Dehydrated processing effects

Grant and coworkers [8] studied the dehydration kinetics of piroxicam monohydrate using both model-free and model-fitting approaches in an effort to understand the effects of lattice energy and crystal structure. The dehydration kinetics was found to differ when determined under isothermal and nonisothermal conditions. Ultimately, the dehydration behavior of piroxicam monohydrate was determined by details of the crystal structure, which was characterized by an absence of channels and a complicated hydrogen-bonding network, and ab initio calculations proved useful in understanding the structural ramifications of the dehydration process. 

Reasonably reliable pATbh+ values for the protonation of weak bases or of weakly basic substrates can be obtained via equation (17), together with m slope parameters that can be used to classify basic molecules as to type, and for an estimate of the solvation requirements of the protonated base. Measurements at temperatures other than 25°C can be handled using equation (22), and enthalpies and entropies for the protonation can be obtained. Protonation-dehydration processes are covered by equation (26). Medium effects on the... 

Shi, J., Le Maguer, M., Wang, S.L., and Liptay, A. 1997. Application of osmotic treatment in tomato processing Effect of skin treatments on mass transfer in osmotic dehydration of tomatoes. Food Res. Int. 30, 669-674. 

A unique aspect of the catalytic activity of CA is the fact that the hydroxo form of the enzyme catalyzes the hydration of CO2 through the direct binding of CO2 to the hydroxo ligand, whereas the aqua form of the enzyme catalyzes the dehydration of hydrogen carbonate through a ligand substitution process. This difference in mechanism is nicely demonstrated by the overall volume profile shown in Figure 23, which was constructed on the basis of the effect of pressure on the catalytic hydration and dehydration processes. Both these catalytic processes show characteristic pH dependencies that center around the pXa value of the coordinated water molecule. Many model Zn(II) and... 

From the discussion presented in the previous paragraphs, we identify the kinetic characteristics of the hydrocarbon evolution reactions (31,291,292) and the clay dehydration processes with the common mechanistic features reversibility and similar characteristic temperatures of onset of the water evolution step. The compensation effects observed for the two groups of related reactions (Table V, R and S) were not identical, however, since the species participating in the equilibria on the surfaces (believed to be represented by the kinetic characteristics described in Appendix I) are different. Undoubtedly, the interaction of hydroxyl groups to yield water was common to both types of reaction (surface desorption and lattice dehydration) and the properties and reactivities of these species probably determine the temperature at which significant surface activity and product evolution becomes apparent. This surface reaction is... 

The enthalpy conservation equation of the multiphase medium, obtained from the sum of the appropriate balance equations of the constituents includes the heat effects due to phase changes and hydration (dehydration) process, as well as the convectional and latent heat transfer,... 

For concrete at high temperature the most important is the effect of cracking and dehydration process on the material properties, e.g. porosity n=f(Thydr)> intrinsic permeability k=/(T/,(/,/r. /7. T), and its deformations. Irreversible part of strains and so called thermal creep are expressed as functions of thermochemical damage parameter V, [8],... 

An in situ detection of the dehydration effect on bovine cortical bone samples has been carried out using 13C 1H CPMAS and 1H MAS.199 Figure 15 shows the dehydration process manifested in the NMR spectra. The dehydration-induced line broadening shown in the 13C spectra has been attributed to a local conformational disorder of the bone matrix and... 

Effect of Impurities on CaS04 Transformation. The transition from gypsum to orthorhombic anhydrite is slow but occurs even at ambient temperatures (44). The relatively large concentration of finely divided sodium chloride present in the plaster in the tomb of Nefertari may have facilitated the dehydration process. The presence of a hygroscopic material, such as sodium chloride, can help promote dehydration reactions. Also, impurities within the lattice of a crystalline structure can weaken the lattice (46, 47) and thereby accelerate thermodynamically favored reactions. These points suggest a strong correlation between the extent to which the dehydration reaction proceeds and sodium chloride concentration, but they do not exclude the possibility that dehydration can take place in the absence of salt. 

Examples of reactions in which acid-base catalysed dehydration was combined with acid-base equilibria either preceding or subsequent to the dehydration process are quoted for the waves of pyridine aldehydes (Tirouflet and Laviron, 1959 Volke, 1958 ManouSek and Zuman, 1964) and of glyoxalic acid (Kuta, 1959). Different dehydration rates were found for pyridinium ions and free pyridine derivatives, as well as for the free glyoxalic acid and its anion. For numerous aldehydic substances the effect of hydration has been observed but a quantitative treatment has not yet been applied. 

During recent years an important improvement in the knowledge of the dehydration process has occurred. Simulation programs of the mathematical models that represent heat and mass transfer during drying have allowed contemporary researchers to substitute expensive experimental work for faster and accurate results as well as to predict the effect of relevant process variables on the performance of the process itself. 

Morita (144) also studied the DTA of several a- and jS-Iinked polygluco-sans, as well as rice starch. An interesting feature of this investigation was the study of the effect of moisture on the DTA curves obtained. This was illustrated by the study of rice starch stored in various types of atmospheres such as vacuum, 100% relative humidity water vapor, and so on. The presence of moisture altered the endothermic peak with a A7 in of 130°C, but not the 275 or 310°C peaks. The results suggest that the original 130°C peak is not entirely due to the loss of residual moisture and that the dehydration process is not completely reversible. 

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