## ABSORBENT COMPOSITION FOR THE SELECTIVE ABSORTPTION OF HYDROGEN SULFIDE AND PROCESS OF USE THEREOF 

[0001] This invention relates to an absorbent composition that is useful in the selective removal of hydrogen sulfide from gas streams containing hydrogen sulfide and carbon dioxide, including use of the absorbent composition, and a method of improving a process for the selective removal of hydrogen sulfide from a gas stream containing hydrogen sul› fide and carbon dioxide. 

[0002] The use of certain amine compounds and solutions for the separation of acidic gases such as CO$_{2}$, H$_{2}$ S, CS$_{2}$ , HCN, and COS from gaseous mixtures is known in the art of gas treating. One early method of separating acidic gases from gaseous mixtures is disclosed in U.S. Pat. No. 3,347, 621. The process disclosed in this patent uses a liquid absor› bent that comprises an alkanolamine and a sulfone that is contacted with a gas mixture containing acidic gas compo› nents. Examples of other early patents that disclose the use of solutions of alkanolamine and sulfone in the treatment of gaseous mixtures that contain significant concentrations of H$_{25}$, CO$_{2 }$and COS include U.S. Pat. No. 3,965,244 and U.S. Pat. No. 3,989,811. 

[0003] In a later patent, U.S. Pat. No. 4,894,178, there is disclosed the use of a mixture of two severely hindered amines in the selective removal ofH$_{25 }$from gas mixtures that contain both H$_{25 }$and CO$_{2}$ . One example presented of a mix› ture of the two severely hindered amines includes bis(tertia› rybutyl aminoethoxy)-ethane (BTEE) and ethoxyethoxy› ethanol-tertiarybutyl amine (EEETB). This mixture is obtained by the one-step catalytic tertiarybutylamination of triethylene glycol to yield a first amine, e.g. BTEE, and a second amine, e.g. EEETB, having a weight ratio of the first amine to second amine in the range of from 0.43: 1 to 2.3: 1. 

[0004] The’ 178 patent indicates that one problem with the use of aqueous solutions of BTEE is that they suffer from phase separation under regeneration conditions. The ’178 patent further indicates that EEETB can be used for the selec› tive removal ofH$_{25 }$in the presence of CO$_{2 }$ and that a mixture of BTEE and EEETB not only provides for better selectivity and higher capacity for H$_{25 }$than EEETB alone, it also does not phase separate under regeneration conditions as do aque› ous solutions ofBTEE. 

[0005] Prior to the use of the amine mixture that is disclosed in the ’178 patent, it is taught that the amine mixture may be contained in a liquid medium such as water, an organic sol› vent and mixtures thereof. The preferred liquid medium com› prises water, but possible other suitable solvents include the physical absorbents described in U.S. Pat. No. 4,112,051. Sulfones, such as sulfolane, are among the suitable physical absorbents. The liquid medium can be a mixture of water and organic solvent and is typically present with the absorbent in an amount in the range of from 0.1 to 5 moles per liter, preferably from 0.5 to 3 moles per liter, of the total absorbent composition. It is not clear, however, what mole units of which the ’178 patent is referring. 

[0006] U.S. Pat. No. 4,961,873 discloses an absorbent com› position that comprises a mixture of two severely hindered amines similar to the mixture disclosed in U.S. Pat. No. 4,894,178 with a weight ratio of a first amine to a second amine being in the range of from 0.43: 1 to 2.3:1, an amine salt and/or a severely hindered aminoacid. The severely hindered amine mixture and severely hindered amine salt and/or ami› noacid additives are dissolved in a liquid medium. The amine 

mixture and additive of the absorbent composition before it is contained in the liquid medium comprises from 5 to 70 wt % amine mixture, from about 5 to 40 wt % additive, and the balance being water with the weight percent being based on the weight of the total liquid absorbent composition. 

[0007] As in the ’178 patent, the ’873 patent teaches that, prior to the use of the liquid absorbent composition that includes the severely hindered amine mixture, it may be con› tained in a liquid medium such as water, an organic solvent and mixtures thereof. The preferred liquid medium comprises water, but possible other suitable solvents include the physi› cal absorbents described in U.S. Pat. No. 4,112,051. Sul› fones, such as sulfolane, are among the suitable physical absorbents. The liquid medium can be a mixture of water and organic solvent and is typically present with the absorbent in an amount in the range of from 0.1 to 5 moles per liter, preferably from 0.5 to 3 moles per liter, of the total absorbent composition. It is not clear, however, what mole units of which the ’873 patent is referring. 

[0008] The amine salt of the absorbent composition dis› closed in the’ 873 patent is the reaction product of the severely hindered amine mixture and either (1) a strong acid, or (2) a thermally decomposable salt of a strong acid, or (3) a com› ponent capable of forming a strong acid or ( 4) a mixture thereof. According to the ’873 patent, suitable strong acids include inorganic acids such as sulfuric acid sulfurous acid phosphoric acid, phosphrous acid, organic a~ids such as ace~ tic acid, formic acid, adipic acid, benzoic acid, etc. The amine salt may be preformed and then added in appropriate ratio to the unreacted severely hindered amine mixture or formed by reacting the strong acid with the severely hindered amine mixture. Alternatively, the amine salt may be formed by react› ing in-situ the strong acid or precursor thereof with the severely hindered amine mixture in the appropriate propor› tions. The mole ratio of the amine salt to the unreacted severely hindered amine mixture in the absorbent composi› tion is at least 0.1: 1 and, preferably, from about 0.1: 1 to 4: 1. The addition of sulfuric acid to an absorbent composition containing BTEE and EEETB appears to increase the selec› tivity of the absorbent composition for H$_{2}$S. 

[0009] U.S. Pat. No. 4,618,481 discloses absorbent solu› tions that comprise one or more severely hindered amines in combination with an amine salt that is a reaction product of a severely hindered amine and either (1) a strong acid, or (2) a thermally decomposable salt of a strong acid, or (3) a com› ponent capable of forming a strong acid or ( 4) a mixture thereof. Also disclosed is that a severely hindered amine may be mixed with a strong acid in any order and with a liquid medium so as to provide an absorbent solution containing the severely hindered amine and amine salt. The ’481 patent indicates that the addition of sulfuric acid to an EETB absor› bent improves its H$_{2}$S selectivity. 

[0010] U.S. Pat. No. 4,892,674 discloses an absorbent that is a combination ofMDEA, which is a non-hindered amine, with a severely hindered amine salt that is the reaction prod› uct of the severely hindered amine and a strong acid. This combination provides a composition that is more selective for H$_{2}$S than the MDEA alone. 

[0011] While the above-described compositions are among the many absorbent compositions of the prior art that may suitably be used in the treatment of gaseous hydrocarbon streams, in the art of gas treating there are ongoing efforts to find new and improved absorbent compositions that are use› ful in the removal of acidic gaseous components contained in 

