Differential heats of adsorption and adsorption isotherms of alcohols on silicalite

Dubinin, M. M.; Rakhmatkariev, G. U.; Isirikyan, A. A.

doi:10.1007/bf00957798

Cited by 21 publications

(32 citation statements)

References 3 publications

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“…Indeed, in the same work, Liu and Monson showed that other water models, such as SPC, predict capillary condensation in narrow pores (6.5 Å < H < 8.8 Å), adsorbing after saturation only in wider pores. Our estimates of the onset pressure in slit graphite pores are of the same order of magnitude as those found in other hydrophobic absorbents such as pure silica MEL or MFI zeolites, 38,48,54 whose structure are characterized by intersecting cylindrical pores with effective diameters in the range 5-5.5 Å. Note that some experimental studies found adsorption of water in MFI at pressures below the bulk vapor saturation pressure, a fact that is often attributed to the presence of silanol defects in the zeolites.…”

Section: B Adsorption Of Water Methanol and Their Mixtures In Graphite Slit Poressupporting

confidence: 78%

Adsorption of water, methanol, and their mixtures in slit graphite pores

Pršlja

Lomba

Gómez‐Álvarez

et al. 2019

The Journal of Chemical Physics

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The behavior of water, methanol, and water-methanol mixtures confined in narrow slit graphite pores as a function of pore size was investigated by Monte Carlo, hybrid Monte Carlo, and Molecular Dynamics simulations. Interactions were described using TIP4P/2005 for water, OPLS/2016 for methanol, and cross interactions fitted to excess water/methanol properties over the whole range of concentrations, which provide a rather accurate description of water-methanol mixtures. As expected for hydrophobic pores, whereas pure methanol is adsorbed already from the gas phase, pure water only enters the pore at pressures well beyond bulk saturation for all pore sizes considered. When adsorbed from a mixture, however, water adsorbs at much lower pressures due to the formation of hydrogen bonds with previously adsorbed methanol molecules. For all studied compositions and pore sizes, methanol adsorbs preferentially over water at liquid-vapor equilibrium conditions. In pure components, both water and methanol are microscopically structured in layers, the number of layers increasing with pore size. This is also the case in adsorbed mixtures, in which methanol has a higher affinity for the walls. This becomes more evident as the pore widens. Diffusion of pure water is higher than that of pure methanol for all pore sizes due to the larger size of the methyl group. In mixtures, both components present similar diffusivities at all pore sizes, which is explained in terms of the coupling of molecular movements due to strong hydrogen bonding between methanol and water molecules. This is particularly evident in very narrow pores, in which pure methanol diffusion is completely impeded on the time scale of our simulations, but the presence of a small amount of water molecules facilitates alcohol diffusion following a single-file mechanism. Additionally, our results indicate that pure water diffusivities display a non-monotonous dependence of pore size, due to effects of confinement (proximity to a fluid-solid-fluid transition induced by confinement as reported in previous work) and the dynamic anomalies of water.

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Section: B Adsorption Of Water Methanol and Their Mixtures In Graphite Slit Poressupporting

confidence: 78%

Adsorption of water, methanol, and their mixtures in slit graphite pores

Pršlja

Lomba

Gómez‐Álvarez

et al. 2019

The Journal of Chemical Physics

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“…Now, in Figure 2 (bottom), we compare our simulated adsorption isotherms for MFI zeolite using the UA-TraPPe 32 model and with experimental data at a somewhat higher temperature, 30 °C. 31 The effects of this small temperature difference are not appreciable at the scale of the figure in the simulation results. As in the case of MEL, saturation capacities predicted by experiments and simulations are nearly coincident but the computational estimate for onset adsorption is somewhat overestimated, especially in the case of methanol.…”

Section: ■ Resultsmentioning

confidence: 89%

“…Obviously, the adsorption capacities of the zeolite increase with decreasing adsorbate molecular size. Now, in Figure (bottom), we compare our simulated adsorption isotherms for MFI zeolite using the UA-TraPPe model and with experimental data at a somewhat higher temperature, 30 °C . The effects of this small temperature difference are not appreciable at the scale of the figure in the simulation results.…”

