Transportadores sólidos de oxigênio à base de ferro e níquel para aplicação no processo de reforma do metano com recirculação química
The actual global energy demand has caused an increase in anthropogenic emissions of greenhouse gases from the burning of fossil fuels. Because of that, energy production processes that release smaller amounts of these gases into the atmosphere have been the target of studies in recent years. Amo...
Na minha lista:
| Autor principal: | |
|---|---|
| Outros Autores: | |
| Formato: | Dissertação |
| Idioma: | pt_BR |
| Publicado em: |
Brasil
|
| Assuntos: | |
| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/28226 |
| Tags: |
Adicionar Tag
Sem tags, seja o primeiro a adicionar uma tag!
|
| Resumo: | The actual global energy demand has caused an increase in anthropogenic emissions of
greenhouse gases from the burning of fossil fuels. Because of that, energy production processes
that release smaller amounts of these gases into the atmosphere have been the target of studies
in recent years. Among these processes, Chemical Looping Reforming (CLR) of methane has
gained attention because, through this process, methane is converted into synthesis gas, a
mixture of carbon monoxide and hydrogen, without the release of CO2. Moreover, hydrogen is
a clean combustion energy source, that means it does not release pollutants into the atmosphere,
since its burning results in only water and heat. One of the determining factors of the CLR
process efficiency lies in the performance of a solid oxygen carrier, which is a metal oxidebased material that promotes the conversion of the fuel into its reaction products, and it is
necessary the development of a material that possess favorable properties and characteristics to
this process. Based on this, this master's thesis aims to synthesize and characterize iron and
nickel-based solid oxygen carriers supported in calcium aluminate and to evaluate the most
promising to be applied in CLR processes. Calcium aluminate support was synthesized from
eggshell as the only calcium source, since it is a rich CaCO3 residue; then, iron and nickel were
impregnated in this support through the incipient wetness impregnation technique, in order to
obtain 4 oxygen carriers: one with iron only, one with nickel only and two containing iron and
nickel in different proportions (30% and 70%). Oxygen carriers were characterized by X-ray
diffraction (XRD), temperature programmed reduction (TPR), scanning electron microscopy
(SEM) with EDS and reactivity by thermogravimetry techniques. Through XRD results,
CaFe2O4 and CaFe5O7 phases were identified, however they suffered an irreversible reduction
after the exposure to methane; oxygen transport to the reaction media was then performed by
the reduction of hematite, magnetite and iron aluminate present in the oxygen carriers. NiO was
the only nickel-based phase identified in the materials. The observation of the reduction profiles
of the oxygen carriers indicates that the increase in the iron content leads to an increase in the
reduction temperatures, suggesting a decrease in the oxygen transport rate. Additionally, it was
observed through SEM images that the oxygen carriers exhibited different morphologies
depending on the oxidation state, and a fine dispersion of the active phases on the support
surface was observed in EDS mapping. From the reactivity tests by thermogravimetry it was
observed that the oxygen carriers presented the capacity of reduction and oxidation in
successive chemical cycles using methane, and an increase in the oxygen transport rate was
reported as the nickel content increased. The iron-only based material achieved a maximum
conversion in the order of only 68% in 155 seconds, being considered as the less reactive of
this study. However, for the nickel containing materials, solids conversions of at least 80% were
achieved in time intervals ranging from 30 seconds in the oxidation step to 66 seconds in the
reduction one. The evaluated oxygen carriers, except for the iron-only based material, are
suitable for application in CLR processes. |
|---|