Purification of methane

Kumer, R., J.K. Van Sloun Purification (of Methane) by Adsorptive Separation, Chem. Eng. Progress, 34 (January 1989). 

Koros, W.J. et al. (2002) Mixed matrix membranes and manufacture and purification of methane from a gas stream, (USA). Application US. 2002056369. 

Methane accounts for approximately 85 percent of the composition of natural gas with heavier hydrocarbons, nitrogen, and, in some regions, helium accounting for the other 15 percent [1]. Purification of methane is carried out at ambient or low temperature absorption (5—10 thousand ppm and 1—2 thousand ppm, respectively) and low-temperature fractionation (100 ppm) [2]. Impurities in the methane, such as heavier hydrocarbons, promote undesirable side reaction. Methane is also produced in an increasing number of organic waste-disposal plants [3]. Methane is used as feedstock to produce many chemicals, including hydrogen cyanide, carbon disulfide, and chlorinated methanes. 

Izumi J, Wang HX (2009) Recovery and purification of methane from fermentation biogas provided with adsorbents PCT Int Appl, WO 2009101669 Al 20090820... 

The most important large application of carbon membrane seems in the production of low cost and high purity nitrogen from air. Other examples are separation of hydrogen from gasification gas, purification of methane [3]. In addition, it is used to recover a valuable chemical (H ) from a waste gas stream without further compression of the feed gas while rejecting a substantial portion of the hydrocarbons [4]. 

Other separation processes include purification of methane as well as the recovery of carbon dioxide in oil fields [15,23]. Besides that they are useful in the removal of acid gases from rratural gas because they can operate in severe environments [15]. 

The carbon black (soot) produced in the partial combustion and electrical discharge processes is of rather small particle si2e and contains substantial amounts of higher (mostly aromatic) hydrocarbons which may render it hydrophobic, sticky, and difficult to remove by filtration. Electrostatic units, combined with water scmbbers, moving coke beds, and bag filters, are used for the removal of soot. The recovery is illustrated by the BASF separation and purification system (23). The bulk of the carbon in the reactor effluent is removed by a water scmbber (quencher). Residual carbon clean-up is by electrostatic filtering in the case of methane feedstock, and by coke particles if the feed is naphtha. Carbon in the quench water is concentrated by flotation, then burned. 

Final Purification. Oxygen containing compounds (CO, CO2, H2O) poison the ammonia synthesis catalyst and must be effectively removed or converted to inert species before entering the synthesis loop. Additionally, the presence of carbon dioxide in the synthesis gas can lead to the formation of ammonium carbamate, which can cause fouHng and stress-corrosion cracking in the compressor. Most plants use methanation to convert carbon oxides to methane. Cryogenic processes that are suitable for purification of synthesis gas have also been developed. 

The use of methane, ethane, ethylene, propylene, and propane pure light hydrocarbons as refrigerants is quite common, practical, and economical for many hydrocarbon processing plants. Examples include ethylene manufacture from cracking some feedstock, ethylene or other hydrocarbon recycle purification plants, gas-treating plants, and petroleum refineries. 

Residual C02 Content. The feed gas to Rectisol gas purification contains 29-36 vol % C02 depending on the rate of shift conversion. The rate of C02 to be washed out will be determined by the requirements of methane synthesis and by the need to minimize the cost of Rectisol purification. 

All solvents used for general applications were of reagent grade. For special purposes, purification of solvents was effected using standard procedures. All other reagents were used as supplied commercially except as noted. A solution of chloromethyl methyl ether (6 mmole/mL) in methyl acetate was prepared by adding acetyl chloride (141.2 g, 1.96 mol) to a mixture of dimethoxy methane (180 mL, 2.02 mol) and anhydrous methanol (5.0 mL, 0.12 mol).20 The solution was diluted with 300 mL of 1,1,2,2-tetrachloroethane and used as a stock solution for the chloromethylation experiments. 

Hydrogen production from carbonaceous feedstocks requires multiple catalytic reaction steps For the production of high-purity hydrogen, the reforming of fuels is followed by two water-gas shift reaction steps, a final carbon monoxide purification and carbon dioxide removal. Steam reforming, partial oxidation and autothermal reforming of methane are well-developed processes for the production of hydro-... 

If the product is a low- or medium-Btu gas, produced for direct combustion, the stream will probably be desulfurized for environmental reasons. In this instance, approximately 95% sulfur removal is typical of a reasonable level of purification - better than direct combustion of the coal by a factor of two, yet not requiring an excessive energy penalty. If the gaseous product is a synthesis gas, as in the production of methane, methanol, or Fishcher-Tropsch liquids, extreme desulfurization is required to protect the sulfur-sensitive downstream catalysts. 

Tetrachloroethane, purification of, 176 Tetradecanoic acid, 938, 940, 941 n-Tetradecyl bromide, 283 1 2 3 4-Tetrahydrocarbazole, 852 Tetrahydrofuran, 271 Tetrahydrofurfuryl chloride, 896, 901 Tetrahydropyran, 271 Tetralin, dehydrogenation of, 948, 949 purification of, 949 a-Tetralone, 728, 737 Tetramethyl base, 987 pp -Tetramethyldiaminodiphenyl-methane, 987... 

The methanation reaction is a highly exothermic process (AH = —49.2 kcal/ mol). The high reaction heat does not cause problems in the purification of hydrogen for ammonia synthesis since only low amounts of residual CO is involved. In methanation of synthesis gas, however, specially designed reactors, cooling systems and highly diluted reactants must be applied. In adiabatic operation less than 3% of CO is allowed in the feed.214 Temperature control is also important to prevent carbon deposition and catalyst sintering. The mechanism of methanation is believed to follow the same pathway as that of Fischer-Tropsch synthesis. 

Figure 19.20. Flowsketches of two processes employing fermentation, (a) Process for enzyme production, showing the use of growing trays, growing drums and stirred tank. Purification steps are the same for all three modes of culture growth, (b) Production of methane-rich gas by anaerobic digestion of finely divided waste solids in a 10-20% slurry. Residence time in the digester is five days [D.M. Considine (Ed.), Energy Technology Handbook, McGraw-Hill, New York, 1977].

Purification of Synthesis Gas. This involves the removal of carbon oxides to prevent poisoning of the NIT3 catalyst. An absorption process is used to remove the bulk of the C02, followed by methanation of the residual carbon oxides in the methanator, Modern ammonia plants use a variety of C02-removal processes with effective absorbent solutions. The principal absorbent solutions currently in use are hot carbonates and cthanolamincs. Other solutions used include methanol, acetone, liquid nitrogen, glycols, and other organic solvents. 

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