Desenvolvimento de catalisadores heterogéneos de baixo custo para aplicação em Processos de Oxidação Avançados
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2019-02-22
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A água representa um recurso natural indispensável à vida, é amplamente e diariamente utilizada pelo Homem, sendo aplicada desde o consumo doméstico até às mais diversas atividadesindustriais. A qualidade da água tem-se vindo a degradar ao longo dos anos, resultado da poluição causada pela sua utilização nas atividades referidas, bem como, por um tratamento inexistente ou ineficiente antes da sua devolução ao ambiente. A indústria vitivinícola representa uma fonte de geração de efluentes com elevada carga orgânica, que se caracterizam pela presença de compostos com grande poder recalcitrante, sendo a sua descarga descontrolada um elevado risco para o ambiente. Deste modo, os Processos de Oxidação Avançados (POA), nomeadamente, os processos Fenton (H2O2/Fe2+) e foto-Fenton (H2O2/Fe2+/UV), surgem como uma alternativa de tratamento atrativa, uma vez que se baseiam na geração de radicais hidroxilo (HO•), espécies que possuem um elevado potencial de oxidação. A utilização de materiais geológicos, quer como adsorventes quer como suportes para catalisadores heterogéneos, representa uma alternativa promissora para a descontaminação de efluentes industriais, uma vez que são abundantes, viáveis do ponto de vista ambiental e possuem um custo bastante reduzido em comparação com outros materiais utilizados. A esmectite (SMT) corresponde a um grupo de minerais argilosos que se caracteriza por um tamanho de partículas inferior a 2 μm e uma estrutura singular, que lhe confere propriedades únicas tais como, elevada capacidade de troca catiónica, elevada área superficial e elevada estabilidade térmica. A clinoptilolite (ZEO), o zeólito natural mais abundante, representa um aluminossilicato hidratado, caracterizado por possuir uma estrutura rígida, tridimensional, com grande área superficial (como consequência da quantidade de poros e do seu diâmetro) que lhe confere uma elevada capacidade de adsorção e de troca catiónica. No presente trabalho foram desenvolvidos catalisadores heterogéneos, utilizando várias técnicas de preparação, baseadas na imobilização de diversos metais, nomeadamente, Fe, Cu e Al, na estrutura da SMT e do ZEO. Os catalisadores heterogéneos preparados foram depois caracterizados utilizando diversas técnicas, como a microscopia eletrónica de varrimento (MEV-EDS), a espetroscopia de absorção no infravermelho por transformação de Fourier (FTIR), a difração de raio-X (DRX) e a determinação da área superficial por adsorção de N2 (77K) (Método BET). Pela comparação dos resultados obtidos para os catalisadores desenvolvidos com os materiais originais (SMT e ZEO), observou-se, de um modo geral, uma diminuição no tamanho da partícula, o aumento da área superficial e o aumento do volume total de poros. Na aplicação prática destes sistemas oxidantes utilizou-se como estudo de caso um efluente vinícola simulado da região do Douro, que representa uma das maiores regiões produtoras de vinho em Portugal. A avaliação da eficiência dos processos de oxidação fotocatalítica foi realizada com base no grau de mineralização da matéria orgânica por determinação do Carbono Orgânico Total, (COT). No processo de oxidação fotocatalítica, a fonte de radiação utilizada foi uma lâmpada de mercúrio de baixa pressão (254 nm). No sentido de otimizar as condições experimentais para obtenção de um maior grau de degradação de matéria orgânica, estudou-se o efeito de vários parâmetros operacionais, nomeadamente a quantidade de H2O2 adicionada, a massa de catalisador e o pH inicial da reação. Os processos foto-Fenton heterogéneos permitiram atingir as maiores percentagens de remoção de COT: 90,4 % (para as condições iniciais de: 3,00 g de Fe-SMT, pH 3,00 e 97,94 mM de H2O2) e 82,9 % (para as condições experimentais de: 1,50 g de Al-Cu-SMT pil., pH 7,00 e 97,94 mM de H2O2). Para avaliar a atividade dos catalisadores a longo prazo, realizaramse três ciclos de regeneração consecutivos e verificou-se que existe uma perda de atividade ao longo dos vários ciclos de regeneração. O catalisador que obteve uma menor perda de atividade ao longo dos três ciclos foi o catalisador de Al-Cu-SMT pil., com uma percentagem perdida de 4,17 %. Da análise aos resultados experimentais obtidos, pode concluir-se que os catalisadores pilarizados, Al-Fe-SMT e Al-Cu-SMT, serão os catalisadores heterogéneos de baixo custo mais interessantes porque permitem um melhor equilíbrio entre uma maior percentagem de remoção de COT e uma menor taxa de lixiviação de metal (Fe e Cu).
