Experimental Study Of Moisture Swing Adsorbent For CO₂Capture From Ambient Air

Capturing carbon dioxide directly from ambient air is an emerging carbon dioxide capture technology. Even through the power plant and other plants that emits mainly part of carbon dioxide, huge amount of carbon dioxide is emitted to ambient by using vehicles such as cars and airplanes. Because of this, the direct carbon dioxide capture from ambient air is proposed as an useful way to control the carbon dioxide concentration in ambient air.Moisture swing technology employs the the free energy of the water to desorb carbon dioxide from adsorbent when it contacts water or vapor. Unlike most of carbon dioxide adsorbent with temperature swing or pressure swing adsorption, the desorption of moisture swing can take place under a room pressure and temperature and is promising to effectively reduce the energy consumption of carbon dioxide capture.In this thesis, the moisture swing process for direct air capture was studied based on an anion exchange resin membrane. The characteristics of moisture swing adsorption, including adsorption/desoption, heat of reaction and some basic parameters under different conditions were explored.A commercially available ion exchange membrane (1-200) with surface modification was investigated for moisture swing adsorption. The surface structure, charge density, water loss characteristics and ambient carbon dioxide adsorbing kinetics of the1-200adsorbent membrane under10,20,30℃were studied. It is found that the porous structure of the1-200adsorbent membrane is positive to carbon dioxide adsorption and carbon dioxide adsorbing velocity increases as the temperature rises.The heat of adsorption of1-200adsorbent membrane under different conditions was studied by DSC method. At the temperature range from30to60℃, the reaction heat is2-5kJ/mol CO2.By measuring the heat of adsorption of1-200adsorbent membrane with different number of hydration water, it is found that the number of hydration water on the resin surface has a significant effect on the reaction heat, but the mechanism is still to be explored.The performance of carbon dioxide adsorpiton of ion exchange membrane was optimized by changing the preparation conditions.The influences of resin particle size, resin mass fraction and the thickness of membrane on the adsotption capacity and the adsotption kinetics were studied. The experimental results show that smaller particle size and higher mass fraction have positive effect on the adsorption performance. Thicker membrane has higher adsotption capacity and better mechanical strength. The adsotbing kinetic is poorer, however.The adsorption performance of the adsorbent membrane prepared under optimization condition was explored under different temperatures and humidity. The desorption was measured under room temperature using moisture swing process. It is found that the temperature has little effect on adsorption capacity, while the temperature and humidity has significant effect on the adsorption kinetics. By utilizing moisture swing process to regenerate adsorbent membrane, it is found that over**%of the adsorbed CO2can be released which shows a reversible moisture swing process. The CO2desorbed is increased linearly with time until the sorbent coverage is less than**%.The energy consumption and economics of capturing carbon dioxide directly from ambient air using the adsorbent membrane were analyzed based on a separation unit with the capacity of one ton carbon dioxide per day. Comparing with the post-combustion carbon dioxide capture system using MEA, capturing carbon dioxide directly from ambient has a higher capture cost but is promising to has lower energy consumption by using moisture swing technology. The sensitive analysis shows that improving adsorbent membrane adsorption kinetics can effectively reduce the cost of CO2capture from the atmosphere.