Influência de elementos terras raras nas propriedades catalíticas de óxidos derivados de hidrotalcitas para produção de biodiesel etílico
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Data
2016-02-25
Autores
Rossi, Jessika de Souza [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Em crescente produção nacional, a síntese de biodiesel industrial ocorre por transesterificação na presença de catalisadores homogêneos alcalinos. Embora esse processo apresente elevado rendimento, as etapas adicionais de purificação do produto e a possibilidade de ocorrer saponificação fazem com que novas formas de produção desse biocombustível sejam desenvolvidas, como, por exemplo, empregando a catálise heterogênea. Dentre os materiais estudados, proponentes à função de catalisadores, tem-se os óxidos mistos de magnésio e alumínio, provenientes da calcinação das hidrotalcitas, que podem ser dopados com diferentes metais, melhorando sua atividade catalítica. O presente trabalho teve como objetivo principal o estudo das características de óxidos mistos provenientes de hidrotalcitas a partir de suas dopagens com lantanídeos. Sendo assim, a discussão dos resultados foi dividida em dois capítulos. O Capítulo 2 apresenta os efeitos que os íons La, Ce e Lu, nas quantidades de 1,0 e 2,0% em mol, promoveram sobre as propriedades físico-químicas das hidrotalcitas e sobre a atividade catalítica dos óxidos na produção de biodiesel. A reação de transesterificação foi realizada com óleo de soja e etanol (proporção 1:20 m/m óleo/etanol) e 20% de catalisador (massa do catalisador/massa de óleo), a 120°C por 14 horas. Os óxidos dopados com 1,0% apresentaram rendimentos superiores a aqueles dopados com 2,0%, sendo MgAl1La e MgAl1Lu os que apresentaram maiores rendimentos, com 80 e 84%, respectivamente. No Capítulo 3, é relatado o efeito que a utilização de energias de alta-frequência, como as micro-ondas e ultrassom, provocou na estrutura, textura e na qualidade dos cristais dos sólidos obtidos. Sendo assim, três séries de hidrotalcitas com 5,0% em mol de lantanídeos (La, Ce, Yb, Lu) foram preparadas por coprecipitação (síntese convencional), coprecipitação assistida por ultrassom e coprecipitação seguida de tratamento com micro-ondas. Os materiais foram caracterizados por difração de raios X (DRX), espectroscopia de infravermelho (FTIR-ATR) e análise da área superficial específica por adsorção de N2. Para os sólidos envolvendo La e Ce, íons com grandes raios, houve formação de fase segregada. No entanto, o uso de ultrassom e micro-ondas apresentaram mudanças significativamente na estrutura do material, indicando melhoras na inserção desses metais na rede lamelar das hidrotalcitas, além de aumento na área superficial dos óxidos.
On increasing national production, the industrial biodiesel synthesis occurs by transesterification in the presence of alkaline homogeneous catalysts. Although this process presents high yield, additional steps of purification of the product and the possibility to occur saponification make new ways of biofuels production are developed, such as heterogeneous catalysis. Among the studied materials for catalysts function there are mixed oxides of magnesium and aluminum from hydrotalcites calcination which may be doped with various metals to improve their catalytic activity. This paper aimed to study the mixed oxide characteristics from hydrotalcites doped with lanthanides. Thus, the discussion of the results were divided into two chapters. The chapter 2 shows the effects of the ions La, Ce and Lu in the amount of 1.0 to 2.0% promoted on the physicochemical properties of the hydrotalcites and the catalytic activity of the oxides in the production of biodiesel. The transesterification reaction was carried out using soybean oil and ethanol (ratio 1:20 w/w oil/ethanol) and catalyst 20% (mass catalyst/oil mass) at 120°C for 14 hours. The oxides doped with 1.0% had higher income than ones doped with 2.0%, and MgAl1La MgAl1Lu being the highest yields with 80 and 84%, respectively. In the Chapter 3 is reported the effect that the use of high-frequency energy such as microwaves and ultrasound have led to the structure, texture and quality of the crystals of solids. Thus, three series of hydrotalcites with 5.0% lanthanides (La, Ce, Yb, Lu) were prepared by co-precipitation (conventional synthesis) co-precipitation assisted by ultrasound and co-precipitation followed by treatment with microwave. The materials were characterized by the X-ray diffraction (XRD), the infrared spectroscopy (ATR-FTIR) and the analysis of the specific surface area by N2 adsorption. For the solids that involve La and Ce, large radius ions, there was segregated phase formation, however, the use of ultrasound and microwaves significantly improved the insertion of these metals lamellar lattice of hydrotalcites, beyond the increase of the surface area of the oxides.
On increasing national production, the industrial biodiesel synthesis occurs by transesterification in the presence of alkaline homogeneous catalysts. Although this process presents high yield, additional steps of purification of the product and the possibility to occur saponification make new ways of biofuels production are developed, such as heterogeneous catalysis. Among the studied materials for catalysts function there are mixed oxides of magnesium and aluminum from hydrotalcites calcination which may be doped with various metals to improve their catalytic activity. This paper aimed to study the mixed oxide characteristics from hydrotalcites doped with lanthanides. Thus, the discussion of the results were divided into two chapters. The chapter 2 shows the effects of the ions La, Ce and Lu in the amount of 1.0 to 2.0% promoted on the physicochemical properties of the hydrotalcites and the catalytic activity of the oxides in the production of biodiesel. The transesterification reaction was carried out using soybean oil and ethanol (ratio 1:20 w/w oil/ethanol) and catalyst 20% (mass catalyst/oil mass) at 120°C for 14 hours. The oxides doped with 1.0% had higher income than ones doped with 2.0%, and MgAl1La MgAl1Lu being the highest yields with 80 and 84%, respectively. In the Chapter 3 is reported the effect that the use of high-frequency energy such as microwaves and ultrasound have led to the structure, texture and quality of the crystals of solids. Thus, three series of hydrotalcites with 5.0% lanthanides (La, Ce, Yb, Lu) were prepared by co-precipitation (conventional synthesis) co-precipitation assisted by ultrasound and co-precipitation followed by treatment with microwave. The materials were characterized by the X-ray diffraction (XRD), the infrared spectroscopy (ATR-FTIR) and the analysis of the specific surface area by N2 adsorption. For the solids that involve La and Ce, large radius ions, there was segregated phase formation, however, the use of ultrasound and microwaves significantly improved the insertion of these metals lamellar lattice of hydrotalcites, beyond the increase of the surface area of the oxides.
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Palavras-chave
Hidrotalcita, Óxidos mistos, Biodiesel, Lantanídeos, Catálise heterogênea, Hydrotalcite, Mixed oxides, Biodiesel, Lanthanides, Heterogeneous catalysis