Pore structure and gaseous diffusion in solid catalysts

Johnson, Marvin F. L.

doi:10.1016/0021-9517(65)90015-1

Cited by 199 publications

(65 citation statements)

References 4 publications

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“…The value for A obtained by solving eqn. (6) is about 2, similar to the value predicted for diffusion across a field ofparallel cylinders (Johnson & Stewart, 1965 M. C. NEVILLE AND M. PEAKER expressed by the ratio of the coefficients at 0 and 37 'C (0-44 + 010) is not very different from the ratios of the diffusion coefficients in aqueous solution at these temperatures, (0 34; Table 4), again consistent with an extracellular origin for the rapid component.…”

Section: Resultssupporting

confidence: 78%

Calcium fluxes in mouse mammary tissue in vitro: intracellular and extracellular calcium pools

Neville

Peaker

1982

The Journal of Physiology

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SUMMARY1. The total Ca content of the mammary gland increased from about 2 to 12 #smole/g tissue during the transition from pregnancy to lactation in the mouse.In tissue from lactating mice at least two thirds of the total Ca exchanged with external Ca in 6 hr. There was little non-exchangeable Ca in tissues from pregnant mice.2. At 37 'C the time courses of influx and efflux of 45Ca in lactating tissues could be analysed by assuming three exponential components with rate constants of about 03, 006 and 0005 min-and containing, respectively, 1-7, 1-5 and 4-7 mole 45Ca/g tissue at the steady state.3. The rapidly effluxing component showed the time-and temperature-dependence characteristic of bulk-phase-limited diffusion through the extracellular space. The diffusion coefficient was about one quarter of the self-diffusion coefficient of Ca in aqueous solution, consistent with a tortuosity factor of about 2. A portion of the Ca in this component was displaced by La3+. The amount remaining in the presence of 3 mM-La3+ was close to that expected for free extracellular Ca. The rapid component was therefore interpreted as originating from an extracellular compartment containing both free and bound Ca.4. The rate of efflux of the intermediate component was slowed by a factor of ten when the temperature was decreased from 37 to 0C giving a Q10 of 2-7, expected for membrane transport. The slow component present at 37 'C was not displaced by EGTA or La3+, suggesting that it is not localized extracellularly. It was not apparent in the 0 'C efflux curves. 5. The biphasic time course of uptake of ionophore (A23187)-releasable 45Ca in particulate fractions obtained by homogenization and centrifugation of tissues which had been incubated with the isotope was consistent with the hypothesis that the two slower components of 45Ca flux originate from intracellular compartments. Mitochondrial uptake probably did not contribute significantly to Ca exchange in these tissues.6. 45Calcium fluxes in mammary tissues from pregnant mice also showed three

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Section: Resultssupporting

confidence: 78%

Calcium fluxes in mouse mammary tissue in vitro: intracellular and extracellular calcium pools

Neville

Peaker

1982

The Journal of Physiology

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“…The effective diffusion coefficients were evaluated with the expressions derived by Rothfeld (1963) for a single pore and the parallel pore model (Johnson and Stewart, 1965) assuming no distribution of pore sizes:…”

Section: Analysis Of Kinetic Datamentioning

confidence: 99%

“…A value of 3.0 was used which is what would be expected if the pore system were isotropic (Johnson and Stewart, 1965).…”

Section: Analysis Of Kinetic Datamentioning

confidence: 99%

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Thermo-chemical energy conversion and storage. Final report

Ritter¹,

DeLancey²,

Schneider³

et al. 1978

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Thrt book WW propirfld ac an iccoont of work ipooMrad by m i|«ncv of 1h« UnlM Stata GoverfMTwmNeithaf ttia UnitaO Suiat Govarnmant nor anv a^ancv thafaof nor any of thair anwtovaas makaa any warranfy axpraas of impfMd of aMufnw any lagat liability or raaponaibility for tha accuracy coinpiatanaM or uaafulnaaa of any mformatton apoaratus product or pro<«« ditdoaad or repraiants tliat its uM MuU not infrmga priyataly ownad riflhts Rafaranca ftarain to aiTy ipacific rommarciai produa procaat or Mrvica by trada nafna tradamark manufacturar or otharyvna doas not nacaaaarily conatituta or imply its andorsamant laojmmandation of fayorins by tha Umtad States Government or any agency thereof The views and opinions of authors expressed herein do not necessarily state or reflect those of the United Slates Government or any agency thereof There is no obi-cf.on trom the patenl poini of view to the pub'.icatKXi or disseminotJc. ' Nc dccumeat{s| . ibted in ih's lc» . r- We have studied the apparent kinetics of the gas-phase catalytic dehydrogenation of cyclohexane to benzene in an internally recirculated -(gradientless) reactor over the temperature range SOO-BOCF at 1 atm at various space velocities. We have also developed a kinetic model basedon a reversible mass-action rate expression and a catalyst effectiveness factor which is able to correlate both the conversion and reaction rate data very well over the temperature range 500-750''F. The data taken at 800°F appear to be qualitatively and quantitatively different than the data taken at the lower temperatures. It is not as yet clear, whether this can be attributed to a change in kinetic mechanism or some reversible alteration of the catalyst surface at the higher temperature.We have also studied the formation of side products in this system over the same .temperature range. Both the number and amount of side product (s). formed -increases with increasing temperature and residence time. Over the temperature range 500-600"F the side products produced appear to be strongly related to the presence of low molecular weight unsaturated hydrocarbon impurities in our (reagent grade) cyclohexane feed and it is possible that no side products would be formed v/ere it not for the presence of these impurities. At temperatures a-bove SOO^F, both the number and amount of side product(s) produced increases markedly.Finally, we have designed and partially fabricated a test loop which will enable us to study the effects of long term continuous cycling of the system on catalyst activity and side product formation. The size of the loop will also enable us to generate design data for scal.eup of a benzene/cyclohexahe thermochemical energy storage/recovery system and gain operating experience with closed loop chemical energy storage systems deliberately designed to.run in a transient mode.

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“…Such an approach was employed by Feng and Stewart (1973). who developed a general class of flux models for multicomponent diffusion in pore networks by extending earlier work by Johnson and Stewart (1965) for binary diffusion.…”

Section: Introductionmentioning

confidence: 98%

Analysis of multicomponent diffusion in pore networks

Sotirchos

Burganos

1988

AIChE Journal

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Diffusion flux models are developed for isobaric diffusion of a multicomponent gas mixture in pore networks of distributed pore size and length constructed by arranging pore segments around the bonds of a lattice of constant coordination number. Eigenvalue-eigevector analysis is used to decompose the dusty-gas model equations, written for each pore segment in the network, into a set of independent single-species diffusion problems, each of which is then treated by combining the effective medium theory for resistor networks with the smooth field approximation (Burganos and Sotirchos, 1987). Results for a ternary mixture diffusing in a porous slab show that direct application of the smooth field approximation underestimates significantly the mass transport resistance.

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Pore structure and gaseous diffusion in solid catalysts

Cited by 199 publications

References 4 publications

Calcium fluxes in mouse mammary tissue in vitro: intracellular and extracellular calcium pools

Calcium fluxes in mouse mammary tissue in vitro: intracellular and extracellular calcium pools

Thermo-chemical energy conversion and storage. Final report

Analysis of multicomponent diffusion in pore networks

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