Abstract
Two series of zeolite X/activated carbon composites with different ratios of zeolite and activated carbon were prepared through a combination process of CO2 activation of the mixtures of elutrilithe and pitch and subsequent hydrothermal crystallization in alkaline solution. An additional surface modification was achieved in diluted NH4Cl solution. CO2 and N2 uptakes on the composites before and after modification were determined for pressures up to 101 kPa at 273 and 298 K, respectively. Langmuir-Freundlich and Toth adsorption models were used to describe the adsorption isotherms of CO2 and the corresponding heats of adsorption were estimated with the Clausius-Clapeyron equation. Both before and after modification, all composites exhibited a remarkable preferential adsorption of CO2 compared to N2, with the modified composites showing a higher adsorption selectivity to CO2 over N2 than the unmodified composites. With an increasing ratio of zeolite in the composites, adsorption capacity and adsorption heat of CO2 on the composites increased simultaneously. Lower adsorption heat was observed both before and after modification especially at the low-loading region and when there was less energetic heterogeneity on the surface of the modified composites. The results may be attributed to the elimination of strong basic sites on the modified composites, which is favorable for desorption of CO2 on the adsorbents and application in pressure swing adsorption processes.
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Ma, J., Si, C., Li, Y. et al. CO2 adsorption on zeolite X/activated carbon composites. Adsorption 18, 503–510 (2012). https://doi.org/10.1007/s10450-012-9440-0
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DOI: https://doi.org/10.1007/s10450-012-9440-0