Browsing by Author "Uzunova S."

Now showing 1 - 4 of 4
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    Extracts from coffee by-products as potential raw materials for fuel additives and carbon adsorbents
    (2013-11-05) Cholakov G.; Toteva V.; Nikolov R.; Uzunova S.; Yanev S.
    Data about coffee consumed world-wide are somewhat contradictory. A conservative estimate, suggests a number of around 8 mln tones per year. Its production involves a comparable amount of by-products, mainly pulp, husks, skins and spent coffee grounds. Thus, a sustainable coffee industry requires the development of methods for utilization of coffee by-products. Among these, the preparation of renewable fuel additives (e.g. biodiesel) and carbon adsorbents is a promising alternative to the eventual dumping of biogenic substances, harmful to the environment. Extraction of coffee by-products is the first step towards their utilization. This work presents results on laboratory extraction of spent coffee grounds (SCG) with different solvents, discussed in the context of the preparation of renewable fuel additives. The aim of the present study is to develop a procedure for extraction of coffee residues, suitable for production of biofuels and adsorbents.
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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.