Dual Amino‐Functionalised Phosphonium Ionic Liquids for CO2 Capture

Abstract

CO2 is locked up: Dual amino‐functionalised phosphonium ionic liquids (ILs; see figure) have been prepared. The ILs have excellent thermal properties, such as low glass transition temperatures and high thermal decomposition temperatures. The supported CO 2 absorption of four of the ILs on porous SiO 2 was found to approach one mol CO 2 per mol IL, a factor of two greater than that reported before.magnified image A series of 20 dual amino‐functionalised phosphonium ionic liquids, (3‐aminopropyl)tributylphosphonium amino acid salts ([aP 4443][AA], in which [AA]−=[Ala]−, [Arg]−, [Asn]−, [Asp]−, [Cys]−, [Gln]−, [Glu]−, [Gly]−, [His]−, [Ile]−, [Leu]−, [Lys]−, [Met]−, [Phe]−, [Pro]−, [Ser]−, [Thr]−, [Trp]−, [Tyr]− and [Val]−), has been prepared. Their physicochemical properties, such as density, viscosity, glass transition and thermal decomposition temperatures and conductivity, have been determined. In particular, the [aP 4443][AA] ionic liquids (ILs) have low glass transition temperatures ranging from −69.7 to −29.6 °C and high decomposition temperatures (all above 200 °C). The effects of the variation of the structure of [AA]− on the above physicochemical properties are discussed. Furthermore, the CO 2 absorption of [aP 4443][Gly], [aP 4443][Ala], [aP 4443][Val] and [aP 4443][Leu], taken as examples, was investigated. It was found that the supported absorption of CO 2 by the [aP 4443][AA] ILs almost reaches equilibrium within 80 min, the chemical absorption of CO 2 by the [aP 4443][AA] ILs approaches 1 mol CO 2 per mol ionic liquid (twice that reported before) and the [aP 4443][AA] ILs can be repeatedly recycled for CO 2 uptake.