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Keywords:

  • adsorption;
  • aluminophosphates;
  • carbon dioxide fixation;
  • hydrophilicity;
  • sustainable chemistry

Abstract

The pressure-swing adsorption method for carbon dioxide capture would ideally be facilitated by adsorbents with a high capacity and a high selectivity for CO2. Several aluminophosphates with 8-ring window apertures (AlPO4-17, AlPO4-18, AlPO4-53, and AlPO4-25) were synthesized by hydrothermal crystallization, calcined, and their CO2 uptake and CO2/N2 selectivity were studied. CO2 and N2 uptake was determined for pressures up to 101 kPa at 273 and 293 K. Langmuir and Toth adsorption models were used to describe the adsorption isotherms. The CO2 and N2 uptakes strongly indicated that the squeezed 8-ring windows of certain aluminophosphates can sieve CO2 from a CO2 and N2 gas mixture. Both AlPO4-53 and AlPO4-25 exhibited a remarkably higher uptake of CO2 compared to N2. The hydrophilicity of the AlPO4 materials was investigated by means of water adsorption, and the results showed that all of the tested aluminophosphates were less water sensitive than a benchmark zeolite (13X). In particular, AlPO4-53 and AlPO4-25 showed a very low degree of water uptake with up to 20–30 % relative humidity. Determination of cyclic adsorption and desorption confirmed the relatively hydrophobic nature of the aluminophosphates, which render them less energy costly for the regeneration of adsorbents.