Study On Kinetics And Thermodynamics Of CO₂ Desorption Of Monoethanolamine Enhanced By Acid Catalysts

The high energy consumption of chemical absorption method based on amine is the key problem of carbon capture technology.However,amine-based CO2 capture is still suffering from the intensive energy penalty of CO2 desorption accounting for>50%of the total energy consumption of CO2 capture.In order to better understand the heat transfer process of the reaction system,four kinds of metal oxides(Al2O3、TiO2、ZrO2、Fe2O3)and their corresponding hydroxyl oxides(AlOOH、TiO(OH)2、ZrO(OH)2、FeOOH)and two kinds of zeolite(HZSM-5,MCM-41)were selected as catalysts.Firstly,the kinetic experiment of catalytic CO2 desocption was carried out,in this paper,the effects of physical and chemical structure of solid acid catalyst on CO2 loading,pH and temperature of the system were analyzed,and mechanisms behind the solid acid catalyst on CO2 was explained.On the other hand,the thermodynamic effects of solid acid catalysts on the CO2 absorption and desorption reaction of MEA were explored in the real heat flux reaction calorimeter.In order to analyze the effect of catalyst on heat absorption,two transition metal ions(Cu2+ and Ni2+)were added as experimental materials,and the real heat flux reaction calorimeter was used as reaction instrument to explore the effect of transition metal ions concentration on absorption and desorption performance.The experimental results show that the kinetics of MEA heterogeneous system enhanced by solid acid catalyst is faster,and the desorption kinetic rate is as follows:ZrO(OH)2>FeOOH>TiO(OH)2>HZSM-5>ZrO2>MCM-41>AlOOH>Al2O3>Fe2O3>TiO2>None,which is the direct reason for the higher cyclic load and desorption efficiency of solid acid catalyst enhanced MEA heterogeneous system.In addition,solid acid catalyst enhanced MEA heterogeneous system.the free alkaline MEA of the system increased with the desorption reaction.The pH value is higher than that of MEA solution.It is worth noting that in addition to the heterogeneous system of MEA enhanced by ZrO2 and TiO2,the heterogeneous system of MEA enhanced by solid acid catalyst shows a faster heating rate in the process of CO2 desorption.On the other hand,The mechanisms of the catalytic CO2 desorption can be explained from chemical and physical aspects.The catalytic CO2 desorption includes several key steps:adsorption of alkaline speciation(such as MEACOO-/HCO3-/CO32-)onto the active sites of the catalyst particles,the protons transfer occurred on the particle surface,the CO2 bubbles generation and detachment.The CO2 desorption performance could be affected by several catalyst properties such surface acid hydroxyls,surface area,pore volume and pore diameter.In the solid acid catalyst enhanced MEA thermodynamics experiment,the solid acid catalyst enhanced MEA system showed higher absorption load,but the average absorption heat increased slightly,and the apparent absorption rate had different effects on the system.At the desorption temperature of 99℃,the desorption efficiency(ZrO(OH)2>FeOOH>TiO(OH)2>HZSM-5>ZrO2>MCM-41>AlOOH>Al2O3>Fe2O3>TiO2>None)was increased by adding catalyst,which was consistent with the experimental results of desorption kinetics.The order of reducing the heat load of CO2 regeneration(FeOOH>TiO(OH)2>ZrO(OH)2>HZSM-5>MCM-41>Al2O3>ZrO2>Fe2O3>AlOOH>TiO2>None)will greatly reduce the energy in the input reactor,the sensible heat of the catalyst enhanced MEA system is reduced by 16%to 30%,and the overall regeneration heat load is greatly affected,and the latent heat is reduced by 8%and 14%.On the other hand,Cu2+/Ni2+can reduce the absorption heat of the system.The higher the concentration of transition metal ions,the lower the absorption heat of the system,but at the same time,due to mixing with MEA solution,the early complexation reaction will reduce the MEA concentration,resulting in the decrease of the absorption load and apparent absorption rate with the increase of transition metal ion concentration.Compared with the solid acid catalyst enhanced MEA system,the absorption heat is lower and more regular.At the desorption temperature of 99℃ compared with the 2 M MEA system,the homogeneous system with 0.4M Cu2+/Ni2+ is more beneficial to the desorption process,can effectively increase the cyclic loading and desorption efficiency of the system,reduce the regeneration heat load,and reduce the latent heat and sensible heat.Compared with the solid acid catalyst enhanced MEA heterogeneous system,0.4 M Ni2+ reinforced MEA homogeneous system has higher cyclic load and desorption efficiency.This may be due to the fact that the ion concentration affects the process of the complexation reaction,and the mechanism still needs to be further proved.