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Aboyade A.O.,Stellenbosch University | Aboyade A.O.,University Of Fort Hare | Hugo T.J.,Stellenbosch University | Carrier M.,Stellenbosch University | And 4 more authors.
Thermochimica Acta | Year: 2011

Corn cobs and sugar cane bagasse are two of the most important agricultural residues in South Africa in terms of availability and potential for use as a bioenergy resource. The thermal devolatilization of samples of these two fuels in an inert atmosphere was studied by non-isothermal thermogravimetric analysis in the heating rate range of 10-50 °C min-1. Friedman's isoconversional method was applied using the AKTS Thermokinetics software to obtain the dependence of activation energy on conversion. The same method was also applied to the kinetic analysis of lignocellulosic pseudocomponents derived from the mathematical deconvolution of the original DTG curves. The results showed that apparent activation energy in the 0.1-0.8 conversion interval ranged from 170-225 kJ mol-1 to 75-130 kJ mol-1 for sugar cane bagasse and corn cobs respectively. The range of apparent activation energy obtained for the pseudocomponents representing hemicelluloses, cellulose and lignin derived from sugar cane bagasse were given as 200-300 kJ mol -1, 163-245 kJ mol-1, and 80-180 kJ mol-1, while for corn cobs the values were 85-110 kJ mol-1, 80-140 kJ mol-1, and 10-60 kJ mol-1 respectively. The derived thermokinetic parameters from both global and pseudocomponent analyses satisfactorily reproduced the experimental curves used for the analysis and could also successfully predict reaction progress at a heating rate outside what was used in the analysis. The fits obtained between simulated and experimental results were comparable to what has been reported in the literature based on conventional model-fitting techniques. © 2011 Elsevier B.V. All rights reserved. Source


Snellings R.,Catholic University of Leuven | Mertens G.,Catholic University of Leuven | Gasharova B.,Institute for Synchrotron Radiation ISS | Garbev K.,Institute of Technical Chemistry | Elsen J.A.N.,Catholic University of Leuven
European Journal of Mineralogy | Year: 2010

The pozzolanic reaction of a natural zeolite-rich tuff and portlandite was investigated by means of IR spectroscopy. The zeolite tuff consisted mainly of Ca-rich clinoptilolite. A detailed analysis of the changes in the bonding environment during reaction presented by the IR spectra showed that the vibrations assigned to the reactant phases were progressively consumed and implied that Si-rich environments were preferentially depleted. The contemporaneous appearance and rise of vibration bands characteristic for calcium-silicate-hydrates and calcium-aluminate-hydrates demonstrated the formation of reaction products. Changes in bonding environment were spatially visualized by means of synchrotron-IR microspectroscopy. Promising results showed the distribution of reactants and reaction products and allowed to analyze spatial trends in IR-vibration frequencies. A shift in calcium-silicate-hydrate mean peak position from 972 to 968 cm-1 indicated a decrease in silicate chain length with increasing distance from the clinoptilolite-matrix interface. © 2010 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart. Source


Kipriyanova E.S.,Voronezh State University | Kravchenko T.A.,Voronezh State University | Konev D.V.,Voronezh State University | Kalinichev A.I.,RAS Frumkin Institute of Physical Chemistry and Electrochemistry | Hoell W.H.,Institute of Technical Chemistry
Russian Journal of Physical Chemistry A | Year: 2010

It was found that the rate of reductive sorption of molecular oxygen on dispersed silver-KU-23 sulfo-cation exchanger nanocomposites depends substantially on the ionic form (H+, Ag+, Na+ forms) of the nanocomposite. It was established that the observed dependence is due to the influence of the composition of the medium in pores of the ion-exchange matrix, which serve as nanoreactors, on the rate of the chemical reaction between silver nanoparticles and dissolved molecular oxygen. © Pleiades Publishing, Ltd., 2010. Source


Kipriyanova E.S.,Voronezh State University | Kravchenko T.A.,Voronezh State University | Konev D.V.,Voronezh State University | Kalinichev A.I.,RAS Frumkin Institute of Physical Chemistry and Electrochemistry | Hoell W.H.,Institute of Technical Chemistry
Russian Journal of Physical Chemistry A | Year: 2010

New silver-containing nanocomposites different in their dispersity of metal were synthesized on the basis of strongly and weakly basic anion-exchange resins. The chemical activity of the nanocomposites with respect to oxygen dissolved in water was investigated. It was shown that silver nanoparticles in samples based on strongly basic anion exchangers and weakly basic anion exchangers in the NO3- salt form are not oxidized by oxygen; for weakly basic matrices in the free amine form, this process occurs to only a small extent. The resistance to oxygen is explained by inhibition of processes of formation of silver oxides. Nano- composites based on strongly basic anion-exchange resins are recommended for testing as to catalytic activity. © Pleiades Publishing, Ltd., 2010. Source

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