Close
Metadata

@MastersThesis{Coelho:2009:FiBaNa,
               author = "Coelho, Nelize Maria de Almeida",
                title = "Filtro a base de nanofibras de carbono para sequestro de enxofre 
                         em efluentes gasosos ricos em H2S",
               school = "Instituto Nacional de Pesquisas Espaciais (INPE)",
                 year = "2009",
              address = "S{\~a}o Jos{\'e} dos Campos",
                month = "2009-09-04",
             keywords = "rea{\c{c}}{\~a}o de Claus modificado, nanofibras de carbono, 
                         n{\'{\i}}quel, remo{\c{c}}{\~a}o de enxofre, cat{\'a}lise 
                         heterog{\^e}nea, modified Claus process, carbon nanofibers, 
                         nickel, sulfur removal, heterogeneous catalysis.",
             abstract = "Nas {\'u}ltimas d{\'e}cadas, a recupera{\c{c}}{\~a}o de 
                         enxofre a partir de efluentes gasosos contendo H2S tem se tornado 
                         cada vez mais importante devido aos rigorosos limites de 
                         emiss{\~a}o impostos pela legisla{\c{c}}{\~a}o de 
                         prote{\c{c}}{\~a}o ao meio ambiente. Este processo, conhecido 
                         como Claus Modificado, se baseia na rea{\c{c}}{\~a}o de 
                         oxida{\c{c}}{\~a}o direta de H2_S em enxofre elementar, o qual 
                         {\'e} um produto de alto valor agregado. No entanto, 
                         limita{\c{c}}{\~o}es termodin{\^a}micas do equil{\'{\i}}brio 
                         desta rea{\c{c}}{\~a}o permitem uma m{\'a}xima efici{\^e}ncia 
                         de 98%, mesmo operando com tr{\^e}s reatores em s{\'e}rie. Este 
                         trabalho contempla um estudo de diferentes par{\^a}metros nesta 
                         rea{\c{c}}{\~a}o, empregando catalisadores de n{\'{\i}}quel 
                         suportados em comp{\'o}sitos macrosc{\'o}picos de nanofibras de 
                         carbono. Estes materiais apresentam a vantagem de um f{\'a}cil 
                         manuseio em aplica{\c{c}}{\~a}o industrial. Para tanto, foi 
                         preparado um suporte catal{\'{\i}}tico {\`a} base de nanofibras 
                         de carbono pela impregna{\c{c}}{\~a}o de 2% (p/p) de 
                         n{\'{\i}}quel sobre um feltro de carbono e, posterior, 
                         decomposi{\c{c}}{\~a}o catal{\'{\i}}tica de uma mistura 
                         contendo etano e hidrog{\^e}nio. Esse suporte foi impregnado com 
                         precursor de n{\'{\i}}quel, de maneira que os teores 
                         met{\'a}licos obtidos ficassem compreendidos entre 0,16 e 15% 
                         (p/p). Tanto o suporte como os catalisadores foram caracterizados 
                         por: microscopia eletr{\^o}nica de varredura; medidas de 
                         {\'a}rea espec{\'{\i}}fica (B.E.T.); e picnometria a 
                         h{\'e}lio. Numa primeira fase de testes, a raz{\~a}o entre os 
                         reagentes O_2/H_2S e o teor de n{\'{\i}}quel impregnado no 
                         catalisador foram estudados atrav{\'e}s da metodologia de 
                         planejamento de experimentos, pelo do m{\'e}todo de 
                         superf{\'{\i}}cie de resposta. Os resultados obtidos permitiram 
                         constatar que o teor de n{\'{\i}}quel, quando aumentado at{\'e} 
                         6%, eleva o n{\'u}mero de s{\'{\i}}tios ativos e o rendimento 
                         em enxofre capturado; no entanto, entre 6-11,6% o mesmo n{\~a}o 
                         ocorre, o que pode indicar um aparente crescimento das 
                         part{\'{\i}}culas met{\'a}licas. Em rela{\c{c}}{\~a}o {\`a} 
                         raz{\~a}o O_2/H_2S, foi poss{\'{\i}}vel constatar que, quando 
                         do emprego da mesma acima da raz{\~a}o estequiom{\'e}trica 
                         (0,5), o aumento da presen{\c{c}}a de O_2 n{\~a}o interferiu no 
                         rendimento da rea{\c{c}}{\~a}o, o que permite supor que, nestas 
                         condi{\c{c}}{\~o}es, a ordem parcial em rela{\c{c}}{\~a}o ao 
                         reagente O2 {\'e} zero. Posteriormente, dois outros 
                         par{\^a}metros foram estudados: temperatura da rea{\c{c}}{\~a}o 
                         e adi{\c{c}}{\~a}o de {\'a}gua ao meio reacional. Em 
                         rela{\c{c}}{\~a}o aos testes com varia{\c{c}}{\~a}o da 
                         temperatura e sem adi{\c{c}}{\~a}o de {\'a}gua ao meio 
                         reacional, dois diferentes fen{\^o}menos foram identificados: a 
                         120C, a aus{\^e}ncia de {\'a}gua no estado l{\'{\i}}quido 
                         dificultou a remo{\c{c}}{\~a}o de enxofre dos s{\'{\i}}tios 
                         catal{\'{\i}}ticos, enquanto que, a 180C, a 
                         liquefa{\c{c}}{\~a}o do enxofre permitiu a 
                         manuten{\c{c}}{\~a}o da atividade em n{\'{\i}}vel elevado por 
                         um tempo prolongado. Quando das rea{\c{c}}{\~o}es com 
                         adi{\c{c}}{\~a}o de 30% (v/v) de vapor de {\'a}gua, foi 
