Capillary Phase Transitions of Linear and Branched Alkanes in Carbon Nanotubes from Molecular Simulation

Jiang, Jianwen; Sandler, Stanley I.

doi:10.1021/la0608720

Cited by 27 publications

(19 citation statements)

References 100 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This can be interpreted as meaning that the desorption boundary of the hysteresis loop in the GCE isotherm is close to the equilibrium branch. Similar behaviour for a CE isotherm has been reported by Nguyen et al [36] using the two volume -canonical MC method, and by Jiang et al [37,38] using gauge-cell MC, but due to the size effects in their simulations, [36] no vertical segment was observed.…”

Section: Finite Pore Lengthsupporting

confidence: 84%

On the existence of a hysteresis loop in open and closed end pores

Fan

Nicholson

2014

Molecular Simulation

View full text Add to dashboard Cite

We have studied the adsorption of argon at 87 K in slit pores of finite length with a smooth graphitic potential, open at both ends or closed at one end. Simulations were carried out using conventional GCMC (grand canonical Monte Carlo) or kMC (kinetic Monte Carlo) in the canonical ensemble with extremely long Markov chain, of at least 2 £ 10 8 configurations; selected simulations with much longer Markov chains do not show any change in the results. When the pore width is in the micropore range (0.65 nm), type I isotherms are obtained for both pore models and for both simulation methods. However, wider pores (1, 2 and 3 nm in width) all exhibit hysteresis loops in the GCMC simulations, while in the canonical ensemble simulations, the isotherms pass through a sigmoid van der Waals type loop in the transition region. This loop locates the true equilibrium transition. For the pores with one closed end, this transition is close to, or coincides with, the adsorption branch of the GCMC hysteresis loop, but for the open-ended pores, it is more closely associated with the desorption branch. In a separate study of adsorption hysteresis in an infinitely long slit pore, using both simulation techniques, the van der Waals loop follows the adsorption branch of the GCMC isotherm to the transition, then reverts to a long vertical section that falls midway between the two hysteresis branches and finally moves to the desorption transition close to the evaporation pressure. An examination of molecular distributions inside the pores reveals two coexisting phases in the canonical simulations, whereas in the grand canonical simulations, the molecules are uniformly distributed along the length of the pores.

show abstract

Section: Finite Pore Lengthsupporting

confidence: 84%

On the existence of a hysteresis loop in open and closed end pores

Fan

Nicholson

2014

Molecular Simulation

View full text Add to dashboard Cite

show abstract

“…Similarly to what happens to molecules inside other confining environments, the restricted space within SWCNT is expected to induce phase changes and local behavior which may not have a parallel in the fluids bulk phases (Alba-Simionesco et al 2006;Gelb et al 1999). Therefore, it is not surprising that along with other confining nanosurfaces, SWCNTs are being actively investigated (Bekyarova et al 2003;Darkrim et al 2002) and, in spite of the current cost and difficulties to mass-produce them, are being considered as possible storage nanomaterials for H 2 and CH 4 , building blocks in composites (Sinnott and Andrews 2001), chemical sensors (Hong et al 2007), and separating agents of organic vapors (Jiang et al 2005;Jiang and Sandler 2006;Mao and Sinnott 2001), amongst other uses. Recently, Funk et al (2007) employed molecular beam scattering experiments to throw some light onto the adsorption of n/isobutane on SWCNTs.…”

Section: Introductionmentioning

confidence: 99%

Behavior of ethylene and ethane within single-walled carbon nanotubes. 1-Adsorption and equilibrium properties

