Study On CO₂ Absorption By Gas-Liquid-liquid Systems In Rotating Packed Bed

The application of gas-liquid-liquid(G-L-L)three phase reaction systems in biochemical reaction,homogeneous catalysis,liquid-liquid extraction and other processes has gradually increased and attracted more attentions.At the same time,the rapid development of high gravity technology has proved that this new process intensification method has gained acceptance.High gravity technology is carried out in a rotating packed bed(RPB),which consists mainly of a shell and a rotor located in the shell,and the rotor is filled with packing materials.The principle of RPB is as follows.The liquid is sprayed on the inner edge of the rotor,and flows through the packing under the action of a strong centrifugal force.During this process the liquid is dispersed and broken into tiny droplets and threads with huge specific surface area by the packing materials,leading to significant intensification of mass transfer and micromixing.In recent years,the greenhouse effect has caused serious problems,and CO2 is a gas that contributes most to the greenhouse effect.Effective recovery of CO2 is thus one of the most important means to address the greenhouse problem.Based on the intensification of RPB for mass transfer and micromixing,this thesis combines RPB with G-L-L three-phase systems to absorb CO2 for the first time.Suitable organic phase and experimental conditions were determined in terms of the CO2 absorption efficiency and the overall mass transfer coefficient(KGa),and the characteristics of gas-liquid-liquid three-phase reaction under the high gravity environment were explored,aiming at developing an efficient CO2 absorption technology.The main results are as follows.1.The absorption of CO2 by the circulation of K-2CO3/KHCO3-organics system in the RPB was studied.The effect of various organics and experimental conditions on CO2 absorption was investigated.It was found that n-octanol and dimethyl carbonate(DMC)had only slight intensification effect on the absorption of CO2,and the advantages of RPB of short residence time and high efficiency in gas-liquid mass transfer were not demonstrated in the circulation absorption process.2.The absorption of CO2 by the continuous flow of the water-organics system in the RPB was studied.The effect of various organics and experimental conditions on CO2 absorption was investigated.It was found that cyclohexane and n-hexane had excellent intensification effect on CO2 absorption in this system,and that a moderate RPB rotation speed(600 to 800 rpm)exhibited superior effect on CO2 absorption into the water-organics system.In addition,the addition of a small amount of Tween 80 and increase of the reaction temperature also boosted the absorption percentage of CO2.3.The absorption of CO2 by the continuous flow of the K2CO3-organics system in the RPB was conducted on the basis of the above studies.The effect of organics species,temperature,RPB rotation speed,gas-liquid ratio,absorbent concentration on CO2 absorption was investigated.The results show that cyclohexane with a volume fraction of 2.5%exhibited excellent intensification effect on CO2 absorption into K2CO3 solution.It was determined that the optimum rotation speed of RPB was 800 rpm,and the optimum concentration of K2CO3 solution was 0.86 mol/L.The addition of Tween 80 increased the mass transfer resistance,which was unfavorable for CO2 absorption.In addition,the increase of the temperature benefited the CO2 absorption process.This thesis studied the absorption of CO2 by G-L-L reaction in the RPB for the first time and determined suitable process conditions,which provides a new route for CO2 emission reduction.