Mechanism Of Mass Transfer With Chemical Reaction Of Co₂Absorption Into The Mixed Aqueous Solution Of MEA And Ionic Liquid

Monoethanolamine (MEA) is one of the most conventional absorbents for CO2capture from flue gas in the past few years and has still suffer several shortcomings. Herein, a mixed absorbent of MEA and ionic liquids was proposed to achieve CO2capture. The aim of the new system is to enhance the MEA process and obtain higher absorbtion capacity, antioxidant activity and regeneration efficiency. The hydrophilic ionic liquids used in this work were commercial-available or were synthesized in our laboratory. The main conclusions of this dissertation are:(1) Screening from some conventional ionic liquids, it was found that the mixed solution of MEA and [Bmim]BF4have a highest absorption capacity compared with pure MEA aqueous. The optimum mole ratio of MEA to [Bmim]BF4was found to be7:3. The mixed absorbent owns higher stability and antioxidant activity compared with aqueous MEA solution in the present of8%O2. Additionally, the absorbent could be well recycled by thermal regeneration after multi-cycle experiments.(2) Based on the zwitterions mechanism and the absorption results, the reaction mechanism of the CO2absorption into the mixed solution of MEA and [Bmim]BF4was clarified. The reaction between CO2and MEA was still the dominant reaction in the mixed absorbent solution. And,[Bmim]BF4has a positive effect on enhancing the hydration of CO2which could improve the whole absorption rate. The reaction rate constant k2k2,mix and k2,IL of the mixed solution of MEA/[Bmim]BF4were found to be3487.6m3·kmol·s-1and1936.7m3·kmol-1·s-1, respectively.(3) A new hydrophilic amino acid ionic liquid ([C20Hmim][Gly]) that was functionalized based imidazolium ionic liquid with glycine anions and hydroxy group was designed for CO2absorption. Since [C20Hmim][Gly] is a solid at room temperature, chemical reaction between CO2and [C20Hmim][Gly] was occurring only in the presence of water. The absorption capacity of [C20Hmim][Gly] was0.575mol CO2/mol absorbent that was similar to the equimolar stoichiometry by the zwitterion mechanism. Furthermore,[C20Hmim][Gly] aqueous solution was mixed with MEA into aqucous solution for CO2capture, and the results showed a great intoxication ability and high regeneration efficiency compared with pure MEA solution, making the CO2capture by this mixture system more efficient and economic.(4) The reaction mechanism of the CO2absorption into the mixed solution of MEA and [C2OHmim][Gly] was clarified. The mass transfer model of this system was established based on the membrane model and permeation model. Some important kinetic parameters such as the reaction rate constant and the enhancement factor were obtained. The reaction rate constant k2,mix and k2AAILs of the mixed solution of MEA/[C2OHmim][Gly] were found to be6506.4m3·kmol·s-1and8980.6m3·kmol·s-1, respectively.The absorption and regeneration of the mixed solution of MEA/[Bmim]BF4and MEA/[C2OHmim][Gly] were contrast discussion. The results indicated that both the [Bmim]BF4and [C20Hmim][Gly] both could enhance the MEA process by great absorbtion capacity, good antioxidant activity and high regeneration efficiency. The results of this work will provide a new pathway for the CO2absorption and also will provide some theoretic data for the industrial application of this new technology.