Ultra-Low Viscosity Carbonyl-Functionalized Deep Eutectic Solvents for Efficient and Selective H2S Separation from CO2 and CH4

Abstract The efficient and selective elimination of H2S from natural gas holds considerable practical and scientific importance for gas purification. However, the lack of suitable media that enable high H2S/CO2 selectivity has constrained the resource-oriented utilization of both gases. Herein, we present for the first time the synthesis of a series of carbonyl-functionalized deep eutectic solvents (CFDESs). Systematic gas absorption evaluations demonstrate that these CFDESs enable selective and efficient capture of H2S over CO2 and CH4. It is noteworthy that the CFDES derived from 4-methylcyclohexanone (4M-DMAEE) achieves a remarkable H2S uptake of 1.80 mol/mol (7.34 mol/kg) under conditions of 313.2 K and 1.0 bar, marking one of the highest recorded values to date. Leveraging the specific recognition ability of carbonyl groups toward H2S and CO2, 4M-DMAEE shows outstanding H2S/CO2 separation selectivity, particularly under low partial pressure conditions. Moreover, the H2S/CH4 selectivity reaches 519–858 under conditions of 313.2 K and 1.0 bar, outperforming most reported materials. Mechanistic investigations combining NMR, FT-IR, and theoretical calculations reveal a cascade H2S capture process involving nucleophilic addition reactions. Importantly, these CFDESs also feature ultra-low viscosity (<5 mPa·s at 40 °C), favorable mass transfer performance, and excellent cyclic regeneration capability. This work offers a highly selective and energy-efficient separation medium for applications requiring preferential H2S removal and recovery in resource-oriented natural gas upgrading.