Síntese de zeólitas LTA para captura de CO2

• Ano de defesa: 2023
• Autor(a) principal: Silva, Aryandson da
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Rio Grande do Norte; Brasil; UFRN; PROGRAMA DE PÓS-GRADUAÇÃO EM QUÍMICA
• Palavras-chave em Português: Zeólita LTA; Adsorção de CO2; Resíduos; Seletividade; Armazenamento; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA
• Link de acesso: https://repositorio.ufrn.br/handle/123456789/53021

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.