@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
120°C, 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 180°C, 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 120°C, the absence of water in
liquid state hindered the sulfur removal from the catalytic sites,
whereas at 180°C, 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/ibi/8JMKD3MGP8W/35R6R88",
targetfile = "publicacao.pdf",
urlaccessdate = "2024, Apr. 28"
}