Phd Degree / Doktora

Permanent URI for this collectionhttps://hdl.handle.net/11147/2869

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Author: search.filters.author.Yılmaz, SelahattinLanguage: search.filters.language.en

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  • Doctoral Thesis
    Epokside Soya Yağı Alkoliz Reaksiyonu için Katı Asit Katalizör Geliştirilmesi
    (2025) Arıkaya, Azime; Yılmaz, Selahattin
    Bu çalışma, metanol ile epoksitlenmiş soya fasulyesi yağının (ESO) alkolizi için çeşitli mezogözenekli katı asit katalizörlerinin sentezlenmesi ve değerlendirilmesine odaklanmıştır. Karışık metal oksit (TiO2-SiO2), mezogözenekli karbon (CMK-3) ve silika (SBA-15) olmak üzere üç farklı türde malzemeler, sülfatlar, sülfonik gruplar, sülfanilik gruplar ve metal katkısı (La ve Sn) ile fonksiyonelleştirilmiştir. Sülfatlanmış La katkılı TiO2-SiO2 (S-La-TiO2-SiO2), sülfonik ve sülfanilik asit ile işlevselleştirilmiş CMK-3 (CMK3-PrSO3H ve CMK3-PhSO3H), sülfanilik asit ile fonksiyonelleştirilmiş SBA-15 (SBA15-PhSO3H), sülfonik asit ile fonksiyonelleştirilmiş Sn katkılı SBA-15 (Sn-SBA15-PrSO3H) hazırlanan katalizörlerdir. S-La-TiO2-SiO2 sülfatlama ile modifiye edilirken ve Sn-SBA15-PrSO3H için ko-kondensasyon yöntemi uygulanırken, diğer katalizörler aşılama ile hazırlanmıştır. Katalizör karakterizasyonu, bu katalizörlerin mezogözenekli olduğunu ve fonksiyonelleştirme sonrasında yüzey alanlarının azaldığını göstermiştir. Katalizörler farklı asitlik değerlerine sahipken Sn-SBA15-PrSO3H 4.5 mmol/g ile en yüksek asitlik değerini göstermiştir. Sadece CMK3-PrSO3H, SBA15-PhSO3H ve Sn-SBA15-PrSO3H katalizörlerinin reaksiyon ortamında kararlı olduğu bulunmuştur. Silan öncüsü kullanılarak ko-kondensasyon metoduyla hazırlanan Sn-SBA15-PrSO3H, en yüksek epoksi dönüşümünü (6 saatte %91.4) ve verimi (%88.2) sağlamış ve 3 döngüye kadar iyi bir yeniden kullanılabilirlik göstermiştir. Bu üstün aktivite, sülfonik gruplardan gelen Brønsted asitleri ile kalaydan gelen Lewis asitlerinin sinerjik etkisine atfedilmiştir. Optimum reaksiyon koşulları 60 °C, katalizör yüklemesi yağın ağırlıkça %3'ü ve ESO-metanol molar oranı 1:9 olarak belirlenmiştir. Elde edilen biyopoliol ürün, 185.4 mg KOH/g OH sayısı ile düşük polimerizasyon (4.07 Pa.s viskozite ve 1187 g/mol moleküler ağırlık) göstermiştir. Elde edilen ürün kaplama amaçları için uygun bulunmuştur. Ayrıca, çift bölgeli Langmuir-Hinshelwood-Hougen-Watson kinetik modeli, deneysel verileri doğru bir şekilde tanımlamıştır. Aktivasyon enerjisi 99.2 kJ/mol olarak belirlenmiştir.
  • Doctoral Thesis
    Catalytic Conversion of Glucose To Alkyl Glucosides
    (Izmir Institute of Technology, 2020) Mutlu, Vahide Nuran; Yılmaz, Selahattin
    In this study, it was pursued to develop acidic mesoporous catalysts for the synthesis of octyl glucosides. Butyl glucoside synthesis was used for catalyst screening. Tungstophosphoric acid (TPA) incorporated mesoporous silica (TPA-SBA-15), sulfated La incorporated titania-silica (SO4/La-TiO2-SiO2), organosulfonic acid functionalized mesoporous silica (Propyl-SO3-SBA-15), and sulfated mesoporous carbon (SO4/CMK-3) catalysts were prepared for this purpose. The effects of the active species (sulfates, tungstophosphoric acid and organosulfonic acid) and promoter (La) on the catalyst properties and activity were investigated. All the catalysts had mesoporous structure and high surface area. The acidity and acid site character varied depending on the catalyst type and amount of the active sites. La promoter was found effective to enhance the sulfation performance and to improve the stability of sulfates. The TPA-SBA-15 catalysts provided high glucose conversions (over 99%) and butyl glucoside yields (over 95%) due to their acidity, Keggin ion structure and pore size. The SO4/La-TiO2-SiO2 catalysts and SO4/CMK-3 catalysts were also active with glucose conversions of 74.4 % and 70 % respectively. The reaction parameters such as the reaction temperature (117 and 100 oC) and catalyst amount (20 and 30 wt% wrt. glucose) were studied in butyl glucoside synthesis over TPA-SBA-15 and SO4/La-TiO2-SiO2 which were the most active catalysts. These catalysts were found to be reusable in glycosidation with 1-butanol. Octyl glucoside synthesis was carried out via direct glycosidation. The octyl glucoside yields obtained over TPA-SBA-15 and SO4/La-TiO2-SiO2 catalysts were above 55 % and 43 % respectively. The catalysts were found promising for further investigations.
