Configurational-bias Monte Carlo Simulations Research Articles

Temperature effects on the spatial distribution of electrolyte mixtures at the aqueous liquid-vapor interface.

The microscopic picture of ions at the aqueous liquid-vapor interface continues to be an important and active area of research. Both experiments and simulations have shown that certain ions, such as Br- and I-, prefer to adsorb at the interface, but there is not yet a consensus as to the relative importance of various ion-specific properties that influence surface solvation. In a previous study, we systematically explored the effect of ion size on determining whether or not a monovalent ion would adsorb at the surface, and found that, for electrolyte mixtures represented by non-polarizable models, the larger/smaller anions are enriched/depleted at the interface. Here, we extend that study to include temperature effects enabling a van't Hoff analysis of the enthalpic and entropic contributions. We perform configurational-bias Monte Carlo simulations in the Gibbs ensemble to investigate the partitioning of mixtures of differently sized ions at the aqueous liquid-vapor interface from 284.09 K to 347.22 K at a pressure of 1 atm. Ions are represented using our own previously developed models that vary only in size (i.e., the Lennard-Jones σ parameter changes, while all other parameters are held constant across ion types). System properties studied include surface tension, interfacial width, ion surface excess, number density profiles, z-dependent transfer free energy, enthalpy, entropy, and anion-cation coordination numbers.

Occupancy Dependency of Maxwell-Stefan Diffusivities in Ordered Crystalline Microporous Materials.

Molecular dynamics simulation data for a variety of binary guest mixtures (H2/CO2, Ne/CO2, CH4/CO2, CO2/N2, H2/CH4, H2/Ar, CH4/Ar, Ar/Kr, Ne/Ar, CH4/C2H6, CH4/C3H8, C2H6C3H8, CH4/nC4H10, and CH4/nC5H11) in zeolites (MFI, BEA, ISV, FAU (all-silica), NaY, NaX, LTA, CHA, DDR) and metal–organic frameworks (MOFs) (IRMOF-1, CuBTC, MgMOF-74) show that the Maxwell–Stefan (M–S) diffusivities, Đ1, Đ2, Đ12, are strongly dependent on the molar loadings. The main aim of this article is to develop a fundamental basis for describing the loading dependence of M–S diffusivities. Using the ideal adsorbed solution theory, a thermodynamically rigorous definition of the occupancy, θ, is derived; this serves as a convenient proxy for the spreading pressure, π, and provides the correct metric to describe the loading dependence of diffusivities. Configurational-bias Monte Carlo simulations of the unary adsorption isotherms are used for the calculation of the spreading pressure, π, and occupancy, θ. The M–S diffusivity, Đi, of either constituent in binary mixtures has the same value as that for unary diffusion, provided the comparison is made at the same θ. Furthermore, compared at the same value of θ, the M–S diffusivity Đi of any component in a mixture does not depend on it partner species. The Đi versus θ dependence is amenable to simple interpretation using lattice-models. The degree of correlations, defined by the ratio Đ1/Đ12, that characterizes mixture diffusion shows a linear increase with occupancy θ, implying that correlations become increasingly important as pore saturation conditions are approached.

Probing Additive Loading in the Lamellar Phase of a Nonionic Surfactant: Gibbs Ensemble Monte Carlo Simulations Using the SDK Force Field.

Understanding solute uptake into soft microstructured materials, such as bilayers and worm-like and spherical micelles, is of interest in the pharmaceutical, agricultural, and personal care industries. To obtain molecular-level insight on the effects of solutes loading into a lamellar phase, we utilize the Shinoda-Devane-Klein (SDK) coarse-grained force field in conjunction with configurational-bias Monte Carlo simulations in the osmotic Gibbs ensemble. The lamellar phase is comprised of a bilayer formed by triethylene glycol mono- n-decyl ether (C10E3) surfactants surrounded by water with a 50:50 surfactant/water weight ratio. We study both the unary adsorption isotherm and the effects on bilayer structure and stability caused by n-nonane, 1-hexanol, and ethyl butyrate at several different reduced reservoir pressures. The nonpolar n-nonane molecules load near the center of the bilayer. In contrast, the polar 1-hexanol and ethyl butyrate molecules both load with their polar bead close to the surfactant head groups. Near the center of the bilayer, none of the solute molecules exhibits a significant orientational preference. Solute molecules adsorbed near the polar groups of the surfactant chains show a preference for orientations perpendicular to the interface, and this alignment with the long axis of the surfactant molecules is most pronounced for 1-hexanol. Loading of n-nonane leads to an increase of the bilayer thickness, but does not affect the surface area per surfactant. Loading of polar additives leads to both lateral and transverse swelling. The reduced Henry's law constants of adsorption (expressed as a molar ratio of additive to surfactant per reduced pressure) are 0.23, 1.4, and 14 for n-nonane, 1-hexanol, and ethyl butyrate, respectively, and it appears that the SDK force field significantly overestimates the ethyl butyrate-surfactant interactions.

