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Abstract(s)
Em Portugal, a percentagem correspondente a resíduos sólidos plásticos (RSP) enviados para aterros (35%) é superior ao valor médio praticado nos demais países europeus. Esse fato, combinado com a baixa degradabilidade dos resíduos plásticos, destaca a necessidade de novas estratégias para reduzir o descarte de RSP e alcançar os objetivos da Diretiva 2008/98-CE e PNRS-12305/2010. Uma alternativa é a valorização dos RSP em materiais nanoestruturados de base de carbono (NMCs), como nanotubos de carbono (CNTs). Este processo requer duas etapas: 1) ocorre a quebra dos RSP em compostos orgânicos voláteis (COV), seguindo-se uma etapa de deposição química em fase vapor (CVD) dos COV sobre um substrato metálico, usado como catalisador para o crescimento de NMCs. A deposição química catalítica em fase vapor (CCVD) permite realizar o controlo do tamanho das nanoestruturas de carbono formadas, com o uso de catalisadores adequados ao processo. Na literatura existem diferentes tipos de metais de transição usados como fase catalítica ativa (Ni, Fe e Co) e outras estruturas usadas como suportes, como zeólitos, alumina (Al2O3) e sílica. Neste trabalho foram sintetizados 8 catalisadores utilizando o método de impregnação húmida (IU) e/ou co-precipitação (CO), seguidos de calcinação a 800 ° C por 3 h: Ni/Al2O3(IU), Ni-Fe/Al2O3(IU), Ni-Fe/Al2O3(CO), Ni-Fe-Al(CO), Ni/HMFI-90(IU), Ni-Fe/HMFI-90(IU), Ni/HBeta-150(IU) e Ni-Fe/H-Beta-150(IU). Os catalisadores foram caracterizados por análise de FTIR e DRX, a fim de identificar estruturas. A formação de óxidos mistos de metais, chamados espinélios, promoveu a estabilização da atividade catalítica, proporcionando rendimentos maiores que 80% para todos os catalisadores sintetizados. Para o mesmo tipo de catalisador (Ni-Fe/Al2O3), sintetizado pelos diferentes métodos, a impregnação húmida apresentou rendimento de 86% enquanto a co-precipitação apresentou rendimento de 83%. A impregnação húmida também apresentou menor número de etapas para operacionalização e menor gasto de insumos, sendo elencada como o método mais viável. Os catalisadores com suporte de zeólitos apresentaram rendimentos superiores a 88% o que configura que possuem estruturas seletivas para as partículas metálicas depositadas. Os NMCs foram obtidos por pirólise térmica do polietileno de baixa densidade (PEBD) com posterior deposição dos COV sobre o respectivo catalisador, excetuando o NMC-Ni/HMFI-90(IU)+Ni/Al2O3(IU) obtido via pirólise catalítica do PEBD com Ni/HMFI-90(IU). Esse NMC apresentou massa residual de 61%, dado pela análise de TGA. O alto valor de impurezas é justificada pela formação de coque e obstrução dos poros do catalisador durante o processo de pirólise catalítica, a qual foi mal sucedida devido a conformação do forno. Os espectros de FTIR para todos os NMCs identificaram bandas para o carbono a 872 cm-1, que caracteriza ligações C-H. O NMC-Ni-Fe-Al(CO) revelou uma massa residual de 12%, o que demonstra baixa estabilidade química das estruturas formadas, fato que justifica bandas de FTIR de baixa intensidade. As imagens da Microscopia Eletrônica de Varrimento (SEM) evidenciaram estruturas tubulares nanométricas, o que demonstra que os catalisadores sintetizados foram constituídos por partículas nanométricas. Contudo, apenas com a análise de SEM não foi possível garantir se as estruturas produzidas são CNTs ou nanofibras (NFCs), o diâmetro médio dos tubos sugere que seja uma mistura de ambas as estruturas.
