Entropy effects in adsorption and diffusion of alkane isomers in mordenite: An investigation using CBMC and MD simulations

被引:55
作者
van Baten, JM [1 ]
Krishna, R [1 ]
机构
[1] Univ Amsterdam, Vant Hoff Inst Mol Sci, NL-1018 WV Amsterdam, Netherlands
关键词
MOR zeolite; multicomponent diffusion; alkane mixtures; single file diffusion; Maxwell-Stefan diffusion; molecular dynamics; configurational-bias Monte Carlo simulations;
D O I
10.1016/j.micromeso.2005.05.025
中图分类号
O69 [应用化学];
学科分类号
081704 ;
摘要
Configurational-bias Monte Carlo (CBMC) simulations were carried out to determine the sorption isotherms for hexane isomers (n-hexane, 2-methylpentane and 2,2-dimethylbutane) and butane isomers (n-butane and iso-butane) in MOR zeolite. The hexane and butane isomers adsorb exclusively within the 12-ring channels. For a given carbon number, the sorption strength, and capacity, increases with the degree of branching. This is due to the increased packing efficiency within the one-dimensional 12-ring channels when the degree of branching increases. Molecular dynamics (MD) simulations were performed to determine both the Maxwell-Stefan (M-S) diffusivities D-i, and the self-diffusivities, D-i.self, of pure components and mixtures, for a range of molecular loadings. Diffusion was found to be uni-dimensional, and no single file diffusion behavior is observed. Entropy effects cause a reversal in the hierarchy of diffusivity values at high loadings. For example, at low loadings the more compact 22DMB diffuses slower than the slimmer nC6 molecule, whereas at high loadings the reverse is true. The diffusion in mixtures of alkane isomers could be predicted very well by the Maxwell-Stefan diffusion formulation, using only pure component adsorption and diffusion data. In these predictions the Reed-Ehrlich model is used to describe the loading dependence of the pure component M-S diffusivities D-i. Furthermore, correlation effects are described by self-exchange coefficients D-ii, obtained from fitting the pure-component diffusion data. The special features of adsorption and diffusion in one dimensional zeolite topologies are emphasized by comparison with simulations in FAU and MFI zeolites. (c) 2005 Elsevier Inc. All rights reserved.
引用
收藏
页码:179 / 191
页数:13
相关论文
共 37 条
[1]   Application of natural zeolites in the purification and separation of gases [J].
Ackley, MW ;
Rege, SU ;
Saxena, H .
MICROPOROUS AND MESOPOROUS MATERIALS, 2003, 61 (1-3) :25-42
[2]  
Baerlocher CH., Database of Zeolite Structures
[3]   SYNTHESIS OF MORDENITE TYPE ZEOLITE [J].
BAJPAI, PK .
ZEOLITES, 1986, 6 (01) :2-8
[4]   Molecular understanding of diffusion in confinement [J].
Beerdsen, E ;
Dubbeldam, D ;
Smit, B .
PHYSICAL REVIEW LETTERS, 2005, 95 (16)
[5]   Fundamentals and applications of pervaporation through zeolite membranes [J].
Bowen, TC ;
Noble, RD ;
Falconer, JL .
JOURNAL OF MEMBRANE SCIENCE, 2004, 245 (1-2) :1-33
[6]   The selectivity of n-hexane hydroconversion on MOR-, MAZ-, and FAU-type zeolites [J].
Calero, S ;
Schenk, M ;
Dubbeldam, D ;
Maesen, TLM ;
Smit, B .
JOURNAL OF CATALYSIS, 2004, 228 (01) :121-129
[7]   Nonequilibrium molecular dynamics simulations of diffusion of binary mixtures containing short n-alkanes in faujasite [J].
Chempath, S ;
Krishna, R ;
Snurr, RQ .
JOURNAL OF PHYSICAL CHEMISTRY B, 2004, 108 (35) :13481-13491
[8]   Siting and segregation effects of simple molecules in zeolites MFI, MOR, and BOG [J].
Clark, LA ;
Gupta, A ;
Snurr, RQ .
JOURNAL OF PHYSICAL CHEMISTRY B, 1998, 102 (35) :6720-6731
[9]   Effects of single-file diffusion on the kinetics of hydroisomerization catalyzed by Pt/H-mordenite [J].
de Gauw, FJMM ;
van Grondelle, J ;
van Santen, RA .
JOURNAL OF CATALYSIS, 2001, 204 (01) :53-63
[10]   Applied molecular simulations over FER-, TON-, and AEL-type zeolites [J].
Domokos, L ;
Lefferts, L ;
Seshan, K ;
Lercher, JA .
JOURNAL OF CATALYSIS, 2001, 203 (02) :351-361