Section: Resultsmentioning

confidence: 97%

“…Single-component adsorption isotherms of methanol (black circles and curves), ethanol (red squares and curves), and 1-butanol (blue triangles and curves) in pure silica MEL (top) and MFI (bottom) zeolites at ambient temperature. Symbols correspond to experimental data obtained in this work (MEL) and taken from Dubinin et al (MFI). Solid curves represent GCMC simulations using UA-TraPPe and dash-dotted curves to AA-OPLS …”

Section: Resultsmentioning

confidence: 99%

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Study of Short-Chain Alcohol and Alcohol–Water Adsorption in MEL and MFI Zeolites

et al. 2018

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In this paper, we present a comparative study of the adsorption behavior of short chain alcohols (pure and in aqueous solution) into silicalite-1 (MFI-type zeolite) and silicalite-2 (MEL-type zeolite). For quite some time, silicalite-1 has been the reference material to address the problem of adsorptive-based separation, mostly for hydrocarbon mixtures. Interestingly, being structurally close to silicalite-1, adsorption studies using silicalite-2 are scarce and to the best of our knowledge, a comparative study of their behavior for alcohol–water mixtures has not been published to date. We have here resorted to molecular simulation techniques to analyze the adsorption and diffusion phenomena in both zeolites at 25 and 50 °C for pure methanol, ethanol, 1-butanol, and water, and for some relevant compositions of alcohol/water mixtures. In addition to the dilute regime in the mixture, our study ranges from intermediate alcohol concentrations to alcohol-rich phases, relevant to alcohol purification processes. Besides, we have performed volumetric and calorimetric measurements of single-component adsorption of alcohols in pure silica MEL zeolite, which were used to validate the model potentials used in the simulations. We observe that the zigzag channels of MFI zeolite are most likely responsible for its somewhat higher affinity for alcohols. This leads to higher adsorption selectivities when compared to those of MEL zeolite. We have also found that the choice of water model strongly conditions water coadsorption into the zeolites and subsequently the predictions of the adsorbent’s selectivity in alcohol/water systems. Despite considerable differences for adsorbed pure components, diffusivities of alcohol and water adsorbed from mixtures are relatively similar, as a consequence of the strong hydrogen bonds between hydroxyl groups and water.

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“…This mild hydrophilicity then leads to type I isotherms for water on ZSM-5 and can also be attributed to the presence of extra framework charged defects. Similarly for ethanol, inflections at low pressures have been reported in both simulation and experimental work (Dubinin et al 1989;Xiong et al 2011), yet often the behaviour is regarded as type I, due to lack of data under these conditions (Oumi et al 2002). Nonetheless, regardless of the exactness of the predictions, the inflections as shown in Figs.…”

Section: Resultsmentioning

confidence: 85%

A priori predictions of type I and type V isotherms by the rigid adsorbent lattice fluid

Verbraeken

Brandani

2019

Adsorption

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Adsorbents exhibiting non type I adsorption behaviour are becoming increasingly more important in industrial applications, such as drying and gas separation. The ability to model these processes is essential in process optimisation and intensification, but requires an accurate description of the adsorption isotherms under a range of conditions. Here we describe how the Rigid Adsorbent Lattice Fluid is capable of a priori predictions both type I and type V adsorption behaviour in silicalite-1. The predictions are consistent with experimental observations for aliphatic (type I) and polar (type V) molecules in this hydrophobic material. Type V behaviour is related to molecular clustering and the paper discusses the model parameters governing the presence/absence of this behaviour in the predicted isotherms. It is found that both the solid porosity and the adsorbate interaction energy/energy density are deciding factors for the isotherm shape. Importantly, the model, whilst thermodynamically consistent, is macroscopic and thus computationally light and requires only a small number of physically meaningful parameters.

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Differential heats of adsorption and adsorption isotherms of alcohols on silicalite

Cited by 21 publications

References 3 publications

Adsorption of water, methanol, and their mixtures in slit graphite pores

Adsorption of water, methanol, and their mixtures in slit graphite pores

Study of Short-Chain Alcohol and Alcohol–Water Adsorption in MEL and MFI Zeolites

A priori predictions of type I and type V isotherms by the rigid adsorbent lattice fluid

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