Síntese de zeólitas LTA para captura de CO2
Global warming is the main environmental problem faced by modern humanity and CO2 is the main gas causing this problem. For this reason, several studies have been carried out to mitigate or reduce its emission into the atmosphere. Among these researches, adsorptive processes using zeolites appear...
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| Formato: | Dissertação |
| Idioma: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/handle/123456789/53021 |
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| Resumo: | Global warming is the main environmental problem faced by modern humanity and CO2
is the main gas causing this problem. For this reason, several studies have been carried
out to mitigate or reduce its emission into the atmosphere. Among these researches,
adsorptive processes using zeolites appear as a possibility to minimize this problem. In
this work, LTA zeolites using three different silicon sources were synthesized to be
applied in CO2 adsorption, namely, LIASA industrial waste, light coal ash waste and
aerosill 200 silica. exchange the sodium present in its structure for calcium being applied
in the adsorption of CO2 at room temperature (23°C) up to 7500 mmHg, and at 200°C
from 3750 mmHg to 18750 mmHg. N2 adsorption tests were also carried out under the
same conditions as CO2 and adsorption with a CO2/CH4 gas mixture in a fixed bed to
calculate adsorption selectivity. Finally, the analysis of adsorption cycles was carried out
under room temperature conditions (23 °C) up to 7500 mmHg. X-ray diffraction analysis
(XRD) and scanning electron microscopy (SEM) indicated that the LTA zeolite was
obtained from all the raw materials used, however, with different crystallinities. The
analyzes of argon adsorption/desorption, at 77K, demonstrated that the cationic exchange
was carried out and, the LTA zeolites in the calcic form, were obtained, being evidenced
by the increase of the specific area, volume of pores and volume of micropores. The
materials used showed good adsorption capacity for CO2, ranging between 2.64 mmol/g
and 4.25 mmol/g at 7500 mmHg, with the standard and commercial materials obtaining
the best results, the materials obtained from coal ash, exhibited the lowest adsorption
capacity, whereas the zeolite synthesized by the LIASA residue showed an adsorption
capacity close to standard zeolite and commercial zeolite. After ion exchange, the amount
adsorbed by all materials increased considerably, maintaining the order of adsorbed
amount, ranging from 2.55 mmol/g to 5.39 mmol/g at 7500 mmHg. When comparing
with the models of Langmuir, Freündlich and Temkin, it was seen that all of them
presented a greater approximation with the model of Temkin, characterizing a primarily
physical adsorption in the material. When analyzing the isotherms under the most extreme
conditions, we see that the material also has a good adsorption capacity, and with
increasing pressure, the amount adsorbed continues to increase even at higher
temperatures. Analyzing the selectivity of the materials for CO2 and N2, we see that the
material synthesized from waste showed greater selectivity both in the sodium form with
5.04 mmolCO2/mmolN2 at 7500 mmHg, and in the calcium form with selectivity equal
to 3.90 mmolCO2 /mmolN2 at 7500 mmHg, which may mean that, due to its lower
crystallinity, part of its porous structure has defects that prevent greater diffusion of N2
compared to CO2. A good selectivity was also observed in the adsorption in a fixed bed
with a CO2/CH4 gas mixture, where it is possible to see that the material has selectivity
to CO2, however, in this case, the commercial zeolite with calcium presented the best
results of adsorption and selectivity, presenting a total selectivity equal to 4.39
mmolCO2/mmolCH4. In the adsorption cycles, it is noticed that all materials show a
small decrease from the second cycle onwards and after five cycles, the greatest reduction
was 0.34 mmol/g for the standard zeolite, which may be related to some process of
chemisorption going on in the material, as the material has not been fully regenerated
with a high vacuum for one hour. |
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