Study Of The Carbon Dioxide(CO₂)desorption Performance In CO₂-loaded Aqueous Monoethanolamine Solution Using Solid Acid-base Catalyst

The continuous emission of greenhouse gases such as CO₂ by human activities has caused the greenhouse effect and global warming.Amine-based CO₂ capture process is currently the most common and effective CO₂ capture method.However,this method suffers from several drawbacks such as,solvent degradation,equipment corrosion,and high solvent regeneration energy consumption,especially the excessive energy consumption for solvent regeneration,which greatly hinders the large-scale industrial application of this technology.Therefore,the reduction of the solvent regeneration heat duty has important scientific significance for the development of CO₂ capture technology.In order to achieve effective and low-energy consumption aminebased CO₂ capture process,various solid acid catalysts and acid-base bifunctional composite catalysts were designed and prepared in this study and used to catalyze the rich amine solution regeneration process.A baseline amine solvent,5 M monoethanolamine solution(MEA)was used as the reaction substrate,the rich CO₂ loading of the MEA solution is 0.50 mol CO₂/mol amine,and the CO₂ desorption temperature is 96-98?.Various characterization methods including,XRD,FT-IR,XPS,SEM,N2 adsorptiondesorption experiment,CO₂/NH3-TPD,Py-IR were adopted to obtain the structure and physicochemical properties of the prepared catalysts.The catalytic CO₂ desorption performances of these catalysts in the CO₂-loaded MEA solution were systematically evaluated in terms of CO₂ desorption rate,the amount of desorbed CO₂ and the regeneration energy consumption.The structure-activity relationships of the catalysts were explored,and a possible catalytic CO₂ desorption mechanism was proposed.The cycle stability of catalyst and the effects of catalytic regeneration on the CO₂ absorption performance of MEA solution were studied.The main research contents and innovative results are as follows.(1)The catalytic CO₂ desorption performances of solid acid catalysts SAPO-34 and SO₄^2-/TiO2 were comprehensively investigated.The results showed that the use of the two catalysts reduced the regeneration energy consumption by 17.1-24.3% and increase the CO₂ desorption rate by 20.0-28.3%.SAPO-34 catalyst presented better catalytic activity than that of SO₄^2-/TiO2.The effect of catalyst dosage on CO₂ desorption performance was investigated,and the results showed that the optimal mass ratio of catalyst to amine solution was between 1.0-1.5 wt%.Also,the acid catalyst SAPO-34 presented good cycle stability.Mesoporous surface area(MSA)and B/L ratio of catalyst play a crucial role in improving the catalytic CO₂ desorption performance.(2)Three supported catalyst SO₄^2-/Zr O₂/?-Al₂O₃(SZA)were prepared by the precipitation-impregnation method,and their catalytic CO₂ desorption performances were studied.The results showed that the SZA catalyst further increased the CO₂ desorption rate and reduced the regeneration heat duty.When the mass ratio of Zr O₂ and Al₂O₃ was 1/1,SZA catalytst displayed the highest catalytic activity,which could increase the CO₂ desorption rate by33.3% and lower the energy consumption by 36.9%.The supported catalyst SZA possesses superior cycle stability.The improved catalytic performance of SZA was mainly attributed to its enhanced B acid,basic site and MSA.(3)Four bifunctional composite catalysts Al₂O₃-HZSM-5(Al-ZSM)were prepared by the ultrasound-assisted precipitation method,and their catalytic CO₂ desorption performances were studied.Compared with the parent catalysts,Al-ZSM revealed enhanced catalytic CO₂ desorption performance.When the mass ratio of Al₂O₃ and HZSM-5 was 2/1,Al-ZSM showed the best catalytic CO₂ desorption performance,which decreased the energy requirement by 34.2% and increased the CO₂ desorption factor by about 3times.The bifunctional catalyst Al-ZSM showed excellent reusability.The enhanced B acid site,MSA and basic site of Al-ZSM catalysts made them presented excellent CO₂ desorption activity.(4)Three different metal oxides(Fe₂O₃,Al₂O₃ and MoO3)modified MCM-41 composite catalysts were prepared by ultrasound-as sis ted postmodification synthesis method,and their catalytic CO₂ desorption performances were evaluated.Fe₂O₃-modified MCM-41 catalyst showed the best catalytic performance.When Fe₂O₃ content was 10 wt%,the composite catalyst showed the best catalytic performance,which could increase the CO₂ desorption factor by 337.1% and reduce the regeneration energy consumption by 32.5%.The composite catalyst displayed good stability.The enhanced B acid sites and basic sites of the catalyst are the key factors to affect the catalytic CO₂ desorption performance.In addition,based on the above experimental results,the systematic investigation of the structure-activity relationships between the physical and chemical properties of the catalyst and the CO₂ catalytic desorption performance were performed.The main promotion mechanism of the solid acid catalyst is that the Br?nsted acid site(B acid)of the solid acid catalyst can provide protons to promote the breakdown of carbamate reaction in the desorption process,while the Lewis acid site(L acid)can further promote the carbamate breakdown reaction.While,the acid-base bifunctional composite catalyst can simultaneously promote the two-step reaction of the solvent regeneration process:(1)B acid and L acid sites can simultaneously promote the carbamate breakdown reaction in the solvent regeneration process;(2)basic site can mimics the role of bicarbonate to facilitate the protonated amine deprotonation reaction in the regeneration process.Through the synergistic catalysis effect of acid-basic sites,acid-base composite catalyst can greatly promote the rich amine solution regeneration process.It is found that the composite catalyst-assisted CO₂ desorption process with acid-base synergistic catalytic effect showed better catalytic CO₂ desorption performance than that of single solid acid catalyst,and has broad potential industrial application prospects for CO₂ capture field.A possible acid-base dual-site catalytic CO₂ desorption mechanism was proposed,which can provide a basic theoretical guideline for the rational design and preparation of high-efficiency catalysts for CO₂ capture with fast CO₂ desorption rate and low energy consumption.