Fuels future sources

The technologically most important isotope, Pu, has been produced in large quantities since 1944 from natural or partially enriched uranium in production reactors. This isotope is characterized by a high fission reaction cross section and is useful for fission weapons, as trigger for thermonuclear weapons, and as fuel for breeder reactors. A large future source of plutonium may be from fast-neutron breeder reactors. 

The future of chemurgy is intercoimected with the economic future of energy, environment, and food. Several scenarios exist for future sources of energy and materials. Some involve the use of nuclear or solar energy (qv) leaving coal and oil available for chemicals and transportation fuels. Some involve... 

South America and Western Europe). But the large reserves of near-surface subbituminous coals and lignites are also being looked upon as future sources of synthetic fuel gases and liquid hydrocarbons that would augment production of synthetic crude oils from, e.g., Northern Alberta s oil sands (4). 

Lower efficiencies as a future renewable fuel from sources other than (fairly limited) biomass. 

Both in the USA and the EU, the introduction of renewable fuels standards is likely to increase considerably the consumption of bioethanol. Lignocelluloses from agricultural and forest industry residues and/or the carbohydrate fraction of municipal solid waste (MSW) will be the future source of biomass, but starch-rich sources such as corn grain (the major raw material for ethanol in USA) and sugar cane (in Brazil) are currently used. Although land devoted to fuel could reduce land available for food production, this is at present not a serious problem, but could become progressively more important with increasing use of bioethanol. For this reason, it is important to utilize other crops that could be cultivated in unused land (an important social factor to preserve rural populations) and, especially, start to use cellulose-based feedstocks and waste materials as raw material. 

Natural gas is a hydrocarbon of low molecular weight consisting of about 85% methane (CH ), which is recovered as an underground gas in areas where petroleum is found. It is also economically produced by conversion of crude oil to gas. Possible future sources of a hydro-gen-based fuel are large frozen methane deposits recently found on ocean bottoms. 

Our long-range energy future clearly must be safe nuclear energy, which should increasingly free still remaining fossil fuels as sources for convenient transportation fuels and as raw materials for synthesis of plastics, chemicals, and other substances. Eventually, however, in the not too distant future we will need to make synthetic hydrocarbons on a large scale. 

Cellulose is the most abundant renewable resource available for con- version to fuel, food, and chemical feedstocks. It has been estimated by Ghose (11) that the annual worldwide production of cellulose through photosynthesis may approach 100 X 109 metric tons. As much as 25% of this could be made readily available for the conversion processes. A significant fraction of the available cellulose, i.e., 4-5 X 109 t/year, occurs as waste, principally as agricultural and municipal wastes. Cellulose must be viewed, therefore, as an important future source of fuel, food and chemicals (see Table I). 

Impurities in the drying atmosphere are exhausted in the air and have been referred to as "blue haze." One company has made substantial progress in collecting the blue haze emissions in a duct where they are directed through a series of water showers, filters and other equipment. Then the water is evaporated leaving a heavy liquefied residue which is collected on a stainless steel belt and deposited in storage vats. Currently this residue is being used as a fuel supplement, but some feel that it may be a future source for development of new chemicals. Apparently, this process meets Environmental Quality Standards with reference to air pollution. 

Tullo, Alexander H. Methane on Ice. Chemical En neering News 83 (August 22, 2005) 16-17. This brief article describes the nature and occurrence of methane hydrate crystals and the prospects of their use as a future source of fuel. 

The metal is a source of nuclear power. There is probably more energy available for use from thorium in the minerals of the earth s crust than from both uranium and fossil fuels. Any sizable demand from thorium as a nuclear fuel is still several years in the future. Work has been done in developing thorium cycle converter-reactor systems. Several prototypes, including the HTGR (high-temperature gas-cooled reactor) and MSRE (molten salt converter reactor experiment), have operated. While the HTGR reactors are efficient, they are not expected to become important commercially for many years because of certain operating difficulties. 

Because of the ovedapping roles of coal in industry, many of the technologies covered here have been developed for synthetic fuel appHcations, but they also have been used or have demonstrated potential for production of significant quantities of chemicals. The scope of an article on coal as a chemical source would not be complete without coverage of synfuel processes, but the focus will be on the chemical production potential of the processes, looking toward a future when coal again may become the principal feedstock for chemical production. 

Because oil and gas ate not renewable resources, at some point in time alternative feedstocks will become attractive however, this point appears to be fat in the future. Of the alternatives, only biomass is a renewable resource (see Fuels frombiomass). The only chemical produced from biomass in commercial quantities at the present time is ethanol by fermentation. The cost of ethanol from biomass is not yet competitive with synthetically produced ethanol from ethylene. Ethanol (qv) can be converted into a number of petrochemical derivatives and could become a significant source. 

Continuing dependence on fossil fuels raises several major ethical issues. Ethical questions concerning our responsibilities to future generations arc raised by the fact that fossil fuels are a nonrenewable energy source, so that eveiy barrel of oil or ton of coal burned today is forever lost to future generations. Further, the by-products of fossil fuel combustion pose hazards to both present and future generations. 

---