Carbon Dioxide Capture by an Amine Functionalized Ionic Liquid: Fundamental Differences of Surface and Bulk Behavior

摘要

Carbon dioxide (CO_2) absorption by the amine-functionalized ionic liquid (IL) dihydroxyethyl dimethylammonium taurinate at 310 K was studied using surface- and bulk-sensitive experimental techniques. From near-ambient pressure X-ray photoelectron spectroscopy at 0.9 mbar CO_2, the amount of captured CO_2 per mole of IL in the near-surface region is quantified to ～0.58 mol, with ～0.15 mol in form of carbamate dianions and ～0.43 mol in form of carbamic acid. From isothermal uptake experiments combined with infrared spectroscopy, CO_2 is found to be bound in the bulk as carbamate (with nominally 0.5 mol of CO_2 bound per 1 mol of IL) up to ～2.5 bar CO_2, and as carbamic acid (with nominally 1 mol CO_2 bound per 1 mol IL) at higher pressures. We attribute the fact that at low pressures carbamic acid is the dominating species in the near-surface region, while only carbamate is formed in the bulk, to differences in solvation in the outermost IL layers as compared to the bulk situation.