Thomas Saleman

Adsorption equilibria and kinetics of CH4 and N2 on commercial zeolites and carbons

Adsorption equilibria and kinetics are two sets of properties crucial to the design and simulation of adsorption based gas separation processes. The adsorption equilibria and kinetics of N2 and CH4 on commercial activated carbon Norit RB3, zeolite 13X, zeolite 4A and molecular sieving carbon MSC-3K 172 were studied experimentally at temperatures of (273 and 303) K in the pressure range of (5–120) kPa. These measurements were in part motivated by the lack of consistent adsorption kinetic data available in the literature for these systems, which forces the use of empirical estimates with large uncertainties in process designs. The adsorption measurements were carried out on a commercial volumetric apparatus. To obtain reliable kinetic data, the apparatus was operated in its rate of adsorption mode with calibration experiments conducted using helium to correct for the impact of gas expansion on the observed uptake dynamics. Analysis of the corrected rate of adsorption data for N2 and CH4 using the non-isothermal Fickian diffusion (FD) model was also found to be essential; the FD model was able to describe the dynamic uptake observed to better that 1% in all cases, while the more commonly applied isothermal linear driving force model was found to have a relative root mean square deviation of around 10%. The measured sorption kinetics had no dependence on gas pressure but their temperature dependence was consistent with an Arrhenius-type relation. The effective sorption rates extracted using the FD model were able to resolve inconsistencies in the literature for similar measurements.

A Numerical Modelling Approach for Dual Reflux PSA Separation of N2 and CH4 in LNG Production

Abstract In this paper, a novel, full Dual Reflux PSA (PSA) model is proposed for separating methane and nitrogen mixtures. The model is a full, integrated ODE model, in contrast to our former work where stripping PSA and enriching PSA were simulated separately and were combined using the total material balance (referred to as a transfer function model). The full model was built rigorously in a commercial simulator in terms of mass balances, energy balances and pressure-flow relationships, and it was numerically solved by the ODE solver which was integrated in the simulator. The transfer function model which was proven to have a close match with experimental data was compared to the results from the full DR-PSA model using the same key parameters, such as feed composition, total throughput, reflux ratios and cycle time, and resulted in a close match. The impact of feed position, feed temperature, feed composition and cycle time on the system was also studied with the new model.