Sorption of xylenes in CoAlPO4-5 molecular sieves

The sorption isotherms of xylenes in CoAlPO4-5 were measured by the gravimetric technique at 342 K. The isotherms of para- and meta-xylenes followed typical type-I and could be well fitted by the Langmuir model; while the isotherm of ortho-xylene did not show a distinct saturation with the increase of pressure and could be then described by the Freundlich equation. In opposition to the adsorption in AlPO4-5, the isotherms of para- and meta-xylene in CoAlPO4-5 lay above that of ortho-xylene. The free energy change (ΔG) of adsorption increased with the loadings, while the diffusivities of xylenes decreased with the loadings. Moreover, the diffusivities of ortho-xylene were slower than those of other two isomers.