Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
Browse
21 results
Search Results
Master Thesis Esterification of oleic acid with methanol on structured solid acid catalysis(01. Izmir Institute of Technology, 2024) Büyükkapancı, Yunus; Şeker, ErolBu çalışmada, Oleik Asit metanol ile birlikte Sülfonlanmış Alüminyum Silika (SAS) heterojen asidik katalizörü üzerinde gerçekleştireceği esterifikasyon reaksiyonu incelenecektir. Araştırma, farklı metanol/yağ asidi mol oranları (9/1-21/1), katalizör miktarları (%10-%20) ve reaksiyon sürelerinin (3s–9s) 105°C sıcaklıkta reaksiyon verimliliği üzerindeki etkisini Box Bhenkhen yardımı ile değerlendirmeyi amaçlamaktadır. Katalizörlerin aktivitesi iki farklı katalizör formu (toz, yapısal) ele alınarak değerlendirilecektir. Bu çalışma, varyans analizi istatistiksel sonuçlarına göre, toz katalizör varlığında gerçekleştirilen deneylerde reaksiyon süresinin dönüşüm değerleri üzerinde en büyük etkiye sahip olduğunu göstermektedir. Reaksiyon süresi uzadıkça dönüşüm oranları hızlı bir şekilde artmıştır. Ayrıca, kullanılan katalizör miktarı da doğrudan etkili olmuş ve en yüksek dönüşüm oranı, Alkol/FFA oranının 9/1 olduğu durumda elde edilmiştir. Ayrıca, yapısal katalizörlerin varlığında gerçekleşen reaksiyonun dönüşüm değerinin, toz formundaki katalizörlerin değerleriyle karşılaştırılabilir olduğu tespit edilmiştir. Ayrıca yapılandırılmış katalizörlerde toz katalizöre göre ayırma adımına gerek kalmamıştır.Master Thesis Molecular Modelling of the Effect of Alkali Promoters on Co Adsorption and Dissociation on the Co(111) Surface(2023) Özbek, Özüm; Kızılkaya, Ali CanFischer-Tropsch Synthesis (FTS) is a surface polymerization process that has been industrially used to convert non-petroleum feedstocks to synthetic transportation fuels. Modification with an alkali promoter of the Co-based catalysts provided promising results to obtain hydrocarbons with enhanced olefin content in FTS. Activation of CO is the key factor to achieve desired end products in FTS, yet the mechanism related to the CO dissociation behavior on alkali promoted cobalt surfaces remains unknown. This study aims to examine the impact of alkali promoters (Li, Na, K) on the adsorption and dissociation characteristics of CO on the Co(111) surface using Density Functional Theory (DFT). Our results revealed that CO adsorption energy increased by 32-37% with alkali addition, yet H adsorption energy remained relatively unchanged. The effect of alkali addition on CO dissociation routes were also examined. The high activation barrier (>200 kJ/mol) makes it improbable for direct CO dissociation to occur on alkali promoted Co(111) surfaces under FTS conditions. For H-assisted pathways, alkali addition increased the activation barrier for HCO and H2CO dissociation, overall reducing the H-assisted CO dissociation rate. It was found that alkali addition makes the surface more carbophilic since the C adsorption energy increased by 7-11% upon alkali addition. Also, with increasing C concentration on the Co(111) surface, subsurface carbon geometries became more stable. Ultimately, it is concluded that alkali promoters of Li, Na and K have similar effects on CO adsorption and dissociation on the Co(111) surface.Master Thesis Esterification of Free Fatty Acid Obtained From Waste Cooking Oil Over Solid Catalyst(Izmir Institute of Technology, 2022) Karacasulu, Cem; Şeker, Erol; Şeker, ErolThe objective of this study was to investigate effect of reaction temperature, catalyst weight percentage and composition of Al2O3/SiO2 on conversion of FFA obtained from waste cooking oil (WCO) to take place esterification reaction by using Box-Behnken design. Statistical analysis demonstrates that catalyst weight percentage and temperature were insignificant statistically. Alumina composition was found as significant parameter at certain conditions by considering statistical analysis. It was seen that conversion of Free Fatty Acid (FFA) increases as composition of Al2O3 in Alumina/Silica catalyst increases. %80 Al2O3/20% SiO2 catalyst was found as promising catalyst since conversion of FFA with the catalyst was 32% at 80°C and 15:1 alcohol to FFA ratio. Besides, it was found that alcohol to FFA ratio affected the conversion reversely. When alcohol to FFA ratio was reduced to 2:1, conversion of FFA increased to 41%. The prepared catalysts were characterized by XRD and TPD analysis. Activity of catalysts were attributed to acidic strength and Bronsted acid sites on the aluminum sulfate in the catalysts. After screening effects of catalysts and reaction conditions, optimum levels of