IL-DMEE Non-water System For CO₂ Capture:Absorption Performance And Mechanism Investigation

Carbon dioxide(CO2)is regarded as one of the main greenhouse gases.With the development of modern industry,the excessive emission of CO2 has caused serious climate issues,therefore,CO2 capture and utilization becomes a hot research area.Various techniques have been developed for the removal of CO2,including chemical absorption,physical adsorption,membrane separation and so on.Among them,chemical absorption of CO2 with absorbents,especially alkanolamines that contain basic groups,are the most commonly applied CO2 removal approach.However,these conventional absorbents have obvious drawbacks including high corrosivity and high regeneration energy cost,thus limiting their industrial applications.In recent years,CO2 capture with ionic liquids(ILs)have attracted much attention because of their superiorities including high thermal and chemical stability,low vapor pressure,and low causticity.Additionally,due to their structural designability,the development of highly functionalized ionic liquids is able to increase absorption capacity and rate greatly.However,structural complexity might lead to high viscosity thus limiting industrial applications.By adding solvents including water,alkanolamines and low-viscosity ionic liquids,the viscosity of functionalized ionic liquids can be efficiently decreased.Among them,application of non-water solvents can greatly decrease the regeneration energy consumption while keeping high regeneration efficiency.In this work,dual amino functionalized ionic liquid tetramethylammonium lysinate([N1111][Lys])was successfully synthesized from tetramethylammonium hydroxide([N1111]][OH])and L-lysine through neutralization reaction.The synthesized ionic liquid was then mixed with 2-[2-(dimethylamino)ethoxy]ethanol(DMEE)with different mass fraction(5%,10%,20%,40%,60%and 100%)to obtain a series of non-water absorbents for CO2 capture.The density and viscosity of the absorbents were measured.Using dual-vessel absorption system,CO2 absorption performance including capacity and rate were investigated as a function of IL mass fraction and the influence of viscosity was discussed correspondingly.Absorbent with IL mass fraction of 20%showed superiorities in both absorption capacity and rate,thus applied in further studies including influences of temperature and regeneration performances.Regeneration experiments proved that this non-water absorbent can be efficiently regenerated under mild conditions(80?),indicating low recycle energy consumption.To quantitatively analysis absorption rate,apparent absorption rate constant was successfully calculated from absorption curves.Based on Two-Film Theory,mass transfer coefficients with constant gas-liquid interfacial area were calculated from apparent absorotion rate constants.13C NMR and FT-IR spectra were applied to indicate the absorption process and mechanism,the results of which verified the zwitterion absorption mechanism.From FT-IR spectra,the non-side-chain amino group of[Lys]-was proved to have higher alkalinity to preferentially take part in the deprotonation reaction.This novel non-water mixed system is believed to have prominent absorption performances with low regeneration energy cost,which are significant in industrial applications.