Effects of solvent and solute configuration on restrictive diffusion in hydrotreating catalysts

Tsai, Chung H.; Massoth, F.E.; Lee, S. Y.; Seader, J. D.

doi:10.1021/ie00049a004

Cited by 26 publications

(24 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Centerline approximation appears accurate for diffusion of a sphere in a cylindrical pore. Configuration effects on hindered diffusion have been studied, and the results revealed that diffusivities of nonspherical solutes deviate to predicted values of spherical solutes 43–45. The difference between our results and those predicted from the Renkin equation might be a result of the configuration effect.…”

Section: Resultscontrasting

confidence: 60%

Dicopper(II) Metallacyclophanes with Electroswitchable Polymethyl‐Substituted para‐Phenylene Spacers

Ferrando‐Soria

Castellano

Ruiz-Garcı́a

et al. 2013

Chemistry A European J

View full text Add to dashboard Cite

Double-stranded anionic dinuclear copper(II) metallacyclic complexes of the paracyclophane type [Cu2L2](4-) have been prepared by the Cu(II)-mediated self-assembly of different para-phenylenebis(oxamato) bridging ligands with either zero-, one-, or four-electron-donating methyl substituents (L=N,N'-para-phenylenebis(oxamate) (ppba; 1), 2-methyl- N,N'-para-phenylenebis(oxamate) (Meppba; 2), and 2,3,5,6-tetramethyl- N,N'-para-phenylenebis(oxamate) (Me4ppba; 3)). These complexes have been isolated as their tetra-n-butylammonium (1 a-3 a), lithium(I) (1 b-3 b), and tetraphenylphosphonium salts (1 c-3 c). The X-ray crystal structures of 1 a and 3 c show a parallel-displaced π-stacked conformation with a smaller deviation from perpendicularity between the two benzene rings and the basal planes of the square planar Cu(II) ions when increasing the number of methyl substituents (average dihedral angles (ϕ) of 58.72(7) and 73.67(5)° for 1 a and 3 c, respectively). Variable-temperature (2.0-300 K) magnetic-susceptibility measurements show an overall increase of the intramolecular antiferromagnetic coupling with the number of methyl substituents onto the para-phenylene spacers (-J=75-95, 100-124, and 128-144 cm(-1) for 1 a-c, 2 a-c, and 3 a-c, respectively; H=-JS1×S2). Cyclic voltammetry (CV) measurements show a reversible one-electron oxidation of the double polymethyl-substituted para-phenylenediamidate bridging skeleton at a relatively low formal potential that decreases with the number of methyl substituents (E1=+0.33, +0.24, and +0.15 V vs. SCE for 1-3, respectively). The monooxidized dicopper(II) π-radical cation species 3' prepared by the chemical oxidation of 3 with bromine exhibits intense metal-to-ligand charge-transfer (MLCT) transitions in the visible and near-IR (λmax=595 and 875 nm, respectively) regions together with a rhombic EPR signal with a seven-line splitting pattern due to hyperfine coupling with the nuclear spin of the two Cu(II) ions. Density functional (DF) calculations for 3' evidence a characteristic iminoquinonoid-type short-long-short alternating sequence of C-N and C-C bonds for both tetramethyl-para-phenylenediamidate bridges and a large amount of spin density of negative sign mainly delocalized along each of the four benzene C atoms directly attached to the amidate N atoms, which is in agreement with a fully delocalized π-stacked monoradical ligand description. Hence, the spins of the two Cu(II) ions (SCu=1/2) that are antiparallel aligned in 3 (OFF state) become parallel in 3' (ON state). Further developments may be then envisaged for this new permethylated dicopper(II) paracyclophane with a redox noninnocent ligand as a prototype for molecular magnetic electroswitch.

show abstract

Section: Resultscontrasting

confidence: 60%

Dicopper(II) Metallacyclophanes with Electroswitchable Polymethyl‐Substituted para‐Phenylene Spacers

