Resumo: Neste trabalho, a polimerização do glicerol na presença de catalisador ácido (H 2 SO 4 ou H 3 PO 4 ) e básico (NaOH), para produzir resinas termofixas foi investigada. Os resultados mostraram que as variáveis como a temperatura de reação, o tipo e a concentração do catalisador são críticas para a obtenção de bons rendimentos e seletividade para materiais poliméricos. Em condições otimizadas, i.e. H 2 SO 4 como catalisador, 140 °C por 24 horas, foi possível obter polímeros com 98% de seletividade. Após polimerização, os materiais obtidos foram submetidos a extrações com diferentes solventes, i.e. água, THF e hexano. Os extratos foram caracterizados por ESI(+)-MS e por espectroscopia na região do infravermelho, que permitiram verificar a presença de oligômeros de até seis unidades monoméricas. Para menores tempos de reação, e.g. 4 horas, foi possível obter elevada seletividade (100%) para oligômeros, mas com baixa conversão de glicerol (25%). Além disso, verificou-se que os outros catalisadores (H 3 PO 4 e NaOH) apresentam baixa atividade para promover a polimerização do glicerol, e.g. rendimento de 25% após 24 horas. Palavras-chave: Glicerol, polimerização, resina termofixa, poliglicerol. Influence of Temperature and Nature of the Catalyst on Glycerol PolymerizationAbstract: In this work, an investigation was made of the glycerol polymerization in the presence of acid (H 2 SO 4 or H 3 PO 4 ) and base (NaOH) catalysts to produce thermosetting resins. The results showed that the reaction temperature and catalyst concentration are critical to obtain good yield and selectivity. Under optimum condition, i.e. H2SO4 catalyst, 140 °C for 24 hours it was possible to obtain polymers with 98% selectivity. After the polymerization the materials were submitted to extractions with different solvents, i.e. water, THF and hexane. The extracts were characterized by ESI(+)-MS (Electro-Spray Ionization Mass Spectrometry) and by FTIR, showing the presence of short-chain oligomers (up to six units). For shorter reaction times, e.g. 4 hours, it was possible to obtain high selectivity (100%) for oligomers, but with low glycerol conversion (25%). It was also observed that the other catalysts (H 3 PO 4 and NaOH) showed low activity to promote glycerol polymerization, e.g. yields of 25% after 24 hours. Keywords: Glycerol, polymerization, thermosetting resin, polyglycerol. IntroduçãoA crescente produção de biodiesel, através da transesterificação [1][2][3] de óleos vegetais ou gorduras animais (Figura 1), em todo o mundo [4] e em especial no Brasil, deve levar a um aumento significativo do volume de glicerol no mercado. Para cada tonelada de triglicerídeos processada, são produzidos pelo menos 100 kg de glicerol [4][5][6] . Como consequência, o preço do glicerol cai fortemente no mercado em todo o mundo [7] . Essa queda de preço é uma tendência mundial, não sendo diferente no Brasil, que em 2005 registrou preços de glicerol em torno de R$ 3000 t -1 , mas já em 2007, a mesma quantidade de glicerol era comercializada por R$ 1700 t -1...
RESUMO: Este trabalho consiste em: (i) análise do conteúdo radiação em livros didáticos de Química e Física; (ii) análise das concepções prévias dos alunos sobre radiação; (iii) desenvolvimento e aplicação de um material didático para suporte ao ensino e aprendizagem de radiação e (iv) aná-lise do conhecimento adquirido pelos estudantes após o estudo do conteúdo. A análise dos livros didáticos de Química mostrou que radiação nuclear é o conteúdo principalmente abordado, enquanto que nos livros de Física são apresentadas principalmente ondas eletromagnéticas. Esse resultado demonstra que o conteúdo não foi ensinado de maneira eficiente. O conhecimento prévio, observado através de questionário, identificou as principais dificuldades dos alunos. Neste contexto, um material didáti-co foi desenvolvido para o ensino e aprendizagem de radiação para minimizar a ideia errada de que a radiação é prejudicial (como foi identificado em 82% das respostas dos estudantes). Através do ensino de radiações, usando esse material, e analisando os resultados deste trabalho, foi possí-vel verificar que os alunos se interessam pelo assunto, reconhecendo e diferenciando vários tipos de radiação presentes no cotidiano. Palavras-chave: Radiação; Ensino e Aprendizagem; Contextualização; Material Didático. CONTEXTUALIZING THE APPROACH OF RADIATION IN THE TEACHING OF CHEMISTRY ABSTRACT:This work is consisted of: (i) analysis of the content of radiation in chemistry and physics textbooks; (ii) analysis of the students' previous knowledge of radiation; (iii) development and implementation of a didactic material to support the teaching and the learning of radiation; and (iv) analysis of the knowledge acquired by the students after the study of the contents. The analysis of chemistry textbooks showed that the only content is nuclear radiation, while physics textbooks presented only electromagnetic waves contents. It demonstrates that the contents are not efficiently taught. The previous knowledge was observed through questionnaires that identified main difficulties of the students. In this context, a didactic material was developed for teaching and learning radiation to minimize the wrong idea that radiation is harmful (as identified in the 82% of students answers). By teaching radiation, using this material, and analyzing the results of this work, it was possible to check that the students are interested in the subject and recognize and differentiate several types and sources of radiation present in everyday life.
This work describes the software Quiptabela, suggests a teaching activity, and analyses responses of general chemistry students from the Biological Sciences distance course at the Federal University of Tocantins. The software was described according to its educational potential, featuring the creation of dozens of charts or tables correlating physicochemical properties of the elements, being Brazilian, and free distribution. The teaching activities suggested analyzed students' ability to create and analyze tables and charts correlating the properties of chemical elements. Some 41% of students tested could define the term "periodic", but failed to use the concept to explain and differentiate changes in mass or atomic radius with the atomic number of elements.
BACKGROUND: Glycerol was used to produce efficient adsorbents with a high surface area for organic contaminants by a combined process based on polymerization, carbonization and activation.RESULTS: Glycerol and sulfuric acid catalyst at concentrations of 0, 0.5, 1, 2 and 5 mol% were heated to 150 °C to form polyglycerol, which was then decomposed at 580 °C and activated with CO2 at 850 °C. The resulting activated carbons had a high specific area (1630 m2g−1) and high adsorption capacity of methylene blue used as a model organic contaminant. This process was also used to produce a special composite adsorbent based on expanded vermiculite (EV) coated with activated carbon. These composites were produced by impregnation of EV with glycerol followed by polymerization, thermal decomposition and activation with CO2 to produce up to 25 wt% carbon and a surface area of 835 m2g−1.CONCLUSIONS: The carbon layer present in the EV composite/activated carbon (GVE4CA2) produces a remarkable increase in the methylene blue adsorption capacity of the expanded vermiculite and strongly decreases undesirable water absorption. Copyright © 2012 Society of Chemical Industry
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