Pore size-excluded low viscous porous liquids for CO2 sorption at room temperature and thermodynamic modeling study

Abstract

Herein, we report porous ionic liquids (type-III) designed to utilize microporous ZIF-8 moieties with functional ionic liquids such as 8-(2-methoxyethyl)-1,8-Diazabicyclo[5.4.0]undec-7-en-8-ium, Bis(trifluoromethane)sulfonamide ([MEDBU][TFSI] and Trioctylammonium 4-para-tert-butylbenzoiate [TOAH][PTBBA]). The prepared materials were thoroughly characterized by means of XRD, FT-IR, SEM, TEM, BET, TGA, DSC and viscometry techniques. The idea of combining the intrinsic properties of ionic liquids with microporous architecture to prepare porous ionic liquids yields promising fluidic materials that have received attention in industrial applications such as gas sorption and separation etc. The prepared porous ionic liquids possess unique physico-chemical properties such as low viscosity, high thermal stability, low vapor pressure, reusability and their fluidic nature renders the materials suitable for CO2 capture. Herein introduced porous ionic liquids (ILs) showed enhanced CO2 uptake (0.92 mmol/g in [TOAH][PTBBA]-Z100 and 1.16 mmol/g in [MEDBU][TFSI]-Z200), or in other words, 15–47% higher sorption capacity compared to neat ionic liquids. This concept overcomes the drawbacks of highly viscous ILs and their limited CO2 sorption capacity. Thermodynamic modeling further demonstrated that the enthalpy of sorption is only −9.99 kJ mol−1, indicating that significantly less energy is required for regeneration. This is promising for the potential use of these fluidic materials in continuous separation processes on an industrial scale, as a better alternative to the existing hazardous amine scrubbing.