Adsorption of nitrogen, methane, carbon monoxide, and their binary mixtures on aluminophosphate molecular sieves

Experimental isotherms describing the adsorption of pure N₂, CH₄ and CO in AlPO₄-11, AlPO₄-17, and AlPO₄-18 were determined using the volumetric method at 40°C and at 23°C (AlPO₄-11 only) over a pressure range up to 123 kPa, and subsequently fitted with the Langmuir or Freundlich equations, as well as the Flory-Huggins Vacancy Solution Theory equation. The capacities for the adsorbates investigated were found to depend on the geometry of the sieve pore size, as well as the molecular dimensions and the polority of the adsorbate involved. At 40°C and over the investigated pressure range, AlPO₄-11 and AlPO₄-17 adsorbed pure CH₄ in the highest amounts, while AlPO₄-18 had a slightly higher capacity for pure CO. The model parameters obtained by fitting the experimental pure-component isotherms permitted the prediction of binary adsorption information for the CO−N₂, CH₄−CO, and CH₄−N₂ gas mixtures at 101.3 kPa total pressure, using the Extended Langmuir Model, the Ideal Adsorbed Solution Theory, and/or the Flory-Huggins Vacancy Solution Theory for mixtures. An explanation of the behaviour predicted by each model for each adsorption system is attempted.