Development Of Absorbents Based On Multiple Site-functionalized Ionic Liquids And Research On The Law Of Carbon Dioxide Capture

The reduction of greenhouse gas emission,which considered as the key factor to mitigate global warming,has made the development of CO2 emission reduction technology become one of the hot topics in the research field of climate and environment.As a promising absorbent for CO2,functionalized ionic liquids have many problems,such as complex preparation,high viscosity,insufficient absorption capacity,high energy consumption of regeneration,corrosive and easy degradation in aqueous solution and poor thermal stability.Therefore,this dissertation researched on multiple site-functionalized ionic liquids for CO2 capture and three types of novel absorbents based on multiple site-functionalized ionic liquid have been developed.On this basis,the reaction mechanism and the mechanism of the ubiquitous phase-change formation in CO2 capture of multiple site-functionalized ionic liquids were discussed in detail.The main research results of this dissertation are as follows:(1)A multiple-amino organic amine with simple structure,cheap and readily available materials was adopted as amino donor to prepare cationic amino functionalized IL,which has multiple reaction sites for CO2 capture and can be synthetized by one-step neutralization reaction.This IL was mixed with anhydrous solvents to reduce viscosity and restrain the problems of corrosion,degradation,regeneration and high energy consumption in the aqueous solution.With a systematic study on the CO2 capture performance under the conditions of different cosolvents,anion,moisture content,temperature,it was found that the best absorption performance of [DETAD]Br could reach 1.184 mol CO2/mol IL in PEG200 solution.The viscosity of the solution after absorption was only 83.2 mPa·s at 50?,which was obviously lower than lots of other functionalized ILs.Additionally,with a focus on the effects of solvent and anion structure on phase change formation,as well as a discussion on the corrosion and oxidation properties,it was indicated that phase-change formation could not only improve CO2 absorption,but also enable [DETAH]Br-PEG200 system to show better corrosion resistance and low oxidation degradation at higher temperature when compared to DETA and MEA aqueous solution.TG-DSC analysis and experimental results of regeneration revealed that the [DETAH]Br-PEG200 system could realize rapid desorption under at 80? with N2 bubbling,and the CO2 absorption could be performed at least for five continuous absorption-desorption cycles without significant loss of CO2 capturing and releasing capability.Furthermore,spectroscopic analysis(UV,ATR-IR,13 C NMR,XRD,SEM,1H NMR),theoretical calculation,experimental data and experimental phenomenon were combined to study the mechanism of reaction and phase change formation in CO2 capture.It was proposed that phase change formation was a dynamic process involving many aspects and multiple levels.Finally,it was proved that a O-H···:N type of H-bonding and the stabilizing effects of bromide ion would be the main factors that contributed to stabilizing the products,keeping the system stable and delaying phase change formation.(2)Based on the fact that anions showed a greater impact on CO2 capture performance of and increasing N atom reaction sites with electronegativity could improve CO2 capture performance,an amino group was introduced into the anion,and anionic and cationic functionalized ionic liquids were prepared,also,several related CO2 absorbents were developed.With a systematic study on the physicochemical properties,CO2 absorption of ionic liquids in PEG200 as well as the improvement effect of ionic liquids on MDEA aqueous solution,it was found that when concentration was 20wt%,the corresponding CO2 capture capacity of [DETAH][Trp]-PEG200 and [DETAH][Pro]-PEG200 could be up to 1.789 mol and 1.513 mol CO2/mol IL,the viscosities were only 47.1 mPa·s and 33.5 mPa·s at 50?,indicating good fluidity.An addition of 6.67wt%[DETAH][Trp] could effectively activate MDEA solution,and significantly increase the CO2 absorption capacity and absorption rate.The experimental results of CO2 release revealed that [DETAH][Trp]-PEG200 could achieve regeneration at 90 ? with N2 bubbling.The recycling performance was stable and the energy consumption was relatively low.In addition,with a change of the experimental conditions and a combination of the viscosity and conductivity analysis results,it was indicated that the absorption performance was more affected by relatively high concentration and temperature due to the stronger anion and cation association.ATR-IR and 13 C NMR analysis on the products revealed that the primary amine groups in [DETAH][Trp] structure absorbed CO2 through 1:2 mechanism to form carbamate.Hydrogen bonding and anion in the system were proposed to maintain the system stable and without phase change formation.(3)A phenol group was introduced into the anion,and the O atom which could realize the equimolar CO2 absorption was used as the reaction site instead of the N atom.It was aimed to prepare amino and phenolic functionalized ionic liquids,which could improve CO2 absorption capacity and regeneration performance.With an analysis on the physicochemical properties of ionic liquids in PEG200 solution,it was found that the density of the ionic liquid solution showed a good linear relationship with temperature.Introducing a halogen atom in phenolic groups will result in hydrogen bond formation,which contributed to an enhancement of anion and cation association,an increase of the viscosity of ionic liquid and a reduction of the conductivity.Additionally,with a systematic study on the CO2 capture performance at different conditions,viscosity changes as well as the improvement effect of ionic liquids on MDEA aqueous solution,it was showed that when the concentration was 20wt%,the corresponding CO2 absorption capacity of [DETAH][2-Br-PhO]-PEG200 and [DETAH][4-Br-PhO]-PEG200 could reach 2.007 and 1.802 molCO2/mol IL,respectively,and the absorption ability kept stable at relatively high temperature and concentration.The viscosities of the mixed solution at 50? were in the range of 20-35mPa·s.An addition of certain amount of [DETAH][2-Br-PhO] and [DETAH][4-Br-PhO] in MDEA aqueous solution could significantly improve the absorption rate and capture capacity.TG-DSC analysis and the experimental results of CO2 release revealed that the systems of [DETAH][2-Br-PhO]-PEG200 and [DETAH][4-Br-PhO]-PEG200 could be rapidly regenerated at 80? with N2 bubbling.The recycling performance was stable and the energy consumption was relatively low,which enabled them be to a competitive and reversible CO2 trapping agent.ATR-IR and 13 C NMR analysis proved that the amino groups of ionic liquid reacted with CO2 through 1:2 mechanism to form carbamate,and phenol groups through 1:1 mechanism to form alkyl carbonate.Besides,strong hydrogen bonds were form between ionic liquids and PEG molecules,which kept the system stable without phase change formation together with the interactions of anions.