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

Abstract

As a highly toxic gas, H 2 S 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 H 2 S with low energy consumption. A homogeneous DBN/NHD solution turns into two immiscible liquid phases upon the absorption of H 2 S, which results from the higher polarity of the product compared to that of the original solution. The loading capacity of H 2 S can reach 0.16 g•g −1 solvent even under a H 2 S partial pressure of 10 kPa at 30 °C. After absorption, more than 94% of the absorbed H 2 S 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 H 2 S. The regeneration energy is 58% lower than that of 30 wt % aqueous solution of N-methyldiethanolamine. 81% of the initial H 2 S loading was maintained after 4 absorption−desorption cycles. In addition, the selectivity of DBN/NHD solution to absorb H 2 S from N 2 containing H 2 S and CO 2 or from N 2 containing H 2 S and CH 4 was investigated. It shows that the selectivity increases with the increase in the volume ratio of H 2 S to CO 2 , which can be as high as 27.8 when the ratio is 1:1. CH 4 cannot be absorbed in the DBN/NHD solution in the presence of H 2 S and N 2 .