Research On Performance Of CO₂ Adsorption Materials And Utilization Based On MoistureSwing Technology

To solve the problem of global warming, CCS is considered to be the most potential technology to reduce carbon emissions in the future. However, for stationary source CO2 capture, there exist some chanllenges such as huge energy consumption for CO2 desorption, high CO2 capture cost and investments. Moreover, even if CO2 capture devices are installed for all the stationary sources of CO2 emissions, and the removal efficiency is 90%, half of the anthropogenic CO2 is still emitted into the atmosphere. Therefore, direct air capture of CO2 is an important choice to solve the problem of global warming. Thermal regeneration method is used in traditional CO2 air capture, but has the problem of high renegeration temperature, large occupation area an9 huge capture cost. To address these problems, moisture swing technology is proposed, in which the free energy of water evaporation is used for adsorbent regeneration, and the heating process is avoided. So the method has advantages of low energy consumption, no pollution and no restrictions by industrial emission source, which can be more flexible and convenient for CO2 utilization. In this way, the transportation cost can be saved. However, moisture swing technology is still in its early stage, the types of adsorbents are limited and systematic research on the kinetics and thermodynamics of moisture swing adsorption is lacking. In this thesis, the kinetic and thermodynamic behaviours of CO2 adsorption during moisture swing were systematically studied through combining theoretical model and the experiments. On the base of the research results, a new approach integrating CO2 capture and its comprehensive utilization was proposed.For the preparation of adsorbents, strong base anion exchange resin with quaternary ammonium type was used. Phase inversion method was adopted to prepare the adsorption material, and heterogeneous adsorption membrane with uniform particle size of resin and porous structure was obtained. Through the homemade revoving bed reactor and CO2 adsorption experimental platform, CO2 adsorption performance of the membrane was tested. In light of the problem that the existing characterization method of CO2 air capture kinetics is simple and rough, a kinetic model was built to analyze the resistances during CO2 adsorption, which can provide a guide for determining the resistance control steps during CO2 adsorption and the optimization of adsorbents.Through theoretical model and experimental studies, the effects of the thicknes of membrane, particle size of resin, humidity and temperature on CO2 adsorption kinetics were systematically investigated. The results indicate that the adsorption kinetics of adsorbent is mainly dominated by resin particles. So the optimization of CO2 adsorption kinetics should mainly focus on resin particle, incluing the preparation of porous resin and the adjustment of resin particle size, etc. The kinetics of CO2 adsorption can be significantely improved by reducing the particle size of resin. The adsorption rate of CO2 increases more than 5 times when the particle size reduces 2 times. For most of the humidity conditions, the share of chemical reaction resistance in total adsorption resistance is comparable with product layer diffusion as the particle size of resin dereases from 20 μm to 1-2 μm. Humidity has great influence on both diffusion and reaction during CO2 adsorption. As the relative humidity increases, both the coefficient of product layer diffusion and the chemical reaction rate constant will decrease, and the CO2 adsorption shows a transition from diffusion dominated kinetics to chemical reaction dominated kinetics. As the temperature increases, both the coefficient of product layer diffusion and the chemical reaction rate constant will increase. When the particle size of resin is reduced to about 5 μm, the influence of temperature and humidity on CO2 adsorption kinetics weakens.Based on the experients, the coupling interaction of CO2 and hydrate water during moisture swing process were systematically analyzed, and the mass transfer behavior and reaction heat during CO2 and H2O adsorption were explored. It was found that the self-cooling phenomenon existed in the moisture swing CO2 adsorption process, and the reason of the phenomenon was revealed. The results show that the reaction heat of CO2 adsorption is -57.18 kJ/mol CO2, and heat of hydrate water release is 47.39 kJ/mol H2O as CO2 reacts with the adsorbents. According to the results, the reaction heat of CO2 and adsorbents under different conditions could be calculated.According to the results of adsorption-desorption kinetics of the adsorbents, a new approach integrating CO2 capture and its comprehensive utilization was proposed. Part of CO2 captured by moisture swing method is utilized to promote the growth of green plants in plant factory, which could provide life safeguard for the residents on Yongxing Island with land scarcity and adverse nature condition. The rest of CO2 could be prepared to diesel through Fischer-Tropsch synthesis, which could provides fuels for ocean ships and aircraft. The energy required during the process is provided by the rich wind energy on Yongxing Island, and self-sufficiency in energy can be achieved. The experimental results show that the cyclic CO2 adsorption capacity of the membrane in the environment of Yongxing Island is 0.29 mmol/g. It is estimated that the captured CO2 could produce 13.55 tons diesel per day, in addition to meeting the daily vegetable demand of the residents on Yongxing Island.