Aqueous absorbent composition for enhanced removal of hydrogen sulfide from gaseous mixtures and method for using the same

Abstract

The present invention relates to an aqueous alkanolamine solution for the removal of hydrogen sulfide from gaseous mixtures containing hydrogen sulfide. The aqueous alkanolamine solution comprises (i) an amino compound with the formula: R 1 R 2 NCH 2 CH(OH)CH 2 OH wherein R 1 and R 2 independently represent lower alkyl groups of 1 to 3 carbon atoms, (ii) piperazine, and (iii) optionally a physical solvent, wherein said solution does not contain a strong acid. Further, the present invention relates to a process for removing hydrogen sulfide from a gaseous mixture containing hydrogen sulfide, and additionally other acid gases, if present, for example carbon dioxide, comprising the step of contacting the gaseous mixture contain hydrogen sulfide with the aqueous alkanolamine solution, preferably wherein the temperature of the aqueous alkanolamine solution is equal to or greater than 140° F. Examples of the gaseous mixtures include natural gas, synthesis gas, tail gas, and refinery gas.

What is claimed is: 
     
         1 . An aqueous alkanolamine solution for the removal of acid gasses including hydrogen sulfide from gas mixtures containing hydrogen sulfide comprising:
 (i) an amino compound with the formula:
   R 1 R 2 NCH 2 CH(OH)CH 2 OH 
   wherein R 1  and R 2  independently represent methyl, ethyl, propyl, or isopropyl groups,   and   (ii) piperazine,   
       wherein said aqueous alkanolamine solution does not contain an acid having a pKa of 8 or less or an acid-forming material capable of forming in aqueous medium an acid having a pKa of 8 or less. 
     
     
         2 . The aqueous alkanolamine solution of  claim 1  wherein
 (i) the amino compound is present in an amount of from 0.1 to 75 weight percent, 
 and 
 (ii) the piperazine is present in an amount of from 0.1 to 15 weight percent, 
 
       wherein weight percent is based on the total weight of the aqueous alkanolamine solution. 
     
     
         3 . The aqueous alkanolamine solution of  claim 1  wherein the amino compound (i) is 3-(dimethylamino)-1,2-propanediol or 3-(diethylamino)-1,2-propanediol. 
     
     
         4 . The aqueous alkanolamine solution of  claim 1  further comprises (iii) a physical solvent. 
     
     
         5 . The aqueous alkanolamine solution of  claim 4  wherein the physical solvent (iii) is selected from cyclotetramethylenesulfone, dimethyl ethers of polyethylene glycol, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, N-formylmorpholine, N-acetylmorpholine, triethylene glycol monomethyl ether, or mixtures thereof. 
     
     
         6 . A process for removing acid gases from a gaseous mixture comprising the step of contacting the gaseous mixture with the aqueous alkanolamine solution of any of the  claims 1  to  3 . 
     
     
         7 . The process of  claim 6  further comprising the step of steam stripping the aqueous alkanolamine solution such that an acid gas-lean aqueous alkanolamine solution is formed which may be used in said contacting step. 
     
     
         8 . The process of  claim 6  wherein the temperature of the aqueous alkanolamine solution is equal to or greater than 140° F.