(189g) Silicoaluminophosphates as CO2 Adsorbent for Pressure Swing Adsorption

Silicoaluminophosphates (SAPO4:s) are potential candidates for CO2 adsorbents in Pressure Swing Adsorption (PSA) processes. There is a good range of SAPO4:s with varying pore sizes and structures. They are structurally similar to aluminophosphates, and SAPO4 materials with low silicon content are less hydrophilic than common zeolitic adsorbents. Furthermore, the dominant physisorption of CO2 of SAPO4:s materials is ideal for PSA processes, in which easy regeneration of the adsorbent material is essential. The presence of charge balancing cations within the cages, opens the pathway for fine tuning the adsorptive properties of SAPO4 materials via ion-exchange experiments. Such exchange can alter the selectivity towards CO2. In this work, a range of SAPO4 materials with 8-membered rings were synthesised and characterised by X-ray diffraction (XRD) and Thermogravimetric Analysis (TGA). Window apertures encircled by 8 atoms could enable a kinetically enhanced CO2-over-N2 selection. The hydrophilicity of these SAPO4:s materials was examined by performing water adsorption measurements. The CO2 and N2 adsorption properties of the as-synthesised materials were investigated. The effect of cation exchange and variations of framework Si content on SAPO4 materials is apparent, and can be demonstrated partly by the changes of CO2 capacity and selectivity. The molecular details of the adsorption and desorption of SAPO4:s were studied extensively using IR spectroscopy with a home-made transmission cell coupled to a vacuum system. Physisorption was clearly dominating but some contributions from chemisorption were identified.