Study On CO₂ Desorption Performance And Mechanism Of Catalytic K-based Sorbent

The global warming caused by the large amount emission of greenhouse gas makes it necessary to capture CO2.Using potassium-based sorbent for CO2 capture is an efficient CO2 separation technology in power flue gas because of the powerful carbonation ability,high recycling rate,low corrosion and other significant advantages,and it has broad application prospects.However,this technology needs further improvement due to the slow regeneration rate of the sorbent and high regenerative energy consumption.Therefore,this paper studied the catalytic CO2 desorption reaction kinetics of potassium-based sorbent.The specific work was as follows:First of all,based on the existing K2CO3/Al2O3 sorbent,the CO2 desorption characteristics of KHCO3/Al2O3 sorbent were studied by thermo-gravimetric analyzer(TGA)under three reaction atmospheres(CO2,Ar and water).The kinetic parameters,like activation energy,were calculated using the reported dynamics model.The results show that,the sorbent start to decompose at 100? under all the three reaction atmospheres.The decomposition rate increases with the increase of temperature,and the conversion efficiency reaches about 0.8 at 180?.The regeneration reaction rate is fastest in moisture among these three atmosphere.The decomposition reaction of the sorbent complies with the first-order reaction model.The apparent activation energies of the sorbent under the atmosphere of CO2,Ar and water were 50.2kJ/mol,47.4kJ/mol and 32.6kJ/mol,respectively.Water is the promising atmosphere of CO2 desorption reaction.Secondly,in order to explore the reaction mechanism and enhance the kinetics of the CO2 desorption reaction,the CASTEP software based on density functional theory(DFT)was used to calculate the catalytic mechanism.The surface properties of the catalyst were judged from the perspective of electron transfer and molecular adsorption performance.The possibility of the reaction pathway was judged from the reaction barrier and reaction energy.The role of hydroxyl group(-OH)on the decomposition of bicarbonate(-HCO3)was obtained,and the regeneration reaction model of TiO2 as catalyst in potassium-based absorbent was established.The dissociative-adsorption behavior of gas product molecules(CO2 and/or H2O)in the model was analyzed in detail.It is considered that the behavior of water vapor dissociating and adsorbing hydroxyl groups on the catalyst surface is the key to improve the kinetics of the absorbent regeneration reaction.The CO2 desorption characteristics of the TiO2-doped modified K-based sorbent was studied in TGA to verify the above theoretical research.The kinetic parameters of the modified K-based sorbent under the three atmospheres were obtained.The activation energy of TiO2 modified K-based sorbent on CO2 desorption reaction were decreased by 31.8%,30.5%and 23.3%,respectively.Further,in order to develop absorbent with better regeneration characteristics,the study of ZrO2 as a catalyst,which has a stronger ability of dissociating and adsorbing water,was carried out.The DFT calculation results showed that the H20 and C02 adsorption performances on ZrO2 surface were better than that of TiO2.It is suggested that the catalytic activity of ZrO2 is stronger than that of TiO2,and the catalyzer which has better H2O adsorption performance has stronger catalytic effect on the CO2 desorption reaction of the sorbent.The CO2 desorption reaction kinetics of ZrO2 modified K-based sorbent was investigated by TGA,and the activation energies of modified sorbent under CO2,Ar and H2O atmosphere was decreased by 37.1%,43.9%,29.4%,respectively.The experiment results verified the theoretical DFT calculated results.The results in this paper provide a theoretical standard for the screening and application of catalyzer for potassium-based sorbent on CO2 desorption reaction,which is an important extension of the existing post-combustion alkali metal based CO2 capture technology.