Sorption thermodynamics, siting, and conformation of long n-alkanes in silicalite as predicted by configurational-bias Monte Carlo integration
- Lawrence Berkeley Lab., CA (United States) Univ. of California, Berkeley, CA (United States)
The low-occupancy adsorption thermodynamics of n-alkanes ranging in length from C[sub 4] to C[sub 25] in the zeolite silicalite is predicted from molecular simulations. A bias Monte Carlo (MC) technique is described which permits these calculations to be carried out with modest computational expense. In addition, a general, systematic coarse-graining methodology is developed which enables the location and shape of chains of arbitrary length to be accurately described using a small number of degrees of freedom. By coupling this methodology with the bias Monte Carlo technique, the free energy of sorbed chains is calculated as a function of the coarse-grained configuration of chains. The results indicate that, at high temperature, n-alkanes probe all the accessible regions of the zeolite pore network, favoring high-entropy conformations that access more than one type of channel environment. As temperature decreases to room temperature, short chains continue to populate all regions of the zeolite, while chains longer than n-octane align along the straight channels in highly localized low-energy configurations. Macroscopic thermodynamic results, such as Henry's law constants and isosteric heats of adsorption, are calculated and compared to experimentally obtained values. 51 refs., 19 figs., 8 tabs.
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6767847
- Journal Information:
- Journal of Physical Chemistry; (United States), Journal Name: Journal of Physical Chemistry; (United States) Vol. 99:7; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
661300 -- Other Aspects of Physical Science-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
99 GENERAL AND MISCELLANEOUS
990200 -- Mathematics & Computers
ADSORPTION
ADSORPTION HEAT
ALKANES
CALCULATION METHODS
DATA
ENTHALPY
HYDROCARBONS
INFORMATION
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MATERIALS
MATHEMATICAL MODELS
MINERALS
MONTE CARLO METHOD
NUMERICAL DATA
ORGANIC COMPOUNDS
PHYSICAL PROPERTIES
SILICATE MINERALS
SIMULATION
SORPTION
SORPTIVE PROPERTIES
SURFACE PROPERTIES
TEMPERATURE DEPENDENCE
THERMODYNAMIC PROPERTIES
THERMODYNAMICS
ZEOLITES