parameters were used to investigate the esterification reaction of model WCO. This reveals that conversion of FFA was found as 11% at 80°C and 15:1 alcohol to FFA ratio. Finally, the proposed catalyst does not have catalytic activity of hydrolysis reaction of oil at applied conditions.Master Thesis Biolubricant Production Over Sulfated Ti-Sba and Tio2-Sio2 Based Mesoporous Catalysts(01. Izmir Institute of Technology, 2022) Özperçin, Tuğçe; Yılmaz, SelahattinProduction of ecofriendly biodegradable lubricants from vegetable oils is an attractive alternative to petroleum derived lubricants for environmental protection. This study presents an investigation for the production of biolubricants via ring opening reaction of epoxidized soybean oil using the mesoporous solid acid catalysts. SO4/SBA- 15, SO4/Ti-SBA-15, SO4/TiO2-SiO2 and SO4/La-TiO2-SiO2 catalysts were prepared and characterized. In addition, effect of increasing titanium content on SO4/Ti-SBA-15 (Si/Ti: 10, Si/Ti: 6) and effect of sulfation source (ammonium sulfate and chlorosulfonic acid) on Ti-SBA-15 and La-TiO2-SiO2 properties, activities and stabilities were studied. Activity and stability of all the catalysts were tested in the ring opening reactions of epoxidized soybean oil with 2-propanol at 80 oC with 10/1 alcohol-epoxide mol ratio. After determination of the two most stable and active catalysts, reactions were also performed with 2-ethylhexanol at 100 oC with 6/1 alcohol-epoxide mol ratio. Products were analyzed by titration, FTIR and H-NMR. Also, thermal stability and low temperature behavior of products were determined by thermogravimetric analysis and differential scanning calorimetry. Prepared catalsysts had mesoporous structure and stronger acid sites by attachment of sulfate groups The catalysts showed a serious leaching when they were sulfated with ammonium sulfate. On the other hand, chlorosulfonic acid treatment enhanced significantly stability of catalyst. Furthermore, increasing of titanium content and sulfation with chlorosulfonic acid increased the acidity of catalysts compared to ammonium sulfate. The SO4/Ti-SBA-15-6(CS) catalyst (Si/Ti:6 mole ratios and chlorosulfonic acid sulfated) was found as the most stable and active catalyst. It provided 62 % (12 h) and 90 % (18 h) conversion in the reactions with 2-propanol and 2-ethylhexanol, respectively. All products were found as thermally stable up to 300 oC showing that ring opening reaction did not affect thermal stability. Nevertheless, it affected positively low temperature properties and better low temperature properties were obtained from the products of reactions with 2-ethylhexanol. However, its influence on the products obtained from 2-propanol was not prominent.Master Thesis Butyl Esters Production From Canola Oil Over Heterogeneous Base Catalysts(01. Izmir Institute of Technology, 2021) Akın, Oğuzhan; Akın, Oğuzhan; Şeker, Erol; Şeker, ErolIn this study, transesterification reaction of canola oil with butanol over calcium oxide alumina catalyst was investigated with varying butanol:lipid molar ratios, catalyst amount and reaction time. Catalysts were prepared with the single step sol-gel method, and the activity of synthesized catalysts were investigated for two different forms of catalysts as powder and structured form. In the case of powdered catalysts, at butanol:lipid molar ratios of 9 and 24 with 6 wt% of lipids as catalyst amount, leaded 32% and 45% butyl esters yield in 1 hour. On the other hand, ~70% butyl esters yield has obtained at butanol:lipid molar ratios of 48 and 60 for the reaction time of 1 hour, while 89% yield had achieved when the reaction lasted for 4 hours at butanol:lipid molar ratio of 48. The necessity of mild basic strength and high butanol:lipid molar ratio was found to obtain high butyl esters yield. At high butanol lipid ratios of 48 and 60, it was observed that glycerolysis reaction occurs and promotes reverse transesterification reactions in first 30 minutes of the experiments. In the case of structured catalysts, lower butyl esters yields than powder catalysts were obtained, yet they eliminated the need for catalysts separation step in the experiments. Reusability tests showed that catalyst activity has decreased due to calcium ion leaching in the first hour of reaction and kept its activity constant for the rest of the reaction.Master Thesis Epoxidation of Soybean Oil Over Mesoporous Titanium and Niobium Incorporated Sba-15 Catalysts(Izmir Institute of Technology, 2019) Kalkandelen, Mustafa; Yılmaz, SelahattinSoybean oil is an abundant, cheap and nontoxic biomass source and contains