Influence of slow diffusing species on mixture diffusion of hexane isomers in silicalite: Characterization by a new cyclic method

The feasibility of mono- and di-branched paraffins separation on silicalite was evaluated by performing cyclic breakthrough experiments in liquid phase with mixtures of 2-methylpentane (2MP), 3-methylpentane (3MP), 2,3-dimethylbutane (23DMB), and 2,2-dimethylbutane (22DMB). For mixtures of the faster diffusing species (2MP, 3MP, and 23DMB), cyclic steady state is obtained from the first cycle. On the other hand, when the slow diffusing species 22DMB is involved, a slow accumulation occurs from cycle to cycle, yielding a change of the breakthrough curves for all the species. Using a diffusion model especially adapted to adsorbent saturation loading, the kinetic and thermodynamic parameters of 22DMB were estimated. Influence of the cycling conditions on the separation performance were finally studied by simulation. (c) 2011 American Institute of Chemical Engineers AIChE J, 2012