Fresh water represents a natural resource indispensable to life, is widely and daily used by society, and is applied from domestic consumption to the most diverse industrial activities. Fresh water quality has been deteriorating over the years as a result of the pollution caused by its use in the activities referred to, as well as by a non-existent or inefficient treatment before being returned to the environment. The winery industry represents a source of effluent generation with high organic load, which is characterized by the presence of compounds with high recalcitrant power, and their uncontrolled discharge is a high risk for the environment. Thus, Advanced Oxidation Processes (POAs), such as the Fenton (H2O2/Fe2+) and photoFenton (H2O2/Fe2+/UV) processes, appear as a more effective treatment alternative, because they are based on the generation of free hydroxyl radicals (HO•), which have a high oxidation potential. The use of geological materials, either as adsorbents or as supports for heterogeneous catalysts for catalytic reactions, represents a promising alternative for the decontamination of industrial effluents, because they are abundant, environmentally viable and have a very low cost compared to other materials used. Smectite (SMT) represents a group of clay minerals characterized by a fine grain size (less than 2 μm of particle size) and a unique structure, which gives it unique properties such as high cation exchange capacity, high surface area and high stability thermal. Clinoptilolite (ZEO) represents a hydrated aluminum silicate, characterized by a rigid, three-dimensional structure with a large surface area (as a consequence of the quantity of pores and their diameter) that gives it a high adsorption and cation exchange capacity. In the present work, heterogeneous catalysts were developed, using several preparation techniques, based on the immobilization of several metals, such as Fe, Cu and Al, in the structure of SMT and ZEO. The heterogeneous catalysts prepared were characterized using various techniques, such as scanning electron microscopy (SEM-EDS), Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and determination of surface area by N2 adsorption (77K) (BET Method). Through the comparing the results obtained for the developed catalysts and for the original material (SMT and ZEO), we generally observed a decrease in particle size, increase of surface area and total pore volume. In the practical application of these oxidizing systems a simulated winery wastewater from the Douro region, which is one of the largest wines producing regions in Portugal, was used as a case study. The evaluation of the efficiency of photocatalytic oxidation processes was carried out based on the degree of organic matter mineralization (Total Organic Carbon - TOC) obtained. In the photocatalytic oxidation process, the source of radiation used was a low pressure mercury lamp (254 nm). In order to optimize the experimental conditions to obtain a greater degree of degradation of organic matter, the experimental parameters were varied, such as, amount of H2O2 added, mass of catalyst and initial pH of the reaction. The treatment processes that obtained the highest percentages of TOC removal were 90.43% (for the initial conditions of: 3.00 g Fe-SMT, pH 3.00 and 97.94 mM H2O2) and 82.86 % (for the experimental conditions of: 1.50 g of Al-Cu-SMT pil., pH 7.00 and 97.94 mM H2O2). In order to evaluate the activity of the catalysts in the long term, three consecutive cycles of regeneration were carried out and it was verified that there is a loss of activity throughout the several cycles of regeneration. Thus, the catalyst that obtained the least loss of activity over the three cycles was the Al-Cu-SMT pil. catalyst, with a percentage of 4.17%. By analysing the experimental results obtained, it can be concluded that the pillared catalysts, Al-Fe-SMT and Al-Cu-SMT, achieve a better balance between a higher TOC removal percentage and the lower amounts of metal leached (Fe and Cu).
