Browsing by Author "Valcheva E."

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    A correlation between the kinetic and thermodynamic adsorption characteristics of an optical brightener on a pulp surface
    (2008-01-01) Radeva G.; Veleva S.; Valcheva E.
    An attempt to find a correlation between the kinetic and thermodynamic terms (e.g. activation energy, pre-exponential factor, isosteric heat, entropy, etc.) of the chemisorption process involved in a commercial optical brightener/pulp system is presented. A linear inter-relationship between the kinetic and thermodynamic characteristics of the system was found. Based on the coefficients obtained in the thermodynamic investigation of the adsorption process, it was possible to calculate the kinetic coefficient of the surface inhomogeneity. The use of both a model employing uniformly inhomogeneous surfaces and an approach involving all the kinetic and thermodynamic data was confirmed by the results obtained.
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    A correlation method in studying chemisorption processes on uniformly inhomogeneous surfaces
    (2010-03-01) Radeva G.; Valcheva E.; Veleva S.
    Chemisorption processes taking place on uniformly inhomogeneous surfaces in the presence of entropic inhomogeneity are examined. A new form of linearity relationship connecting the current rate and the equilibrium constant at definite degrees of surface coverage is derived. The relationship can be applied to complex chemisorption processes when determination of the rate constant is impossible. Linear correlations between the activation energy and the adsorption enthalpy, as well as between the entropy characteristics and pre-exponential factors, are obtained. The complex effect of the energy and entropy factors on the kinetics and the equilibrium is discussed theoretically and verified experimentally. These factors operate through a thermodynamic and a kinetic compensation effect. The present paper illustrates the correlation methods employing experimental results derived from the study of the chemisorption of the optical brighteners Leucophor AP and Tinopal UP onto pulp, of Fe 3+ and Cu2+ ions onto fibrous polyampholyte and of hydrolysis-modified polyacrylonitrile (HMP) onto pulp.
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    The role of the entropy factor on the adsorption of an optical brightener on pulp
    (2009-09-21) Radeva G.; Valcheva E.; Veleva S.
    The present paper reports results of the thermodynamic study of adsorption of 2 optical brighteners (Tinopal UP and Leucophor AP) on pulp. The entropy non-homogeneity of the pulp surface was confirmed and the coefficients of entropy non-homogeneity were determined. The entropy effect on the variation of Gibbs free energy of the process studied was followed. © Tübi̇ tak.