Solid extractants chemical kinetics

A. K. Galwey, Reactions in the Sohd State, in Bamford and Tipper, eds.. Comprehensive Chemical Kinetics, vol. 22, Elsevier, 1980. Galwey, A. K., Chemistry of Solids, Chapman and Hall, 1967. Sohn, H. Y, and W. E. Wadsworth, eds.. Rate Frocesses of Extractive Metallurgy, Plenum Press, 1979. Szekely, J., J. W. Evans, and H. Y. Sohn, Gas-Solid Reactions, Academic Press, 1976. Uhmann, ed., Enzyklopaedie der technischen Chemie, Uncatalyzed Reactions with Solids, vol.. 3, 4th ed., Verlag Chemie, 1973, pp. 395-464. 

Chemical Kinetics of Metal Ion Adsorption on Solid Extractants.249... 

CHEMICAL KINETICS OF METAL ION ADSORPTION ON SOLID EXTRACTANTS... 

There are cases of metal ion adsorption on solid extractant surfaces where the rate of chemical chelation or ion exchange is the rate determining process. Under these conditions, it is useful to develop a kinetic model to describe this rate process for use in design equations. The kinetic processes are similar to chemical catalytic reactions and also may include electrostatic effects [31]. 

Mass transfer coefficients provide especially useful descriptions of diffusion in complex multiphase systems. They are basic to the analysis and design of industrial processes like absorption, extraction, and distillation. Mass transfer coefficients are not useful in chemistry when the focus is on chemical kinetics or chemical change. They are not useful in studies of the solid state, where concentrations vary with both position and time, and lumped-parameter models do not help much. 

In favourable systems, selective dissolution of components from reactant—product mixtures, that have been heated for appropriate time intervals, coupled with chemical analyses, have been used to obtain kinetic data for solid—solid reactions [419], Thus MgO is the only component which will dissolve in dilute HC1 and, therefore, can be specifically extracted from mixtures reacting as follows... 

Various models of SFE have been published, which aim at understanding the kinetics of the processes. For many dynamic extractions of compounds from solid matrices, e.g. for additives in polymers, the analytes are present in small amounts in the matrix and during extraction their concentration in the SCF is well below the solubility limit. The rate of extraction is then not determined principally by solubility, but by the rate of mass transfer out of the matrix. Supercritical gas extraction usually falls very clearly into the class of purely diffusional operations. Gere et al. [285] have reported the physico-chemical principles that are the foundation of theory and practice of SCF analytical techniques. The authors stress in particular the use of intrinsic solubility parameters (such as the Hildebrand solubility parameter 5), in relation to the solubility of analytes in SCFs and optimisation of SFE conditions. 

Freidig, A.P., Garciano, E.A., Busser, F.J.M., and Hermens, J.L.P. (1998) Estimating impact of humic acid on bioavailability and bioaccumulation of hydrophobic chemical in guppies using kinetic solid-phase extraction. Environ. Toxicol. Chem. 17, 998-1004. 

For example, when we consider the design of specialty chemical, polymer, biological, electronic materials, etc. processes, the separation units are usually described by transport-limited models, rather than the thermodynamically limited models encountered in petrochemical processes (flash drums, plate distillations, plate absorbers, extractions, etc.). Thus, from a design perspective, we need to estimate vapor-liquid-solid equilibria, as well as transport coefficients. Similarly, we need to estimate reaction kinetic models for all kinds of reactors, for example, chemical, polymer, biological, and electronic materials reactors, as well as crystallization kinetics, based on the molecular structures of the components present. Furthermore, it will be necessary to estimate constitutive equations for the complex materials we will encounter in new processes. 

This report deals with the dynamic response of the solid-state gas sensors when the gaseous composition of the atmosphere is intentionally varied. The study is focused on the featuring of the chemical composition of the atmosphere using the information extracted from the transients of the response. Theoretical analysis of the surface processes in the sensors is aimed at a description of the response kinetics by a set of the parameters acceptable for the featuring of an odour. The method was tested by experimental investigations of the response kinetics under exposure to various volatile compounds including that Ifom TNT based explosives. 

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