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In this study the transesterification of rapeseed oil with methanol towards methyl esters, for use as biodiesel, was investigated over various MgO oxides as heterogeneous catalysts. The solids were prepared via precipitation from Mg(NO 3 ) 2 solutions using NH 3 in the presence, or absence, of Poly-Vinyl-Alcohol (PVA) at pH = 10. The catalysts were characterized by X-Ray Diffractometry (XRD), N 2 Adsorption-Desorption Porosimetry, Thermogravimetric Analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). The transesterification reaction took place in a batch reflux reactor and gas chromatography was employed for the analysis of the products. The oxidic catalysts synthesized in the presence of PVA showed high catalytic performance and methyl ester yield was above 97–98% after 8 h reaction time. On the contrary the activity of the samples synthesized without PVA was quite low in the range of 3–5%. The role of PVA in the catalyst preparation and the resulting enhanced catalytic activity is discussed. [ABSTRACT FROM AUTHOR]

Alkaline transesterification of Cynara cardunculus L. seed oil with methanol for biodiesel production is investigated. Both in situ transesterification and conventional transesterification were studied using ultrasonication (24 kHz, without external heating) and mechanical stirring (600 rpm, 60 °C). For in situ transesterification, the use of ultrasonication and mechanical stirring led to similar high % FAME content (96.0 and 93.0% respectively) after 20 min. However the % yield of the extracted methylesters using mechanical stirring was lower compared to ultrasonication (50.4 and 85.1% respectively). For in situ transesterification via ultrasonication the optimum conditions were: 9.5% NaOH w/w of oil and a 550:1 methanol to oil molar ratio. In conventional transesterification, using ultrasonication, a high % FAME content of methylesters (97.0%) was obtained after 20 min. Respective % FAME content for mechanical stirring was 95.8% after 1 h. In both cases of conventional transesterification 1% w/w of oil NaOH as catalyst and a 7:1 methanol to oil ratio were used. The kinetics used for methanolysis reaction using sonication or mechanical stirring involved the irreversible second order reaction followed by the reversible second order reaction close to equilibrium. Cynara biodiesel properties determined, comply with the specifications of the European Standard EN 14214. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, the transesterification reaction of rapeseed oil with methanol, in the presence of alkaline catalysts, either homogeneous (NaOH) or heterogeneous (Mg MCM-41, Mg–Al Hydrotalcite, and K+ impregnated zirconia), using low frequency ultrasonication (24 kHz) and mechanical stirring (600 rpm) for the production of biodiesel fuel was studied. Selection of heterogeneous catalysts was based on a combination of their porosity and surface basicity. Their characterization was carried out using X-ray diffraction (XRD), Nitrogen adsorption–desorption porosimetry and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The activities of the catalysts were related to their basic strength. Mg–Al hydrotalcite showed particularly the highest activity with conversion reaching 97%). The activity of ZrO2 in the transesterification reaction increased as the catalyst was doped with more potassium cations, becoming thus more basic. Use of ultrasonication significantly accelerated the transesterification reaction compared to the use of mechanical stirring (5 h vs. 24 h). Given the differences in experimental design, it can be concluded that the homogeneous catalyst accelerated significantly the transesterification reaction, as compared to all heterogeneous catalysts, using both mechanical stirring (15 min vs. 24 h) and ultrasonication (10 min vs. 5 h). However, the use of homogeneous base catalysts requires neutralization and separation from the reaction mixture leading to a series of environmental problems related to the use of high amounts of solvents and energy. Heterogeneous solid base catalysts can be easily separated from the reaction mixture by simple filtration, they are easily regenerated and bear a less corrosive nature, leading to safer, cheaper and more environment-friendly operations. [Copyright &y& Elsevier]