Preparation Of Doped CO₂ Calcium-based Adsorbent And Study On Its Cyclic Adsorption Performance

The climate change caused by the greenhouse effect,which caused by carbon dioxide(CO2)is receiving more and more attention in the international community.The calcium-based adsorbent has a very research prospects due to the advantages of large adsorption capacity,CO2 separation under high temperature and cheap raw materials.However,calcium-based sorbents lead to sintering after repeated calcinations.The researchers at home and abroad have done a lot of studies in order to solve the problems of easy sintering and low conversion rate of calcium-based adsorbents.At present,the most of studies is doped modification.As a populous country,China produces hundreds of millions of tons of solid waste each year,and the disposal of solid waste has added to the burden on the environment.The main component of carbide slag is CaCO3.In this study,we use carbide slag(CS)to prepare calcium-based adsorbent.The research is divided into four parts:(1)The dopant lithium silicate(Li4SiO4)was prepared by solid state reaction at high temperature,and commercial CaO and CS as a calcium source for doping modification.Effect of the amount of doping,pre-calcination time and temperature on the cyclic adsorption performance were investigated to obtained the optimal preparation conditions of calcium-based sorbent.The results showed that:the cycle conversion of calcium-based sorbent was significantly improved after the modification.In addition,due to the impurities of CS,the calcium source of CS take placed the "autocatalytic" phenomenon after doping modification and pre-calcination.Through the characterization of XRD,the CS doped with Li4SiO4 will generate Li2O,which is favorable for the CO2 cycles capture as an active component.According to the morphological characterization,it was found that a stable "hard skeleton"structure was formed after CS-LS-5-4-850 adsorbent circulated.(2)Silicon nitride(Si3N4)was prepared by sol-gel method and the effect of CS doping with Si3N4 on the cyclic CO2 adsorption was studied.Firstly,CS doping with three types of Si3N4(a-type Si3N4,?-type Si3N4 and the Si3N4 was prepared by myself).According to the results of the conversion rate after the cycle,and found that CS doped with self-prepared Si3N4 has the best adsorption performance of CO2.Secondly,effect of the dopant content,precalcining time and temperature on the CO2 cyclic adsorption performance were investigated.Through the characterization of XRD,the Si3N4 was prepared by myself not only contains a-type Si3N4,but also?-type Si3N4.In addition,Si3N4 did not react with CaO after doping.According to the morphological characterization,it was found that Si3N4 plays a role in stabilizing the pore structure and a stable "hard skeleton" structure was formed after doping.(3)According to the above study,the adsorbents of CaO-LS-15-4-800,CS-LS-5-4-850 and CS-Si3N4-5-4-850 were prepared by the optimum conditions.In this paper,the sorbents after a long series cycles were tested.The results show that:CS-LS-5-4-850 adsorbent has a good adsorption performance.CS-LS-5-4-850 after 20 cycles the conversion was 37.71%and 15.66%improvement of CaO-LS-15-4-800 and CS-Si3N4-5-4-850 respectively.(4)The adsorption kinetics of the CS-LS-5-4-850 and CS-Si3N4-5-4-850 were studied by Avrami-Erofeev equation in the common mechanism function.The adsorption process is divided according to dX/dt = 0.02,0?8 min is the rapid reaction stage and 8?90 min is the slow stage.The results showed that the activation energy of CS-LS-5-4-850 sorbent was 39.50 kJ/mol in the fast stage and 68.84 kJ/mol in the slow stage.The activation energy of CS-Si3N4-5-4-850 sorbent is 68.17 kJ/mol and 102.34 kJ/mol respectively.The lower of the activation energy and the energy required for reaction is lower.That is,the process of adsorbing CO2 by the sorbent in this paper is divided into a rapid stage and a slow stage.The results of research agree quite well with actual CO2 adsorption processes.