Investigating the non-idealities in adsorption of CO2-bearing mixtures in cation-exchanged zeolites

• Non-idealities are caused by inhomogeneous distribution of adsorbates. • The extent of thermodynamic non-idealities also depend on the Si/Al ratio. • Models for activity coefficients must include the influence of the adsorption potential. • Non-ideal adsorption may influence separation performance of fixed bed adsorbers. Cation-exchanged zeolites have significant potential for capture of CO 2 from a wide variety of mixtures containing N 2 , H 2 , alkanes and alkenes. The strong coulombic interactions of CO 2 with extra-framework cations result in strong binding and selective capture. Published experimental data on mixture adsorption indicate that the Ideal Adsorbed Solution Theory (IAST) fails to provide accurate estimates of mixture adsorption equilibrium. The reasons for the quantitative failure of IAST estimates are investigated with the aid of Configurational-Bias Monte Carlo (CBMC) simulations of mixture adsorption. Computational snapshots indicate that the failure of the IAST is traceable to inhomogeneous distribution of adsorbates within the zeolite framework.

Monte Carlo simulations probing the liquid/vapour interface of water/hexane mixtures: adsorption thermodynamics, hydrophobic effect, and structural analysis

ABSTRACTKnowledge about the interfacial properties of water/oil mixtures is important for the petrochemical industry and for understanding detergency and hydrophobic effects. Here, we probe the liquid/vapour interface of water/n-hexane mixtures using configurational-bias Monte Carlo simulations in the osmotic Gibbs ensemble. We study the effect of n-hexane at several partial pressures ranging from 25% to 95% of its saturated vapour pressure and observe that the surface tension decreases with increasing n-hexane pressure. Additionally, we analyse the simulation trajectories to provide molecular-level insights on the spatial distribution of n-hexane and the structure of the interface. The n-hexane molecules strongly adsorb from the vapour phase onto the liquid interface with a preferentially parallel orientation with respect to the interface. The surface excess, from the Gibbs adsorption isotherm equation, is calculated and used to systematically define the domain of adsorbed n-hexane. Integrating over this gives the free energy of adsorption of n-hexane, which is highly favourable, varying from to kJ/mol as the partial pressure of n-hexane is increased. The enrichment of n-hexane molecules on the interface yields a positive deviation from Henry's law at higher partial pressures, providing evidence for favourable adsorbate-adsorbate interactions.

Understanding Brønsted-Acid Catalyzed Monomolecular Reactions of Alkanes in Zeolite Pores by Combining Insights from Experiment and Theory.

Acidic zeolites are effective catalysts for the cracking of large hydrocarbon molecules into lower molecular weight products required for transportation fuels. However, the ways in which the zeolite structure affects the catalytic activity at Brønsted protons are not fully understood. One way to characterize the influence of the zeolite structure on the catalysis is to study alkane cracking and dehydrogenation at very low conversion, conditions for which the kinetics are well defined. To understand the effects of zeolite structure on the measured rate coefficient (kapp ), it is necessary to identify the equilibrium constant for adsorption into the reactant state (Kads-H+ ) and the intrinsic rate coefficient of the reaction (kint ) at reaction temperatures, since kapp is proportional to the product of Kads-H+ and kint . We show that Kads-H+ cannot be calculated from experimental adsorption data collected near ambient temperature, but can, however, be estimated accurately from configurational-bias Monte Carlo (CBMC) simulations. Using monomolecular cracking and dehydrogenation of C3 -C6 alkanes as an example, we review recent efforts aimed at elucidating the influence of the acid site location and the zeolite framework structure on the observed values of kapp and its components, Kads-H+ and kint .

