Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 8Citation - Scopus: 9Polymeric Thermal Analysis of C+h and C+h+ar Ion Implanted Uhmwpe Samples(Elsevier Ltd., 2007) Kaya, N.; Öztarhan, Ahmet M.; Urkaç, Emel Sokullu; Ila, D.; Budak, S.; Oks, E.; Tıhmınlıoğlu, Funda; Muntele, C.Chemical surface characterization of C + H hybrid ion implanted UHMWPE samples were carried out using DSC (differential scanning calorimeter) and TGA (thermal gravimetric analysis) techniques. Samples were implanted with a fluence of 10(17) ion/cm(2) and an extraction voltage of 30 kV. The study of TGA and DSC curves showed that: (1) Polymeric decomposition temperature increased, (2) T-m, Delta C-p and Delta H-m values changed while Delta C-p and Delta H-m increased. T-g value could not be measured, because of some experimental limitations. However, the increase in Delta H-m values showed that T-g values increased, (3) the branch density which indicated the increase in number of cross-link (M-c) decreased in ion implanted samples and (4) increase in Delta H-m values indicated increase in crystallinity of implanted surface of UHMWPE samples.Article Citation - WoS: 2Catalytic Activity of Heteropolytungstic Acid Encapsulated Into Mesoporous Material Structure(Walter de Gruyter GmbH, 2007) Gündüz, Gönül; Dimitrova, Rayna P.; Yılmaz, SelahattinThe paper presents a spectroscopic and catalytic study of encapsulated Keggin type heteropoly acid (12-tungstophosphoric acid, HPW) in the mesopores of MCM-41 molecular sieves. Nitrogen physisorption, FTIR, SEM, XRD and catalytic methods have been used to characterize and compare the properties of the samples. Methanol conversion, alpha-pinene isomerization and ethyl acetate oxidation have been applied as model reactions for the evaluation of acid site activity. The combined physicochemical and catalytic investigations clearly show that the introduction of 12-tungstophosphoric acid into MCM-41 causes significant changes in the properties of the sample.Article Citation - WoS: 25Citation - Scopus: 33Novel Phytochemical Cissus Quadrangularis Extract-Loaded Chitosan/Na-carboxymethyl Cellulose-Based Scaffolds for Bone Regeneration(SAGE Publications, 2018) Tamburacı, Sedef; Kimna, Ceren; Tıhmınlıoğlu, FundaMedicinal plants are attracting considerable interest as a potential therapeutic agent for bone tissue regeneration. Cissus quadrangularis L. is also a medicinal plant known with its osteogenic activity. In this study, a phytochemical scaffold was produced by incorporating Cissus quadrangularis with chitosan/Na-carboxymethyl cellulose blend by lyophilization technique. The effect of Cissus quadrangularis loading on the mechanical, morphological, chemical, and degradation properties as well as in vitro cytotoxicity, cell proliferation, and differentiation of the composites was investigated. Scanning electron microscopy images showed that porous Cissus quadrangularis-loaded scaffolds were obtained with an average pore size of 148-209 mu m which is appropriate for bone regeneration. Cissus quadrangularis incorporation enhanced the compression modulus of scaffolds from 76 to 654 kPa. In vitro cell culture results indicated that Cissus quadrangularis/chitosan/Na-carboxymethyl cellulose scaffolds provided a favorable substrate for the osteoblast adhesion, proliferation, and mineralization. Results supported the osteoinductive property of the Cissus quadrangularis extract-incorporated scaffolds even without osteogenic media supplement. Cissus quadrangularis extract increased the alkaline phosphatase activity of the SaOS-2 cells on scaffolds on 7th and 14th days of incubation. The investigation of characterization and cell culture studies suggest that Cissus quadrangularis-loaded osteoinductive Cissus quadrangularis/chitosan/Na-carboxymethyl cellulose scaffold can serve as a potential biomaterial for bone tissue engineering applications.Article Citation - WoS: 17Citation - Scopus: 19Heavy Naphtha Upgrading by Catalytic Reforming Over Novel Bi-Functional Zeolite Catalyst(Springer, 2018) Ahmedzeki, Nada S.; Al-Tabbakh, Ban A.; Antwan, Maher B.; Yılmaz, SelahattinNaphtha catalytic reforming process using bimetallic platinum and titanium loaded on nano synthesized HY zeolite