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Abstract: Biodiesel, a mixture of fatty acid methyl esters, is widely used as renewable bio-based alternative fuel for internal combustion engines. Kinetic model of non-catalytic biodiesel synthesis at elevated temperature and pressure, based on triglycerides conversion, is presented in this study. The model was developed using experimental reaction data of non-catalytic biodiesel synthesis at 150 and 210°C, and under pressures of 1.0 and 4.5MPa, respectively. The phase transition during transesterification at different conditions (subcritical and supercritical) and limitations of mass transfer between two liquid phases were included in the model. This complex reaction was represented by kinetic model with three consecutive and parallel reversible reactions, while kinetic parameters were calculated using simplified procedure based on triglycerides conversion as the only variable. The developed model was found to fit the experimental data for triglyceride conversion with high accuracy. [Copyright &y& Elsevier]

Abstract: Modelling and optimization of the extraction of St. John''s Wort using supercritical fluid is the subject of this study. Applying conservation of mass, two partial differential equations were written for solute concentration in both solvent and solid phase. The equilibrium constant of St. John''s Wort extract between solid and solvent phase was determined using genetic algorithm optimization technique. The differential equations were solved using numerical techniques simultaneously and were compared with experimental data. The results showed a good agreement between model results and experimental data. Simulation and optimization according to genetic algorithm have shown that 313K and 20MPa were the optimum temperature and pressure for supercritical carbon dioxide extraction of St. John''s Wort. [Copyright &y& Elsevier]

Abstract: Biodiesel synthesis by ethanolysis of triglycerides conducted under high pressure and at elevated temperature can lead to high levels of conversion and biodiesel yield over short reaction time. The vapour–liquid or vapour–liquid–liquid equilibrium and phase distribution of ethanol and triolein were investigated in order to determine the range of pressure and temperature required for high oil conversion. The phase equilibrium of the triolein and ethanol mixture (1:40 and 1:26 molar ratio of triolein to ethanol) was monitored in a view cell in order to determine the phase transition during heating of mixture up to 195°C (the corresponding pressure was 25 and 26bar). The experimental data were simulated using ASPENplus® and UniSim® software and results obtained using RK-Aspen EOS were found to correlate well with the experimental data. Simulation results show the important influence of the phase equilibrium on the reaction mechanism and overall kinetics under subcritical conditions (T <270°C at 200bar) since the two liquid phases exist at the beginning of reaction, thereby limiting the contact between the reactants. In case of single reaction phase (T >270°C at 200bar) the initially high reaction rate is limited at high conversion levels due to increasing extent of reversible reaction. [Copyright &y& Elsevier]

The paper presents the results of a comparative study on accelerated aging of specially designed experimental transformers and their corresponding laboratory models. The experimental transformers are 300 kVA, with insulation in line with medium size and large mineral oil immersed power transformers, having different initial water contents in the standard Kraft paper insulation of ca. 1 and 4 %. These transformers were subjected to the rated current and voltage conditions, operating in the irregular parallel operation, whereby the temperature of windings were measured with fiber optics sensors and kept at 105 °C for 460 days. Each transformer was equipped with a removable tank which allowed access to the outer surface of the HV windings. Laboratory experiments were simulating experimental transformers and were performed in Erlenmeyer flasks, containing oil, paper materials, copper and iron in the same proportions as in the active part of the experimental transformers. The parameters that were monitored during aging were the following: degree of polymerization of paper, hot-spot temperature of transformers, water content in paper, and water and furans content in the oil. Estimations of water content in solid insulation of experimental transformers using frequency domain spectroscopy and the Perrier-Lukic moisture equilibrium chart were performed. The experimental results show that shortening of the insulation life, defined by the value of degree of polymerization, increased 2.5 times with increasing moisture content in the cellulose from ca. 1 to 4 %. For both experimental transformers and laboratory models, the relationships between the paper degree of polymerization and the furans content for dry and wet insulation was developed and is presented in the paper. [ABSTRACT FROM AUTHOR]

Abstract: Contamination of groundwater by methyl tertiary butyl ether (MTBE), that is detected in wastewater of petrochemical industry, is an increasing problem to water supply companies. The subjects of this research were the methods of photolytic, photocatalytic and microbiological degradation of methyl tertiary butyl ether (MTBE) dissolved in wastewaters. The effects of concentrated solar radiation simulated with sodium lamp (SONT UV 400) have been investigated in laboratory experiments. Our result indicated that bacteria Pseudomonas strain CY, isolated from the kerosene, and added alone, was able to gradually degrade MTBE and to decrease its concentration for 93.6% in 12 h. However, the percentage of photolytic degradation decrease in only 4 h was 99.2%. By adding Pseudomonas strain CY after 4 h of light treatment, the degradation was enhanced to 99.55% in additional 5 h. The photocatalytic process was performed in slurry-catalyst reactor with different concentrations of TiO2 catalyst: 5, 0.5 and 0.25 g/L. The MTBE degradation producing carbon dioxide reached 91% in only 150 min, when 5 g/L of catalyst was used. [Copyright &y& Elsevier]