triglycerides with unsaturated fatty acids which can be easily modified by epoxidation. In this study, mesoporous Ti-SBA-15 with two different Si/Ti molar ratios, MoO3/Ti-SBA-15 with two different MoO3 mass ratios and Nb-SBA-15 with two different Si/Nb molar ratios were prepared as catalysts for soybean oil epoxidation reactions. Tertbutanol and ethyl acetate was used as solvent and H2O2 was utilized as oxidant. BET analysis indicated existence of high surface area of the catalysts which ranged between 650 and 950 m2/g. XRD analysis indicated successful incorporation of Nb and Ti into SBA-15 structure. Epoxidation reactions were carried out successfully using Ti-SBA-15 and Nb-SBA-15 catalysts in tertbutanol at 75 ºC for 6 h. Utilizing ethyl acetate as solvent was caused undesired catalyst behaviour such as precipitation, gelation and aggradation. No further investigations were carried out with ethyl acetate. Epoxidation products were analysed with H-NMR, FTIR and analytic methods. Ti-SBA-15 catalysts provided only 10 % double bond conversion and 49 % epoxide selectivity. They were not very active. Nb-SBA-15 catalysts exhibited high acidity. They provided 28 % double bond conversion and 31 % epoxide selectivity. Best yield was obtained with Nb-SBA-15 (10) catalyst as 6.49 %. Stability tests of catalysts indicated that Nb and Ti did not leach whereas severe leaching was observed with Mo. Also, homogenous epoxidation reaction with H2SO4 was carried out for comparison with heterogenous catalysts. Results indicated that, heterogenous catalysts were not competitive with homogenous catalyst.Master Thesis A Comparative Study on the Photocatalytic Activity of Dye-Sensitized and Non-Sensitized Graphene Oxide-Ti̇o2 Composites Under Simulated and Direct Sunlight(01. Izmir Institute of Technology, 2019) İlhan, Hatice; Varlıklı, Canan; Demir, Mustafa MuammerAmine modified graphene oxide (mGO) and TiO2 composite was synthesized by low temperature hydrothermal method. Characterization of the synthesized material was carried out by using X-ray diffraction, X-ray photoelectron spectroscopy, and BET analysis techniques. The films of mGO:TiO2 and formerly synthesized TiO2, N-TiO2, GO-TiO2 and GO:N-TiO2 were fabricated by doctor blade method and employed as photocatalysts for the photodegradation of Rhodamine-B (RhB) dye under simulated (Xe lamb) and direct sun-light. P25 was also used as reference photocatalyst for all of the synthesized ones. Photodegradation of RhB was monitored by UV-Vis spectroscopy. Among all the catalysts, GO:N-TiO2, the composite of GO and N-doped TiO2, presented the best photocatalytic activity and although the activity of mGO:TiO2 was better than the activities of P25 and TiO2, it presented lower degradation rate constant even than that of the N-TiO2. It is proposed that increased abundance of C-C bonds and decreased number of oxygenated functional groups on mGO:TiO2, in addition to the morphological difference between GO (sheet like) and mGO (dot like) has great influence on their photocatalytic activities. Among the GO containing photocatalysts including mGO:TiO2, specific surface area (SSA) and number of RhB molecules per film volume were the lowest and particle size was the highest for mGO:TiO2. Although the number of RhB molecules per film volume was higher in mGO:TiO2 than that of the N-TiO2, it is thought that approximately 2 folds higher SSA of N-TiO2 allowed better photocatalytic performance. Additionally, the films were sensitized with PTE dye to obtain effective catalysts in visible region and reusability of the films were also tested. Degradation rate constants of all fabricated films have increased under both of the irradiation media and no significant change in rate constants were detected after the reusability tests.Master Thesis Carbon Dioxide Hydrogenation on Alumina Supported Ruthenium Catalysts(Izmir Institute of Technology, 2019) Hamza, Gökmen Oğuzcan; Şeker, ErolIn this study the effect of basicity of catalyst is investigated using different metal oxide supported Nickel and Ruthenium catalyst. The basic strength of catalysts was orchestrated with using different types of metals and different composition of supports. In this study Al2O3-CaO, Al2O3-MgO, Al2O3-BaO supports were used with nickel and ruthenium catalyst, which synthesized with sol-gel method. Different mass ratios of supports were used such as; 100%, 70%/30%, %50/50%, 20%/80% respectively. For all metal oxides Nickel loadings are 1 %, 5% and Ruthenium loading is 0.5%. Calcination temperature was 500 0C with 6 hours. All catalysts were used in methanation reaction