Abstract Dielectric properties of a material are of paramount importance in many areas of knowledge. All scientific fields that deal with the interaction of electromagnetic radiation with matter demand this information. Consequently, suitable methods for obtaining accurate dielectric data are required. In the microwave community, the dielectric metrology with the coaxial probe method is well known due to its simplicity and practicality. It is also pointed out as a broadband and wide temperature range technique. Despite this, a detailed study of the implications of thermal effects at calibration with this technique has not been plainly reported in the literature. In the present work, a concise exposition of the problem is made. Using air, short and water as standards, we have analyzed a set of calibration procedures with different thermal conditions and compared them with the isothermal case. With the aid of statistical analysis, we have made recommendations for precise and accurate dielectric measurements at high temperatures. Using glycerol as material under test (MUT) we also demonstrated that measurements at temperatures up to 50°C above the calibration temperature can provide reliable data. Thus, measurements of glycerol up to 140°C were performed by calibrating the system with water at 90°C. This important issue was raised due to the lack of standard material data in the literature for temperatures above 100°C. From the measured data we also have derived the Cole-Davidson model parameters of glycerol from 30 to 140°C.

<p>Triacetin (or glycerol triacetate) was obtained by acetylating the glycerol by-product of biodiesel production process. This procedure is an interesting alternative that follows the principles of green chemistry. In this work, triacetin was synthesized using reactions between glycerol and acetic acid, as well as glycerol and acetic anhydride, using homogeneous and heterogeneous acid catalysis. The goal is to use this product as an additive for biodiesel produced from palm oil, which is a fuel with physical properties that require improvement. The products were characterized by Fourier transform infrared spectroscopy (FTIR), ¹³C nuclear magnetic resonance (NMR) and gas chromatography (GC). The reaction between glycerol and acetic anhydride was the most effective for obtaining the desired product, with an approximate selectivity of 98% for triacetin. The triacetin was added to diesel fuel oil and biodiesel in proportions from 5 to 10% v/v, and the mixtures were tested in an electrical generator. In the test, the engine showed no problems during operation, and incorporating the mixtures did not result in significant consumption. Small reductions were detected in CO, O₂ and opacity, but no changes were observed in the emissions of NO_x and CO₂.</p>

Ésteres metílicos e etílicos foram preparados a partir de ácido láurico, sob aquecimento convencional e irradiação de microondas para determinar as melhores condições de esterificação de ácidos graxos. Estas condições foram então aplicadas na conversão de resíduo de caixa de gordura a biodiesel. Este resíduo é uma matéria-prima potencial para a produção de biodiesel, devido ao seu baixo custo e fácil esterificação. A esterificação catalítica do resíduo com metanol foi realizada sob aquecimento convencional e irradiação de microondas. Foi possível obter conversões elevadas com o aquecimento convencional, mas sob aquecimento por microondas, o equilíbrio da reação de esterificação foi atingido muito mais rapidamente. O biodiesel obtido a partir do resíduo em reações com irradiação de microondas mostrou uma alta conversão (96%), mesmo em condições brandas de reação (razão molar gordura:metanol 1:6, 1,0% H2SO4, 393 K, 10 minutos). Embora estas experiências iniciais tenham sido realizados com um aparelho de laboratório de pequena escala, o procedimento poderia ser facilmente adaptado para um processo comercial contínuo.

Methyl and ethyl esters were prepared from lauric acid under conventional heating and microwave irradiation to determine the best fatty acid esterification conditions. These conditions were then applied in the conversion of trap grease (brown grease) to biodiesel. The trap grease is a potential feedstock for biodiesel production, due to its low cost and easy esterification. In this paper, trap grease catalytic esterification with methanol was performed under conventional heating and microwave irradiation. It was possible to obtain high conversions with conventional heating, but under microwave heating, the esterification reaction equilibrium was attained much faster. The trap grease biodiesel obtained from microwave assisted reactions showed a high conversion (96%) even at mild reaction conditions (trap grease:methanol molar ratio 1:6, 1.0% H2SO4, 393 K, 10 minutes). While these initial experiments were performed in a small-scale laboratory unit, the procedure could be easily scaled-up to a commercial continuous process.

Os processos industriais mais utilizados na produção de combustíveis líquidos semelhantes ao diesel usam catalisadores homogêneos básicos através das metanólise e etanólise de óleos tais como os de soja, canola, palma entre outros. Desse modo, se obtém o biodiesel. Por sua vez, transformações termo-catalíticas usando as facilidades existentes nas refinarias de petróleo são alternativas que merecem atenção devido a sua viabilidade econômica. De fato, três processos industriais já estão em funcionamento e novos projetos estão em fase final para comercialização. O presente trabalho analisa os experimentos já realizados por pesquisadores brasileiros nas áreas do craqueamento, do craqueamento catalítico e do hidrocraqueamento catalítico dos óleos vegetais puros ou modificados. A partir dos resultados descritos, são sugeridas novas direções destas pesquisas para os próximos anos.

The most used industrial processes for the production of liquid fuels like diesel type are based on the methanolysis and ethanolysis of various oil reactants, such as palm, soybean and rapeseed oils, in the presence of homogeneous base catalysts. However, thermal and catalytic transformations of vegetable oils using available reactors and industrial processes are possible alternatives and deserve attention. In fact, three industrial processes are operating and new projects are announced. The present work analyses the experimental studies performed up to now by Brazilian researchers in the field of cracking, catalytic cracking and hydrocracking of pure or modified vegetable oils. From the published results, some research areas for the near future are suggested.