Cyclic-amine-comprisng absorption medium for removing acid gases

Abstract

An absorption medium for removing acid gases from a fluid stream comprises an aqueous solution of A) at least one cyclic amine compound having solely tertiary amine groups and/or sterically hindered secondary amine groups and B) at least one cyclic amine compound having at least one sterically unhindered secondary amine group. The absorption medium comprises, e.g., an aqueous solution of A) 1-hydroxyethylpiperidine and/or triethylenediamine and B) piperazine. The absorption medium is particularly suitable for separating off carbon dioxide from flue gases and satisfies the following criteria: (i) sufficient capacity at low CO 2 partial pressures; (ii) sufficiently rapid absorption rate at low CO 2 partial pressures; (iii) stability toward oxygen; (iv) low vapor pressure for reducing solvent losses; and (v) low energy requirement for regeneration of the absorption medium.

1 - 13 . (canceled) 
     
     
         14 . An absorption medium for removing acid gases from a fluid stream, which absorption medium consists essentially of
 A) at least one cyclic amine, compound having solely tertiary amine groups   
       and
 B) at least one cyclic amine compound having at least one sterically unhindered secondary amine group, 
 
       wherein A) and B) are present as an aqueous solution and wherein the total concentration of A)+B) is 10 to 60% by weight. 
     
     
         15 . The absorption medium according to  claim 14 , wherein the weight ratio of A) to B) is 0.5 to 4. 
     
     
         16 . The absorption medium according to  claim 14 , wherein the cyclic amine compound A) has a 5- to 7-member ring of the general formula I, 
       
         
           
           
               
               
           
         
       
       where m is 1, 2 or 3; R is C 1 -C 4 -alkyl or C 2 -C 4 -hydroxyalkyl; or, in the event that in is 2, two moieties R together can form a C 2 -C 3 -alkylene bridge; R′ is H, C 1 -C 4 -alkyl or C 2 -C 4 -hydroxyalkyl; R″ is H or C 1 -C 4 -alkyl; Z is a bond or C 1 -C 6 -alkylene. 
     
     
         17 . The absorption medium according to  claim 16 , wherein the cyclic amine compound
 A) is selected from the group consisting of   triethylenediamine, 1-hydroxyethylpiperidine, bis(hydroxyethyl)piperazine, N,N′-dimethylpiperazine and 1-methyl-2-pyrrolidineethanol.   
     
     
         18 . The absorption medium according to  claim 14 , wherein the cyclic amine compound B) has the general formula II 
       
         
           
           
               
               
           
         
       
       where Z is C 2 -C 4 -alkylene which is optionally interrupted by 0 or a group NR′″, where R′″ is H, C 1 -C 4 -alkyl or C 2 -C 4 -hydroxyalkyl, and which is optionally monosubstituted or polysubstituted by C 1 -C 4 -alkyl or C 2 -C 4 -hydroxyalkyl. 
     
     
         19 . The absorption medium according to  claim 18 , wherein the cyclic amine compound B) is selected from the group consisting of piperazine, homopiperazine, 1-hydroxyethylpiperazine, 4-hydroxyethylpiperidine, 1-methylpiperazine and 2-methylpiperazine. 
     
     
         20 . The absorption medium according to  14 , consisting essentially of an aqueous solution of
 A) 1-hydroxyethylpiperidine and/or triethylenediamine; and   B) piperazine.   
     
     
         21 . A method of removing acid gases from a fluid stream, which comprises bringing the fluid stream into contact with an absorption medium according to  claim 14 . 
     
     
         22 . The method according to  claim 21 , wherein the partial pressure of carbon dioxide in the fluid stream is less than 500 mbar. 
     
     
         23 . The method according to  claim 21 , wherein the fluid stream originates from
 a) the oxidation of organic substances,   b) the composting or storage of waste materials comprising organic substances, or   c) the bacterial decomposition of organic substances.   
     
     
         24 . The method according to  claim 21 , wherein the fluid stream is contacted with the absorption medium in a scrubbing column operated in countercurrent flow in the presence of activated carbon present in the interior of the scrubbing column, wherein a discontinuous liquid absorption medium phase develops in the interior of the scrubbing column. 
     
     
         25 . The method according to  claim 21 , wherein the loaded absorption medium is regenerated by
 a) heating,   b) expanding,   c) stripping with an inert fluid   
       or a combination of two or all of these steps.