Study On Mass Transfer And Reaction Performance For CO₂ Absorbed By Ionic Liquid/MEA Mixture In Microchannel

Excessive CO2 emissions have caused serious global warming effect,therefore,it is essential to carry out CO2 capture.Ionic liquids,as a new type of green solvent,has a broad application prospect in absorbing CO2 with its highly efficient and environmentally friendly absorption method.However,the high viscosity of the ionic liquids hinders its gas-liquid mass transfer.In this paper,ionic liquid([NH2e-mim][BF4]),with lower viscosity but higher CO2 absorption capacity and rate,and ethanolamine(MEA)was mixed with their respective advantages in reducing carbon dioxide,which is expected to improve the deficiency of the current alcohol amine process and meet the needs of large-scale industrial CO2 emission reduction.MicroChannel reactors,as a process intensification reactor,are becoming an attractive altermative to traditional equipment,considering their unique advantages of large surface area,small reaction system volume and enhanced mass transfer and heat rates.In this paper,the kinetic equation,hydrodynamic performance,gas-liquid mass transfer and reaction performance of CO2 absorbed by[NH2e-mim][BF4]/MEA mixture in microchannel were studied.The kinetic parameters of the absorption of CO2 in MEA and[NH2e-mim][BF4]were first measured.The initial pressure increased,the absorption rate increased;the concentration of the absorbent increased and the reaction rate increased;when the temperature gradually increased,the absorption decreased,but the reaction rate increased.The activation energy of CO2 absorbed by MEA is 28990 J·mol-1.The activation energy of CO2 absorbed by[NH2e-mim][BF4]is 19373 J·mol-1.The smaller the activation energy was,the easier the reaction occurred.Then,the VOF model was used to calculate the hydrodynamics performance of the CO2-[NH2e-mim][BF4]/MEA mixture system in the T-junction microchannel with a diameter of 2 mm.The simulation showed five different flow patterns and gas-liquid two-phase flow distribution patterns at different gas and liquid apparent rates in the microchannel.The influence of gas and liquid apparent velocity on Taylor patterns under Taylor flow was simulated,and the variation of gas holdup,Taylor bubble length and liquid slug length with gas and liquid apparent velocity was obtained.The velocity and pressure distributions under Taylor flow were investigated.The fluid flowed downward at the liquid film.There were vortexes at the Taylor bubble hemisphere cap,which enhanced the mass transfer.The CO2 in the Taylor unit was mainly distributed at the center line of the Taylor unit,near the wall of the Taylor bubble and at the wall of the microchannel,indicating that the concentration field and the velocity field have synergistic effects.Finally,using the measured kinetic parameters,the species transport model and the reaction model were used to simulate the mass transfer and reaction performance of the CO2-[NH2e-mim][BF4]/MEA mixture system in Taylor unit by CFD.As the bubble rising velocity and the liquid film length increased,the mass transfer coefficient of the cold model and the reaction would increase.As the length of the Taylor unit and the thickness of the liquid film increased,the mass transfer coefficient become smaller and smaller.The decrease in diameter was beneficial to mass transfer.It was found that the mass transfer and the reaction were consistent and could promote each other.The mass transfer performance could be enhanced by 3 to 8 times in the presence of the reaction,and the correlation of the liquid phase mass transfer coefficient was fitted according to the simulation results.