Highly Efficient Nonaqueous Phase Change Absorbent for H2S Absorption with Low Energy Consumption

As a highly toxic gas, H2S is conventionally removed via a chemical absorption process. However, the high regeneration energy is still a challenge. 1,5-Diazabicyclo[4.3.0]non-5-ene (DBN)/polyethylene glycol dimethyl ether (NHD) solution was developed as an efficient nonaqueous phase change absorbent for the removal of H2S with low energy consumption. A homogeneous DBN/NHD solution turns into two immiscible liquid phases upon the absorption of H2S, which results from the higher polarity of the product compared to that of the original solution. The loading capacity of H2S can reach 0.16 g·g–1 solvent even under a H2S partial pressure of 10 kPa at 30 °C. After absorption, more than 94% of the absorbed H2S is concentrated in the lower phase, which can be regenerated at 90 °C with an energy consumption estimated to be 1.69 GJ·t–1 H2S. The regeneration energy is 58% lower than that of 30 wt % aqueous solution of N-methyldiethanolamine. 81% of the initial H2S loading was maintained after 4 absorption–desorption cycles. In addition, the selectivity of DBN/NHD solution to absorb H2S from N2 containing H2S and CO2 or from N2 containing H2S and CH4 was investigated. It shows that the selectivity increases with the increase in the volume ratio of H2S to CO2, which can be as high as 27.8 when the ratio is 1:1. CH4 cannot be absorbed in the DBN/NHD solution in the presence of H2S and N2.