Two Kinds Of Quaternary Ammonium-based Crosslinked Polymeric Ionic Liquids And Their Applications In Separating CO₂ By Pressure Swing Absorption

The emission of large amount of carbon dioxide(CO2)from the burning of fossil fuels is considered to be the main cause of global warming.Poly(ionic liquid)s(PILs)have been widely studied due to its high thermal stability,designed cations and anions,and high selectivity to CO2.PILs are becoming a new research hotspot for CO2 capture.However,the CO2 absorption by PILs is relatively low according to literature report.With respect to the problem,this work focuses on the development of quaternary ammonium-based crosslinked PILs(clPILs)as the absorbents of CO2.Consequently,two kinds of quaternary ammonium-based clPILs were designed and synthesized,and different drying methods were employed to study the influence of clPILs structure(crystal forms)on their absorption to CO2,and finally selected clPILs were applied to the CO2 separation performance from high-pressure syngas(H2/CO/CO2).EGDMA-crosslinked-P[VBTMA][Cl]was prepared via a one-step synthesis by copolymerizing ethylene glycol dimethacrylate(EGDMA)and the ionic liquid[VBTMA][C1]with different mass ratios.The as-prepared clPIL was characterized using energy dispersive spectrometer(EDS),infrared rpectrum(FTIR),X-ray diffraction(XRD)and differential scanning calorimetry(DSC)techniques.The influence of the dosage of EGDMA and drying methods on its CO2 absorptionance was researched by using the high-presure spring quartz method;the method was also used to evaluate the stability by cyclic CO2 absorption-desorption test and selectivity for CO2 absorption at 296.2 K and 5.0 MPa.Results showed that within a certain mass ratio(5:1,10:1,15:1)of IL to EGDMA,the less crosslinking agent was,the higher the absorption capacity of the clPIL had.The clPIL possessed different crystallinity forms through different drying methods(supercritical CO2 drying,freeze drying,ambient pressure drying);the CO2 absorption decreased with the increase of crystallinity.The clPIL showed excellent stability,regeneration and selectivity for CO2 absorption.P[CnDVBTMA][Cl]with different carbon chains were prepared with 4-vinylbenzyl chloride and tetramethyl diamine with different chain lengths(tetramethylenedi amine,tetramethylethylenediamine,tetramethylenediamine)by the free radical polymerization.The as-prepared clPILs were characterized using NMR,FTIR,XRD and DSC techniques.Then the influence of the carbon chain lengths and drying methods on CO2 absorptionance was studied by using the high-presure spring quartz method;the method was also used to evaluate the stability by cyclic CO2 absorption-desorption test and selectivity for CO2 absorption at 303.2 K and 5.0 MPa..Results showed that the longer the carbon chain was,the higher the absorption capacity of the clPIL had.The clPILs possessed different crystallinity forms from different drying methods.Again,the CO2 absorption decreased with the increase of crystallinity.The clPIL showed excellent stability,regeneration and selectivity for CO2 absorption.Furthermore,results showed that XRD could not tell the difference of crystallinity of clPILs,but DSC could reveal the crystallinity degree of clPILs.A pressure swing absorption apparatus was established for examining the performance of CO2 separation from the H2,CO and CO2 mixture at 296.2 K,5.0 MPa by using EGDMA-crosslinked-P[VBTMA][Cl]as the absorbent and 303.2 K,5.0 MPa a by using P[C3DVBTMA][Cl]as the absorbent,respectively.Results showed that EGDMA-crosslinked-[VBTMA][Cl]could reduce the CO2 in the syngas from 19.0%to 2.4%,while P[C3DVBTMA][Cl]could reduce CO2 from 19.0%to 0.Both the materials can selectively capture CO2,but P[C3DVBTMA][Cl]has better performance than EGDMA-crosslinked-P[VBTMA][Cl].