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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]