Sweetening of natural gas

Alkanolamines in aqueous soludon react widi carbon dioxide and hydrogen sulfide to yield salts, important to gas condidoiiing reactions. Tlie dissociation of die salts upon heating results in recovery of the original starting material. Tliese reactions fomi the basis of an important industrial apphcadon, ie, die "sweetening" of natural gas. 

Acid gas, a mixture of hydrogen sulfide and carbon dioxide, is a toxic by-product of the sweetening of natural gas. Acid-gas injection has become an environmentally friendly way to dispose of this by-product. In the remainder of this book, the detailed design considerations for acid-gas injection are presented. 

Water is almost always associated with the acid gas resulting from the sweetening of natural gas. This is not produced water, which contains dissolved salts, which causes additional problems - this is condensed water and contains no dissolved solids. Since the water in the acid gas is present originally in the gas phase, there is no concern regarding brine. 

Still further process variations use physical absorption of hydrogen sulfide by the solvent, rather than chemical reaction with it, to effect the sweetening of natural gas. 

C02/CH4 Sweetening of natural gas Amine absorption Cellulose acetate Offshore platforms in Thailand gulf. 

Many of these membranes are designed for sweetening of natural gas and therefore exhibit high permeabilities for H2S and CO2 with large selectivity relative to methane [34], A large number of membranes demonstrate selectivity towards H2S over CO2, attributed to the higher condensability of H2S (for critical temperature see Table 11.2) within the membrane, compared to CO2. Similar to SO2, H2S has been reported to plasticize or swell polymeric membranes [35]. 

GASEP Systems. This system was developed by Envirogenics and also uses cellulose acetate spiral-wound modules. These systems have been used for the sweetening of natural gas by removing CO2 and H2S, and the separation of C02/methane mixtures in landfills, and the separation of hydrogen in coat... 

GS Gas separation Similar to RO membranes Recovery of H2 in ammonia plants, separation of Nj ft om air, sweetening of natural gas... 

Osenton, J. B., and Knight, A. R., 1S170, Reaction of Carbon Disulphide with Alka-nolamines used in the Sweetening of Natural Gas, paper ptesented at the Canadian Gas Processing Assoc., Fourth Quarterly Meeting, Calgary, Nov. 20. 

Examples of the former are the drying of air or natural gas, the removal of solvent vapours from air streams, the sweetening of natural gas, the removal of diethylbenzene from aromatics and the purification of liquid organic compounds. An example of the bulk separation of components by thermal swing adsorption is the extraction of water from ethanol. 

Process for Recovery of Natural Gas Liquids From a Sweetened Natural Gas Stream, U.S. Patent 4,421.535, Dec. 20, 1983. 

Hydrocarbons are a significant impurity in an acid gas mixture. If an aqueous solution is used to sweeten the natural gas, then the hydrocarbon content of the acid gas can be 2 to 4 mol%. If a physical... 

Gas Purification. The best-known purification process using 4A is that of natural gas this involves two benefits, namely, peak-shaving whereby the calorific value of fhe gas is adjusted by CO2 (and water) removal, and sweetening by H2S removal. The latter purification also is used in LPG treatment. Another example is the trapping of hydrocarbons in gas and vacuum circuits. 

Separation of CO2 from gas streams is required in four areas (1) purification of natural gas (gas sweetening), (2) separation of CO2 from enhanced oil recovery (FOR) gas streams, (3) removal of CO2 from flue gas, and (4) removal of CO2 from biogas. A fifth area vital for the space age should be mentioned removal of CO2 from life support systems onboard space ships, and also in submarines. All these applications have different specifications for the purified gas or for the recovered CO2, and future membrane applications will most likely be based on tailor-made materials. 

Diverse methods have been used to recover this element commercially to cope with the varied forms in which sulfur occurs (Table 9.2). For example, about 85% of Canada s sulfur production is from sulfides removed from natural gas to sweeten it. It results from, or is an involuntary by-product of natural gas production and not a product sought for its own sake. Poland, on the other hand, obtains about 80% of its annual sulfur by employing Frasch recovery of natural sulfur which is more directly responsive to markets in its volume of production. 

Rezakazemi, M., Niazi, Z., Mirfendereski, M., Shirazian, S. 2011. CFD simulation of natural gas sweetening in a gas-liquid hollow-fiber membrane contactor. Chem. Eng. J. 168 1217-1226. 

The purification of natural gas by removal of CO2 (natural gas sweetening) is, in principle, the same separation process as for upgrading of biogas, although it... 

A large use of molecular sieves ia the natural gas industry is LPG sweetening, in which H2S and other sulfur compounds are removed. Sweetening and dehydration are combined in one unit and the problem associated with the disposal of caustic wastes from Hquid treating systems is eliminated. The regeneration medium is typically natural gas. Commercial plants are processing from as Htde as ca 30 m /d (200 bbl/d) to over 8000 m /d (50,000 bbl/d). 

Other Uses. Other appHcations for sodium nitrite include the syntheses of saccharin [81-07-2] (see Sweeteners), synthetic caffeine [58-08-2] (22), fluoroaromatics (23), and other pharmaceuticals (qv), pesticides (qv), and organic substances as an inhibitor of polymerization (24) in the production of foam blowing agents (25) in removing H2S from natural gas (26) in textile dyeing (see Textiles) as an analytical reagent and as an antidote for cyanide poisoning (see Cyanides). 

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