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Milosavljevic M.M.,Economics Institute | Marinkovic A.D.,University of Belgrade | Veljkovic V.B.,University of Nis | Milenkovic D.D.,High Chemical Technological School
Monatshefte fur Chemie

The kinetics of the syntheses of N-alkyl, N,N-dialkyl, and N-(4-substituted phenyl) O-ethyl thioncarbamates from sodium ethyl xanthogenacetate, ten alkylamines, and eight substituted anilines were studied at 25, 30, 35, and 40 °C. The reactions were found to follow second-order kinetics. The kinetic (Arrhenius) parameters, such as the activation energy and the frequency factor, as well as the Eyring parameters, such as the standard entropy, the standard Gibbs energy, and the standard enthalpy of activation, were calculated from the second-order rate constants. The mechanism of the reaction was postulated based on the kinetic studies presented and the optimization of the reaction mechanism using the MOPAC PM6 semi-empirical method. © 2011 Springer-Verlag. Source

Milenkovic D.D.,High Chemical Technological School | Bojic A.L.,University of Nis | Veljkovic V.B.,University of Nis
Ultrasonics Sonochemistry

This study was aimed at removal of 4-dodecylbenzene sulfonate (DBS) ions from aqueous solutions by ultrasound-assisted adsorption onto the carbonized corn cob (AC). The main attention was focused on modeling the equilibrium and kinetics of adsorption of DBS onto the AC. The AC was prepared from ground dried corn cob by carbonization and activation by carbon dioxide at 880 °C for 2 h in a rotary furnace. The adsorption isotherm data were fitted by the Langmuir model in both the absence and the presence of ultrasound (US). The maximum adsorption capacities of the adsorbent for DBS, calculated from the Langmuir isotherms, were 29.41 mg/g and 27.78 mg/g in the presence of US and its absence, respectively. The adsorption process in the absence and the presence of US obeyed the pseudo second-order kinetics. The intraparticular diffusion model indicated that the adsorption of DBS ions on the AC was diffusion controlled as well as that US promoted intraparticular diffusion. The ΔG° values, -24.03 kJ/mol, -25.78 kJ/mol and -27.78 kJ/mol, were negative at all operating temperatures, verifying that the adsorption of DBS ions was spontaneous and thermodynamically favorable. The positive value of ΔS° = 187 J/mol K indicated the increased randomness at the adsorbent-adsorbate interface during the adsorption of DBS ions by the AC. © 2012 Elsevier B.V. All rights reserved. Source

Ciric S.,University of Prishtina | Petrovic O.,University of Novi Sad | Milenkovic D.,High Chemical Technological School
Chemical Industry and Chemical Engineering Quarterly

The possibility of using low-nutrient R2A medium for determining the total count of aerobic mesophilic bacteria was investigated. Sampling of water from particular points of water treatment and distribution at Kruševac drinking water treatment plant was conducted. The samples were inoculated simultaneously on Plate Count Agar (PCA) and R2A media, and incubated at 37 °C and at room temperature. The bacterial count was determined after 48, 72, 120 and 168 h. The statistical analysis of the results showed significantly higher bacterial count on R2A medium compared to PCA. Moreover, a significantly higher bacterial count developed at room temperature compared to the temperature of 37 °C. R2A medium recorded 3.6% of unsafe samples in the distribution system after the 7-day incubation at room temperature. On the basis of the obtained results, an optimum method for determining the total count of aerobic mesophilic bacteria for all investigated waters has been defined. The process of incubation is predictable and it can be described by a mathematical model in the form of a polynomial of the second or the third power. Source

Bojic D.,University of Nis | Momcilovic M.,Vinca Institute of Nuclear Sciences | Milenkovic D.,High Chemical Technological School | Mitrovic J.,University of Nis | And 3 more authors.
Arabian Journal of Chemistry

Practical aspects of Lagenaria vulgaris shell conversion to activated carbon were examined along with its use in ranitidine adsorption. Kinetics and isotherms of adsorption onto Lagenaria vulgaris carbon (LVC) were correlated to several theoretical adsorption models. The best fit was found in the case of Langmuir and pseudo-second-order model indicating monolayer adsorption. The influence of pH under kinetic study showed slightly hindered adsorption below pH 4. The optimal adsorbent dosage was set to 1g/L. LVC was characterized by several complementary techniques, including wet chemical techniques such as Boehm's titrations and determination of pHPZC and pH of LVC, which revealed neutral nature of the adsorbent. N2 sorptometry determined specific surface area of 665m2/g and significant ratio of micropores in the sample with maximum wall's diameter of 2.2nm. Fourier transform infrared spectroscopy (FTIR) confirmed the role of lignin and cellulose in the formation of the final LVC structure. Porous structure of the material was proved by using scanning electron microscopy. Preparation of LVC material drew attention as an easy and low-cost process for production of a highly efficient adsorbent which exhibited fast kinetics of ranitidine removal in the first minutes of contacting and large adsorption capacity (315.5mg/g) at equilibrium. © 2015 The Authors. Source

Todorovic D.A.,High Chemical Technological School | Milenkovic D.D.,High Chemical Technological School | Milosavljevic M.M.,University of Prishtina
Hemijska Industrija

This paper presents the results of gelatin and benzotriazole (BTA) inhibitory action on copper in the acid medium by the method of weight loss. The investigation was carried out in the citric acid solution (1, 5 and 20%) at the temperature of 293 K. Under such conditions, the gelatin showed higher efficiency of corrosion protection in comparison to BTA. The results, obtained through the Gibbs and Langmuir adsorption isotherm, show that gelatin adsorption on copper surface obey the Langmuir adsorption isotherm model, as well as that the adsorption in a spontaneous process. The polarization measurements show the potential of full passivation shift towards more negative values, and the increase of corrosion current in both cases but being more pronounced with the BTA. The results obtained in this paper indicate that the inhibition gelatin can be used as the BTA substitute for the copper corrosion protection. Source

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