Carbon dioxide absorber and carbon dioxide separation/recovery method using the absorber

Abstract

The present invention provides a carbon dioxide absorber capable of efficiently and stably removing carbon dioxide in a gas or solution. This carbon dioxide absorber contains an amine compound, a weakly acidic compound and water, the pKb value of the amine compound in an aqueous solution at 30° C. is 4.0 to 7.0, the pKa value of the weakly acidic compound in an aqueous solution at 30° C. is 7.0 to 10.0, and the weakly acidic compound is present in an amount within the range of 0.01 equivalents to 1.50 equivalents with respect to amino groups of the amine compound.

1 . A carbon dioxide absorber containing an amine compound, a weakly acidic compound and water;
 wherein,   the pKb value of the amine compound in an aqueous solution at 30° C. is 4.0 to 7.0,   the weakly acidic compound is a boric acid or a borate ester having a pKa value of 7.0 to 10.0 in an aqueous solution at 30° C., and   the weakly acidic compound is present in an amount within the range of 0.01 equivalents to 1.50 equivalents with respect to amino groups of the amine compound.   
     
     
         2 . The carbon dioxide absorber according to  claim 1 , wherein the pH of the carbon dioxide absorber at 30° C. is 8.5 to 11.0. 
     
     
         3 . The carbon dioxide absorber according to  claim 1 , wherein the content of the boric acid or the borate ester is within the range of 0.05 equivalents to 0.30 equivalents with respect to amino groups of the amine compound. 
     
     
         4 . The carbon dioxide absorber according to  claim 3 , wherein 25% to 99% of the boric acid neutralizes amino groups of the amine compound. 
     
     
         5 . The carbon dioxide absorber according to  claim 1 , wherein a compound having a pKb value in an aqueous solution at 30° C. of less than 4.0 is not contained. 
     
     
         6 . The carbon dioxide absorber according to  claim 1 , wherein the amine compound has a primary and/or secondary amino group. 
     
     
         7 . The carbon dioxide absorber according to claim  1 , wherein the content of the amine compound is 30% by mass to 55% by mass, and the amount of the water is 40% by mass or more. 
     
     
         8 . The carbon dioxide absorber according to  claim 1 , further containing 1.0% by mass to 6.0% by mass of piperazine and/or 2-methylpiperazine, and containing the weakly acidic compound within the range of 0.5 moles to 2.0 moles with respect to 1 mole of the piperazine and/or 2-methylpiperazine. 
     
     
         9 . The carbon dioxide absorber according to  claim 1 , further containing diethanolamine. 
     
     
         10 . A method for regenerating a carbon dioxide absorber, comprising following steps:
 absorbing carbon dioxide into the carbon dioxide absorber described in  claim 1 , and   releasing the carbon dioxide by heating the carbon dioxide absorber.   
     
     
         11 . A method for separating and recovering carbon dioxide, comprising following steps:
 absorbing carbon dioxide by contacting a gas containing carbon dioxide with the carbon dioxide absorber according to  claim 1 , and   regenerating the carbon dioxide absorber by releasing the carbon dioxide by subsequently heating the carbon dioxide absorber.