Selexol, carbon dioxide removal

In line with other modem processes, the Kellogg process can utilize one of the latest low-energy consumption carbon dioxide removal processes, such as Selexol or Lo-heat Benffeld. 

Figure 14-8. Flow diagram of SELEXOL process for selective hydrogen sulfide removal and complete carbon dioxide removal.

Swanson, C. G 1978, Carbon Dioxide Removal in Ammonia Synthesis Gas by Selexol, paper presented at 71st AIChE Meeting, Miami Beach, FL, Nov. 12-16. 

Carbon dioxide removal with the Selexol process. 

Carbon dioxide removal by the Selexol process compression to synthesis pressure before final purification. 

Gas purification by conventional shift carbon dioxide removal normally by Selexol or Benfield methanation drying of synthesis gas with molecular sieves. 

Selexol process for carbon dioxide removal and located in a cold climate is reported in (766). Energy consumption is reported to be below 29 GJ (LHV)/MT of ammonia. 

Gas purification shift conversion with medium and low temperature catalysts, both copper-based carbon dioxide removal by MDEA or Selexol methanation. 

Gas purification is by conventional shift conversion followed by a physical carbon dioxide removal (e.g. Selexol) and final purification in a cryogenic unit. The hydrogen to nitrogen ratio of the synthesis gas at the cryogenic unit inlet is 1.0-1.8. 

The solvent can be tailored to provide selective acid gas removal based on the Hquid—gas solubiHties. For example, the Selexol process, Hcensed by Union Carbide Corporation, uses the dimethyl ether of polyethylene glycol (DMPEG) to provide high hydrogen sulfide selectivity. The solubiHty of hydrogen sulfide in DMPEG is 8—10 times that of carbon dioxide. 

The reaction produces additional hydrogen for ammonia synthesis. The shift reactor effluent is cooled and tlie condensed water is separated. The gas is purified by removing carbon dioxide from the synthesis gas by absorption with hot carbonate, Selexol, or methyl ethyl amine (MEA). After purification, the remaining traces of carbon monoxide and carbon dioxide are removed in the methanation reactions. 

The Selexol process removes acid gases from hydrocarbon gas streams by selective absorption in polyethylene glycol dimethyl ether (DMPEG). It absorbs H2S, C02, COS, and mercaptans. The process has been used to remove carbon dioxide from syngas, natural gas, and coal gas. The process was developed by Allied Chemical in the 1960s and is now... 

Sodium carbonate is a less costly absorbent, but also less efficient. Other acid gas removal techniques use physical absorption of carbon dioxide in organic solvents, such as the dimethyl ether of polyethylene glycol, or methanol (the Selexol or Rectisol processes). For effective absorption these require high gas pressures. Regeneration of solvent is done by pressure letdown plus some air stripping (sparging of air through the solvent). 

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. 

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