739. The rate of dehydration of chrome alum

Anous, M. M. T.; Bradley, R. S.; Colvin, J. Ross

doi:10.1039/jr9510003348

Cited by 19 publications

(5 citation statements)

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“…Acock et al (1 947) utilized a Langmuirian adsorption isotherm to describe the reversible dehydration kinetics of ammonium, potassium, and other mixed alums. Likewise, with minor variations, Anous et al (1951) applied these ideas to the dehydration of chrome alum, Ball and Norwood (1 973) to the calcium sulfate-water system, Horlock et al (1 963) to the decomposition of magnesium hydroxide, and Gardet et al (1976) to the dehydration of calcium sulfate dihydrate. Benton and Drake ( 1934) considered the influence of adsorbed oxygen in the dissociation kinetics of Ag,O, and Spencer and Topley (1 929) considered the influence of adsorbed CO, on the decarbonation kinetics of Ag2C0,.…”

Section: Influence Of Water Vapor On the Chemical Kineticsmentioning

confidence: 97%

Pore structure and kinetics of the thermal decomposition of Al(OH)₃

Candela

Perlmutter

1986

AIChE Journal

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The isothermal decomposition of gibbsite (aluminum hydroxide) was studied under controlled, pure water vapor pressures from 50 to 3,000 Pa over the temperature range from 458 to 508 K; the effect of sample particle size was also investigated. The partial conversion to boehmite (AIOOH) and the subsequent formation of a p-transition alumina product phase were followed with respect to the reactor operating conditions. Nitrogen and water vapor adsorption measurements were used to evaluate the chemical kinetics of the formation of p-alumina in terms of an interface velocity, and to interpret the observed dependencies on temperature and water vapor pressure. An adsorption /decomposition model is presented for these kinetics. The interpretation is consistent with the observation that decomposition rate is inversely proportional to the square of the water vapor pressure. The apparent activation energy of 342 f 15 kJ/mol includes a water adsorption energy, as well as the chemical decomposition contribution of 260 * 20 kJ/mol.

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Section: Influence Of Water Vapor On the Chemical Kineticsmentioning

confidence: 97%

Pore structure and kinetics of the thermal decomposition of Al(OH)₃

Candela

Perlmutter

1986

AIChE Journal

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“…Self-cooling may introduce significant errors into kinetic studies of endothermic decomposition reactions of solids.11, 12 Inert gases have been added to help eliminate such errors by conduction of heat to the sample29 11 The run shown by the single point at 65°C for crystalline powder ( fig. 2) was made in the presence of the optimum pressure of helium, i.e., the pressure of helium at which the rate of dehydration was a maximum; nonetheless it is considerably below the extrapolation of the lower temperature data.…”

Section: Self-coolingmentioning

confidence: 99%

Anisotropic solid-state reaction. Dehydration of manganous formate dihydrate

Eckhardt¹,

Flanagan²

1964

Trans. Faraday Soc.

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The kinetics of dehydration of crystalline powder and individual single crystals of manganow formate dihydrate have been investigated in vacuo from 20 to 75°C. Dehydration takes place by surface nucleation followed by anisotropic penetration of a reaction interface into the hydrate matrix. Dehydration kinetics of approximately parallelopiped single crystals are well described by an isotropic contracting envelope model. Comparison of the data with the Polanyi-Wigner equation gives a normal frequency factor. The heat of dehydration has been measured and is comparable to the activation energy. The dehydration has been studied as a function of water vapour pressure.

