On the Diffusion of Cyclohexane in ZSM-5 Measured by Zero-Length-Column Chromatography

and, Warwick L. Duncan; Möller, K.P.

doi:10.1021/ie9907573

Cited by 16 publications

(20 citation statements)

References 18 publications

(58 reference statements)

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“…The apparent (Cavalcante and Ruthven 1995b;Duncan and Moller 2000;Magalhaes et al 1998;Xiao and Wei 1992) diffusion coefficients for the smaller crystals are about an order of magnitude smaller than that of the larger crystals. Surface resistance is therefore not negligible in these conditions.…”

Section: Estimation Of the Surface Resistancementioning

confidence: 77%

Diffusion in zeolites: is surface resistance a critical parameter?

et al. 2010

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Gravimetric uptake measurements were performed with cyclohexane for different Silicalite-1 crystals sizes. It was observed that the apparent diffusion coefficients vary with crystal size, confirming the existence of a surface resistance. Considering that surface and the intracrystalline characteristic diffusion times are additives, it was possible to dissociate the two resistances.Surface mass transfer coefficient was found to be in the same order of magnitude for the different samples and activated with temperature. The contribution of surface resistance to mass transfer limitation is lower at high temperatures and for the bigger crystals. Surface resistance is far from being negligible for the smaller crystals: for crystals of 2 µm, surface resistance represents more than 60% of the total mass transfer resistance at 398 K. And crystals of that size (in the order of 2 µm) are usually used industrially, in order to minimize mass transfer resistance.The surface of one of our sample was purified by etching with a solution of hydrogen fluoride, without any enhancement of the adsorption kinetic. Surface resistance may not be located at the extreme surface of the crystals but in a layer of non negligible thickness of distorted crystal structure around the crystals.

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Section: Estimation Of the Surface Resistancementioning

confidence: 77%

Diffusion in zeolites: is surface resistance a critical parameter?

et al. 2010

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“…22−24 Previous work has suggested, as with other systems, that the interparticle diffusion of cyclohexane from between small ZSM-5 crystals is slower than that between larger particles. 17,25 Ruthven measured the diffusion of mesitylene in cyclohexane through zeolites, and reported coefficients in the range of 2.8 × 10 −19 to 6.0 × 10 −15 m 2 s −1 ; he also attributed the low values to the small crystal size of 1−2 μm of the zeolites, with diffusion likely to be controlled by interparticle rate processes. 15 The dead space within the HPLC flow line, detector chamber, and ZLC entry and exit ports caused the liquids to mix in a manner similar to a chromatographic line broadening effect.…”

Section: ■ Introductionmentioning

confidence: 99%

Diffusion and Tortuosity in Porous Functionalized Calcium Carbonate

Levy

Matthews

Laudone

et al. 2015

Ind. Eng. Chem. Res.

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Calcium carbonate can be "functionalized" by use of etching agents such as phosphoric acid to create inter-and intraparticle porosity with a range of morphologies. Functionalized calcium carbonate has potential for use as a carrier for the delayed release of actives, such as drugs, plant protection chemicals, and food additives such as flavors. The drug or flavor is released slowly by permeation and diffusion. In order to measure the effective rate of diffusion within a range of morphologies, and hence gain insights into the optimum mode of functionalization, the diffusion of vanillin in ethanol is reported. Effective diffusion coefficients D′ were measured in a flow cell connected to a high performance liquid chromatograph (HPLC). Samples were also subjected to mercury intrusion porosimetry. The resulting percolation characteristics were inverse modeled using the PoreXpert package to generate representative void structures with estimated tortuosities. It is shown that the primary particle size of a sample was a better predictor of D′ calculated from the experimental diffusion curves, and also of the porosity-scaled tortuosity values, than the porosity or surface area. There was also a correlation between intraparticle tortuosity, scaled by porosity, and diffusion coefficient. The approach is validated by experimental evidence from this and related studies. ■ INTRODUCTION"Functionalized" calcium carbonate (FCC) is produced by etching calcium carbonate particles and reprecipitating modified surface structure with in situ or externally supplied CO 2 in the form of carbonic acid. To facilitate the in situ production of CO 2 , acids such as phosphoric acid can be used, resulting in a mixed mineral morphology. Variations in the etching process produce a range of morphologies with recrystallized surfaces, consisting of incorporated hydroxyapatite (HAP) in the case of phosphoric acid, which are dual porous (i.e., inter-and intraparticle porosity).FCCs are proving to have a wide range of novel applications. In particular, they are being proposed as an excipient and a pharmaceutical ingredient, 1,2 because the porous nature of calcium carbonate offers a good stability of the ingredients, slow biodegradability, is easily produced, tasteless, stable, and biocompatible. 3−6 The use of HAP as a drug carrier has also been discussed in the literature. 7−12 FCC offers benefits over HAP because the current commercial methods used to produce HAP give a low yield mixed with several phases, so that the product is expensive and suitable only for small-scale and timeconsuming production. 13 Adjustments to the FCC production process can be used to produce a wide range of different morphologies, and raise the possibility of tailoring the void structures of the particles to provide controlled release delivery vehicles for actives across many fields, including drugs and flavors. (The term "active" encompasses active ingredients, active constituents, and bulk actives.) However, such tailoring can only be fully optimized by a fundamental ch...

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“…For model A, a reduction in surface area should yield an unchanged D and a reduction in K , while model B would produce a reduced D and an unchanged K . Experiments were performed with catalyst modified by the liquid phase deposition of both pure and dilute tetraethoxy silane, the parent being Sample C of Duncan and Möller (2000). It was found that the changes in sorption behavior of the dilute modified samples corresponded most closely to the pore mouth blockage mechanism in which the area for flux is reduced throughout the particle volume (i.e.…”

Section: Discussionmentioning

confidence: 99%

“…This paper presents the results of a detailed study, using the zero length column method (Eic and Ruthven, 1988), into the diffusion characteristics of cyclohexane in ZSM-5 modified by the liquid phase deposition of tetraethoxy silane (TEOS). These results may be compared to those presented in Duncan and Möller (2000) for unmodified ZSM-5. The parent sample of this paper is Sample C of that work.…”

Section: Introductionmentioning

confidence: 93%

Diffusion in Surface Modified ZSM-5 Studied Using the ZLC Method

Duncan

Möller

2005

Adsorption

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Deposition of silane on a zeolite's external surface is a well established method of increasing its shape selective properties by modifying diffusion resistances. In this work the intracrystalline diffusivity of cyclohexane in both a parent and silanized ZSM-5 samples were measured using the zero length column technique. It was found that the apparent intracrystalline diffusivity did indeed decrease in the modified samples. Models based on a surface barrier approach to describe pore mouth narrowing and an increase in intracrystalline tortuosity as a result of pore blockage were used to interpret the experimental data. It is found that the data correspond most consistently with the model describing pore blockage.

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On the Diffusion of Cyclohexane in ZSM-5 Measured by Zero-Length-Column Chromatography

Cited by 16 publications

References 18 publications

Diffusion in zeolites: is surface resistance a critical parameter?

Diffusion in zeolites: is surface resistance a critical parameter?

Diffusion and Tortuosity in Porous Functionalized Calcium Carbonate

Diffusion in Surface Modified ZSM-5 Studied Using the ZLC Method

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