International audienceThis work provides a new mass transfer model based on the Maxwell-Stefan theory, especially adapted to represent adsorbed phase multicomponent diffusion at high-adsorbent loading. In our model - contrarily to the well-known model developed by Krishna et al. (Chem Eng Sci. 1990;45:7:1779-1791; Gas Sep Purif. 1993;7:91-104; J Phys Chem B. 2005;109:6386-6396) - the hypothesis that the micropores are saturated does not imply a dependency between the adsorbed phase diffusion coefficients. Experimental liquid phase breakthrough curves of 2-methylpentane (2MP), 3-methylpentane (3MP), 2,3-dimethylbutane (23DMB), and 2,2-dimethylbutane (22DMB) were measured at 458 K in silicalite. The self-diffusion coefficients and Langmuir parameters of the different species were determined using binary exchange breakthrough curves. The Maxwell-Stefan diffusion coefficients obtained for the different isomers are in the order D3MP,nc+1 > D2MP,nc+1 D23DMB,nc+1, and vary between 4 × 10-15 m2 s-1 for 3MP to 6 × 10-16 m2 s-1 for 23DMB. The 22DMB diffusion coefficient is so low that it could not be estimated (the quantity of 22DMB entering silicalite during the experiment is not significant). The model was then validated by comparing experimental breakthrough curves at different feed concentrations and simulations using the independently estimated parameters. Even though the diffusion coefficients of the different isomers vary by one order of magnitude, the agreement between simulated and experimental curves is very satisfactory, showing the good predictive power of our model
International audienceAbstract In this study, a new experimental method based on cyclic breakthrough curves is presented, in order to estimate the co-diffusion coefficients for mixtures at high adsorption loadings. For this purpose, cyclic liquid phase breakthrough curves of mixtures of 2-methylpentane 3-methylpentane (fast-diffusing species) and 2,2-dimethylbutane (slow-diffusing species) have been measured experimentally for different feed compositions at 185°C. Estimation of Langmuir coefficients and self-diffusivities was attempted from simple binary breakthrough curves with the above components using a modified Maxwell-Stefan-type model. However, for the slow-diffusing species, the parameters cannot be estimated accurately from such experiments, because the quantity of 22DMB entering the zeolite network in the experiment duration is not sufficient. On the other hand, a clear influence of the slow diffusing species (22DMB) on the fast diffusing species (3MP) breakthrough curves during cycles has been demonstrated. This phenomenon confirms that 22DMB slowly accumulates in the adsorbent during the cycles, and that is becomes therefore possible to estimate the 22DMB parameters from the cyclic data
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