with conditions varies between 300-600 0C, inlet ratio of CO2/H2 1/4 to 1/6 and GSHV 5000h-1/10000h-1. The products were analyzed using GC and catalysts were analyzed using XRD NH3-TPD and BET. Nickel load selected as 1%, magnesium supported catalysts' the main crystallites were aluminum oxide and magnesium oxide for 30%,50%,80; respectively. Calcium supported catalyst had had alumina and calcium oxide crystallites for 30%,50% respectively. Barium supported catalysts had had alumina and barium mix oxide crystallites for 30%,50% respectively. For 5% Nickel loaded 70-30% alumina magnesia mix oxide catalyst magnesia and alumina crystallites are found. Aluminum magnesium mix oxide catalysts had higher basicity than aluminum barium mix oxide catalysts for 1% nickel catalysts. Ruthenium based magnesium alumina mix oxide catalyst had higher basicity than nickel-based magnesium alumina catalysts. Ruthenium catalysts had higher total performance towards both of the reverse water gas shift reaction and carbon dioxide methanation than nickel-based catalysts.Master Thesis Development of Kinetic Model for Industrial Ethylene Oxide Catalyst by Using Model-Targeted Experimentation Approach(Izmir Institute of Technology, 2019) Sarrafi, Şahin; Şeker, Erol; Arkun, Ziya YamanEthylene oxide (EO) is produced via selective oxidation of ethylene with oxygen using a Ag supported on -Al2O3 catalyst. The ethylene epoxidation reaction is desired, whereas the ethylene and EO combustion reactions are not. Proposed study is aimed at developing a tailor-made kinetic model in order for making use in the industrial ethylene oxide reactors which are of paramount importance from the viewpoint of process economics and the greenhouse gas (GHG) induced various environmental exposures. With aging of the catalyst, the trade-off between selectivity and productivity becomes gradually more prominent. Along with the compensation of loss of active sites under the favor of increasing of the temperature, catalyst still provides sustainable commercial yields at the expense of excess feedstock consumption which in turns leads to boost GHG emissions by releasing more carbon dioxide (CO2) into the atmosphere. To maintain catalyst activity for a longest period possible, controlling process variables more preciously with a robust model is very demanding issue throughout the last two decades. Within the scope of this thesis, model-targeted experimentation approach was used assisting by gPROMS software in determining intrinsic kinetics of the commercial catalyst in use through integral reactor coupled with gas chromatography. During the course of the kinetic experiments, the effect of VCM used as a promoter together with inhibiting effects of product gases such as CO2 and EO were also investigated and included into the kinetic model to be derived.Master Thesis Effects of Manganese Promotion on Reactants and Intermediates of Fischer Tropsch Synthesis on a Model Cobalt Surface-A Density Functional Theory Investigation(Izmir Institute of Technology, 2019) Gençoğlu, Merve; Kızılkaya, Ali Can; Sevinçli, HaldunThe effects of manganese promotion on the adsorbates and specific elementary reactions of Fischer-Tropsch Synthesis (FTS) was investigated using periodic Density-Functional Theory (DFT) calculations on a close packed cobalt surface, Co(111). In particular the effects of MnO promotion on the adsorbates of CO, HCO, CH, CH2, C2H2, OH, H2O, C, O and on the reactions of direct CO dissociation, H-assisted CO dissociation and carbon hydrogenation were studied for MnO coverages of 0.25 ML and 0.11 ML. Mn was modeled in the chemical form of MnO. MnO was modeled as a singular monomer on the Co(111) surface, based on the findings from experimental studies. The results indicate that MnO promotion increases the adsorption energies of all adsorbates, except H and C2H2. In particular, CO and H2O adsorption energies increase significantly, which indicate that the selectivity increases to long chain hydrocarbons is mainly due to an increased surface coverage of CO with respect to H. The results also indicate that the relative effect of MnO on adsorption energies are strongly dependent on MnO coverage. MnO promotion is found to decrease the activation barriers for HCO and CH formation, while increasing the activation barriers for direct CO dissociation and HCO dissociation. The results point out that MnO does not promote the direct dissociation of CO and the activity increase due to Mn promotion is most probably due to a H or OH assisted CO dissociation pathway or another rate limiting step.
- «
- 1 (current)
- 2
- 3
- »