Polyamines, synthesis method thereof and use thereof for the selective elimination of H2S from a gaseous effluent comprising CO2

A process for selectively removing H2S with respect to CO2 from a gaseous effluent comprising H2S and CO2, in which a step of absorption of the acid compounds is carried out by bringing the gaseous effluent into contact with an absorbent solution comprising:

• (a) water,
• (b) at least one main nitrogenous compound comprising at least one tertiary amine function or one secondary amine function comprising two secondary carbons in the α and α′ positions with respect to the nitrogen atom or at least one tertiary carbon in the alpha or beta position with respect to the nitrogen atom, and
• (c) at least one secondary nitrogenous compound belonging to a polyamine family, resulting from the reaction between piperazine and an epihalohydrin or a 1,3-dihalo-2-propanol, and corresponding to formula (I):
• in which:
• n is between 2 and 100,
• each R1 is independently a hydrogen atom or an alkyl radical comprising between 1 and 8 carbon atoms or a hydroxyalkyl radical corresponding to formula (II):
• in which:
• each R2 is independently a hydrogen atom or an alkyl radical comprising between 1 and 6 carbon atoms,
• two R2 radicals may be linked to one another by a covalent bond so as to form a ring when said two R2 radicals are alkyl radicals comprising between 1 and 6 carbon atoms.