Natural gas sweetening using tailored ionic liquid-methanol mixed solvent with selective removal of H2S and CO2

Abstract

Natural gas is often preferred in various energy applications due to its many advantages over conventional fossil fuels such as oil and coal. However, the removal of pollutants from natural gas, particularly hydrogen sulfide (H2S) and carbon dioxide (CO2), requires complex treatment strategies, significantly impacting the cost of natural gas production. In this work, we propose a mixed solvent combining ionic liquid (IL) and methanol, which can selectively and simultaneously remove H2S and CO2 by customizing the IL structure and its ratio in the solvent. This purification process offers improved efficiency and energy savings compared to traditional methods. To determine the optimal IL structure in the mixed solvent, a computer-aided design method was employed. Through solving the formulated MINLP problem, the IL 1-methyl pyridinium trifluoroacetate ([C1OHPy][TFA]) was identified as having the highest affinity for H2S, making it suitable for use in the IL-methanol mixed solvent. Furthermore, the upgrading process of high-sulfur natural gas using the IL-methanol mixed solvent was simulated and evaluated, comparing it to the benchmark natural gas upgrading (Rectisol) process. The results demonstrate that the IL-methanol mixed solvent natural gas upgrading process achieved a 55.57 % power savings and reduced the annual total cost (TAC) by 23.90 % compared to the Rectisol process. These findings highlight the significant potential of our tailored IL-methanol mixed solvent in natural gas production.