Estudo da degradação do CH4 e da mistura CH4/CO2 por plasma térmico de argônio: identificação e caracterização dos prdutos obtidos

Autor: Baldissarelli, Vanessa Zanon
Přispěvatelé: Universidade Federal de Santa Catarina, Debacher, Nito Angelo, Souza, Ivan Gonçalves de
Jazyk: portugalština
Rok vydání: 2012
Předmět:
Zdroj: Repositório Institucional da UFSC
Universidade Federal de Santa Catarina (UFSC)
instacron:UFSC
Popis: Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em Química. Na presente tese, um sistema de plasma térmico de argônio foi aplicado para promover a pirólise do CH4 e da mistura CH4/CO2. O principal produto obtido na conversão do CH4 e CO2 por plasma térmico foi o gás de síntese (H2 + CO), com rendimento máximo de 72 % e 59 % de CO e H2 respectivamente. Na reforma do CH4, os resultados mostraram que a conversão do metano aumentou com o aumento da vazão de metano no sistema, chegando ao valor máximo de 98 %. O principal produto gasoso formado na reforma do metano foi o H2, que apresentou rendimento máximo de 98 %. Além de H2 e CO, foram identificados também: C2H2, C2H4, C3H4, C4H6 e C6 +. O produto sólido da reação foi caracterizado como sendo negro de carbono (carbon black) quando a reação foi realizada sem a presença de catalisador no sistema e nanotubos de carbono foram formados na presença de catalisadores. Para os estudos de adsorção, o negro de carbono foi ativado quimicamente com KOH e fisicamente com CO2, sendo que o potencial adsorvente do negro de carbono foi testado na remoção do corante Reativo Preto 5 em solução mostrando uma boa capacidade adsorvente. Na investigação das propriedades superficiais da amostra, o negro de carbono sem ativação apresentou SBET = 66 m2.g-1, enquanto as amostras de negro de carbono ativadas com KOH e OH/CO2 apresentaram SBET = 122 m2.g-1 e SBET = 480 m2.g-1 respectivamente, mostrando que os processos de ativação foram favoráveis ao aumento da área específica do negro de carbono. Por fim, nos estudos de pirólise realizados na presença dos catalisadores 10Ni/Al2O3, 10Ni/5Ce e 5Ni/Al2O3 foram obtidos nanotubos de carbono, sendo confirmados por espectroscopia Raman e MET. Environmental problems are a direct result of human intervention in the different ecosystems around the globe. Due to increased industrial activity, the release of gases has become a serious environmental problem and there is a clear need to seek alternatives to promote the reduction of greenhouse gases in the atmosphere and also to develop processes capable of producing stable materials with added value. Of all the gases, CH4 and CO2 deserve special attention because they contribute to the greenhouse effect. In this context, one alternative to promote the reduction of such greenhouse gases in the atmosphere and obtain materials that have commercial application is thermal plasma pyrolysis, and the main products of interest obtained in the plasmainduced reactions are: hydrogen, different allotropic forms of carbon, and syngas. In this context, the focus of this research was to apply the thermal plasma of argon to promote the pyrolysis of CH4 and a CH4/CO2 mixture. The plasma torch used for the ionization of the argon arc was the non-transferred electric arc with a direct current (DC) power source. The gaseous products were identified and quantified by GC and the solid product was characterized by Raman spectroscopy, SEM, FEG, TEM, enthalpy of combustion, specific area, pore volume and average pore diameter. The effect of the gas flow and conversion ability were investigated. The results showed that the degradation of CH4 decreased with increased CO2 in the system, and the average conversion of CH4 in the CH4/CO2 mixture was 82.7%. The degradation percentage of CO2 also decreased with increased CO2 in the fixed system while maintaining the flow of methane. The main product in the conversion of CH4 and CO2 by thermal plasma was the synthesis gas (CO + H2), with maximum yields of 72.2% and 59.1% CO and H2, respectively. In the reforming of CH4 by thermal plasma, without the presence of CO2 in the system, the results showed that the conversion of methane increased with increasing flow of methane in the system, reaching a maximum value of 98.4%. The main gaseous product formed in the methane reforming was H2, which showed a maximum yield of 98.7%. In addition to CO and H2, the following were also identified: C2H2, C2H4, C3H4, C4H6 and C6 +. The solid product of the reaction was characterized as carbon black when the reaction was performed without the presence of a catalyst system and carbon nanotubes were formed in the presence of catalysts. TEM analysis of the carbon black showed the formation of aggregates and branching, with many open spaces expected, thus providing good adsorbent properties. For adsorption studies, the carbon black was activated chemically with KOH and physically with CO2, and the black carbon showed a high capacity as an adsorbent when tested in the removal of Reactive Black 5 dye in solution. In the investigation of the surface properties of the sample, the carbon black showed no activation (SBET = 66 m2.g-1) while the carbon black samples activated with KOH and KOH/CO2 gave values of SBET = 122 m2.g-1 and SBET = 480 m2.g-1 respectively. These results show that the activation processes favored an increase in the specific area of carbon black. In the analysis of porous materials, the carbon black samples which were non-activated and activated with KOH were characterized as macroporous materials, while the sample activated with CO2 was mesoporous. Carbon nanotubes were obtained in the studies conducted in the presence of 10Ni/Al2O3, 10Ni/5Ce and 5Ni/Al2O3 catalysts, as confirmed by Raman spectroscopy and TEM. In the Raman spectroscopy, the ID/IG ratio for all samples indicated the presence of carbon nanotubes with defects or impurities, and the sample obtained with 5Ni/Al2O3 had the lowest value for the ID/IG ratio indicating that the carbon nanotubes of this sample had higher purity than that of the other samples.
Databáze: OpenAIRE
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