation process, cellulose is hydrolyzed by either acids or enzymes into sugars. The sugars are then fermented into ethanol. This process uses an economical, non-food starting material – cellulose as contained in wood or even municipal solid waste. Cellulose hydrolysis has been tried for over 50 years without sustained commercial success. There are inherent reaction rate and reaction yield constraints that prevent its success. The concept has been reviewed relatively recently.20 While not a fermentation process, another source of biomass-based transportation fuel should be noted. That source is vegetable oils and animal fats that can be converted into a good diesel fuel, by a relatively simple chemical process, transesterification with methanol. This process reduces the viscosity of vegetable oils so they become a good diesel fuel frequently called biodiesel. The major problem with biodiesel is that the primary raw material, vegetable oil, costs on the order of $3/gal. Used cooking oils and inedible tallow are available in limited amounts. They also have value in animal rations and in pet foods. The Hydrogen Economy Hydrogen for fuel cells is receiving increasing attention as a potential route for transportation fuels. It should be noted that the most economic source of hydrogen is the reforming of natural gas, as discussed earlier. This concept is already being used for fuel-cell-powered buses in California, 21 but there is little mention of cost on an unsubsidized basis. Coal gasification is also a potential source of hydrogen for fuel cells. Low-molecular-weight hydrogen would be a more difficult fuel to transport on a vehicle than even natural gas, which is already considered inconvenient for use as a transportation fuel. Hydrogen also has special safety issues. For this reason, on-board reforming of hydrocarbons to produce hydrogen is being considered. Designing an economic miniaturized reformer for on-vehicle hydrogen production would seem a difficult, if not impossible task. Global Warming This topic is not considered in this paper, for a good reason. The limited reductions in emissions of fossil carbon dioxide, which might be specified by the Kyoto accord, are more easily accomplished at electric power generation facilities, not on vehicles. Several options to reduce fossil CO2 emissions associated with electric power production, including:
Using a selection of the above options for reducing fossil CO2 emissions associated with electric generating facilities is far more easily accomplished than constraining the use of carbon-containing liquid transportation fuels. Conclusion In summary, the above discussions indicate that: 1)
premium transportation fuels from natural gas via gasification are commercial now in some locations, and these
facilities are expected to increase; 2) proven commercial technology exists for coal gasification, to produce
premium transportation fuels; 3) other sources of organic carbon for transportation fuels are more difficult
to process economically, so they will not be developed for the foreseeable future; and 4) the rate at which
facilities for gasification / reforming natural gas and coal are built will depend on companies’ and
independent investors’ perceptions of stable, relatively high prices for petroleum.
Acknowledgment This article was prepared from the paper, "After the petroleum is gone, what then? Organic carbon sources for alternative transportation fuels," presented at the 48th Annual Southwestern Petroleum Short course, April 25 – 26, 2001, Lubbock, Texas Literature Cited 1 Duncan, R. C., "The peak of world oil production and the road to the Olduvai Gorge," Summit 2000, Geological Society of America, Reno, Nevada, Nov. 13, 2000. 2 Campbell, C. J., and J. H. Laherrere, "The end of cheap oil," Scientific American, March 1998, pp. 78 – 83. 3 Barker, H. W., "2005 – Peak in petroleum production or pinching Hubbert’s pimple," Paper 45, Proceedings of the 45th Annual Southwestern Petroleum Short Course, Lubbock, Texas, April 21 – 22, 1999, pp. 366 – 378. 4 Energy Information Administration, Reported by Reuters News Service, Published by Houston Chronicle, Nov. 29, 2000. 5 Nehring, R., "Innovation overpowering reserves depletion in U.S.," Oil and Gas Journal, Nov. 9, 1998, pp. 87 – 90. 6 Houston Chronicle News Services, "Natural gas jets past $9 mark," Houston Chronicle, Dec. 11, 2000. 7 Anon., "Energy alternatives: A comparative analysis," The Science and Public Policy Program, University of Oklahoma, Norman, Oklahoma, 1975, p. 1.3. 8 Weeks, L. G., "The next hundred years’ energy demand and sources of supply," Geotimes, 1960, pp. 18 – 21, 51 – 55 (As cited in Youngquist, 1999). 9 Youngquist, W., "Shale oil – The elusive energy," Hubbert Center Newsletter 98/4, http://hubbert.mknes.edu/news/v98n4/young-quist.html. (1998). 10 Janka, J. C., and J. M. Dennison, "Devonian oil shale," Synthetic Fuels from Oil Shale Symposium, Institute of Gas Technology, Chicago, Dec. 3 – 6, 1979, p. 24. 11 Collett, T. S., and V. A. Kuuskraa, "Hydrates contain vast store of world gas resources," Oil and Gas Journal, May 1998, pp. 90 – 95. 12 Parker, H. W., "Engine fuels from biomass," ASME Trans-Journal of Energy Resources Technology, Dec. 1981, pp. 344 – 351. 13 Rhodes, A. K., "Kansas refinery starts up coke gasification unit," Oil and Gas Journal, Aug. 5, 1996, pp. 32 – 36. 14 Parker, H. W., "Logic behind transportation fuels from coal and lignite," Chemical Technology, Crown Publications, Bedfordview, South Africa, Jan. 2000, pp. 3 – 5. 15 Rouhi, A. M., "Amoco, Ahaldor Topsoe develop dimethyl ether as alternative diesel fuel," Chemical and Engineering News, May 25, 1995, pp. 37 – 39. 16 Anon., "Shell clinches deal to build GTL plant in Egypt," Oil and Gas Journal, Dec. 11, 2000, p. 69. 17 Anon., "Unocal to close sole U.S. commercial oil shale plant," Oil and Gas Journal, April 8, 1991, p. 38. 18 Parker, H. W., "Liquid synfuels via pyrolysis of coal in association with electric power generation," Energy Progress, March 1982, pp. 4 – 8. 19 Feldkirchner, H. B., and J. C. Janka, "The HYTORT process," Symposium Papers: Synthetic Fuels from Oil Shale, Atlanta, Georgia, Dec. 3 – 6, 1979, pp. 489 – 518. 20 McCoy, M., "Biomass ethanol inches forward," Chemical and Engineering News, Dec. 1998, pp. 29 – 32. 21 Hummel, G., S., Lelewer and H. Skip, "Benefits of methane reforming / hydrogen generation for early alternative fueling stations," Paper 315b, American Institute of Chemical Engineers Annual Meeting, Los Angeles, California, Nov. 12 – 17, 2000. 
|
||||||||||||
ire
predictions regarding the availability of petroleum and continuation of our present civilization are indicated
by the title of a recent presentation, "The peak of world oil production and the road to the Olduvai
Gorge," which predicts the crash of civilization in 2030.1 There are other more conservative
predictions for just a peak in petroleum production in 2005.2 In a previous paper, the author
projected the peak in oil production in 2040.3
CO + H2
