Highly selective absorption separation of H2S and CO2 from CH4 by novel azole-based protic ionic liquids

Recently, the selective removal of H 2 S and CO 2 has been highly desired in natural gas sweetening. Herein, four novel azole-based protic ionic liquids (PILs) were designed and prepared through one-step neutralization reaction. The solubility of H 2 S (0–1.0 bar), CO 2 (0–1.0 bar), and CH 4 (0–5.0 bar) was systematically measured at temperatures from 298.2 to 333.2 K. NMR and theoretical calculation were used to investigate the reaction mechanism between these PILs and H 2 S. Reaction equilibrium thermodynamic model (RETM) was screened to correlate the H 2 S solubility. Impressively, 1,5-diazabicyclo[4,3,0] non-5-ene 1,2,4-1H-imidazolide ([DBNH][1,2,4-triaz]) shows the highest H 2 S solubility (1.4 mol/mol or 7.3 mol/kg at 298.2 K and 1.0 bar) and superior H 2 S/CH 4 (831) and CO 2 /CH 4 (199) selectivities compared with literature results. Considering the excellent absorption capacity of H 2 S, high H 2 S/CH 4 , and CO 2 /CH 4 selectivity, acceptable reversibility, as well as facile preparation process, it is believed that azole-based PILs provide an attractive alternative in natural gas upgrading process.