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

Experimental isotherms describing the adsorption of pure N-2, CH4 and CO in AlPO4-11, AlPO4- 17, and AlPO4-18 were determined using the volumetric method at 40 degrees C and at 23 degrees 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 polarity of the adsorbate involved. At 40 degrees 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-N-2, CH4-CO, and CH4-N-2 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.