An imidazole-based DES serving as a “courier” for the efficient coupling of HCl capture and conversion under mild conditions

Abstract

Many studies have been focused on the selective separation of hydrogen chloride (HCl) gas, but its capture and conversion in situ is still at a standstill. Herein, a pioneering attempt to employ a deep eutectic solvent (DES) as a “courier” to combine HCl capture and in situ conversion has been presented. Impressively, the highest HCl absorption capacity is determined to be 3.95 mol/mol, or 0.672 g/g, or 18.4 mol kg⁻¹ at 1.0 bar and 30 °C in a binary DES based on EmimCl/Im. The internal transmission mechanism between imidazole and HCl was revealed by DFT-based theoretical calculations. The reaction between HCl and epoxides achieved 99% conversion under mild conditions in the absence of a solvent, making the entire reaction ecologically benign. Water extraction was used to recycle the DES from the reaction system, and it maintained good catalytic performance after ten cycles. The exhaust HCl–SO₂ mixed gases from the sucralose industry were further investigated, which proved the possibility of selective conversion of HCl. Furthermore, a plausible reaction–separation–integration (RSI) strategy was proposed to avoid the high energy consumption of desorption, which provides a novel insight into future applications. It is believed that the good results, combined with the simplicity of operation and the high recyclability of the catalyst, make this green method environmentally friendly and cost-effective. This work reveals an effective approach for the coupling of HCl capture and conversion under mild conditions.