Browsing by Author "Uzunov I."

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    Biogenic amorphous silica as filler for elastomers
    (2018-06-01) Dishovsky N.; Malinova P.; Uzunov I.
    Natural products from agricultural wastes are finding importance in the polymer industry due to their many advantages such as being lightweight, low cost and environmentally friendly. In the present study the potential of the two types of rice husk ash (RHA) prepared under different conditions as fillers in natural rubber-based elastomer composites was investigated. The fillers were prepared by rice husks incineration and characterized by means of X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) specific surface area, Hg-porosimetry and N2-adsorption. The evaluation involved determining the vulcanization characteristics of the compounds and their physical and mechanical characteristics, resistance to thermal aging as well as the dynamic properties of the vulcanizates containing RHA. It has been found that the ash from rice husk has good potential as filler in elastomers, especially as a substitute for synthetic commercially available silica. RHA improves the grip on ice and snow better than standard silica and may be used in formulations for shoe soles used for winter sports, extreme hiking footwear, ski boot soles, winter tire protectors, etc. Its quality depends on the conditions under which rice husk is incinerated. It is recommended to run the process at a temperature not higher than 800 °C. In particular, cases in which the vulcanizates contain biogenic silica have very interesting characteristics like improved modulus at 300% of elongation, lower residual elongation, higher mechanical loss angle tangent at 0 °C and lower at 60 °C, and are superior to those of the vulcanizates containing commercially available filler Ultrasil® 7000 GR.
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    Liquid-phase sorption of oil by carbonized rice husks: Impact of grain size distribution on the sorption kinetics
    (2013-11-05) Uzunova S.; Uzunov I.; Angelova D.
    The use of sorbents, obtained from renewable wastes to purify the hydrosphere from various hazardous pollutants is an innovative approach with multiplied environmental effect. In this regard, there is interest in the processing of rice husks and converting them into an effective biosorbent for purification of water from oil pollution. By slow pyrolysis of rice husk at 480°C pyrolysis charcoal was obtained. The product was divided into fractions with sizes in the range from 0,4 to 2,0 mm. Each fraction was tested with respect to adsorption of crude oil from water surface gravimetrically and as emulsified in aqueous media by a batch-method. The aim of this study was to determine the influence of the factor ``granulometry of the adsorbent`` on the sorption kinetics and efficiency of the material for both cases of contamination. An attempt had been made the kinetics of the process to be described by kinetic models, most often used for adsorption from aqueous media: Lagergren's equation; second order kinetics equation; Weber-Morris's diffusion equation and Elovich equation.
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    Modelling of Aromatic Sulfur Compounds Adsorption from Hydrocarbon Fuels by Biochar Based Adsorbent
    (2022-03-10) Uzunova S.; Minchev L.; Uzunov I.
    In this work model fuel containing thiophene, benzothiophene and dibenzothiophene in different concentration combinations were treated with biochar. The quantity of total sulfur into the stock mixed solutions was below 1000 ppm. The adsorbent was prepared by pyrolysis of rice husks. The investigation aimed to use the method of multiple linear regression to derive a mathematical model, describing the adsorption of the three aromatic sulfur compounds from single and multi-component solutions of model fuel. The model describing the adsorption from multi-component solutions, based on the experimental results, has a correlation coefficient of 0.961. It reveals that the degree of desulfurization does not depend on the concentration of thiophene, but only on the concentrations of benzothiophene and dibenzothiophene in the fuel. The model can be used to predict the level of the adsorptive purification of the fuel if the content of benzothiophene and dibenzothiophene in it is known.
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    Selective adsorption of thiophene and its polyaromatic derivatives from fuels on pyrolyzed rice husks: A thermodynamic study
    (2019-01-01) Uzunova S.; Uzunov I.; Atanasova G.; Angelova D.; Ivanov I.
    This work presents the study of the adsorption affinity of biobased adsorbent prepared by pyrolysis of rice husks (PRH) toward thiophene (T), benzothiophene (BT) and dibenzothiophene (DBT) in single and mixed solutions in a batch mode using a model fuel and real diesel. A degree of desulfurization higher than 40 % is observed in case of an initial sulfur concentration in the fuel not higher than 1000 ppm. The adsorption selectivity of PRH from single solutions of the three aromatic sulfur heterocycles (ASHs) decreases following the line: T > BT > DBT. The theoretical equilibrium adsorption capacity of PRH in regard to the three sulfur compounds adsorption is determined using the adsorption isotherms of Langmuir, Freundlich, Dubinin-Radushkevich and Temkin. The calculated values of the thermodynamic parameters, such as the Gibbs energy, ΔG0, the entropy, ΔS0, and the enthalpy, ΔH0, indicate that the adsorption in PRH-ASHs-fuel system proceeds at normal and high temperature values through simultaneous physical and chemical interactions.
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    Waste Copper Slag/Aluminium Dross-Based Geopolymer
    (2021-01-01) Mihailova I.; Uzunov I.; Mehandjiev D.
    One of the important issues of the modern world is the ecological problems, which raise the issues of rational and efficient use of natural resources and the reduction of industrial waste. Materials synthesized from industrial waste are an example of producing new useful materials for various applications as well as efficient utilization of waste. The present study aims to synthesize amorphous aluminosilicates from metallurgical waste - waste copper slag, aluminum dross as well as from agricultural waste (rice husks). A synthesis method was applied by which the necessary silica and alumina were extracted from the waste products by chemical treatment in an alkaline environment. Two types of aluminosilicate materials were obtained depending on the experimental procedure. In the first case during the synthesis, there was a stage of polymerization and gel formation and in the second - of co-precipitation. Accordingly, the materials designated as geopolymer and amorphous aluminosilicate were characterized experimentally. They were found to be X-ray amorphous by XRD. FTIR spectroscopy proved that their structure was characterized by a three-dimensional aluminosilicate network with a high degree of connectivity of silicon and aluminum tetrahedra. The microstructure of the materials was established by SEM-EDS and their homogeneity was confirmed. However, due to the difference in synthesis, some differences in the chemical composition and structure of the geopolymer and the amorphous aluminosilicate were experimentally established. Their composition, the structural and textural features of the obtained geopolymer and amorphous aluminosilicate show that such materials can find application as catalyst carriers.