Desenvolvimento e aplicação de vanadossilicatos lamelares como catalisadores na conversão do glicerol
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Data
2018-07-30
Autores
Vieira, Luiz Henrique [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A conversão catalítica em produtos de maior valor agregado é apresentada como alternativa interessante para a valorização do excesso de glicerol disponível como coproduto no processo de produção do biodiesel. Este estudo apresenta o desenvolvimento e o aplicação de um processo para a transformação eficiente do glicerol em ácido acrílico pela rota da desidratação oxidativa em única etapa, e glicerol em solketal pela rota da cetalização com acetona, utilizando catalisadores do tipo vanadossilicatos derivados de estruturas zeolíticas. Devido às propriedades oxidantes e ácidas únicas que surgem com a substituição isomórfica de vanádio em comparação ao alumínio, em estruturas zeolíticas, o projeto envolve o desenvolvimento de vanadossilicatos onde os sítios ativos apresentem características bifuncionais para a desidratação oxidativa do glicerol, ou seja, em uma primeira etapa desidratam o glicerol a acroleína e em uma segunda etapa oxidam a acroleína para produzir ácido acrílico. Outro aspecto avaliado foi a acidez dos sítios ativos necessária na cetalização do glicerol com acetona para a produção do solketal. Foram utilizadas estruturas zeolíticas lamelares com o intuito de possibilitar uma maior acessibilidade aos sítios ativos pelos reagentes. Dentre os materiais lamelares destaca-se a zeólita ITQ-6, de estrutura FER, que possui desempenho catalítico destacado em relação as zeólitas puramente microporosas e, portanto, foram os catalisadores desenvolvidos e investigados neste trabalho. Foram sintetizados dois tipos de materiais, sendo eles, vanadossilicatos, onde o precursor de vanádio foi adicionado a mistura de síntese, e silicatos impregnados com vanádio, onde foi realizada a impregnação via úmida de um sal de vanádio sobre os catalisadores seguida de calcinação. Foram aplicados aos materiais um amplo conjunto de técnicas que permitiram desvendar e entender os mecanismos de formação de vanadossilicatos, seu comportamento como catalisador na reação, a identificação e funcionalidade dos sítios ativos. Foram realizadas caracterizações estruturais, texturais e superficiais ex situ e in situ, entre elas, difração de raios X, fisissorção de nitrogênio, ressonância magnética nuclear de 29Si, espectroscopias na região do UV-Visível e no infravermelho com transformada de Fourier, espectroscopia de absorção de raios X, dessorção a temperatura programada de amônia, termogravimetria e espectroscopia de fotoelétrons excitados por raios X. Com estas informações foram, sistematicamente, estabelecidas as condições de operação durante a síntese e a atividade catalítica desses materiais. A combinação entre acessibilidade, alta dispersão, acidez moderada e alto potencial oxidativo dos sítios ativos nos materiais micro/mesoporosos V-ITQ-6, foram fatores determinantes no aumento considerável na produtividade de ácido acrílico para a desidratação oxidativa e, solketal para a cetalização, quando comparados aos vanadossilicatos puramente microporosos, V-FER, e ao pentóxido de vanádio não poroso.
