Experimental Investigation On Layered Double Hydroxide Based Adsorbent For H₂/CO₂ Separation At Elevated Temperature

H₂/CO₂ separation technology is significantly important for pre-combustion CO₂ capture in the Integrated Gasification Combined Cycle?IGCC?system.The dessertation aimed to solve following four crucial aspects regarding for active chemical adsorbent development,powder pelleting of amorphous adsorbent,reactor model development of a PSA system,and continous running of stability by a pilot-scale test system for H₂/CO₂,to realize high efficiency low cost separation of H₂/CO₂ at elevated temperature?250-400oC?by pressure swing adsorption?PSA?.Potassium promoted magnesium-aluminum-layered double hydroxides?LDHs?were developed based on Mg-Al LDH precursor,which effectively avoided the effects of physical adsorption ascribing to the elevated operating temperature.The adsorbent could effectively avoid the effects of competitive adsorption of H₂ O to improve the CO₂ adsorption selectivity.CO₂ surface adsorption mechanism and potassium promotion mechanism were concluded by thermal gravimetric analysis under both atmospheric and elevated pressure,Fouriour transformation infrared spectroscopy and temperature programmed desorption.It was shown that chemical adsorption of CO₂ on the surface of LDH based adsorbent at elevated temperature enjoyed low adsorption heat?about2.5-60.4 kJ/mol?,isothermal desorption achieved by changing partial pressure,selectivity to CO₂,and relatively low specific surface area,which was useful in PSA practice.Potassium promoted stearate-intercalated LDH was developed by expanding its basal spacing and controlling its basic sites density,which had a CO₂ capacity of1.93-1.97 mmol/g under ambient pressure at 300 oC.In the need of running on a fixed-bed and a pilot-scale system and in order to avoid the disadvantage of amorphous transformation and weight loss during LDH pelleting,alumina sol coagulation by potassium carbonate solution to form K-promoted pseudo boehmite was studied and introduced in the extruding process of LDH powder for enhancing both CO₂ capacity and crushing mechanical strength of pellets.MG63/K-promoted pseudo boehmite composite?LDH based adsorbent?was synthesized.It had an average mechanical strength above 70 N per pellet,which was applicable for pelleting of LDH based adsorbent at industrilized scale.Initial H₂/CO₂ separation by LDH based adsorbent was achieved on a single column fixed-bed and a double column fixed-bed,which provided useful experimental results for model development and scale up validation.Both nonequilivrium kinetic reaction model and quasi two dimensional column module available for PSA process simulation under elevated pressure were built and validated,followed by completion of reactor model development of a PSA system.The effects of adsorption and desorption parameters on the H₂ recovery rate and CO₂ capture rate,and PSA process design of a pilot-scale test system were also studied.A pilot-scale test system based on H₂/CO₂ separation at medium temperature was constructed.This system was capable of processing shift gas at the flow rate of 4.0-6.6 Nm3/h at medium temperature range from250 to 400 oC.This system had reached 1089 hours in accumulated operating hours in stable condition and 75 continuous operating hours keeping CO₂ removal rate higher than 91.7%.The feasibility for industry application of H₂/CO₂ separation at medium temperature was tentatively demonstrated.