In Portugal, the percentage corresponding to plastic solid waste (PSW) sent to landfills (35%) is higher than the average value among all european countries. This fact, combined with the low degradability of plastic waste, highlights the need for new strategies to reduce the disposal of PSW and to achieve the objectives of Directive 2008/98-EC and PNRS-12305/2010. An alternative is the valorization of PSW into high-added value products, such as nanostructured carbon-based materials (NMCs), namely carbon nanotubes (CNTs). This process requires two steps: 1) the cracking of the PSW into volatile organic compounds (VOCs) and 2) the chemical vapour deposition of the VOCs on a metal substrate, used as catalyst, to grow NMCs. The catalytic chemical vapor deposition (CCVD) also allows to control the size of the carbon nanostructures, requiring the use of suitable catalysts for the process. In the literature, there are different types of transition metals used as active catalyst phase (Ni, Fe and Co) and other structures used as supports, such as zeolites, alumina and silica. In this work, 8 catalysts were prepared by wetness impregnation (IU) and/or co-precipitation (CO) followed by calcination at 800°C for 3 h: Ni/Al2O3(IU), Ni-Fe/Al2O3(IU), Ni-Fe/Al2O3(CO), Ni-Fe-Al(CO), Ni/HMFI-90(IU), Ni-Fe/HMFI-90(IU), Ni/HBeta-150(IU), Ni-Fe/HBeta-150(IU). The catalysts were characterized by FTIR and XRD analysis, in order to indentify structures. The synthesis of mixed metal oxides, called spinel, promoted stabilization of the catalytic activity, offering yields (all above 80%). For the same type of catalyst (Ni-Fe/Al2O3) synthesized by different methods, wet impregnation showed a yield of (86%) while co-precipitation showed a yield of 83%. Wet impregnation also showed a lower number of steps for operationalization and lower input expenditure, being listed as the most viable method. The catalysts with zeolite support showed high yields, which means that it has selective structures for the deposited metallic particles. The NMCs were synthesized by thermal pyrolysis of low density polyethylene (LDPE) with subsequent deposition of VOCs on the respective catalyst, except the NMC-Ni/HMFI-90(IU) + Ni/Al2O3 (IU) synthesized via catalytic pyrolisis of LDPE with Ni/HMFI-90 (IU). This NMC showed a residual mass of 61%, by TGA analysis. This high degree of impurities is justified by formation of a carbonaceous material called coke and clogging of the catalyst pores during the process catalytic pyrolysis, which was poorly placed due to the conformation of the oven.The FTIR spectra have been identified in all NMCs in the band at 872 cm-1, which characterizes C-H bonds. The NMC-Ni-Fe-Al(CO) indicated a residual mass of 12%, which demonstrates low chemical stability of the structures formed, a fact that justifies low intensity FTIR bands for itself. The Scanning Eletron Microscopy (SEM) images show nanometric tubular structures, which demonstrates that the synthesized catalysts were made up of nanometric particles. However, only with SEM analysis it was not possible to confirm whether the structures produced were CNTs or nanofibers (NFCs). Due to the average diameter of the tubes, it is believed in the mixture of both structures.
In Portugal, the percentage corresponding to plastic solid waste (PSW) sent to landfills (35%) is higher than the average value among all european countries. This fact, combined with the low degradability of plastic waste, highlights the need for new strategies to reduce the disposal of PSW and to achieve the objectives of Directive 2008/98-EC and PNRS-12305/2010. An alternative is the valorization of PSW into high-added value products, such as nanostructured carbon-based materials (NMCs), namely carbon nanotubes (CNTs). This process requires two steps: 1) the cracking of the PSW into volatile organic compounds (VOCs) and 2) the chemical vapour deposition of the VOCs on a metal substrate, used as catalyst, to grow NMCs. The catalytic chemical vapor deposition (CCVD) also allows to control the size of the carbon nanostructures, requiring the use of suitable catalysts for the process. In the literature, there are different types of transition metals used as active catalyst phase (Ni, Fe and Co) and other structures used as supports, such as zeolites, alumina and silica. In this work, 8 catalysts were prepared by wetness impregnation (IU) and/or co-precipitation (CO) followed by calcination at 800°C for 3 h: Ni/Al2O3(IU), Ni-Fe/Al2O3(IU), Ni-Fe/Al2O3(CO), Ni-Fe-Al(CO), Ni/HMFI-90(IU), Ni-Fe/HMFI-90(IU), Ni/HBeta-150(IU), Ni-Fe/HBeta-150(IU). The catalysts were characterized by FTIR and XRD analysis, in order to indentify structures. The synthesis of mixed metal oxides, called spinel, promoted stabilization of the catalytic activity, offering yields (all above 80%). For the same type of catalyst (Ni-Fe/Al2O3) synthesized by different methods, wet impregnation showed a yield of (86%) while co-precipitation showed a yield of 83%. Wet impregnation also showed a lower number of steps for operationalization and lower input expenditure, being listed as the most viable method. The catalysts with zeolite support showed high yields, which means that it has selective structures for the deposited metallic particles. The NMCs were synthesized by thermal pyrolysis of low density polyethylene (LDPE) with subsequent deposition of VOCs on the respective catalyst, except the NMC-Ni/HMFI-90(IU) + Ni/Al2O3 (IU) synthesized via catalytic pyrolisis of LDPE with Ni/HMFI-90 (IU). This NMC showed a residual mass of 61%, by TGA analysis. This high degree of impurities is justified by formation of a carbonaceous material called coke and clogging of the catalyst pores during the process catalytic pyrolysis, which was poorly placed due to the conformation of the oven.The FTIR spectra have been identified in all NMCs in the band at 872 cm-1, which characterizes C-H bonds. The NMC-Ni-Fe-Al(CO) indicated a residual mass of 12%, which demonstrates low chemical stability of the structures formed, a fact that justifies low intensity FTIR bands for itself. The Scanning Eletron Microscopy (SEM) images show nanometric tubular structures, which demonstrates that the synthesized catalysts were made up of nanometric particles. However, only with SEM analysis it was not possible to confirm whether the structures produced were CNTs or nanofibers (NFCs). Due to the average diameter of the tubes, it is believed in the mixture of both structures.
Description
Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do Paraná
Keywords
Valorização Resíduos sólidos plásticos Catalisador Deposição química em fase vapor Nanoestruturas de carbono