Atomistic Investigations of the Effects of Si/Al Ratio and Al Distribution on the Adsorption Selectivity of n-Alkanes in Brønsted-Acid Zeolites

The adsorption of n-alkanes onto Brønsted-acid sites is a key step in the catalytic cracking of alkanes. Employing configurational-bias Monte Carlo simulations, we have investigated how the ratio of equilibrium adsorption constants for central C–C bonds relative to terminal bonds of n-alkanes (i.e., the adsorption selectivity ratio) in Brønsted-acid zeolites is influenced by the Si/Al ratio and the Al distribution. A new computational approach was implemented, and the developed force field was validated by a comprehensive comparison between simulation results and experimental data for a number of Brønsted-acid zeolites. While the adsorption selectivity seems to be relatively insensitive to the Si/Al ratio, our results reveal that the Al distribution plays a crucial role in determining the adsorption selectivity. Changes in the Al distribution result in a change of as much as 2-fold in the adsorption selectivity ratio for n-hexane. The selectivity generally shows larger variations with respect to Al distribution in zeolites with a larger Si/Al ratio. The two factors identified by this work that substantially influence the selectivity ratio are the siting of Al atoms among T-sites and their spatial proximity, and an atomic-level understanding of each of these effects was achieved. The siting of Al atoms at more or less selective T-sites significantly influences the overall selectivity ratio, and Al atoms in close proximity can synergistically enhance the adsorption of central C–C bonds, leading to a higher selectivity ratio relative to isolated Al atoms. We anticipate that these results will have important implications for future large-scale computational screenings and the development of advanced synthesis approaches to target certain Al distributions in zeolites.

Methodologies for screening and selection of crystalline microporous materials in mixture separations

Abstract Ordered crystalline microporous materials such as zeolites, metal-organic frameworks (MOFs), and zeolitic imidazolate frameworks (ZIFs) offer considerable potential for separating a wide variety of mixtures. There are basically two different separation technologies that can be employed: (1) pressure swing adsorption (PSA) unit with a fixed bed of adsorbent particles, and (2) membrane device, wherein the mixture is allowed to permeate through thin micro-porous crystalline layers. The fundamental physico-chemical principles underlying the separations in these two devices are fundamentally different. In fixed bed adsorbers, diffusional effects are usually undesirable because these tend to produce distended breakthroughs and diminished productivities. For membrane separations, both intra-crystalline diffusion and mixture adsorption equilibrium determine permeation selectivities, and diffusion selectivities are often the primary drivers for separations. Using Configurational-Bias Monte Carlo (CBMC) simulations of mixture adsorption equilibrium, and Molecular Dynamics (MD) simulations of guest diffusivities in a wide number of guest/host combinations, we demonstrate that adsorption and diffusion do not, in general, proceed hand-in-hand. Strong adsorption often implies lowered mobility. Consequently, the best material for use in fixed bed adsorbers does not always coincide with the ideal choice for use as thin layers in membrane devices. Methodologies for screening microporous materials for use in fixed-bed units and membrane devices are discussed using a large number of examples of industrially important separations.

Modeling of Adsorption Thermodynamics of Linear and Branched Alkanes in the Aluminum Fumarate Metal Organic Framework

Aluminum fumarate is one of the most stable metal–organic frameworks (MOFs), showing good cycling performance in water adsorption and desorption. Because of its rather small pore size, this MOF shows shape selectivity in the adsorption of linear and branched alkanes. In this work, the interaction of a broad series of alkanes with this MOF was studied through molecular simulations. We expand the transferability of a periodic density functional theory (DFT)-derived force field previously reported by Kulkarni and Sholl to the case of alkane adsorption on this aluminum fumarate MOF. With this force field and using configurational bias Monte Carlo simulations (CBMC), low coverage adsorption enthalpies, adsorption entropies, and Henry’s adsorption constants were calculated. Experimental enthalpies of adsorption (−ΔH0) of C5–C8 n- and iso-alkanes are accurately reproduced by our calculations, e.g., within 5% relative error for n-alkanes. Interestingly, a compensation effect between adsorption enthalpy and adsorption entropy is found in the simulations, with a calculated slope almost identical to the experimental value. This indicates that the force field is very well capable of predicting tendencies with respect to the energetic interactions between the confined molecules and the MOF pore walls. Our calculations also predict separation between linear and branched alkanes with very good accuracy.

