Enhanced acid gas capture in Rectisol process with methanol-DES mixed absorbents

Rectisol process is a widely used technology to absorb the acid gases such as CO₂ and H₂S produced from the coal gasification. The low operating temperature and the high operating pressure cause the high energy consumption of the absorption process. To achieve energy efficiency, the deep eutectic solvent (DES) choline chloride-monoethanolamine (1:5), which features high capacity for absorbing acid gases, was selected as the key component of the mixed absorbent blended with methanol. The key physicochemical properties of methanol-DES mixed absorbents with different mass ratios, which significantly affect practical application, were investigated experimentally. The mixed absorbents with different mass ratios were used to absorb CO₂ and H₂S in the shifted gas absorption column and mixing effects were analyzed. The results show that the mixed absorbent with the mass ratio of 6:4 exhibits the lowest refrigeration cost. The dynamic control structure of the process was also developed to maintain the absorption performance under ±10 % CO₂ composition disturbances. A multi-proportion control structure was explored to control the shifted gas absorption column well. This comprehensive approach not only boosts economic viability but also supports environmental sustainability, making it a viable solution for industrial applications.