Fresh water represents a natural resource indispensable to life, is widely and daily used by society, and is applied from domestic consumption to the most diverse industrial activities. Fresh water quality has been deteriorating over the years as a result of the pollution caused by its use in the activities referred to, as well as by a non-existent or inefficient treatment before being returned to the environment. The winery industry represents a source of effluent generation with high organic load, which is characterized by the presence of compounds with high recalcitrant power, and their uncontrolled discharge is a high risk for the environment. Thus, Advanced Oxidation Processes (POAs), such as the Fenton (H2O2/Fe2+) and photoFenton (H2O2/Fe2+/UV) processes, appear as a more effective treatment alternative, because they are based on the generation of free hydroxyl radicals (HO•), which have a high oxidation potential. The use of geological materials, either as adsorbents or as supports for heterogeneous catalysts for catalytic reactions, represents a promising alternative for the decontamination of industrial effluents, because they are abundant, environmentally viable and have a very low cost compared to other materials used. Smectite (SMT) represents a group of clay minerals characterized by a fine grain size (less than 2 μm of particle size) and a unique structure, which gives it unique properties such as high cation exchange capacity, high surface area and high stability thermal. Clinoptilolite (ZEO) represents a hydrated aluminum silicate, characterized by a rigid, three-dimensional structure with a large surface area (as a consequence of the quantity of pores and their diameter) that gives it a high adsorption and cation exchange capacity. In the present work, heterogeneous catalysts were developed, using several preparation techniques, based on the immobilization of several metals, such as Fe, Cu and Al, in the structure of SMT and ZEO. The heterogeneous catalysts prepared were characterized using various techniques, such as scanning electron microscopy (SEM-EDS), Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and determination of surface area by N2 adsorption (77K) (BET Method). Through the comparing the results obtained for the developed catalysts and for the original material (SMT and ZEO), we generally observed a decrease in particle size, increase of surface area and total pore volume. In the practical application of these oxidizing systems a simulated winery wastewater from the Douro region, which is one of the largest wines producing regions in Portugal, was used as a case study. The evaluation of the efficiency of photocatalytic oxidation processes was carried out based on the degree of organic matter mineralization (Total Organic Carbon - TOC) obtained. In the photocatalytic oxidation process, the source of radiation used was a low pressure mercury lamp (254 nm). In order to optimize the experimental conditions to obtain a greater degree of degradation of organic matter, the experimental parameters were varied, such as, amount of H2O2 added, mass of catalyst and initial pH of the reaction. The treatment processes that obtained the highest percentages of TOC removal were 90.43% (for the initial conditions of: 3.00 g Fe-SMT, pH 3.00 and 97.94 mM H2O2) and 82.86 % (for the experimental conditions of: 1.50 g of Al-Cu-SMT pil., pH 7.00 and 97.94 mM H2O2). In order to evaluate the activity of the catalysts in the long term, three consecutive cycles of regeneration were carried out and it was verified that there is a loss of activity throughout the several cycles of regeneration. Thus, the catalyst that obtained the least loss of activity over the three cycles was the Al-Cu-SMT pil. catalyst, with a percentage of 4.17%. By analysing the experimental results obtained, it can be concluded that the pillared catalysts, Al-Fe-SMT and Al-Cu-SMT, achieve a better balance between a higher TOC removal percentage and the lower amounts of metal leached (Fe and Cu).
Descrição
Dissertação de Mestrado em Engenharia do Ambiente apresentada à Universidade de Trás-os-Montes e Alto Douro
Palavras-chave
Efluentes vinícolas , Processos de Oxidação Avançados , minerais aluminossilicatos , catalisadores heterogéneos , reação fotocatalítica