Abstract
The capture of CO2 from post-combustion streams or from other mixtures, such as natural gas, is an effective way of reducing CO2 emissions, which contribute to the greenhouse effect in the atmosphere. One of the developing technologies for this purpose is physisorption on selective solid adsorbents. The ideal adsorbents are selective toward CO2, have a large adsorption capacity at atmospheric pressure and are easily regenerated, resulting in high working capacity. Therefore, adsorbents combining molecular sieving properties and low heats of adsorption of CO2 are of clear interest as they will provide high selectivities and regenerabilities in CO2 separation process. Here we report that some aluminophosphate (AlPO) and silicoaluminophosphate (SAPO) materials with LTA, CHA and AFI structures present lower heats of adsorption of CO2 (13–25 kJ/mol) than their structurally analogous zeolites at comparable framework charges. In some cases, their heats of adsorption are even lower than those of pure silica composition (20–25 kJ/mol). This could mean a great improvement in the regeneration process compared to the most frequently used zeolitic adsorbents for this application while maintaining most of their adsorption capacity, if materials with the right stability and pore size and topology are found.
Highlights
Carbon dioxide is a greenhouse gas that is emitted to the atmosphere due to a large number of industrial processes
We have studied the adsorption of CO2 on AlPOs and SAPOs with LTA, CHA, and AFI structures (Baerlocher and McCusker), and compared the calculated isosteric heats of adsorption with those of analogous zeolites previously reported
AlPO-42, with LTA structure, was synthesized according the method reported in Schreyeck et al (1998) and SAPO42 materials with different Si distribution were prepared as reported in Martínez-Franco et al (2015)
Summary
Carbon dioxide is a greenhouse gas that is emitted to the atmosphere due to a large number of industrial processes. CCS from air is the only way of reducing CO2 presence in the atmosphere, while CCS from large point sources (i.e., power plant or cement factory exhaust) is the best way of minimizing future emissions (Boot-Handford et al, 2014; Leung et al, 2014; The National Academies of Sciences, Engineering and Medicine, 2018). The currently most common technology for CCS from large point sources is amine scrubbing, which involves flowing the CO2-containing mixture through a liquid solution of amines and its thermal regeneration afterwards. This is a highly energy demanding process, which as well presents problems with reactant stability and corrosion of the equipment.
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