• Energy Research

The aim of this work was to evaluate the performance of different extruded catalysts containing K2CO3 as active phase and adding conveniently γ‐Al2O3 and/or sepiolite and magnetic particles on the biodiesel production from sunflower oil by the ethanolic route. Firstly, the content of the Fe3O4 on the catalyst (0.1, 0.2, 0.3, and 0.4 g Fe3O4/g of K2CO3/γ‐Al2O3), after calcination step, was evaluated to verify the separation facility of the catalysts with magnetic properties from reactional medium, using an external magnetic field, at the end of biodiesel synthesis. After that, three different catalysts were considered for comparative purposes: (a) K2CO3/γ‐Al2O3; (b) K2CO3/γ‐Al2O3/Fe3O4; (c) K2CO3/γ‐Al2O3/Sepiolite/Fe3O4 and subsequently characterized by dynamometry, TGA, SEM, VSM, BET, and XRD to determine their mechanical, structural, magnetic, and textural properties. However, their catalytic activities were determined through biodiesel production that was carried out in a glass volumetric reactor during 4 h, under magnetic stirring with 5% wt. of the catalyst and oil : ethanol molar ratio (1 : 12) at 80°C reaction temperature. The best result, i.e., around 88% of biodiesel conversion, was obtained with catalyst K2CO3/γ‐Al2O3/Sepiolite/Fe3O4 which showed also satisfactory textural and mechanical strength properties comparatively with the other catalytic derivatives. In addition, no agglomeration of the particles was observed during the reaction, and the magnetic property of this catalytic system was satisfactory for adequate separation from reactional medium seeking further reuse. The attained results are attractive for possible implementation at industrial scale and can be considered to mitigate drawbacks which resulting by using of homogeneous catalysts in the conventional processes.

Abstract Two techniques based on the measurements of the refractive index (nD) of the alcoholic phase at 20 °C ( n D , AL 20 ) and the speed of propagation of sound (us) in the reaction mixture are presented for monitoring the methanolysis of vegetable oils. Application of these techniques for the real-time monitoring of the synthesis of biodiesel is described for the first time. Size exclusion chromatography has been used as reference method. Both n D , AL 20 and us increase linearly with the oil conversion due to the contribution of the glycerol formed. Good correlations have been found whose coefficients depend on the initial methanol/oil ratio and in the case of us also on the temperature Due to flow instabilities in the refractometer chamber, monitoring based on nD has been possible only off-line whereas the measurement of us allowed an effective, fast, accurate and cheap real-time monitoring of the process.

The sound propagation speed measurement us is used for monitoring triglyceride ethanolysis in a broad range of reaction conditions (mainly, temperature: 23–50 °C; ethanol/oil: from 6 to 24 mol/mol). Experimentally, us slightly increased with the reaction time in all cases as a result of the contribution of its dynamic mixture components. Nomoto’s expression for homogeneous mixtures offered suitable us estimation but with values notably higher than the experimental ones due to the resistance to sound propagation offered by the ethanol/oil interphase (non-homogeneous medium). Our strategy was based on both the comparison of the experimental us values and the theoretical ones correlated by means of triglyceride conversion and on the estimation of the sound speed of oil/ethanol that could emulate the resistance offered by the interphase. The evolution of the reactions was predicted quite well for all the experiments carried out with very different reaction rates. Nevertheless, at the beginning of the reaction, the estimated conversion (outside of industrial interests) showed important deviations. The presence of the intermediate reaction products, diglycerides, and monoglycerides could be responsible for those deviations.