  • Doctoral Thesis
    Development of Carbon Nanotube Embedded Polyacrilonitrile/Polypyrrole Electrospun Nanofibrous Scaffolds
    (Izmir Institute of Technology, 2017) İnce Yardımcı, Atike; Yılmaz, Selahattin
    In this study, electrospun polyacrilonitrile (PAN)/ polypyrrole (PPy) nanofibers containing different PPy content (10, 25, and 50 wt%) were prepared. Different carbon nanotube (CNT) amounts (1, 2, 3, and 4 wt%) were embedded into PAN/PPy nanofibers to improve their mechanical and electrical properties. CNT functionalization was carried out to solve agglomeration problem and functional CNTs effects on PAN/PPy nanofiber morphology was examined. Alignment of nanofibers was studied to improve mechanical properties of nanofibers. Obtained PAN/PPy and PAN/PPy/CNT nanofibers were utilized as kerotinocytes scaffold. PAN/PPy/CNT and aligned and randomly oriented PAN/PPy nanofibers were examined for bone marrow osteogenic differentiation of mesenchymal stem cells (MSCs). 10 wt% PPy content was optimum in terms of mechanical properties and usage with CNTs. Higher strain was observed for 10 wt% PPy content which was 23.3 %. When as-grown MWCNTs were added into PAN/PPy, disordered nanofibers were formed. To improve interficial properties of these composites, as-grown CNTs were functionalized with H2SO4/HNO3/HCl solution. Upon functionalization, formation of hydroxylic and carboxylic groups were detected on the CNT surfaces. TEM examination of the nanofibers obtained with these CNTs showed decrease in beads formation. The functionalized CNTs were well dispersed within the electrospun nanofibers and aligned along the direction of nanofibers. The electroactivity of the fibers indicated that these nanofibers could be used as electrochemical actuator in acidic solutions. PAN/PPy and PAN/PPy/CNT nanofibers supported the attachment and proliferation of keratinocytes and osteogenic differentiation of MSCs. It was found that these nanofibers could be utilized as scaffolds for both cell types.
  • Doctoral Thesis
    Selective Fructose Dehydration To 5-Hydroxymethylfufural by Heterogeneous Sulfated Catalysts in Different Solvents
    (Izmir Institute of Technology, 2016) Kılıç, Emre; Yılmaz, Selahattin
    In the present study, different sulfated (SO4/ZrO2, SO4/SiO2, SO4/AC, SO4/TiO2SiO2 and SO4/Ti-SBA-15) and zirconium sulfate loaded (ZrSO4/SiO2 and ZrSO4/AC) catalysts were prepared and characterized. Effect of sulfur content (2.5, 3.0 and 3.5 wt. %) in SO4/ZrO2, effect of Ti content (2 and 6 wt. %) in SO4/ TiO2SiO2 and SO4/Ti-SBA-15, also La incorporation in to SO4/TiO2SiO2 and SO4/Ti-SBA-15 were investigated. Prepared catalysts were tested in fructose dehydration using dimethylsulfoxide (DMSO), water and biphasic aqueous solvents which were water-MIBK and water- MIBK-butanol. Effect of reaction temperature (110, 160 and 200 oC) and effect of fructose/catalyst weight ratio (WFr/Wcat = 0.5, 1.0 and 2.0) on activity and selectivity were investigated. Activity tests were performed in a batch reactor under N2 atmosphere. Reusability tests were carried out up to 4 times. Sulfated catalysts showed different activities. However, there was sulfur leaching in all of them except SO4/TiO2SiO2 and SO4/Ti-SBA-15. This was due to chelating bidendate bond formation between S, Ti and S. Sulfur leaching was also observed over zirconium sulfate loaded catalysts. Acidity of the catalysts increased with sulfur and Ti content; and also La addition. Sulfation created Brønsted acid sites. The most active, selective and stable catalyst was found to be SO4/La-TS-6 (95 % HMF selectivity at 58 % fructose conversion at 110 oC) in DMSO. Testing of this catalyst in water gave high amount of byproducts. Introducing second phase (MIBK) to water, improved HMF selectivity significantly (up to 78 %) and reduced conversion (by 7 %). Fructose dehydration kinetics was also investigated over this catalyst in water- MIBK-butanol (the most selective environmental benign solvent). Selectivity to HMF increased with reaction temperature up to 160 oC, above which it dropped. Increase in WFr/Wcat from 0.5 to 2.0, reduced the selectivity to HMF from 98 to 82 % at high fructose conversions (~90 %). Reaction was found to be 1st order in fructose concentration.