Natural gas carbon dioxide removal from

Meyer, H. S., and Gamez, J. P., 1995, Gas Separation Membranes Coming of Age for Carbon Dioxide Removal from Natural Gas, Proceedings of the 45th Annual Laurance Reid Gas Conditioning Conference, Norman, OK, Feb. 26-March 1, pp. 284-306. 

Activated Carbon Sulfur removal from natural gas by adsorption at ambient temperature on carbon, activated with cupric oxide, is widely used. Carbon physically adsorbs sulfur compounds to its surface and the cupric oxide reacts with hydrogen sulfide. The activated carbon is typically regenerated every 30 days by passing steam through the bed at a temperature of 230°C (450°F) for 8—10 hr while air is injected. Oxygen in the air reacts with the metal sulfide to form the metal oxide and sulfur dioxide. These reactions are ... 

Recently, a new type of polymer material was reported to have a great potential for carbon dioxide separation from natural gas. It very selectively removed carbon dioxide by permeation through hourglass-shaped pores of molecular size, while impeding that of methane through these same pores [7]. 

For example, hydrogen sulfide and carbon dioxide can be removed from natural gas by reaction with monoethanolamine in an absorber according to the following reactions ... 

Example 11.7 Carbon dioxide is sometimes removed from natural gas by reactive absorption in a tray column. The absorbent, typically an amine, is fed to the top of the column and gas is fed at the bottom. Liquid and gas flow patterns are similar to those in a distillation column with gas rising, liquid falling, and gas-liquid contacting occurring on the trays. Develop a model for a multitray CO2 scrubber assuming that individual trays behave as two-phase, stirred tank reactors. 

The reason I say "poorly indexed" is that out of several thousand entries in the 10th collective index to Chemical Abstracts (1977-81), relating to carbon dioxide, only two entries contained the term "solubility" and neither of these pertained to the solubility of carbon dioxide in a liquid phase. On the other hand, the many entries under terms like "removal from natural gas" implied that quite a lot of data could be found with enough effort. 

Fig. 7.11 A section of the Qadirpur, Pakistan, carbon dioxide removal plant built by UOP (Separex). The plant reduces the carbon dioxide content of natural gas from 6.5% to less than 2%. The original plant...

The vast majority of current power plants use coal or natural gas as the fuel source and air as the source of oxygen. In these plants, the stack gas is at essentially atmospheric pressure and contains a large concentration of nitrogen (76 mol%). A small amount of excess air is used, which gives a stack composition of 4.8 mol% O2. The carbon dioxide concentration is only 13.2 mol%. The principal proven method for carbon dioxide removal from a low-concentration, low-pressme gas uses amine absorption, which involves chemical reaction of carbon dioxide with an amine, such as monoethanolamine (MEA). 

However, the ability of these and other forms of plant life to absorb carbon dioxide is not keeping up with the increase in carbon dioxide. Most scientists agree that the primary source of the increase of carbon dioxide is the burning of fossil fuels such as gasoline, coal, and natural gas. The cutting and burning of trees in the rain forests (deforestation) also reduces the amount of carbon dioxide removed from the atmosphere. 

The separation of CO2 from gas streams is reasonably well known. The most obvious example is its removal from natural gas. In some cases, the amounts may be quite large some economically recoverable natural gas reservoirs contain significant amounts of carbon dioxide. The Sleipner West field in the North Sea (for example) contains 10% by volume CO2 the sales specification is not more than 2.5%. Statoil (the Norwegian state oil company), which operates the field, uses an anune solvent technique to separate the excess, which is then pumped into a reservoir 1 km below the seabed. Approximately 1 million tonnes of CO2 is separated annually, which is about 40% of the model Kenosha plant described above. 

The Selexol process has found a very wide range of applications. It was originally used to remove CO2 from an ammonia plant in Nebraska, followed soon after by H2S and CO2 removal from natural gas in the U.S. and in Europe. Other applications include desulfurization and CO2 removal from synthesis gas derived from the partial oxidation of heavy petroleum stocks and from coal gasification. Natural gas treating applications include several, where in addition to production of pipeline specification gas, a relatively pure stream of carbon dioxide is produced for reinjection into oil formations, so-called enhanced oil recovery or EOR. A relatively new use for the process dating back to 1979 is the purification of landfill gas drawn from the biological degradation of municipal waste in sanitary landfills. This application is characterized by the occurrence of chlorinated and aromatic hydrocarbons as impurities in the landfill gas. 

Carbon Dioxide, Hydrogen Sulfide, and Water Removal, 1270 Helium Removal from Natural Gas, 1281 Air Separation, 1282 Solvent Vapors, 1288... 

Acid constituents such as carbon dioxide and hydrogen sulfide should be removed from natural gas in central field treating plants or in gas refiners before transmission of the gas for sale. Similarly, these constituents must be removed from plant gas streams, as in steam cracking of hydrocarbons for ethylene production, before the gases are subjected to low-temperature fractionation. 

The solvents most used in carbon dioxide removal from ammonia synthesis gas can be characterized according to the nature of the absorption process. Chemical absorption, i.e. processes where the carbon dioxide reacts with the solvent by a chemical reaction which is reversed in the solvent regeneration stage, is most often based on the use of alkanolamines, mainly MEA (mono-ethanolamine) [273], or hot solutions of potassium carbonate [274] as solvents. 

Carbon-dioxide-selective separation is becoming an important issue in areas such as petrochemical engineering (e.g., CO2 removal from natural gas), environment (e.g., CO2 removal from flue gas), agriculmre (e.g., control of CO2 concentration), and other related industries. Membranes can selectively separate CO2 from industrial processes. 

Ammonia production from natural gas includes the following processes desulfurization of the feedstock primary and secondary reforming carbon monoxide shift conversion and removal of carbon dioxide, which can be used for urea manufacture methanation and ammonia synthesis. Catalysts used in the process may include cobalt, molybdenum, nickel, iron oxide/chromium oxide, copper oxide/zinc oxide, and iron. 

CNG [Consolidated Natural Gas] A process for removing acid gases from natural gas and syngas, using supercritical carbon dioxide. Under development since 1973 by the Consolidated Natural Gas Research Company with assistance from the U.S. Department of Energy and Helipump Corporation. Liquid carbon dioxide is first used to extract the sulfur compounds. Crystallization at the triple point separates these sulfur compounds from the... 

Deoxy A process for removing small concentrations of oxygen from natural gas. The gas is passed over a hot catalyst, which converts the oxygen to carbon dioxide. 

Fluor Solvent A process for removing carbon dioxide from natural gas and various industrial gas streams by dissolution in propylene carbonate. Carbon dioxide is much more soluble than other common gases in this solvent at low temperatures. The process cannot be used when hydrogen sulfide is present. The process was invented in 1958 by A. L. Kohl and F. E. Miller at the Fluor Corporation, Los Angeles. It is now licensed by Fluor Daniel. The first plant was built for the Terrell County Treating plant, El Paso, TX in 1960 by 1985, 13 plants were operating. 

GAS/SPEC CS-Plus A process for removing carbon dioxide and hydrogen sulfide from natural gas by washing with a solution of a special amine. Developed and offered by Dow Chemical Company. Operated since 1988. 

Lacy-Keller A process for removing hydrogen sulfide and mercaptans from natural gas by absorption in a proprietary solution. Elemental sulfur precipitates as a colloid and is separated from the solution by means of an electrolytic flotation cell. The process does not remove carbon dioxide. 

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