Liquid desulfurizer

Due to proton transfer, the reaction between H2S and MDEA (N-methyldiethanolamine) is almost an instantaneous chemical reaction controlled by gas film.


H2S+R2NCH3=[R2NHCH3]+[HS]-


Because MDEA is a tertiary amine, CO2 reacts with amine only after it forms bicarbonate with water.


CO_2+H_2+R2NCH_3 R2NHCH_3+HCO_3


Because CO2 and water need a slow intermediate process, the huge difference in reaction rate constitutes the basis of selective absorption, that is, MDEA has a high selectivity for H2S absorption in the presence of CO2.


The acid tail gas is washed out by water to remove CH3OH and HCN, then enters the bottom of the absorption tower and contacts with the lean amine liquid added from the top countercurrent. The purified gas after desulfurization escapes from the top of the absorption tower. The rich amine solution is heated by heat exchanger and lean amine, and then regenerated in the regeneration tower. The regenerated acid gas containing H2S and CO2 removed is fed into the Claus unit, and lean amine is pumped to the absorption tower through cooling.