was investigated for the product octane number enhancement. The activity of five samples of the prepared catalyst with different bimetallic loading of 0.13, 0.25 wt% Pt and 0.75, 1, 2.2 wt% Ti were investigated for Iraqi heavy naphtha catalytic reforming at the temperature range of 490, 500 and 510 degrees C and pressure of 10 bar in a packed bed pilot plant reactor. The best result of the research octane number was 84 for reformate product using the sample of 0.13% Pt-0.75% Ti%/HY zeolite at temperature 510 degrees C and 10 bar achieving 47% increase. All samples of the prepared catalyst showed a good stability during the operation at severe conditions and the maximum carbon content was about 9% due to the deposition of coke precursor on the catalyst surface. The reformate yield was investigated for all catalyst samples under 10 and 20 bars and the same range of temperature and ranged from 89 to 94%. These results are encouraging for future possible replacement of the conventional catalyst by the local synthetic zeolite. Octane number was correlated on the basis of constituent's boiling points. The maximum absolute error between the experimental and predicted octane number was about 3 and 5% using 10 and 20 bar respectively.Article Effective Synthesis of Cetyl Palmitate Over Co-Precipitated Wo3-Zro2 Catalysts(Springer Verlag, 2018) Mutlu, Vahide N.; Yılmaz, SelahattinThis study is focused on the development of solid acid catalysts for the synthesis of long chain fatty acids. A series of WO3-ZrO2 catalysts were prepared by co-precipitation method and tested in the synthesis of cetyl palmitate. The effect of WO3 loading (10, 15, and 20 wt% WO3) and calcination temperature (700 and 800 degrees C) on the catalyst properties and activity was investigated. XRD and Raman analysis confirmed that WO3 loading stabilized the tetragonal zirconia phase. Higher calcination temperature enhanced the acidities of the catalysts. WO3-ZrO2 catalysts were found to be very efficient for the synthesis of cetyl palmitate with high selectivity. These catalysts were tested for different reaction temperatures (135 and 162 degrees C), feed composition and catalyst amounts. The highest cetyl palmitate yield (98.4%) was obtained over the catalyst calcined at 800 degrees C with 15 wt% WO3, which had the highest total acidity. The catalysts preserved their activities up to three reuse.Article Citation - WoS: 1Citation - Scopus: 1Mineralization of Olive Mill Wastewater Under Hydrothermal Conditions(Desalination Publications, 2019) Ersanlı, Çağlar; Yüksel Özşen, AslıOlive mill wastewater (OMW) is highly dangerous for land and aquatic environments because of its high phenolic content, acidity, and salinity. Hence, hydrothermal degradation of OMW in subcritical water medium with and without using external oxidizer (H2O2) was studied to decrease its total organic carbon (TOC), total phenolic content (TPC), and color. Effects of reaction temperature (150 degrees C-250 degrees C), reaction time (30-120 min), and H2O2 content (0-100 mM) on TOC and TPC of OMW were investigated. Box-Behnken-type experimental design and statistical analysis (analysis of variance) were practiced by Design Expert 11. According to statistical analysis, effect of reaction temperature significantly affected TOC removal efficiency. The best TOC reduction (31.65%) was achieved without using H2O2 at 250 degrees C for 120 min.Article Citation - Scopus: 2The Surface Charge of Unsupported Nano-Structured Titania Ceramic Membrane Top Layers With Varying Calcination Temperatures(University of Chemical Technology and Metallurgy, 2019) Erdem, İlker; Çiftçioğlu, MuhsinTitania is one of the most preferable ceramic membrane materials of superior durability (as zirconia) when compared to that of other ceramics, e.g. alumina or silica. The surface charge of the membrane top layer is an important parameter of the separation performance of the multilayer ceramic membrane due to the Donnan exclusion mechanisms. In this study, the change of the surface charge of unsupported nano-structured titania top layer is investigated with calcination temperature variation. The effect observed indicates the possibility of preparation of tailor-made top layers for