Dual Amino‐Functionalised Phosphonium Ionic Liquids for CO₂ Capture

CO 2 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.