Ferrando‐Soria

Castellano

Ruiz-Garcı́a

et al. 2013

Chemistry A European J

View full text Add to dashboard Cite

show abstract

“…Configuration effects on hindered diffusion have been studied, and the results revealed that diffusivities of nonspherical solutes deviate to predicted values of spherical solutes. [43][44][45] The difference between our results and those predicted from the Renkin equation might be a result of the configuration effect.…”

Section: -40contrasting

confidence: 83%

Hindered diffusion of residue narrow cuts through polycarbonate membranes

Chen

Gao

et al. 2010

AIChE Journal

View full text Add to dashboard Cite

Hindered diffusion plays an important role in catalytic processing of residue and heavy oil because of large size molecules in these feedstocks. Vacuum residue of Athabasca oil sand bitumen was fractionated into 13 narrow fractions and an end-cut by supercritical fluid extraction and fractionation (SFEF). Diffusion transport of five SFEF cuts through four polycarbonate membranes was investigated using a diaphragm cell at 308 K. The results showed that diffusion coefficients of the five SFEF cuts decreased as the experiment proceeded, which illustrates that these cuts are polydisperse in size. The effective diffusion coefficients varied with molecular size and pore size. Hindered diffusion of the five SFEF cuts is significant in the membranes with nominal pore diameter of 15 nm, which is around the average pore size of typical hydrotreating catalyst. Comparisons between experimental data and theoretical prediction revealed that the actual hindered degree for diffusion of the five SFEF cuts is higher than that calculated by the Renkin equation. There were slight differences in diffusivity among saturate, aromatic, and resin constituents.

show abstract

“…In other words, the increased hindrance effects caused by the adsorbed solute layer would be reflected in an increased tortuosity value in the UPM. Tsai et al (1991) considered the experimental variation of tortuosity with molecule/pore size ratio and concluded that the use of a single average value of tortuosity up to ,1.0 = 0.35 was justified by their data. Smith (1986) has studied theoretically the effect of molecule/pore size on the tortuosity, finding the tortuosity variation to be a complex function of a pore constrictivity parameter.…”

Section: Diffusion Experiments and Model Simulationmentioning

confidence: 99%

Effects of Solute Adsorption on Hindered Diffusion Uptake Rates in Finite Bath Experiments

Yang

Guin

1996

Chemical Engineering Communications

View full text Add to dashboard Cite

This work investigates the effects of solute adsorption on hindered diffusion behavior in porous catalysts.A mathematical model describing the adsorptive diffusion process is developed. The model, termed the shrinking pore model, incorporates the local reduction in catalyst pore diameter due to the adsorption of solute molecules on the pore walls. The influence of the adsorbed solute layer is found to depend on two additional parameters, reflecting the relative degree of adsorption and molecule/pore size ratio. Hindered diffusion experiments are performed for diffusion controlled adsorptive uptakes of two solute molecules, quinoline and polystyrene, from cyclohexane on a porous catalyst. Comparison of the experimental data and model simulation results shows that for the larger polystyrene solute the shrinking pore model better represents the uptake behavior than the conventional model which assumes constant catalyst properties, e.g. pore diameter, during the uptake process. Experimental measurements were found to be in good agreement with model simulations after accounting for additional hindered diffusional effects due to an adsorbed solute layer on the pore walls. The additional hindrance due to the adsorbed solute was found to be very significant for the uptake of the larger polystyrene solute, whereas it was not significant for the smaller quinoline solute.

show abstract

Effects of solvent and solute configuration on restrictive diffusion in hydrotreating catalysts

Cited by 26 publications

References 25 publications

Dicopper(II) Metallacyclophanes with Electroswitchable Polymethyl‐Substituted para‐Phenylene Spacers

Dicopper(II) Metallacyclophanes with Electroswitchable Polymethyl‐Substituted para‐Phenylene Spacers

Hindered diffusion of residue narrow cuts through polycarbonate membranes

Effects of Solute Adsorption on Hindered Diffusion Uptake Rates in Finite Bath Experiments

Contact Info

Product

Resources

About