Conversion of n-hexane and n-dodecane over H-ZSM-5, H-Y and Al-MCM-41 at supercritical conditions

Catalytic reactions of supercritical n-hexane and n-dodecane were studied over H-ZSM-5, H-Y and Al-MCM-41 at pressures between 4 and 6MPa and temperatures between 558 and 748K, using a combination of experimental and theoretical approaches. The primary reaction for n-hexane conversion over H-ZSM-5 was cracking, whereas the primary reaction over H-Y and Al-MCM-41 was isomerization. In contrast, cracking was the primary reaction of n-dodecane over all of the aluminosilicates. Turnover frequencies (TOFs) for n-hexane and n-dodecane conversion over H-ZSM-5 were much greater than for H-Y and Al-MCM-41 under all tested reaction conditions. The invariance of TOFs for n-hexane conversion over H-ZSM-5 and H-Y over the pressure range studied indicated that the reaction was nearly zero-order in hydrocarbon at the supercritical conditions used here. Configurational-bias Monte Carlo simulations indicate that the loadings of reactant molecules reached only about half of their saturation values at the experimental conditions, but plateaus in the adsorption isotherms of n-hexane in H-ZSM-5 and of n-dodecane in both H-ZSM-5 and H-Y zeolites account for the nearly zero-order kinetics. At supercritical conditions, the apparent activation energy of n-dodecane cracking over H-ZSM-5, H-Y and Al-MCM-41 as well as that for n-hexane cracking over H-ZSM-5 was associated with the rate constant for CC bond cleavage (156–200kJmol−1). Density-functional theory calculations show that for n-hexane conversion over H-ZSM-5, β-scission from the bound alkoxide possesses the highest barriers, ranging from 167–177kJmol−1 depending on the mode of cracking. The intrinsic activation barriers for isomerization and hydride transfer reactions were calculated to be significantly lower, at 94 and 96–124kJmol−1, respectively, although still higher than the experimentally observed value of 74±6kJmol−1 for n-hexane conversion over H-Y. Rate expressions derived for monomolecular cracking, bimolecular cracking, and isomerization reactions suggest that the differences between the apparent barriers determined experimentally and the intrinsic barriers calculated theoretically are likely due to the competing hydrocarbon adsorption or quasi-equilibrated exothermic reaction steps. The increased selectivity to cracking over isomerization for n-hexane in H-ZSM-5 was attributed to the difficulty of product removal from the zeolite and, for n-dodecane, to the greatly reduced β-scission barriers and the much stronger product adsorption.

Theoretical Analysis of the Influence of Pore Geometry on Monomolecular Cracking and Dehydrogenation of n-Butane in Brønsted Acidic Zeolites

Recent experimental work has shown that variations in the confinement of n-butane at Bronsted acid sites due to changes in zeolite framework structure strongly affect the apparent and intrinsic enthalpy and entropy of activation for cracking and dehydrogenation. Quantum chemical calculations have provided good estimates of the intrinsic enthalpies and entropies of activation extracted from experimental rate data for MFI, but extending these calculations to less confining zeolites has proven challenging, particularly for activation entropies. Herein, we report our efforts to develop a theoretical model for the cracking and dehydrogenation of n-butane occurring in a series of zeolites containing 10-ring channels and differing in cavity size (TON, FER, -SVR, MFI, MEL, STF, and MWW). We combine a QM/MM approach to calculate intrinsic and apparent activation parameters, with thermal corrections to the apparent barriers obtained from configurational-bias Monte Carlo simulations, to account for configurational c...

Molecular Simulation of Olefin Oligomer Blend Phase Behavior

Configurational-bias Monte Carlo simulations in the Gibbs ensemble are used to study the thermodynamic and structural properties associated with the miscibility of binary olefin oligomer mixtures representing poly(ethylene-alt-propylene), polypropylene, and head-to-head polypropylene. Single-component simulations are performed to compute the cohesive energy densities, ΠCED, of different oligomers that are often utilized in estimating the miscibilities of compounds in the liquid phase but are not measurable for high-boiling compounds, such as polymers. Extrapolating simulation data for C5 to C36 oligomers allows for determination of the infinite-chain-length ΠCED values of three polyolefins. The results agree remarkably well with values deduced from small-angle neutron scattering experiments on high-molecular-weight polymers. In addition, the Flory–Huggins χ parameters based on the free energy of mixing for pairs of olefins are calculated directly from simulations of binary mixtures. The binary propylene a...

Adsorptive Separation of 1-Butanol from Aqueous Solutions Using MFI- and FER-Type Zeolite Frameworks: A Monte Carlo Study.

