Under what circumstances would a physical solvent based acid gas removal process like Selexol be preferred over an amine based process?

A physical solvent-based acid gas removal process like Selexol is preferred over an amine-based process under circumstances characterized by high partial pressures of acid gases, especially CO2, and when selective removal of H2S from CO2 is desired. Selexol, which uses a physical solvent like dimethyl ether of polyethylene glycol (DMPEG), relies on the physical absorption of acid gases into the solvent based on their partial pressures. Amine-based processes, on the other hand, involve a chemical reaction between the amine solvent and the acid gases. When the partial pressures of acid gases are high, physical solvents exhibit a higher loading capacity compared to amines, leading to reduced solvent circulation rates and smaller equipment sizes, translating to lower capital and operating costs. Also, physical solvents are more effective at bulk CO2 removal when high CO2 concentrations are present. Selexol also demonstrates a higher selectivity for H2S over CO2 compared to many amine solvents. This selectivity is crucial when it's necessary to remove H2S while minimizing the co-absorption of CO2, for example, when the CO2 needs to be sequestered or used for enhanced oil recovery. Furthermore, physical solvents are less susceptible to degradation and foaming compared to amine solvents, particularly in the presence of contaminants like hydrocarbons or oxygen. Physical solvents also require less energy for regeneration as they rely on pressure reduction or stripping with a non-reactive gas, rather than the high-temperature stripping needed for amine regeneration, which lowers operating costs. Therefore, high acid gas partial pressures, selective H2S removal requirements, and the need for lower energy consumption favor the use of physical solvent processes over amine-based processes.