(622f) Ability of the New Kinetically Limited Linear Driving Force Model to Predict the Behavior of Kinetically Limited Gas Separations in Light of Penetration Theory

The new kinetically limited linear driving force (KLLDF) model was compared against the LDF model to predict the separation of CH₄/N₂ and CH₄/CO₂ via pressure swing adsorption (PSA) using carbon molecular sieve (CMS) 172K. The PSA cycle was carried out at room temperature in a single one liter bed and consisted of the following cycle steps: feed pressurization, feed, three equalizations down, countercurrent depressurization, light reflux, three equalizations up and idle. Three 3.8 liter tanks were used to temporarily store the gas during the equalization steps. In the case of CH₄/N₂ separation the PSA cycle was carried out with an 85/15 mixture with the pressures oscillating between 28 and 606 kPa. In the case CH₄/CO₂ separation the PSA cycle was carried out also with an 85/15 mixture with the pressures oscillating between 101 and 345 kPa. The results show that for both separations the KLLDF model consistently displayed a superior predictive ability than the LDF model under all conditions, especially for CH₄/CO₂ where experiments and modelling displayed excellent agreement. In the case of CH₄/N₂ separation, deviations were observed between predictions and experiments with the KLLDF model that became more significant with shorter cycle times. Such deviations resulted from apparently larger mass transfer coefficients observed by the experimental results. These deviations were consistent with penetration (Carta, 1993; Alpay and Scott, 1992; Nakao and Suzuki, 1983) because of the slow kinetics of N₂, which is the faster diffusing species in the CH₄/N₂ system. These results also explain why from this theory no such deviations were observed with the CH₄/CO₂ system. Specific details about how these two systems respectively agree with and disagree with penetration theory will be provided.

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