The catalytic conversion to higher value-added products is presented as an interesting alternative for the valorization of excess of glycerol available as a co-product in the biodiesel production process. This study presents the development and application of a process for the efficient transformation of glycerol into acrylic acid by single-step oxidative dehydration route, and glycerol into solketal by ketalization route, using vanadosilicate catalysts derived from zeolitic structures. Due to the unique oxidizing and acidic properties that arise with the isomorphic substitution of vanadium, compared to aluminum, in zeolitic structures, the work involves the development of vanadosilicates with the active sites presenting bi-functional characteristics for the oxidative dehydration of glycerol, where, in a first step dehydrate the glycerol to acrolein and in a second step oxidize the acrolein to produce acrylic acid. Another aspect evaluated was the acidity of the active sites required in the ketalization of glycerol with acetone to produce solketal. Lamellar zeolitic structures were used in order to allow greater accessibility to the active sites by the reagents. Among the lamellar materials, the ITQ-6 zeolite, with FER structure, has outstanding catalytic performance in relation to the purely microporous zeolites and, therefore, were the catalysts developed and investigated in this work. Two types of materials were synthesized, vanadosilicates, where the vanadium precursor was added to the synthesis mixture, and vanadium-impregnated silicates, where the wet impregnation of a vanadium salt was carried out on the catalysts followed by calcination. A wide range of techniques were applied to the materials that allowed to unveil and understand the mechanisms of formation of vanadosilicates, their behavior as a catalyst in the reaction, the identification and functionality of the active sites. Structural, textural and superficial characterizations were carried out ex situ and in situ, among them, X-ray diffraction, nitrogen physisorption, 29Si nuclear magnetic resonance, spectroscopies in the UV-Visible region, in the infrared region with Fourier transform and X-ray absorption, temperature-programmed desorption of ammonia, thermogravimetry and X-ray photoelectron spectroscopy. With this information, the operating conditions were systematically established during the synthesis and catalytic activity of these materials. The combination of accessibility, high dispersion, moderate acidity and high oxidative potential of the active sites in the micro-mesoporous materials V-ITQ-6 were determinant factors in the considerable increase of acrylic acid productivity for oxidative dehydration and solketal productivity for ketalization, when compared to purely microporous vanadosilicates, V-FER, and non-porous vanadium pentoxide.
The catalytic conversion to higher value-added products is presented as an interesting alternative for the valorization of excess of glycerol available as a co-product in the biodiesel production process. This study presents the development and application of a process for the efficient transformation of glycerol into acrylic acid by single-step oxidative dehydration route, and glycerol into solketal by ketalization route, using vanadosilicate catalysts derived from zeolitic structures. Due to the unique oxidizing and acidic properties that arise with the isomorphic substitution of vanadium, compared to aluminum, in zeolitic structures, the work involves the development of vanadosilicates with the active sites presenting bi-functional characteristics for the oxidative dehydration of glycerol, where, in a first step dehydrate the glycerol to acrolein and in a second step oxidize the acrolein to produce acrylic acid. Another aspect evaluated was the acidity of the active sites required in the ketalization of glycerol with acetone to produce solketal. Lamellar zeolitic structures were used in order to allow greater accessibility to the active sites by the reagents. Among the lamellar materials, the ITQ-6 zeolite, with FER structure, has outstanding catalytic performance in relation to the purely microporous zeolites and, therefore, were the catalysts developed and investigated in this work. Two types of materials were synthesized, vanadosilicates, where the vanadium precursor was added to the synthesis mixture, and vanadium-impregnated silicates, where the wet impregnation of a vanadium salt was carried out on the catalysts followed by calcination. A wide range of techniques were applied to the materials that allowed to unveil and understand the mechanisms of formation of vanadosilicates, their behavior as a catalyst in the reaction, the identification and functionality of the active sites. Structural, textural and superficial characterizations were carried out ex situ and in situ, among them, X-ray diffraction, nitrogen physisorption, 29Si nuclear magnetic resonance, spectroscopies in the UV-Visible region, in the infrared region with Fourier transform and X-ray absorption, temperature-programmed desorption of ammonia, thermogravimetry and X-ray photoelectron spectroscopy. With this information, the operating conditions were systematically established during the synthesis and catalytic activity of these materials. The combination of accessibility, high dispersion, moderate acidity and high oxidative potential of the active sites in the micro-mesoporous materials V-ITQ-6 were determinant factors in the considerable increase of acrylic acid productivity for oxidative dehydration and solketal productivity for ketalization, when compared to purely microporous vanadosilicates, V-FER, and non-porous vanadium pentoxide.
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Palavras-chave
Glicerol, Ácido acrílico, Solketal, Zeólita, Vanádio, Desidratação oxidativa, Cetalização, Glycerol, Acrylic acid, Zeolite, Oxidative dehydration, Ketalization