Kinetics of rehydration of crystalline anhydrides. Manganous formate

Eckhardt, R.; Fichte, Peter M.; Flanagan, Ted B.

doi:10.1039/tf9716701143

Cited by 12 publications

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“…Even though metal formate dihydrates are model compounds for hydration/dehydration experiments and their decomposition properties have been well documented, [14] their dehydration products have only been characterized by Xray powder diffraction (Mg, [15] Mn, [16] Fe, [17] Zn [18] ), and their structures are not known. The dehydration of nickel and cobalt formate dihydrate only results in amorphous products.…”

Section: Introductionmentioning

confidence: 99%

Solvothermal Synthesis and Structure of Anhydrous Manganese(II) Formate, and Its Topotactic Dehydration from Manganese(II) Formate Dihydrate

et al. 2003

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Section: Introductionmentioning

confidence: 99%

Solvothermal Synthesis and Structure of Anhydrous Manganese(II) Formate, and Its Topotactic Dehydration from Manganese(II) Formate Dihydrate

et al. 2003

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“…The rehydration of manganous formate produced from the vacuum dehydration of the dihydrate has been studied in detail by Eckhardt et al (1971). This material was found to rehydrate smoothly and completely to the dihydrate composition, unlike nickel and manganous oxalates, which rehydrate only very slowly after an initial, rapid reaction.…”

Section: Introductionmentioning

confidence: 99%

Rate processes in cycling a reversible gas‐solid reaction

Stanish

Perlmutter

1984

AIChE Journal

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Rate studies arc reported of the effect of rehydrationdehydration cycling on the vapor hydration behavior of solid KzCO3. Isothermal rate data were obtained a t different temperatures and water vapor pressures for the reaction of narrowlysized anhydrous particles. Effects of different particle preparation histories on the rehydration rate were investigated and correlations of rate with particle pore structure explored. Rehydration rates of dehydrated K2C03*3/2IIzO were found to depend on the conditions of the prior dehydration. Rehydration is comparatively very slow at relative pressures below PIP,., N 1.5; rates increase linearly with pressure above PIP, -3. Hydration rates of KzCO3 particles obtained as anhydrous are substantianyslower than those of identically-sized crystals produced by prior dehydration of KpC03*3/2II20; after one rehydrationdehydration cycle, rehydration rates are increased by as much as two orders of magnitude and this distinction between sources virtually disappears. Diffusional resistances based on calculated water vapor diffusivities are qualitatively consistent with the observed effects of cycling but d o not by themselves account fully for the observations. M. SCOPEThe hydration reaction of KzCO:, with water vapor is of interest from two different perspectives. First, this system serves as a convenient prototype for the study of kinetics in reversible gas-solid reactions of inorganic salts, a topic of recognized industrial importance. Second, water and KzCO3 were shown (Stanish and Perlmutter, 1981) to hold significant promise as a refrigerant-absorbent pair in a low-temperature heat pump cycle. Since little information is available concerning the kinetics of hydration and dehydration in the water-KzC03 system, a n experimental study of these phenomena is needed to more accurately determine the feasibility and potential of a real KzC03-based heat pump device.The objectives of this study were to identify the variables that are most important in determining the rehydration rate of KzCO3 particles and to quantify their effects. This investigation includes evaluation of the importance of the source of the solid and the method of preparation in determining the rate of rehydration. In addition, the effect of water vapor pressure on reaction rate is quantified. Finally, changes in rehydration rate with rehydrationdehydration cycling are explored, and correlations are sought with the differences in particle pore structure revealed by mercury intrusion porosimctry data. The behavior of this system is compared to that reported for thc rcvcrsiblc decomposition of AglC03. CONCLUSIONS AND SIGNIFICANCEThe rate of rehydration of dehydrated K&O3*3/2HzO crystals is affected by the prior dehydration conditions; samples that were dehydrated more rapidly (at higher temperature and/or lower pressure) were subsequently found to rehydrate more rapidly as well. Slow rehydration and the appearance of induction and acceleration in rehydration conversion time curves were characteristics of KzC03*3/2HzO dehydrat...

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“…The behavior is quite similar to that of K Z C O~.~/~H~O in that the rate is very strongly inhibited by small pressures of water vapor. The reported activation energy tu = 1.20 X 10-19J; vapor pressure data (Eckhardt et al, 1971) were employed to compare the predictions of this model to the reported rate data using the following convenient form of Eq. 16:…”

Section: Dehydratlon Ratesmentioning

confidence: 99%

Kinetics of hydration‐dehydration reactions considered as solid transformations

Stanish¹,

Perlmutter²

1984

AIChE Journal

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A mechanism is proposed for the dehydration-rehydration process in solid inorganic salts, and model rate equations are derived and applied to the observed behavior of potassium carbonate. Quantitative expressions for the effect of pressure on the reaction rates are derived using basic principles from nucleation and heterogeneous phase transformation theory. Model equation predictions agree with experimental dehydration and rehydration rate data at all but extreme pressures. The basic rate equation is also used to interpret the data of Eckhardt and Flanagan (1964) for the effect of pressure on the dehydration of manganous formate dihydrate. The mechanism on which the model equations are based is also consistent with the observed effects of cycling and of high temperature pretreatment on the KzC03 rehydration rate. SCOPEA new mechanistic interpretation is offered for the analysis of the kinetics of gas-solid reactions and applied in detail to the reversible dehydration and rehydration of solid inorganic salts. These processes are considered as solid-solid transformations, and an expression is derived for the intrinsic rate of reaction in terms of the velocity of the movement of the boundary separating the reactant and product phases. The rate dependence on pressure and temperature predicted by the model equations is compared to those observed for both dehydration and rehydration in experiments with potassium carbonate hydrate and to that reported in the literature for the dehydration of manganous formate dihydrate. In addition, the effects of cycling and of high-temperature pretreatment on the reaction rates of KzCO3 are presented, and the ability of the proposed mechanism to account for these effects is discussed.A new mechanistic rate model has been formulated for reversible gas-solid reactions and applied to interpret the dehydration and rehydration kinetics of salt hydrates. Quantitative rate expressions predicting the effects of pressure and temperature were derived using basic principles from nucleation and heterogeneous phase transformation theories. The dehydration model rate equation provides accurate quantitative predictions for the velocity of movement of the KzCOs*3/2HzO dehydration interface at all three temperatures studied. The dehydration equation also provided a close correlation with data from the literature for the dehydration of manganous formate dihydrate.A comparison of the rehydration model equation with experimental KzC03 particle rehydration rates revealed good agreement of the model with the experimental data for reduced pressures within the range 1 < (Pes/P) < 2. At higher rehydration pressure, the reaction rates are not controlled by the transformation process at the reaction interface and the model equations are not applicable. Within the range of moderate pressures both above and below the equilibrium pressure, the model effectively describes the rapid decline of both dehydration and rehydration rates as the equilibrium pressure is approached.The model equations imply that reaction ra...

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Kinetics of rehydration of crystalline anhydrides. Manganous formate

Cited by 12 publications

References 0 publications

Solvothermal Synthesis and Structure of Anhydrous Manganese(II) Formate, and Its Topotactic Dehydration from Manganese(II) Formate Dihydrate

Solvothermal Synthesis and Structure of Anhydrous Manganese(II) Formate, and Its Topotactic Dehydration from Manganese(II) Formate Dihydrate

Rate processes in cycling a reversible gas‐solid reaction

Kinetics of hydration‐dehydration reactions considered as solid transformations

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