Separation of CO2 from CO2-CH4 mixtures is an important issue in natural gas and biogas purification. The design of such separation processes depends on the knowledge of the behavior of multicomponent adsorption, particularly that of CO2-CH4 mixtures. In this study, we present a series of experimental binary equilibrium isotherms for CO2-CH4 mixtures on an activated carbon at 293 K and compare them with predicted values using the Ideal Adsorption Solution Theory (IAST) and the Extended Langmuir (EL) model. Even at concentrations of ca. 20% for all binary isotherms, CO2 already presents higher adsorbed amounts with respect to CH4. A maximum selectivity of around 8.7 was observed for a nearly equimolar mixture at 0.1 MPa. The IAST in conjunction with the Toth equation showed slightly better results than IAST using the Langmuir equation and both showed better results than the EL model.

In this study, the fixed - bed adsorption of carbon dioxide and a carbon dioxide - nitrogen mixture on zeolite 13X was investigated. The adsorption equilibrium and breakthrough curves were determined at different temperatures - 301 - 306 K, 323 K, 373 K and 423 K. A model based on the LDF approximation for the mass transfer, considering the energy and momentum balances, was used to describe the adsorption kinetics of carbon dioxide and a carbon dioxide - nitrogen mixture. The model acceptably reproduced all of the breakthrough curves and can be considered as adequate for designing a PSA cycle to separate carbon dioxidenitrogen mixtures.

The simulated moving bed (SMB) technology has attracted considerable attention for its efficiency as a chromatographic adsorptive separation. It has been increasingly applied to the separation of binary mixtures with low separation factors, namely to separate isomers. Although quite a vast amount of information has been published concerning the simulation and design of operating conditions of existing SMB plants, fewer works have addressed the question of design and optimisation of geometric parameters and operating conditions of a new adsorber, especially when mass transfer resistances are significant. The present work extends an algorithm developed elsewhere to design SMB equipment and optimize its operating conditions and applies it to the case of fructose-glucose separation using a cation-exchange resin as stationary phase in order to obtain nearly pure fructose in the extract and glucose in the raffinate. The constraints were set as 99% purity for both products. The objective function was chosen to be the adsorbent productivity. The algorithm attempted to find the minimum column lengths for increasing throughputs, which met the required purity constraint. Then, the best construction parameters and operating conditions were chosen as those for which the adsorbent productivity was maximum. The effects of the safety margins applied on the velocity ratios in sections 1 and 4 were examined and a heuristic rule for optimum eluent flowrate was derived. The effect of the purity requirements was also investigated. Finally, the calculated optimal operating points, in terms of flowrate ratios in SMB sections 2 and 3, were analysed in the frame of the equilibrium theory. Sound coherence was verified, which confirmed the accuracy and adequacy of the extended algorithm for the design and optimisation of a SMB adsorber with strong mass transfer effects.