The CO₂ Uptake Performance Study Of Amine-and Aprotic Heterocyclic Anion-based Dual Functionalized Ionic Liquid Solutions

Functionalized ionic liquids?FILs?were put forward as potential absorbent for CO₂ capture.Increasing the number of amino groups on ions is a traditional way to promote the CO₂ uptake performance of FILs,however,limited by the steric hinderance and stability of carbamates,the number of amino groups couldn't augment infinitely.Distinguished from amine-based FILs,the aprotic heterocyclic anion?[AHA]^-?-based FILs could equimolarly capture CO₂ and be easilier desorbed.Therefore,this work aims to synthesize the novel amine and aprotic heterocyclic anion-based dual functionalized ionic liquids?[DETAH][AHA]?by combining diethylenetriamine?DETA?with imidazole,pyrazole,triazole?Im,Py,Tz?,respectively,for highly-reversely CO₂ capture.This work introduced quantum chemistry calculation technology for assisting the synthesization of FILs,both the computer simulation technology and experimental research were applied to study the CO₂ capture performance of such FILs.Next,the CO₂absorption-desorption mechanism of the FILs was characterized by carbon nuclear magnetic resonance(¹³C NMR)characterization.Then,the relative model was built to study the mass-transfer kinetics of FILs absorbing CO₂.Finally,the heat duty of such saturated FIL solutions was investigated to evaluate its energy-saving potentials.The innovative results from this work were listed below:?1?The quantum chemistry calculation results of CO₂ capture into[DETAH][AHA]:The values of natural bond orbital?NBO?charges of N atom of amino groups on[DETAH]⁺are higher than those of N atoms from deprotonated azoles,which indicated that the[DETAH]⁺has higher CO₂affinity over azoles.The length of newly formed N-H bond is positively correlated with the basicity of FILs,and the interaction energies??E?of FIL are negatively correlated with the viscosity and thermal stability of FILs,which help to predicted the physicochemical property of FILs.The?E as well as reaction enthalpy changes??H?between different[AHA]^-and CO₂ follows[Im]^->[Py]^->[Tz]^-,the stronger?E and?H indicated the functional groups would be easilier to interact with CO₂.Additionally,the[AHA]^-would easilier to react with CO₂ forming carbamate than promote CO₂ hydrolysis.Introducing protonated[AHA]-H product will lower the activation energies(?E_act)of the regeneration reaction,which means the introduction of[AHA]^-helps to promote the CO₂ desorption of the FILs.?2?The CO₂ absorption-desorption performance measurement of the[DETAH][AHA]:Under 40^oC,the CO₂ absorption capacity of 0.5 M[DETAH][Im],[DETAH][Py]and[DETAH][Tz]were 11.94,11.39?10.10mol CO₂/kg IL,respectively,which were all higher than that of traditional MEA solution.Regeneration under 120^oC and 90 min,the 1^stregeneration efficiencies of[DETAH][Im],[DETAH][Py]and[DETAH][Tz]were 93.66%,94.62%and 97.93%,respectively.Under the same condition,the regeneration efficiencies of[DETAH][AHA]were still kept above 90%after 5^thcyclic regeneration.The experimental results were consistent with the prediction of quantum chemistry calculation,which proved the reliability of theoretical calculation.?3?Based on ¹³C NMR spectra analysis,the CO₂ absorption-desorption mechanism of[DETAH][AHA]was clarified.During the absorption process,the amino groups on[DETAH]⁺would react with CO₂ forming carbamate,the[DETAH]⁺would be prior than[AHA]^-to react with CO₂,which contributing to the main CO₂ absorption capacity;the[AHA]^-could directly react with CO₂to produce carbamates and finally hydrolyze to carbonates and protonated[AHA]-H products to increase the CO₂ absorption capacity of the solution;then,the carbamates would be hydrolyzed to HCO₃^-/CO₃^2-.During the desorption process,carbamates and HCO₃^-/CO₃^2-would decompose to release active amino groups and CO₂.More importantly,the protonated[AHA]-H products could contribute the carbamates to decompose into HCO₃^-/CO₃^2-,and release active amino groups.Therefore,[AHA]^-has synergistic effect with[DETAH]⁺in CO₂ absorption-desorption process to ensure the outstanding CO₂ absorption-desorption capability of[DETAH][AHA].?4?The kinetics and regeneration heat duty evaluation of[DETAH][AHA]:According to the linear fitting of(lnk_2,FIL)to?1/T?,the Arrhenius relational expression of CO₂ capture into[DETAH][Im]solution was k₂?28?1.0365?10^{1 2}exp?7?-5873.67/T?8?,whose CO₂absorption barrier?E_a?was 48.83kJ/mol;meanwhile,the Arrhenius relational expression of CO₂ capture into[DETAH][Tz]solution wask₂?28?3.5361?10^{1 2}exp?7?-6380.60/T?8?,whose CO₂absorption barrier?E_a?was 53.05 kJ/mol.The total energy consumption of[DETAH][Im]and[DETAH][Tz]solutions were 2.94 and 2.84 GJ/ton CO₂,which were 18.56%and 21.33%lower than Q_totalotal of traditional MEA solution.[DETAH][AHA]solutions present as a potential candidate for CO₂ capture.