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“…Anous et al (1951) reported that the self-cooling of chrome alum at 298 K in a vacuum was nearly the same for all crystals larger than 1 g, but that it decreased rapidly with decreasing size for smaller particles. Also, the temperature during dehydration was nearly constant for the larger crystals.…”

Section: Introductionmentioning

confidence: 96%

“…Other investigators have studied these reactions in a variety of ambient atmospheres, among which the most relevant to absorption heat pump appli-dehydration carried out at 412 K and 27 kPa water vapor partial pressure. cations are those that consider rate dependence on water vapor pressure (Acock et al, 1946;Anous et al, 1951;Fichte and Flanagan, 1971;Gardet et al, 1976). The effect of diffusional resistances on dehydration rate was recognized by Smith and Topley (1931), who labelled the phenomenon "impedance".…”

Section: Introductionmentioning

confidence: 96%

Kinetics and transport effects in the dehydration of crystalline potassium carbonate hydrate

Stanish

Perlmutter

1983

AIChE Journal

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The reaction kinetics and physical transport processes governing the thermal dehydration of solid KzCOy3/2HzO particles were investigated. Isothermal reaction rate data were gathered using a thermogravimetric balance in which narrowly-sized KzC03*3/2HzO crystals were dehydrated under a water vapor atmosphere at different pressures and temperatures. The magnitudes of the heat and mass transfer resistances external to and within the solid product were estimated from solutions of the relevant pseudosteady-state transport equations. In the temperature range 320 to 358 K, the vacuum dehydration of K~COs*3/2HzO crystals smaller than 710 pm (-25 +30 mesh) are accurately modeled by the spherical shrinking-core equation for the chemical rate control regime. In the presence of water vapor, external heat transfer to the particles was sufficient to prevent significant self-cooling; heat and mass transfer resistances within the particles were negligible. The activation energy for K2C03*3/2H20 dehydration is approximately 91 kJ/mol in vacuum; the reaction becomes extremely slow at relative pressures SCOPEOf the literature reports concerned with the dehydration of solid inorganic salt hydrates, a majority are based on information from experiments done in vacuum or in dry atmospheres; as a consequence, the dehydration reaction is most often treated as an irreversible thermal decomposition. The possible application of salt hydrates as absorbents in chemical heat pumps (Stanish and Perlmutter, 1981) provides an incentive to investigate the dehydration of these materials in greater detail and suggests that this process should be treated instead as one part of a reversible gas-solid reaction. This paper reports the results of experimental rate studies of the dehydration of KzC03*3/2H20, a salt hydrate that holds promise as a heat pump absorbent. Experimentally-measured particle reaction data are interpreted in terms of a shrinkingcore gassolid reaction model. The dehydration rate dependence on ambient water vapor pressure is of primary interest and is quantitatively determined for temperature in the range 338 to 358 K. Internal and external heat and mass transfer resistances are estimated for the conditions employed and their roles in the overall particle hydration process are evaluated. CONCLUSIONS AND SIGNIFICANCEThe dehydration of small crystals of KzCO3*3/2HzO may be accurately modeled by the spherical shrinking-core equation for the chemical rate control regime. In the presence of water vapor, heat transfer rates to the particles are sufficiently high to prevent significant self-cooling. Under vacuum conditions, self-cooling becomes important; particle temperature corrections were calculated from a heat balance equation that takes account of the radiation heat transfer to the solid particles and supporting sample pan. In either atmosphere, heat transfer resistance within the particle is negligible. Diffusional resistances within the product layer are not important for particles smaller than about 710 pm (-25 +30 mesh), but are...

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739. The rate of dehydration of chrome alum

Cited by 19 publications

References 0 publications

Pore structure and kinetics of the thermal decomposition of Al(OH)₃

Pore structure and kinetics of the thermal decomposition of Al(OH)₃

Anisotropic solid-state reaction. Dehydration of manganous formate dihydrate

Kinetics and transport effects in the dehydration of crystalline potassium carbonate hydrate

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739. The rate of dehydration of chrome alum

Cited by 19 publications

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Pore structure and kinetics of the thermal decomposition of Al(OH)3

Pore structure and kinetics of the thermal decomposition of Al(OH)3

Anisotropic solid-state reaction. Dehydration of manganous formate dihydrate

Kinetics and transport effects in the dehydration of crystalline potassium carbonate hydrate

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Product

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Pore structure and kinetics of the thermal decomposition of Al(OH)₃

Pore structure and kinetics of the thermal decomposition of Al(OH)₃