Physical/chemical solvent processes

Hybrid solvent processes use a mixture of a physical solvent with a chemical solvent and combine some ofthe advantages of physical solvent processes with those of chemical solvent processes. The Sulfinol process has numerous industrial applications in sour gas de-acidification. Its energy requirement is relatively low, but hydrocarbon co-absorption is higher than that of an amine process. 

All three major processes - post-combustion capture, oxy-fuel combustion, pre-combustion capture - require a step that, variously, involves the separation of carbon dioxide, oxygen or hydrogen from a bulk gas stream (flue gas, air or syngas, respectively). These separations can be accomplished by means of physical/chemical solvents, membranes, solid sorbents or cryogenic processes. 

The Rectisol and Amisol processes, which were developed in Germany by Liirgi, are physical and physical-chemical absorption processes using organic solvents to remove acid gas and sulfur, respectively, from various gas streams. Both processes use methanol as the physical absorption solvent the Amisol process also uses monoethanolamine (MEA) as the chemical absorber to improve the overaU purification efficiency. The MEA used in the Amisol process is not pertinent to our topic. Only methanol used in the Retisol process is discussed here, and the discussion is also applicable to the physical absorption by methanol used in the Amisol process. 

Hybrid Processes. A number of processes have been developed which use both chemical and physical absorption solvents to offer high purity treat gas and low energy solvent regeneration. The operation of these processes is usually similar to that of the individual chemical or physical absorption processes. The solvent composition is typically customized to meet the requirements of individual appHcations. 

The Sulfinol process from Shell Development Company is a good example of the physical/chemical type of process. It blends a physical solvent and an amine to obtain the advantages of both. The physical solvent is Sulfolane (tetrahydrothiophene dioxide) and the amine is usually DIPA (diisopropanol amine). The flow scheme is the same as for an amine plant. ... 

The same disadvantages with heavy hydrocarbons in the feed as other physical solvents High priced chemicals and process royalty, but losses are low and the licensee receives many engineering services."... 

Licensed by Shell the Sulfinol process combines the properties of a physical and a chemical solvent. The Sulfinol solution consists of a mixture of sulfolane (tetrahydrothiophene 1-1 dioxide), which is a physical solvent, diisopropanolamine (DIPA), and water. DIPA is a chemical solvent that was discussed under the amines. 

LOCAT units can be used for tail-gas clean-up from chemical or physical solvent processes. They can also be used directly as a gas sweetening unit by separating the absorber/oxidizer into two vessels. The regenerated solution is pumped to a high-pres.sure absorber to contact the gas. A light slurry of rich solution comes off the bottom of the absorber and flows to an atmospheric oxidizer tank where it is regenerated. A dense slurry is pumped off the base of the oxidizer to the melter and sulfur separator. 

Processing pressure - generally, the carrying capacity of physical solvents increases with absorption pressure much more rapidly than that of chemical solvents (A). Therefore, AGR at high-pressures may make physical solvents look attractive, while low-pressure operation favors chemical solvents. 

With this vast variety, it is usually possible to tailor the solvents to specific chemical reactions. Ionic liquids have a range of physical chemical properties that can be tuned with a precision that is hard to imagine for a given reaction. Ionic liquids are good solvents for a wide range of inorganic, organic, and polymeric materials. There are ionic liquids that will dissolve covalent compounds. Ionic liquids can lead to process intensification. 

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