Methane environmental sources

Table 6-4. Hydrocarbon Emissions from Anthropogenic Sources (a) In the United States, Including Methane (Environmental Protection Agency, 1976 Mann, 1981) (b) On a Global Scale, Nonmethane Hydrocarbons Only (Ehhalt et al., 1986) (c) Source Apportionment in Sidney, Australia (Nelson et al., 1983)...

Mechanism 20.7 outlines the steps involved in the haloform cleavage of a methyl ketone. The boxed essay The Haloform Reaction and the Biosynthesis of Trihalo-methanes describes its involvement as an environmental source of chloroform and bromoform. 

Some petroleum geologists believe that there may be more methane trapped in hydrates than what is associated with natural gas reserves. However, as an energy source, there is considerable uncertainty whether this methane can ever be recovered safely, economically, and with minimal environmental impact. The Russians have experimented with the use of antifreeze to break down hydrates at some onshore locations in Siberia. But perhaps a more promising approach would be to pipe warm surface water to the bottom to melt the hydrates, with a collector positioned to convey the gas to the surface. Another approach might be to free methane by somehow reducing the pressure on the methane hydrates. 

Compare using methane from natural gas with using methane from methane hydrates in terms of environmental impact and efficiency. You will need to do some research to find out extraction methods for each source of methane. 

Breas, O., Guillou, C., Reniero, F. Wada, E. 2002. The global methane cycle Isotopes and mixing ratios, sources and sinks. Isotopes In Environmental and Health Studies, 37, 257-379. 

The recovered sulfur industry exists primarily as a result of the necessity of removing sulfur values from hydrocarbon fuels before combustion so that sulfur emissions to atmosphere are reduced. In the case of sour gas, the principal source of recovered sulfur, the product that results from recovery of the sulfur is clean-burning, non-polluting methane. In the case of refineries handling high sulfur crude the product is low sulfur gasoline and oils. Thus every ton of sulfur recovered is a ton that is not added to the atmosphere. The recovery process itself however, is also the subject of optimization and recent developments in recovery efficiency have further ensured that the environmental impact in the immediate vicinity of these desulfurization facilities will be minimized. 

Reasons for interest in the catalyzed reactions of NO, CO, and COz are many and varied. Nitric oxide, for example, is an odd electron, hetero-nuclear diatomic which is the parent member of the environmentally hazardous oxides of nitrogen. Its decomposition and reduction reactions, which occur only in the presence of catalysts, provide a stimulus to research in nitrosyl chemistry. From a different perspective, the catalyzed reactions of CO and COz have attracted attention because of the need to develop hydrocarbon sources that are alternatives to petroleum. Carbon dioxide is one of the most abundant sources of carbon available, but its utilization will require a cheap and plentiful source of hydrogen for reduction, and the development of catalysts that will permit reduction to take place under mild conditions. The use of carbon monoxide in the development of alternative hydrocarbon sources is better defined at this time, being directly linked to coal utilization. The conversion of coal to substitute natural gas (SNG), hydrocarbons, and organic chemicals is based on the hydrogen reduction of CO via methanation and the Fischer-Tropsch synthesis. Notable successes using heterogeneous catalysts have been achieved in this area, but most mechanistic proposals remain unproven, and overall efficiencies can still be improved. 

The evolution of a large amount (1.12 x 1018 g of CH4) of methane from hydrates is the only plausible hypothesis that has been offered to explain this environmental perturbation. The abnormal 8 l3C isotope indicates that source... 

It is fair to state that by and large the most important application of structured reactors is in environmental catalysis. The major applications are in automotive emission reduction. For diesel exhaust gases a complication is that it is overall oxidizing and contains soot. The three-way catalyst does not work under the conditions of the diesel exhaust gas. The cleaning of exhaust gas from stationary sources is also done in structured catalytic reactors. Important areas are reduction of NOv from power plants and the oxidation of volatile organic compounds (VOCs). Structured reactors also suggest themselves in synthesis gas production, for instance, in catalytic partial oxidation (CPO) of methane. 

The production of hydrogen from methane is important because it has a low environmental impact. The production of hydrogen via steam reforming has a H2/C02 ratio of 4 (Table 1), the lowest C02 impact of any fossil fuel source. The dc plasma system produces a H2/C02 ratio of about 1000 in the effluent stream. However, CO is a major product of the system. If the water-gas shift reaction were used to convert all of the produced CO into C02 via reaction [5], the resulting H2/C02 ratio would be approximately 9 for either system. This value is still considerably better than that of other fossil fuels, including steam reforming. 

Although the actual use of hydrogen in a fuel cell produces only energy and water as a byproduct, it is in the actual production of hydrogen as previously discussed that the environmental effects of carbon dioxide and carbon monoxide releases are realized. With the current ability to use fuel cells with existing fuel sources such as methane and methanol, the pursuit of a purely hydrogen fuel cell may not be the environmental solution that is often implied by its proponents. 

See Environmental Protection Agency (EPA), Current and Future Methane Emissions from Natural Sources. Available online at http // www.epa.gov/ghginfo/reports/curr.htm. Accessed December 10, 2003. 

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