An investigation of the characteristics of Maxwell-Stefan diffusivities of binary mixtures in silica nanopores
An investigation of the characteristics of Maxwell-Stefan diffusivities of binary mixtures in silica nanopores
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DOI：
10.1016/j.ces.2008.10.045
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发表时间：
2009-03-01
影响因子：
4.7
通讯作者：
van Baten, J. M.
中科院分区：
文献类型：
--
作者：
Krishna, R.;van Baten, J. M.
使用分子动力学（MD）研究了纯组分（氢（H（2））、氩（Ar）、氪（Kr）、甲烷（C1）、乙烷（C2）、丙烷（C3）、正丁烷（nC 4）和正己烷（nC 6））在直径为1、1.5、2、3、4、5.8、7.6和10 nm的二氧化硅纳米孔中的扩散。Maxwell-Stefan（M-S）扩散系数（D（i，s））和自扩散系数（D（i，self，s））在10个分子nm（-3）的孔负载范围内测定。MD模拟表明，零负载扩散系数D（i，s）（0）始终低于经典Knudsen公式的预期值，最高可达10倍：差异随着吸附强度的增加而增加。只有当吸附可以忽略时，D（i）（0）才接近Knudsen扩散系数值。还进行了不同孔隙中二元混合物C1-H（2）、C1-Ar、C1-C2、C1-C3、C1-nC 4、C1-nC 6、C2-nC 4、C2-nC 6和nC 4-nC 6中扩散的MD模拟，以确定二元混合物扩散的M-S公式中出现的三个参数D（1.s）、D（2.s）和D（12）。当在相同的总孔负载下进行比较时，发现混合物中的D（i，s）与一元扩散获得的值实际上相同。此外，任何组分的Di实际上是相同的，与混合物中的伴侣分子无关。此外，分子间物质相互作用参数D（12）可以用与二氧化硅纳米孔内相同浓度的流体混合物中的二元M-S扩散率来识别。所获得的结果强调了M-S理论在纳米孔中混合物扩散中的压倒性优势。我们的研究强调了常用的粉尘气体方法在孔扩散中的局限性，其中Knudsen和表面扩散机制被认为是可加性的。(C)2008爱思唯尔有限公司保留所有权利。
Diffusion of pure components (hydrogen (H(2)) argon (Ar), krypton (Kr), methane (C1), ethane (C2), propane (C3), n-butane (nC4), and n-hexane (nC6)) in silica nanopores with diameters of 1, 1.5, 2, 3, 4, 5.8, 7.6, and 10 nm were investigated using molecular dynamics (MD). The Maxwell-Stefan (M-S) diffusivity (D(i,s)) and self-diffusivities (D(i,self,s)) were determined for pore loadings ranging to 10 molecules nm(-3). The MD simulations show that zero-loading diffusivity D(i,s)(0) is consistently lower, by up to a factor of 10, than the values anticipated by the classical Knudsen formula: the differences increase with increasing adsorption strength. Only when the adsorption is negligible does the D(i)(0) approach the Knudsen diffusivity value. MD simulations of diffusion in binary mixtures C1-H(2), C1-Ar, C1-C2, C1-C3, C1-nC4, C1-nC6, C2-nC4, C2-nC6, and nC4-nC6 in the different pores were also performed to determine the three parameters D(1.s), D(2.s), and D(12), arising in the M-S formulation for binary mixture diffusion. The D(i,s) in the mixture were found to be practically the same as the values obtained for unary diffusion, when compared at the same total pore loading. Also, the Di, of any component was practically the same, irrespective of the partner molecules in the mixture. Furthermore the intermolecular species interaction parameter D(12), could be identified with the binary M-S diffusivity in a fluid mixture at the same concentration as within the silica nanopore. The obtained results underline the overwhelming advantages of the M-S theory for mixture diffusion in nanopores.Our study underlines the limitations of the commonly used dusty-gas approach to pore diffusion in which Knudsen and surface diffusion mechanisms are considered to be additive. (C) 2008 Elsevier Ltd. All rights reserved.