multilayer ceramic membranes. © 2019, University of Chemical Technology and Metallurgy.Article Effect of Temperature on Stability of Lipid Microbubbles(Turkish Chemical Society, 2019) Kılıç, SevgiThe effect of temperature on stability of lipid microbubble shell containing polyethyleneoxide-40-stearate (PEG40St) as emulsifier was investigated. Microbubbles at 4 °C were subjected to different temperatures up to 48 ºC (down-to-up) and it was found that both the number and the size of microbubbles remained unchanged in the population up to a certain time, so called “onset time”. The onset time was about 6 hours at 10 °C, 2 hours at 20 °C and shorter at elevated temperatures, exhibiting an exponential decrease with increasing temperature. Once the onset time was reached, the number of microbubbles started to decrease and the average size of the population started to increase. Observation of single microbubbles on a constant temperature heating stage exhibited that each microbubble had its own onset time, with the smaller microbubbles vanishing earlier than the larger ones. The Langmuir monolayer studies showed that hydration degree of the emulsifier PEG chains decreased with temperature, causing them go through conformational changes and subsequently destabilization of the shell. By subjecting the freshly produced microbubbles directly to the desired temperatures in up-to-down fashion, more stable microbubbles were able to be produced, with their onset time increased 40% at 10 °C to 500% at 38 °C. Overall, the results suggest that the new strategies need to be developed to control the collapse process in the microbubble shell resulting from the conformational changes in the PEG chains of the emulsifier for the design of more stable microbubbles. © 2019, Turkish Chemical Society. All rights reserved.Article Citation - Scopus: 1Synthesis of Stable Nano Calcite(Turkish Chemical Society, 2018) Kılıç, SevgiSynthesis of calcium carbonate (CaCO3) particles in the presence of a population of carbon dioxide (CO2) bubbles was investigated in the calcium hydroxide (Ca(OH)2) solution, which is a natural stabilizer for CaCO3. Possible chemical speciation reactions were presented for an inorganic synthesis of hollow nano-CaCO3 particles. In the progress of CaCO3 synthesis, some of the particles started to dissolve at their edges and turned into hollow nano-CaCO3 particles. Some of the pores closed at the end of crystallization as a result of dissolution-recrystallization mechanism. Hollow nano-CaCO3 particles with sizes of about 300 nm were synthesized with a narrow size distribution. It was concluded that the hollow nano-CaCO3 particles could be advantageous due to lower weights and higher surface areas.Article Citation - Scopus: 7Binder Effect on Electrochemical Performance of Zinc Electrodes for Nickel-Zinc Batteries(Turkish Chemical Society, 2018) Ebil, Özgenç; Cihanoğlu, GizemPolyethylene glycol (PEG) and polyvinyl alcohol (PVA) were used as a zinc electrode binder at different concentrations to enhance the electrochemical behavior of zinc electrodes for nickel-zinc (NiZn) batteries. ZnO powders synthesized by mechanochemical and hydrothermal precipitation methods were mixed with lead oxide, calcium hydroxide and binder to prepare zinc electrodes in pouch cell NiZn batteries. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analysis reveal that initial morphology of zinc electrode changes drastically regardless of the binder type and its loading after charge/discharge process, and even the charge/discharge process is not complete. The results show that the presence of PEG causes better discharge capacity compared to that of PVA as a binder. Zinc electrode prepared using commercial ZnO powder and 3 wt.% PEG gives the optimum discharge capability, with a specific capacity of approximately 311 mAhg-1, while zinc electrodes prepared using ZnO powder synthesized from ZnCl2 and Zn(NO3)2.6H2O and 6 wt.% PEG exhibit high specific energy of 255 and 275 mAhg-1, respectively. The results suggest a relationship between binder loading and battery capacity, but in-situ analysis of microstructural evolution of zinc electrode during charge/discharge process is needed to confirm this relationship.