Anaerobic fermentation can transform carbohydrates to yield a multicomponent mixture comprising mainly of acetone, 1-butanol, and ethanol (ABE) in a typical weight ratio of 3:6:1. Compared to ethanol, 1-butanol, the main product of ABE fermentation, offers significant advantages as a biofuel or a fuel additive. However, the toxicity of 1-butanol for cell cultures requires broth concentrations to be low in 1-butanol (≈1-2 wt %). An energy-efficient recovery method that performs well even at low 1-butanol concentrations is therefore necessary to ensure economic feasibility of the ABE fermentation process. In this work, configurational-bias Monte Carlo simulations in the Gibbs ensemble are performed to probe the adsorption of 1-butanol/water solutions onto all-siliceous zeolites with the framework types MFI and FER. At low solution concentration, the selectivity and capacity for 1-butanol in MFI are larger than those in FER, while the opposite is true for concentrations at or above those of ABE broths. Structural analysis at various loadings sheds light on the different sorbate-sorbate and sorbate-sorbent interactions that govern trends in adsorption in each zeolite.

Structure and Phase Behavior of Mixed Self-Assembled Alkanethiolate Monolayers on Gold Nanoparticles: A Monte Carlo Study.

Configurational-bias Monte Carlo (CBMC) simulations are carried out to investigate the structure and phase behavior of self-assembled monolayers consisting of equimolar alkanethiolate mixtures chemisorbed on the surface of gold nanoparticles. The simulations probe the effects of variations in the chain length, nanoparticle curvature, and exchange of alkanethiolates between nanoparticles. The TraPPE-UA force field is used for the alkanethiolates, whereas the nanoparticle is represented by gold atoms placed on the surface of a sphere. CBMC identity exchange moves are used to enhance sampling of the spatial distribution of the different ligands and to ensure that thermodynamic equilibrium is reached. At a temperature of 298 K, mixtures differing in length by four methylene units exhibit some degree of local segregation. In contrast, the hexanethiolate/tetradecanethiolate mixture yields Janus-like arrangement when the ligands are confined to a single nanoparticle but global demixing when the ligands are allowed to distribute between two nanoparticles.

A Monte Carlo simulation study of the liquid–liquid equilibria for binary dodecane/ethanol and ternary dodecane/ethanol/water mixtures

Obtaining knowledge of the mutual miscibility of alkanes, surfactants, and water over a wide range of temperatures and pressures is of great relevance for the energy industry. Molecular simulations using advanced sampling techniques and transferable force fields can serve as a predictive method to study a variety of phase equilibria at different temperatures, pressures, and overall compositions. In this work, configurational-bias Monte Carlo simulations in the NpT Gibbs ensemble with the Transferable Potentials for Phase Equilibria (TraPPE) force field are applied to investigate the binary mixture of n-dodecane and ethanol at pressures of 0.1 and 100MPa and the ternary mixture of these compounds with water at one state point. The simulations qualitatively reproduce the increase of the upper critical solution temperature (UCST) with increasing pressure, but the miscibility gap is overestimated at both pressures and the UCSTs are shifted up by about 50K compared to the experimental values. The TraPPE model correctly shows a gradual decrease for the ethanol solubility in the n-dodecane-rich phase upon addition of water to the mixture.

Selective Adsorption of Water from Mixtures with 1-Alcohols by Exploitation of Molecular Packing Effects in CuBTC

The selective removal of water from mixtures with methanol, ethanol, and 1-propanol is an important task in the processing industries. With the aid of configurational-bias Monte Carlo simulations of unary and mixture adsorption, we establish the potential of CuBTC for this separation task. For operations close to pore saturation conditions, the adsorption is selective to water that has a significantly higher saturation capacity compared to that of 1-alcohols. The water-selective separation relies on subtle entropy effects that manifest near pore saturation conditions. A further distinguishing feature is that mixture adsorption is determined to be strongly nonideal, and the activity coefficients of the constituent components deviate strongly from unity as pore saturation is approached. The predictions of the ideal adsorbed solution theory (IAST), though qualitatively correct, do not predict the component loadings for mixture adsorption with adequate accuracy. Consequently, the activity coefficients, after ...

Separation of benzene from mixtures with water, methanol, ethanol, and acetone: highlighting hydrogen bonding and molecular clustering influences in CuBTC.

