Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Özkan, Seher Fehime

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  • Master Thesis
    Gas adsorption in volumetric system
    (Izmir Institute of Technology, 2003) Becer, Metin; Özkan, Seher Fehime; Özkan, Seher Fehime; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    In this study, nitrogen adsorption on natural zeolitic tuff from Gördes, (Fındıcak) region and on its acid treated forms was studied. The natural zeolite, identified as clinoptilolite, has been treated with HCl, H2SO4, HNO3, and H3PO4 solutions at several concentrations to obtain the acid treated forms. Structural modifications arising from the acid treatments were determined by the techniques, namely XRD, FTIR, ICP, EDX, SEM, DTA, TGA, and microcalorimeter. Adsorption characteristics of zeolites, such as external and total surface areas, micropore volumes and pore size distributions were compared.Acid treatment of natural zeolite showed that as the acid concentrations were increased, more cations were removed from the structure, changing the Si/Al ratios from 4.04 (original zeolite) to 5.35 with H2SO4, to 6.39 with HNO3, to 10.8 with HCl and to 5.01 with H3PO4 treatments respectively. With acid treatment, the maximum nitrogen adsorption capacity at P/Po . 0.89 of natural zeolite (0.015 cm3/g) was increased to 0.089, 0.090, 0.086, and 0.050 cm3/g for HCl, HNO3, H2SO4 and H3PO4 treatments respectively. Nitrogen adsorption capacities of the zeolites increased with increasing Si/Al ratios, but further increase in concentrations caused to decrease the adsorption capacity for HCl and HNO3 treatments. HCl behaved in a different way that, dilute (1M) and highly concentrated (10 M) solutions has effect on the framework structure much more than the middle range concentrations (3 M and 5 M HCl) decreasing the nitrogen adsorption after Si/Al . 8.4 (5 M HCl).Dubinin-Raduskhevich model was used to determine the volume accessible to nitrogen (limiting micropore volume). It increased with increasing Si/Al ratios, but further increase in concentrations caused to decrease in microporous structure. The highest limiting micropore volumes (0.078 and 0.082 cm3/g), and Langmuir surface areas (213 and 226 m2/g) were obtained with the 5 M HCl and 2 M HNO3 treated samples respectively without any noticable loss in crystallinity.
  • Master Thesis
    Co2, N2 and Ar Adsorption on Modified Zeolites
    (Izmir Institute of Technology, 2004) Ertan, Aslı; Özkan, Seher Fehime; Özkan, Seher Fehime; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    In this study, CO2 and N2 adsorption on synthetic zeolites namely, 5A and 13X, and acid treated natural zeolites was investigated by using volumetric adsorption device, ASAP 2010. The natural zeolites and its acid treated forms with HCl (1M, 3M and 5M), HNO3 (2 M), and H3PO4 (1.1 M) solutions at 60 oC for 6 or 3 hours were used as adsorbent. The effect of the acid treatment and temperature on the adsorption properties of the zeolites for the CO2 and N2 gases at 5 and 25 oC was studied. Langmuir, Sips, Vrial and Dubinin-Astakhov model equations were applied to the adsorption data in order to determine the affinity and the heterogeneity of the adsorbents.Calorimetric properties of the zeolites were also studied using CO2, N2 and Ar gases through a Tian-Calvet calorimeter, Setaram C80 at 25 oC. Isosteric heat of adsorption of the gases adsorbed on the adsorbents under investigation was determined at 5 oC and 25 oC using Clasius- Clapeyron equation. These results were compared with the heat of adsorptions obtained from the calorimetric studies directly.The zeolite treated with 1.1 M H3PO4, P1 has the highest adsorption capacity (2.24 mmol/g and 0.67 mmol/g) for CO2 and N2 while the natural zeolite has only 2.08 mmol/g and 0.51 mmol/g respectively at 5 oC. Synthetic zeolites 13X and 5A have higher CO2 (6.82 mmol/g and 5.46 mmol/g respectively) and N2 adsorption capacities (0.31mmol/g and 0.91 mmol/g respectively) than natural zeolites at 5 oC. Langmuir b parameter called the affinity constant decreased as adsorption temperature increased for CO2 and N2 adsorption. The Sips model t parameter characterizing the system heterogeneity is higher for CO2 adsorption than N2 adsorption and decreases with increasing temperature. This indicates that the CO2 molecules give more specific interactions than N2 molecules. The pure component selectivities of CO2 over N2 calculated from Langmuir equation, are the highest for NCW zeolite as 408 at 25 oC. This value follows by P1 zeolite which is 151 at the same temperature.The highest differential heat of adsorption value (80.29 kJ/mol) at zero coverage for CO2 also belongs to P1 sample. The heterogeneity parameters of the model equations applied also indicated that P1 sample is more heterogeneous when compared to other acid treated natural zeolites. Finally as expected, for both N2 and CO2 as temperature increased from 5 to 25 oC, the adsorbed amounts decreased when fresh samples were used at each run in the experiments. The temperature difference had a greater effect on N2 adsorption rather than CO2.
  • Master Thesis
    Chemical Behaviour of Clinoptilolite Rich Natural Zeolite in Aqueous Medium
    (Izmir Institute of Technology, 2005) Polatoğlu, İlker; Özkan, Seher Fehime; Özkan, Seher Fehime; 03.02. Department of Chemical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    In this study the chemical behavior of natural zeolite from Gördes Türkey and its Na2CO3 treated form was investigated in acid (hydrochloric acid, lactic acid, acetic acid) and basic (sodium hydroxide) solutions. Synthetic gastric juice (hydrochloric acid and 0.4 % pepsin at pHi.2) was also prepared in order to examine the neutralizing capacity of zeolite for high acid concentration of stomach. The change in proton and hydroxyl concentration with time was studied by putting the different amount of zeolites into the various concentrations of acid and base solutions.It was found that natural zeolite tended to increase the pH of acidic solution while decreased the pH of basic solution depending on the concentration of proton or hydroxyl ions in solution and zeolite amount. The proton or hydroxide ions entered to the zeolite could not balance the cations released from zeolite structure. Therefore not only ion exchange, but also adsorption, cation hydrolysis, dissolution of Al and Si, complex formation and precipitation can be occurred. The neutralizing capacity of modified zeolite with sodium carbonate was higher than untreated ones. In the study conducted with synthetic gastric juice, 0.5 g modified zeolite did not significantly affect the pepsin activity of the medium and increased the pH to 2.9 which was between the normal ranges of stomach acid (2.9-3.1). In all aqueous studies conducted by using natural zeolite there was no change observed at the surface charge of the zeolite. According to characterizations performed it is understood that there was no significant change and the structure was stable. For these reason zeolite can be used as solid buffer in aqueous medium.