Numerical simulation of the generalized maxwell-stefan model for multicomponent diffusion in microporous sorbents
Numerical simulation of the generalized maxwell-stefan model for multicomponent diffusion in microporous sorbents
复制标题
微孔吸附剂中多组分扩散的广义 Maxwell-Stefan 模型的数值模拟
DOI：
10.1135/cccc19920687
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发表时间：
1992
影响因子：
--
通讯作者：
J. Moulijn
中科院分区：
文献类型：
--
作者：
J. Loos;Peter JT Verheijen;J. Moulijn
给出了不同条件下多组分在微孔吸附剂中的瞬时表面扩散模拟结果。用广义Maxwell-Stefan理论描述了扩散现象。对扩散方程进行了数值求解。对二元混合物的交换吸收和两种山梨醇在平板中的反向扩散进行了模拟。给出了多组分扩散的一些显著现象。讨论了与多组分传质线性化理论得到的近似解的关系。将模拟结果与文献中的各种结果进行了比较。在固体吸附剂(如沸石)上发生的分离和转化过程通常在非平衡条件下进行。了解和模拟混合物在这些材料中的扩散行为具有重要的现实意义，因为它影响到这些分离和反应的选择性。表面扩散在物理化学中也是很重要的。原则上，在表面上运动的分子可以被视为与表面以及与其附近的其他分子相互作用的探测器。微孔(尺寸小于2nNi)中的扩散与温度和浓度密切相关。扩散的分子确实离开了表面的力场。在沸石中，晶内的孔洞或开口是分子尺寸的，扩散的分子很可能在高表面占有率时相互阻碍。多组分扩散行为特别令人感兴趣。快速扩散弱吸附物种和慢扩散强吸附物种的混合物在沸石中的瞬时吸收是典型的：在接近平衡情况时，快速扩散物种的吸收超过平衡值(见参考文献*-4)。研究了微孔吸附剂对混合物组分的瞬时吸附
The results of simulations of transient multicomponent surface diffusion in a microporous adsorbent are given for various conditions. The generalized Maxwell-Stefan theory was applied to describe the diffusion phenomena. The diffusion equations were solved numerically. The tranqient uptake of a binary mixture and the counterdiffusion of two sorbate species in a slab were simulated. Some striking phenomena of multicomponent diffusion are presented. The relation to the approximate solution obtained by the linearized theory of multicomponent mass transfer is discussed. The simulations are compared with various results found in the literature. Separation and conversion processes taking place on solid sorbents, e.g. zeolites often proceed under non-equilibrium conditions. The understanding and modelling of the diffusion behaviour of mixtures in these materials has practical importance because of its influence on the selectivity of these separations and reactions. Surface diffusion is also of fundamental interest in physical chemistry. In principle, a molecule moving over a surface can be seen as a probe of the interactions with the surface and with the other molecules in its vicinity. Diffusion in micropores (size smaller than 2 nni) is strongly temperature and concentration dependent. The diffusing molecules neker really leave the force field of the surface. In zeolites the intracrystalline pores or openings are of molecular dimensions and the diffusing molecules are likely to hinder each other at high surface occupancies. Multicomponent diffusion behaviour is of special interest. The transient uptake of a mixture of a fast diffusing-weakly adsorbing species and a slow diffusing-strongly adsorbing species in zeolites is typical: the uptake of the fast diffusing species exceeds the equilibrium value in the approach to the equilibrium situation (see e.g. refs*-4). The transient uptake of mixture components in microporous sorbents has been