Configurational-bias Monte Carlo (CBMC) simulations are used to establish the potential of CuBTC for separation of water/benzene, methanol/benzene, ethanol/benzene, and acetone/benzene mixtures. For operations under pore saturation conditions, the separations are in favor of molecules that partner benzene; this is due to molecular packing effects that disfavor benzene. CBMC simulations for adsorption of quaternary water/methanol/ethanol/benzene mixtures show that water can be selectively adsorbed at pore saturation, making CuBTC effective in drying applications. Ideal Adsorbed Solution Theory (IAST) calculations anticipate the right hierarchy of component loadings but the quantitative agreement with CBMC mixture simulations is poor for all investigated mixtures. The failure of the IAST to provide reasonable quantitative predictions of mixture adsorption is attributable to molecular clustering effects that are induced by hydrogen bonding between water-water, methanol-methanol, and ethanol-ethanol molecule pairs. There is, however, no detectable hydrogen bonding between benzene and partner molecules in the investigated mixtures. As a consequence of molecular clustering, the activity coefficients of benzene in the mixtures is lowered below unity by one to three orders of magnitude at pore saturation; such drastic reductions cannot be adequately captured by the Wilson model, that does not explicitly account for molecular clustering. Molecular clustering effects are also shown to influence the loading dependence of the diffusivities of guest molecules.

Uncommon Synergy between Adsorption and Diffusion of Hexane Isomer Mixtures in MFI Zeolite Induced by Configurational Entropy Effects

While n-hexane (nC6) can adsorb at any location within the MFI zeolite pore network, configurational considerations cause the branched isomer 2-methylpentane (2MP) to locate preferentially at the channel intersections. For adsorption of nC6/2MP mixtures, infrared microscopy (IRM) measurements show that the adsorption selectivity favors the linear isomer by about one order of magnitude when the total mixture loading, Θt, exceeds four molecules per unit cell at which all intersection sites are fully occupied. The IRM data are in quantitative agreement with configurational-bias Monte Carlo (CBMC) simulations. IRM monitoring of the transient uptake of nC6/2MP mixtures within crystals of MFI exposed to step increases in the pressures shows that the configurational entropy effect also leaves its imprint on the uptake characteristics. For operating conditions in which Θt > 4, increase in the 2MP partial pressure in the bulk gas phase leads to a reduction in the 2MP uptake; this reduction leads to a concomitant a...

Specific and Non-Specific Protein Association in Solution: Computation of Solvent Effects and Prediction of First-Encounter Modes for Efficient Configurational Bias Monte Carlo Simulations

Weak and ultraweak protein-protein association play a role in molecular recognition and can drive spontaneous self-assembly and aggregation. Such interactions are difficult to detect experimentally, and are a challenge to the force field and sampling technique. A method is proposed to identify low-population protein-protein binding modes in aqueous solution. The method is designed to identify preferential first-encounter complexes from which the final complex(es) at equilibrium evolve. A continuum model is used to represent the effects of the solvent, which accounts for short- and long-range effects of water exclusion and for liquid-structure forces at protein/liquid interfaces. These effects control the behavior of proteins in close proximity and are optimized on the basis of binding enthalpy data and simulations. An algorithm is described to construct a biasing function for self-adaptive configurational-bias Monte Carlo of a set of interacting proteins. The function allows mixing large and local changes in the spatial distribution of proteins, thereby enhancing sampling of relevant microstates. The method is applied to three binary systems. Generalization to multiprotein complexes is discussed.

Monte Carlo Simulation of Adsorption Isotherms of Pure C5-C7 Linear Alkanes in Pillared Layered Materials

The adsorption equilibria of pure linear alkanes, involving n-pentane, n-hexane, and n-heptane in pillared layered materials are simulated using configurational-bias Monte Carlo (CBMC) techniques in grand canonical ensemble. In the CBMC simulation, pillared layered pores are modelled by a uniform distribution of pillars between two solid layered walls with a given size of interlayer gallery. And a grid model is employed here to calculate the interaction between fluid molecules and two layered boards. Our simulation results are in a good agreement with the reported experimental data on the adsorption of nitrogen at 77 K, indicating that the grid model used in this work is effective. Then, a series of CBMC simulations of the adsorption isotherms of pure n-pentane, n-hexane, and n-heptane in pillared layered pores with three different porosities ψ = 0.98, 0.94 and 0.87, and three pore widths H = 1.02, 1.70 and 2.38 nm at temperature T = 300 K has been carried out.