Investigation On Elevated Temperature CO/CO₂ Purification Of Potassium Promoted Mg-Al Layered Double Oxides From H₂-Rich Gas

The reactive separation process based on the coupling of water gas shift（WGS）catalysts and elevated temperature CO₂ adsorbents is able to produce high purity hydrogen directly from H₂-rich gas.This purification technology avoids the sensible heat loss of syngas and the heat regeneration,thus being significantly important to the mitigation of the carbon emission pressure,the development of fuel cel-based energy system,and the reduction of energy consumption in coal chemical industries.This work investigated the potassium promoted magnesium-aluminum layered double oxide（K-LDO）based CO/CO₂ purification technology,which focused on the development of adsorption model,the analysis of adsorption mechanism,the design of reactor and process,the optimization of system process,and the analysis of energy consumption,to provide theoretical foundation for industrial scale-up.First,a testing method for actual high pressure adsorption kinetics was proposed,which avoided the replacement effect in conventional characterization methods.Based on this method,the adsorption kinetics of K-LDO at 300–450°C,0.1–2 MPa was discussed,and a non-equilibrium Elovich-type adsorption/desorption model was built.In addition,in situ techniques were adopted to il ustrate the elevated temperature CO₂adsorption mechanism of K-LDO.There was a synergistic effect of K⁺ions and Mg/Al ratio.After adsorbing CO₂,bidentate carbonates were formed on the surface of K-LDO.However,when the Mg/Al ratio was lower than 2,unidentate carbonates with stronger binding force were also formed,which led to the trace CO₂ purification ability.To further increase the CO₂ adsorption performance of K-LDO,the aqueous miscible organic solvent treatment（AMOST）was introduced during the co-precipitation process.By exfoliating the layered double hydroxide precursor into nanosheets,more CO₂ adsorption sites were exposed and the K⁺ions were better dispersed.In the reactor-scale study,the trace CO/CO₂ purification ability of the adsorption column after adding high temperature WGS catalysts was discussed.The effect of adsorption temperatures,pressures,inlet CO concentrations,balanced gases,and steam-to-gas ratios were investigated,and the self-purification phenomenon was discovered.The residual CO concentration of the composite system mainly depended on the thermodynamically balanced CO₂ partial pressure of adsorbents.When the adsorbents/catalysts volume ratio was fixed at 5,the residual CO concentration was reduced from 5%–20%to less than 10 ppm,which met the requirement of fuel cel s.A composite column model by coupling the CO₂ adsorption and WGS catalysis kinetics,the column mass and momentum balance,and the dynamic boundary conditions was built.The model was calibrated with the fixed-bed experimental data and was applied to predict17 cases with various operating conditions.To achieve continuous hydrogen production,a two-train elevated temperature pressure swing adsorption（ET-PSA）with an 8-column 13-step and a 2-column 7-step processes was built.By adding the high pressure steam rinse and low pressure steam purge steps,the system achieved both high H₂ purity（>99.999%）and H₂ recovery ratio（>95%）.The energy loss of ET-PSA mainly came from the total steam consumptio n,which could be controlled within 0.451 by adopting the tail gas of the second-train ET-PSA as the purge gas for the first-train ET-PSA.When applied in an integrated gasification fuel cell system,the calculated CO/CO₂ purification energy consumption of ET-PSA was 1.11–1.13 MJ/kg,which was 35.1%–36.2%lower than that of the Selexol process.