                         constatado que, para qualquer temperatura, a reatividade foi 
                         mantida em um n{\'{\i}}vel m{\'a}ximo (t100=100%), por um tempo 
                         prolongado, que mesmo ap{\'o}s 288h, n{\~a}o apresentou qualquer 
                         ind{\'{\i}}cio de desativa{\c{c}}{\~a}o. Importante frisar 
                         que, nesta {\'u}ltima condi{\c{c}}{\~a}o, o carregamento em 
                         enxofre atingiu cerca de 60% da massa inicial do catalisador, 
                         indicando que a capacidade de armazenamento de enxofre pelos 
                         materiais aqui investigados {\'e} superior {\`a}queles relatados 
                         na literatura. ABSTRACT: Over the last few decades, sulfur 
                         recovery from the H2S-containing acid gases have become more and 
                         more important due to the ever increasing standards of efficiency 
                         required by environmental protection measures. The general trend 
                         is to selectively transform H_2S into elemental sulfur which is a 
                         valuable product, by the modified Claus process. However, due to 
                         thermodynamic limitations of the Claus equilibrium reaction, 
                         typical sulfur recovery efficiencies are only 96% for a three 
                         stage reactor plant. The present work studies different parameters 
                         in this reaction, employing nickel supported on macro-structured 
                         carbon nanofibers. These materials have the advantage of easy 
                         handling in industrial application. A carbon nanofibers based 
                         catalytic support was prepared by impregnation of 2wt.% of nickel 
                         on a carbon felt, followed by a catalytic decomposition of a 
                         mixture containing ethane and hydrogen. Later, this support was 
                         impregnated with the nickel precursor, so the metal levels 
                         obtained were between 0.16 and 15wt.%. The support and the 
                         catalysts were characterized by: scanning electron microscopy; 
                         specific area analysis (BET); and helium picnometry. In the first 
                         phase of testing, the O_2/H_2S ratio and the nickel impregnated in 
                         the catalyst were studied using design of experiments methodology, 
                         by the surface response method. The results revealed that the 
                         nickel loading, when increased until 6%, raises the number of 
                         active sites and the sulfur yield, however, between 6-11,6% it 
                         does not occur, which may indicate an apparent growth of metal 
                         particles. Regarding the O_2/H_2S ratio, it was possible to 
                         observe that when employing it above of the stoichiometric ratio 
                         (0.5), the increasing of O_2 did not affect the yield of the 
                         reaction, which suggests that, in these conditions, the partial 
                         order on the O_2 reagent is zero. Afterwards, two other parameters 
                         were studied: the reaction temperature and the addition of water 
                         to the reaction medium. For tests with temperature variations and 
                         without addition of water to the reaction medium, two different 
                         phenomena were identified: at 120C, the absence of water in 
                         liquid state hindered the sulfur removal from the catalytic sites, 
                         whereas at 180C, the sulfur liquefaction allowed the maintenance 
                         of high activity for a long time. For the reactions performed with 
                         addition of 30vol.% of water vapor, it was observed that, for any 
                         temperature, the reactivity was maintained at a maximum level 
                         (t100=100%) for a long time and, even after 288h, did not present 
                         any evidence of deactivation. Its important to mention that, in 
                         this last condition, the sulfur loading was about 60% of the 
                         catalyst initial mass, indicating that the sulfur storage capacity 
                         for the materials investigated here is higher to those reported in 
                         the literature.",
            committee = "Nono, Maria do Carmo de Andrade (presidente) and Vieira, Ricardo 
                         (orientador) and Cruz, Gilberto Marques da and Cobo, Ant{\^o}nio 
                         Jos{\'e} Gomes",
           copyholder = "SID/SCD",
         englishtitle = "Carbon nanofibers based filter to sulfur removal from efluents 
                         rich in H2S.",
             language = "pt",
                pages = "107",
                  ibi = "8JMKD3MGP8W/35R6R88",
                  url = "http://urlib.net/rep/8JMKD3MGP8W/35R6R88",
           targetfile = "publicacao.pdf",
        urlaccessdate = "2019, Dec. 11"
}


Close