Absorbent for selective removal of hydrogen sulfide from a fluid stream

A process for the selective removal of hydrogen sulfide over carbon dioxide from a fluid stream, said process comprising:

• contacting the fluid stream which is selected from gases and which has a total pressure of at least 3.0 bar, with an absorbent, comprising an aqueous solution comprising:
• a) a tertiary amine;
• b) a sterically hindered secondary amine of the general formula (I)
• in which R1 and R2 are each independently selected from C1-4-alkyl and C1-4-hydroxyalkyl;
• R3, R4, R5 and R6 are each independently selected from hydrogen, C1-4-alkyl and C1-4-hydroxyalkyl, with the proviso that at least one R4 and/or R5 radical on the carbon atom bonded directly to the nitrogen atom is C1-4-alkyl or C1-4-hydroxyalkyl when R3 is hydrogen;
• x and y are integers from 2 to 4 and z is an integer from 1 to 4;
• where the molar ratio of b) to a) is in the range from 0.3 to 0.7, and
• c) an acid in an amount, calculated as neutralization equivalent relative to the protonatable nitrogen atoms in a) and b), of 1.0 to 9.0%;
• wherein
• the absorbent does not comprise a sterically unhindered primary or secondary amine,
• there is a partial hydrogen sulfide pressure of at least 0.1 bar and/or a partial carbon dioxide pressure of at least 0.2 bar in the fluid stream;
• and wherein the selectivity for hydrogen sulfide over carbon dioxide is less than 1.6.