Effect of acidic products from degradation of N-methyldiethanolamine amine on CO₂/H₂S capturing from natural gas

To evaluate the impact of heat-stable salts on the CO₂/H₂S separation from natural gas using 45 wt% of MDEA amine, we comprehensively and systematically examined essential parameters, such as acid gas loading, solvent makeup flowrate, and reboiler duty, in the presence of various acidic oxidative products with Aspen Hysys version 9. We also investigated the pH of an acid/solvent amine aqueous solution at feed amine conditions. Acidic products from the MDEA oxidation considered were glycolic, oxalic, formic, acetic, thiosulfuric, sulfuric, phosphoric, and thiocyanic products. The simulation results showed that the presence of acids with different chemical structures can minimize both the pH of the solution and acid gas loading. However, the energy demand in the reboiler was reduced. Some of these acids, namely thiosulfuric, formic, and thiocyanic acids, worked as promoters in the desorption process and reduced the solvent makeup flowrate by − 51.71%, − 62.24%, and − 86.39%, respectively, compared with fresh 45 wt% MDEA. Furthermore, a countermeasure for exploiting the reduced reboiler energy demand and promoting the desorption rate in the presence of these acids was proposed. The study outputs can serve as a guide for classifying acid impact and developing a countermeasure for using MDEA amine in managing the formation of heat-stable salts during the absorption of acid gases.