Studies On Multicomponent Adsorption Equilibrium Of Supercritical Gas Mixture On Porous Solids

Knowledge of multicomponent supercritical adsorption equilibrium is important to the design of separation processes and the progress of theory. However, only few research had been done on multicomponent supercritical adsorption equilibrium. Therefore, multicomponent supercritical adsorption equilibrium was studied systematically. The research progress in the experiments and theories of multicomponent adsorption equilibria was reviewed in detail. Pure component adsorption isotherms of methane, nitrogen, and hydrogen on JX-101 activated carbon were measured by the volumetric method and acted as basic data for predicting multicomponent adsorption equilibrium. The experiment condition covered the range 283-313K and pressures 0-10(105Pa. In addition, the adsorption equilibrium data of the CH4-N2-H2 mixtures of various composition on JX-101 activated carbon were measured by the dynamic method in the range of 283K(313K, 0(6(105Pa.Several well-known models to predict multicomponent adsorption equilibrium were tested by experimental data presently. The models tested include (1) the extended Langmuir model (EL); (2) the laden ratio correlation (LRC); (3) the ideal adsorption solution theory (IAST); (4) the Flory-Huggins vacancy solution theory (FHVSM); (5) the model basing on micropore size distribution and the extended Langmuir equation (MPSD-EL); and (6) the model for mixture including supercritical component (MISC). Performance of multicomponent adsorption equilibrium models is compared with experimental data. It was found that the FHVSM model and the MISC model can give better predictions for the experimental data in the classical models. However, the adsorption equilibrium is treated as a gas-liquid equilibrium between the gas phase and the adsorbed phase in these models. But it is not correct that the adsorbed phase is considered as saturated liquid for multicomponent supercritical adsorption equilibrium. A new model, SAEM, to predict multicomponent adsorption was proposed assuming (1) The energetic heterogeneity of adsorbent surface can be described by micropore size distribution; (2) The adsorbed phase is visualized as a two-dimensional non-ideal compressed gas, whose state can be described by two-dimensional virial equation. The new model was applied to the experimental data measured. It is found that the SAEM model predicted much better than all classical models. In addition to our own data, the SAEM model was applied to the data published by other researchers, which are widely used in the testing of adsorption models. The results showed that the SAEM model gave the best predictions for multicomponent supercritical adsorption equilibrium and was only inferior to the MISC model for the gas mixture including supercritical and sub-critical component. Therefore, it was proved that the SAEM model was reasonable and reliable.