Diffusion of p-xylene in single and binary systems in zeolites investigated by FTIR spectroscopy

Nießen, W.; Karge, Hellmut G.

doi:10.1016/0927-6513(93)80003-d

Cited by 91 publications

(37 citation statements)

References 6 publications

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“…The magnitude of the activation enthalpies of slow desorption (60-70 kJ mol -1 ) seems to be in the polymer diffusion range (>60 kJ mol -1 (1,9,11,13)) rather than in the pore diffusion range [20-40 kJ mol -1 (11,(14)(15)(16)]. Therefore intra-organic matter diffusion may better explain the slow desorption from the sediments used by us than pore diffusion.…”

Section: Discussionmentioning

confidence: 99%

“…By measuring the magnitude of the activation energy of slow adsorption and desorption, indications on the relative importance of organic matter diffusion [which can probably be regarded as polymer diffusion (11,12)] and micropore diffusion to these processes may be obtained. Activation energies for the diffusion through polymer materials are typically above 60 kJ mol -1 (11,13), whereas they are mostly lower (approximately 20-40 kJ mol -1 ) for diffusion through liquids (11) and through the interior of micropores (14)(15)(16). Rates of slow desorption from sediments have been observed to increase strongly with increasing temperature; reported activation enthalpies are 66 (8), 46 (17), and -28 to +29 kJ mol -1 (18).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Temperature Dependence of Slow Adsorption and Desorption Kinetics of Organic Compounds in Sediments

Cornelissen

Noort

Parsons

et al. 1997

Environ. Sci. Technol.

293

242

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The purpose of the present study was to determine the temperature dependence of slow adsorption and desorption kinetics of some chlorobenzenes, polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs) in a lab-contaminated and a field-contaminated sediment. The kinetics of desorption were measured by means of a technique in which Tenax TA beads are used as "sink" for desorbed solute. A first-order kinetic model with three sediment compartments described the desorption of the test compounds from the sediments. Apart from a rapidly desorbing fraction, two sediment fractions were distinguished, one slowly desorbing with a rate constant of (1-4) × 10 -3 h -1 and a very slowly desorbing one with rate constants approximately 10-50 times smaller. From temperature dependence studies, the activation enthalpies for slow desorption appeared to be 60-70 kJ mol -1 for both the lab-contaminated and the field-contaminated sediments; the values were approximately constant for all compounds studied. From adsorption studies at two temperatures, enthalpies of sorption to the slow sediment compartment appeared to be slightly negative. Because slow desorption is much faster at elevated temperatures, the measurement of high-temperature desorption kinetics can provide information on long-term desorption kinetics and, probably, on the feasibility of bioremediation of aged contaminants.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Temperature Dependence of Slow Adsorption and Desorption Kinetics of Organic Compounds in Sediments

Cornelissen

Noort

Parsons

et al. 1997

Environ. Sci. Technol.

293

242

View full text Add to dashboard Cite

show abstract

“…25c), whereas in the desorption cycle, influences of coupling decrease because the total loadings decrease with time. For benzene-p-xylene mixtures, Niessen and Karge 46 found that the adsorption cycle in MFI zeolites proceeds nine times faster than the desorption cycle. The asymmetrical influences of [G] also cause the adsorption and desorption cycles to follow distinctly different equilibration composition trajectories, as is evident in the results shown in Fig.…”

Section: View Article Onlinementioning

confidence: 99%

Uphill diffusion in multicomponent mixtures

2015

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Molecular diffusion is an omnipresent phenomena that is important in a wide variety of contexts in chemical, physical, and biological processes. In the majority of cases, the diffusion process can be adequately described by Fick's law that postulates a linear relationship between the flux of any species and its own concentration gradient. Most commonly, a component diffuses down the concentration gradient. The major objective of this review is to highlight a very wide variety of situations that cause the uphill transport of one constituent in the mixture. Uphill diffusion may occur in multicomponent mixtures in which the diffusion flux of any species is strongly coupled to that of its partner species. Such coupling effects often arise from strong thermodynamic non-idealities. For a quantitative description we need to use chemical potential gradients as driving forces. The transport of ionic species in aqueous solutions is coupled with its partner ions because of the electro-neutrality constraints; such constraints may accelerate or decelerate a specific ion. When uphill diffusion occurs, we observe transient overshoots during equilibration; the equilibration process follows serpentine trajectories in composition space. For mixtures of liquids, alloys, ceramics and glasses the serpentine trajectories could cause entry into meta-stable composition zones; such entry could result in phenomena such as spinodal decomposition, spontaneous emulsification, and the Ouzo effect. For distillation of multicomponent mixtures that form azeotropes, uphill diffusion may allow crossing of distillation boundaries that are normally forbidden. For mixture separations with microporous adsorbents, uphill diffusion can cause supra-equilibrium loadings to be achieved during transient uptake within crystals; this allows the possibility of over-riding adsorption equilibrium for achieving difficult separations. Key learning points(1) Coupling effects in mixture diffusion may cause uphill transport of a component (2) Uphill diffusion results in transient overshoots and serpentine equilibration trajectories (3) Non-ideal phase equilibrium thermodynamics is often the major source of diffusional coupling effects (4) Chemical potential gradients are the proper driving forces for diffusion (5) Uphill transport can be exploited to achieve difficult and unusual separations

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“…Single-component diffusion data obtained by this novel method were in good agreement with well-established results in the literature. However, the FTIR technique also permitted the measurement of diffusivities under the conditions of co-diffusion and counter-diffusion in two-component systems such as benzene/ ethylbenzene [172,173] or benzene/ p-xylene [174].…”

Section: Motion Diffusion and Reaction Of Guest Molecules In Zeolitesmentioning

confidence: 99%

Characterization of Zeolites — Infrared and Nuclear Magnetic Resonance Spectroscopy and X-Ray Diffraction

Karge¹,

Hunger²,

Beyer³

1999

Catalysis and Zeolites

Self Cite

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Diffusion of p-xylene in single and binary systems in zeolites investigated by FTIR spectroscopy

Cited by 91 publications

References 6 publications

Temperature Dependence of Slow Adsorption and Desorption Kinetics of Organic Compounds in Sediments

Temperature Dependence of Slow Adsorption and Desorption Kinetics of Organic Compounds in Sediments

Uphill diffusion in multicomponent mixtures

Characterization of Zeolites — Infrared and Nuclear Magnetic Resonance Spectroscopy and X-Ray Diffraction

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