Non-edible vegetable oils are characterized by high contents of free fatty acids (FFAs) that prevent from using the conventional basic catalysts for the production of biodiesel. In this work, solid acid catalysts are used for the simultaneous esterification and transesterification with methanol of the FFAs and triglycerides contained in sunflower oil acidified with oleic acid. Molybdenum oxide (MoO3), which has been seldom considered as a catalyst for the production of biodiesel, was used in bulk and alumina-supported forms. Results showed that bulk MoO3 is very active for both transesterification and esterification reactions, but it suffered from severe molybdenum leaching in the reaction medium. When supported on Al2O3, the MoO3 performance improved in terms of active phase utilization and stability though molybdenum leaching remained significant. The improvement of catalytic performance was ascribed to the establishment of MoO3-Al2O3 interactions that favored the anchorage of molybdenum to the support and the formation of new strong acidic centers, although this effect was offset by a decrease of specific surface area. It is concluded that the development of stable catalysts based on MoO3 offers an attractive route for the valorization of oils with high FFAs content.

A novel magnetic monolithic catalyst based on K2CO3/γ-Al2O3/Sepiolite/γ-Fe2O3 was developed seeking to convert efficiently soybean oil and bioethanol to ethanolic biodiesel and glycerol. The magnetic monolithic was attained by extrusion method and characterized by EPR, VSM, SEM, Dynamometry, XRD, BET, and CO2-TPD, showing satisfactory magnetic, morphological, mechanical, structural and textural properties. The catalytic performance of this monolithic catalyst was also evaluated in a reactor assisted by magnetic field. The reactor was operated in a closed loop, recycling the reaction mixture. High oil conversion to biodiesel was obtained using 5 wt% of catalyst with 1:12 oil/ethanol molar ratio at 70 °C after 1.5 h. The magnetic properties of this monolithic catalyst allowed the bed stabilization under magnetic field and the catalysts separation, enabling its reuse by four reaction cycles. The authors are grateful to the State University of Northern of Rio de Janeiro for the Postdoctoral Position Fellow (No. 001/2017), Institutional Program of the Estacio de Sá University for Research Productivity Fellow and the Brazilian agencies: FAPERJ (E-26/210.508/2014) and CAPES (Finance Code 001) for the financial support.

Catalytic biodiesel production from sunflower oil and ethanol using K2CO3/γ-Al2O3 in different configurations has been studied. To prepare the catalysts, boehmite was extruded with the aid of a binder and different percentages of K2CO3 active phase (15–45%) impregnated on the supports for comparative purposes. The transesterification reactions were carried out during 4 h using 5 wt% of the catalyst and the effects of oil: alcohol molar ratio and temperature were investigated to improve biodiesel formation. The best result (99.3% conversion) was obtained when 35% K2CO3/65% γ-Al2O3 hollow cylinder catalyst was used at 80 °C and 1:12 oil: ethanol molar ratio, showing their potential as promising alternative to conventional homogeneous catalytic systems used for biodiesel production at industrial scale. The authors are grateful to Program of the Madrid Community AlcCones, S2013/MAE-2985, Spain and to the Brazilian agencies: Carlos Chagas Filho Research Foundation of the Rio de Janeiro State (FAPERJ) (Process no. E- 26/210.508/2014 ) and The National Council for Scientific and Technological Development (CNPq) (process no. 165577/2013-14 and 311942/2015-6 ) for the financial support.

Methanolysis of vegetable oils in the presence of homogeneous catalysts remains the most important process for producing biodiesel. However, there is still a lack of accurate description of the reaction kinetics. This is in part due to the complexity of the reacting system in which a large number of interconnected reactions take place simultaneously. In this work, attention is focused on the biphasic character of the reaction medium, formed by two immiscible liquid phases. The behavior of the phases is investigated regarding their physicochemical properties, mainly density and mutual solubility of the components, as well as composition. In addition, two kinetic models with different level of complexity regarding the biphasic character of the reaction medium have been developed. It has been found that a heterogeneous model considering the presence of the two phases and the distribution of the several compounds between them is indispensable to get a good description of the process in terms of oil conversion and products yields. The model captures the effects of the main variables of an isothermal batch methanolysis process: methanol/oil molar ratio, reaction time and catalyst concentration. Nevertheless, some adjustment is still required as concerns modelling of the saponification reactions and catalyst deactivation.