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LABORATORY. The contextualized understanding of concepts in Chemistry by students from other areas is a challenging task. In this experiment, the synthesis of biodiesel is done by base catalyzed transesterification of refined soy oil with methanol at room temperature and common glassware found in any chemistry laboratory. The proposal permits introducing several concepts, such as that of emulsion, viscosity and catalysis to illustrate an activity based on an actual problem. In this didactic approach, some common problems of biodiesel production, such as soap formation and phase separation, are introduced into the procedure in order to raise questions and motivate the students to participate in the experimental work and stimulate reflections about critical aspects of biodiesel production. This experiment was carried out in the first semester of 2006, in experimental general chemistry taken by physics and agricultural, civil and chemical engineering students of UNICAMP.Keywords: biodiesel; emulsion; viscosity. INTRODUÇÃO . O uso de óleos vegetais como combustível pode parecer insignificante hoje em dia. Mas com o tempo (estes óleos) tornar-se-ão tão importantes quanto o petróleo e o carvão são atualmente"3,4 . Entretanto, o óleo mineral tornou-se o combustível para esse tipo de motor desde o início do século XX, devido ao seu menor custo e a melhores propriedades físico-químicas em comparação com os óleos vegetais. O óleo mineral é comumente chamado óleo diesel em reconhecimento a R. Diesel. Atualmente, as mudanças climáti-cas associadas à liberação de gases da queima de combustíveis fós-seis, o alto preço internacional do petróleo e a preocupação com o desenvolvimento sustentável começam a retomar a intenção original de Diesel do emprego de óleos vegetais aos motores movidos a óleo mineral 5 . Os óleos vegetais são constituídos predominantemente de substâncias conhecidas como triglicerídeos (também chamadas de triacilgliceróis ou triacilglicerídeos), que são ésteres formados a partir de ácidos carboxílicos de cadeia longa (ácidos graxos) e glicerol 6 . Além dos triglicerídeos, os óleos vegetais apresentam em sua composição quantidades apreciáveis de ácidos graxos livres (originados dos processos de extração dos óleos vegetais), fosfolipídeos, esteróis e tocoferóis. A Tabela 1 traz a distribuição de ácidos graxos de alguns óleos e gorduras. Os ácidos graxos constituintes dos triglicerídeos mais comuns apresentam 12, 14, 16 ou 18 átomos de carbono. Entretanto, outros ácidos graxos com menor ou maior nú-mero de átomos de carbono ou ainda contendo a função álcool também podem ser encontrados em vários óleos e gorduras. Um exemplo interessante é o óleo de mamona, que apresenta o ácido ricinoléico, CH 3 (CH 2 ) 5 CH(OH)CH 2 CH=CH(CH 2 ) 7 COOH, como maior constituinte de seus triglicerídeos (cerca de 80%). Os óleos vegetais apresentam várias vantagens para uso como combustível, como elevado poder calorífico, ausência de enxofre em suas composições e são de origem renovável. Contudo, o uso direto de óleos vegetais como...

The adsorption of Congo red and tinopal CBS dyes on cellulose fibers was investigated using electronic absorption and fluorescence spectroscopies. Hydrogen bonds appear to be relevant for the dye-fiber interactions as indicated by the solvatochromism of Congo red in water, methanol, and dimethyl sulfoxide solutions, and when adsorbed on cellulose fibers. We also demonstrate that electrostatic interactions play an important role in the dye-medium interaction, through the analysis of absorption spectra of Congo red and fluorescence spectra of tinopal in aqueous solutions containing salt and in layer-by-layer nanostructured films with poly(allylamine hydrochloride). For instance, dye adsorption was enhanced when salt was added to the dipping solution, which was explained by the synergistic effect between the conformational changes of the cellulose and changes in the solvation layer around the cellulose chains and around dye molecules. On the basis of the fluorescence results for tinopal CBS, we inferred that dye aggregation is not relevant for adsorption on the fibers. In addition, fluorescence spectroscopy is proven very sensitive for studying the organization of dye molecules in layer-by-layer films, particularly those undergoing irreversible structural changes.

Direct infusion electrospray ionization mass spectrometry (ESI-MS) of aqueous/methanolic extracts of biodiesel samples is shown to permit simple and fast fingerprinting typification, identification of the alcohol used in the trans-esterification process, monitoring of degradation and adulteration, and screening of residual glycerin and mono-, di-, and tri-glycerides. As proof-of-principle cases, ESI-MS fingerprints in both the positive and the negative ion modes were acquired for biodiesel samples derived from soybean oil, sunflower oil, canola oil, olive oil, castor oil, jatropha curcas oil, palm oil, lard, and tallow. In the negative ion mode, characteristic sets of ions corresponding to de-protonated fatty acids were detected for each type of biodiesel, thus allowing their reliable typification via these taxonomic markers. Biodiesel degradation was also monitored by ESI(-)-MS with the detection of degradation markers, mainly oxidized fatty acids. When using ESI(+)-MS, the main diagnostic ions detected were the protonated fatty esters, which reveal therefore both the oil source and the alcohol (methanol or ethanol, or other heavier alcohols) used for trans-esterification. Residual glycerin and mono-, di-, and tri-glycerides are also detected, which makes ESI-MS also applicable for laboratory and on-site screening of biodiesel quality.

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Acidic lanthanum and aluminum diphosphates were prepared and characterized (surface area, XRD, FT-IR, 31P-NMR and 27Al-NMR). These materials were used as catalyst for the esterification of oleic acid and transesterification of soybean oil. Under optimized conditions the methyl and ethyl ester yields were above 95%. Although the catalysts are recyclable, they slowly lost their catalytic activities, due to leaching of the phosphate.