Cruz

Müller

2009

Adsorption

View full text Add to dashboard Cite

Endohedral adsorption properties of ethylene and ethane onto single-walled carbon nanotubes were investigated using a united atom (2CLJQ) and a fully atomistic (AA-OPLS) force fields, by Grand Canonical Monte Carlo and Molecular Dynamics techniques. Pure fluids were studied at room temperature, T = 300 K, and in the pressure ranges 4 × 10 −4 < p < 47.1 bar (C 2 H 4 ) and 4 × 10 −4 < p < 37.9 bar (C 2 H 6 ). In the low pressure region, isotherms differ quantitatively depending on the intermolecular potential used, but show the same qualitative features. Both potentials predict that ethane is preferentially adsorbed at low pressures, and the opposite behavior was observed at high loadings. Isosteric heats of adsorption and estimates of low pressure Henry's constants, confirmed that ethane adsorption is the thermodynamically favored process at low pressures. Binary mixtures of C 2 H 4 /C 2 H 6 were studied under several (p, T ) conditions and the corresponding selectivities towards ethane, S, were evaluated. Small values of S < 4 were found in all cases studied. Nanotube geometry plays a minor role on the adsorption properties, which seem to be driven at lower pressures primarily by the larger affinity of the alkane towards the carbon surface and at higher pressures by molecular volume and packing effects. The fact that the selectivity towards ethane is similar to that found earlier on carbon slit pores and larger diameter nanotubes points to the fact that the peculiar 1-D geometry of the nanotubes provides no particular incentive for the adsorption of either species.

show abstract

“…• Molecular simulation (Ambrose et al (2012), Coasne et al (2009), Sing et al (2009), Demontis et al (2003, Dukovski et al (2000), Giovambattista et al (2009), Jiang andSandler (2006), Nicholson and Parsonage (1982), Severson and Snurr (2007)). …”

Section: Introductionmentioning

confidence: 99%

Using Simplified Local Density/ Peng-Robinson Equation of State to Study the Effects of Confinement in Shale Formations on Phase Behavior

Jamili

2014

SPE Unconventional Resources Conference

View full text Add to dashboard Cite

A large amount of hydrocarbon fluids in shale formations are stored within the organic matters where the pore sizes are in the order of nanometer scales. Inside these nanopores, the interactions between the fluid molecules and porous walls play such an important role that can change the phase behavior as well as transport mechanisms of the hydrocarbon fluids. For a shale gas reservoir, the natural gas in the reservoir is usually stored in two forms, free gas and adsorbed gas. The region where free gas is stored has negligible fluid-wall interactions while the region for adsorbed gas is under strong pore wall influence. The current available equations of state cannot capture the phase behavior of the adsorbed gas phase due to the ignorance of the fluid-wall interactions.This work focuses on modifying the Peng-Robinson equation of state (PR-EOS) using the Simplified Local-Density (SLD) theory. From the modified PR-EOS, the fluid density at any arbitrary position inside the pore can be calculated using the local density approximation. A density profile for any particular hydrocarbon fluids can be obtained by calculating the local densities of the fluids at each discretized interval along the pore. From the density profile one can distinguish the regions of adsorbed phase, transition phase and bulk phase of the fluids. The thickness and averaged fluid densities for each phase can also be obtained from the model. Once the thickness of the absorbed phase is known, it is possible to determine whether adsorption is a single layer or multilayer.Our preliminary results show that depending on fluid types, either a single layer or multilayer adsorption is presented in those nanometer pores near the pore wall. The pore size range we focused on was from 100 nm to 1 nm. Methane and n-Butane were considered as fluids. When the pore size gets smaller and smaller, the absorbed layers at opposite pore walls can be merged together and result in the absence of the bulk fluid phase in the center areas of the pores. In this case, all the fluids in the pore are under influence of the wall. Our results also indicate that the fluid-wall interactions can have a much larger impacts on light components (methane) rather than heavy components (n-butane). That is, the density of the adsorbed phase of methane is more than two times the free gas density of methane (bulk density), while the n-butane adsorbed density is only slightly higher than its bulk density. The model has also been validated with molecular simulations for accuracy approval. IntroductionAs more and more development and production activities are involved in shale plays, the shale gas transport in nanoscale porous media draws attention recently. It is well known that in typical shale formations especially inside the organic content, the pore throat diameter tends to be in the order of nanometers whereas the molecule sizes tend to vary from a minimum of 0.373 nm for methane to significantly larger values for higher carbon number hydrocarbons. In general, fluids under confinement e...

show abstract

Capillary Phase Transitions of Linear and Branched Alkanes in Carbon Nanotubes from Molecular Simulation

Cited by 27 publications

References 100 publications

On the existence of a hysteresis loop in open and closed end pores

On the existence of a hysteresis loop in open and closed end pores

Behavior of ethylene and ethane within single-walled carbon nanotubes. 1-Adsorption and equilibrium properties

Using Simplified Local Density/ Peng-Robinson Equation of State to Study the Effects of Confinement in Shale Formations on Phase Behavior

Contact Info

Product

Resources

About