Study On Novel Absorbent Systems For CO₂ Capture And Its Regeneration Characteristics

Chemical absorption is the most mature and commercially available carbon dioxide capture technique.However,high capital cost and large energy consumption required for solvent regeneration still remain major disadvantages which results in delaying the worldwide large-scale deployment of this technology.Several newly developed absorbents have been recently proposed to solve the main issue as for energy-efficient capture process.Besides solvent development,solid acid catalysts can also reduce the energy requirement in the solvent regeneration of a CO₂ capture process.In this work,the regeneration of rich CO₂-loaded monoethanolamine?MEA?solvent with several typical catalysts?solid acid resin,TiO₂ and TiO?OH?₂?was investigated in order to reduce the energy requirement for solvent regeneration.Then TiO?OH?₂ was further prepared as magnetic catalyst so it can be easily recovered by the external magnetic field,with great importance for meeting the requirement of current chemical process.Several newly developed absorbents were investigated and evaluated in the energy consumption evaluation device at various temperatures.The findings will summarize the regularity of regeneration energy consumption,with great scientific value and practical significance.In this thesis,we have investigated the catalytic activity,recycling performance and stability of the newly development catalysts.5 M MEA with an initial CO₂ loading of 2.4mol CO₂/kg amine solution was regenerated with and without catalyst.Two kinds of Fe₃O₄@SiO₂@TiO?OH?₂ were synthesized successfully by chemical co-precipitation method and hydrothermal method.The structure of the catalyst was analyzed by means of XRD,TEM,FT-IR and VSM.The regeneration behavior with and without catalyst of a 5M MEA solution with an initial CO₂ loading of 2.4 mol CO₂/kg amine at 373 K was studied to compare catalytic performance of the two kinds of catalysts.Several absorbents including 5 M MEA/H₂O,2.5 M LysK/H₂O,5 M MEA/EGME,5 M MAE/EGME,5 M MAE/DEGDME,3 M ProK/EGME/H₂O were investigated in the energy consumption evaluation device at various temperatures.The CO₂ desorption amount,power consumption and other data were used to analyze the regularity of regeneration energy consumption.Cyclic capacity and heat duty were investigated by using aqueous MEA and blends of MEA with EGME in a packed tower to analyzed the effect of regeneration operation on the regeneration energy consumption of the absorption system.Through the investigation of several catalysts,the solid acid resin,TiO₂ and TiO?OH?₂ was desired as a catalyst to significantly accelerate the decomposition of aqueous MEA.The flowrate of CO₂ generated from 5 M MEA/H₂O at 358K with TiO?OH?₂ is¹10%of that generated without the presence of catalyst.And the total amount of CO₂ released was improved by 13%under at 373 K.TiO?OH?₂ has a stable cycle catalytic capacity under proper regeneration operation and has little effect on the solution concentration.However,the solid acid resin will cause the concentration of the solution to drop significantly,which will impact on the solution circulation.TiO?OH?₂ as a catalyst can also increasing the rates of CO₂ desorption from spent 5 M MEA/EGME by over 100%at 357 K with stable cycle catalytic capacity.Both chemical co-precipitation method and hydrothermal method were used to produce Fe₃O₄.Then magnetic catalyst Fe₃O₄@SiO₂@TiO?OH?₂ was prepared by hydrolysis of Tetraisopropyl titanate.In the regeneration experiment,the mass of magnetic catalyst based on chemical co-precipitation method has a serious loss while magnetic catalyst based on hydrothermal method has less mass loss in experiment.The prepared Fe₃O₄@SiO₂@TiO?OH?₂ nanoparticles were mainly spherical and the particle size is about 500 nm which have superparamagnetic and good dispersion in water.The cores of them consist of single Fe₃O₄ nanoparticles with SiO₂ shell and the outer layer was TiO?OH?₂.Under the amount of 8wt%magnetic catalyst added,the flowrate of CO₂generated from 5 M MEA/H₂O at 358 K is¹00%of that generated without the presence of catalyst.And the total amount of CO₂ released was improved by 10%at 373 K,and the magnetic catalyst was easily to recycle under magnetic field.Several absorbents including 5 M MEA/H₂O,2.5 M LysK/H₂O,5 M MEA/EGME,5M MAE/EGME,5 M MAE/DEGDME,3 M ProK/EGME/H₂O were investigated in the energy consumption evaluation device at various temperatures.The CO₂ desorption amount,power consumption and other data were used to analyze the regularity of desorption energy consumption.For experiment at 373 K,the overall heat duty for aqueous 5.0 M MEA was estimated to be 415 kJ/mol CO₂ and 455 kJ/mol CO₂ for aqueous 2.5 M LysK.The proposed nonaqueous blends,liquid biphasic systems or water-lean solvents have lower overall energy consumption,in the range of 190-225kJ/mol CO₂.For thoes newly developed absorbents,they showed about 50%decrease in overall energy consumption,and for single-phase nonaqueous absorbents,they showed similar CO₂ desorption efficiency.For non-aqueous systems,the regeneration temperature has little effect on the regeneration energy consumption,but will have a great impact on the circulation capacity.The sensible heat of solution heating and latent heat of vaporization account for more than 50%of energy consumption.When absorbents were regenerated in the packed tower,the physical properties of the solution?specific heat capacity,viscosity,etc.?would have a significant impact on the regeneration energy consumption and the operating parameter range of the device.In this case,the regeneration energy consumption of 5 M MEA/EGME system was reduced by 25%compared to 5 M MEA/H₂O system.In summary,TiO?OH?₂,with stable catalytic effect,can significantly accelerate the CO₂ desorption,and lower temperature and thus energy requirements for CO₂ capture.The magnetic catalyst based on TiO?OH?₂ is easily to recycle under magnetic field while maintaining its excellent properties of TiO?OH?₂.The newly developed nonaqueous blends,liquid biphasic systems and water-lean solvents can significantly reduce the regeneration energy consumption due to their higher boiling point,lower specific heat capacity and enthalpy of evaporation.