Phd Degree / Doktora

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Author: search.filters.author.Ülkü, SemraDepartment: search.filters.department.Thesis (Doctoral)--İzmir Institute of Technology, Chemical Engineering

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Now showing 1 - 7 of 7
  • Doctoral Thesis
    The Effect of Microwaves on Ion Exchange in Zeolites
    (Izmir Institute of Technology, 2009) Akdeniz, Yelda; Ülkü, Semra
    Recent innovations of microwave field lead many scientists to focus on this phenomenon and it has been begun to be applied in different fields of zeolite applications. The purpose of this study is to determine the effect of microwave irradiation on ion exchange degree and on the structure of natural zeolite. The clinoptilolite rich mineral from Western Anatolia was used throughout the experiments. The ion exchange experiments were performed using AgNO3, Co.(NO3)26H2O and Cu (NO3)25/2H2O within 0.01M - 1M and 40 oC - 80 oC concentration and temperature range in conventional waterbath and microwave. Different solid and solution conditions on ion exchange degree were determined, as well. Metal exchanged minerals were characterized by using instrumental techniques. Antibacterial activity of the Agexchanged clinoptilolite against E. coli was determined by Kirby.Bauer method. The Ag +, Co2+ and Cu2+ amounts within the mineral increased with decreasing S/L while increased with increasing temperature and time. For some utilized parameters microwave treatment was effective however on the whole it did not significantly improved the degree of ion exchange compared to waterbath treatment. The inspection of XRD patterns and FTIR spectra of metal exchanged minerals confirmed that no transition of clinoptilolite phase and no shifts in peak positions occurred with exchange methods applied. The sorption processes are controlled mainly by external-phase mass transfer. Ag+, Co2+ and Cu2+ sorptions on NaCLI exhibited a good fit to Freundlich model and Langmuir models. All metal exchanged minerals showed considerable superiority against E.Coli.
  • Doctoral Thesis
    An Experimental and Theoretical Study on the Improvement of Adsorption Heat Pump Performance
    (Izmir Institute of Technology, 2008) Demir, Hasan; Ülkü, Semra
    Adsorption heat pumps, which have considerably sparked attentions in recent years, have the advantage of being environmentally friendly and operating with heat sources such as waste heat, solar and geothermal energies as well as storing the energy.The present investigation covers working principle of adsorption heat pumps, a detailed literature survey on the performed studies, information about adsorption phenomena, experimental results of two differently designed and constructed systems, numerical simulation of heat and mass transfer in an annular adsorbent bed, and microcalorimetric study for obtaining isosteric heat of adsorption for water vapor-silica gel pair. The two intermittent adsorption heat pumps can operate without any leakage. The silica gelwater was employed as the adsorbent-adsorbate pair in both of the systems. The temperature and pressure in the evaporator, condenser and adsorbent bed were measured and the coefficients of performance, total entropy generation, the second law efficiency, specific heating and cooling power values were calculated based on these measured values for all of the representative cycles. The heat transfer area of the second designed adsorption heat pump is 550% greater than the first designed adsorption heat pump and this increase resulted in 170% and 200% of improvements in specific heating power (SHP) and specific cooling power (SCP) values respectively. The silica gel granules were mixed with small size metal pieces in order to accelerate heat transfer in the bed. Experiments were performed to measure the thermal diffusivity through the adsorbent bed in which adsorbent is mixed with metal pieces. It was observed that the mixing of silica gel grains with 10wt% of small size aluminum pieces increases the SHP and SCP values of the second heat pump by 250%.
  • Doctoral Thesis
    Integrated Approach To Whey Utilization Through Natural Zeolite Adsorption/ Desorption and Fermentation
    (Izmir Institute of Technology, 2009) Polat, Zelal; Ülkü, Semra
    In this thesis, the usage of clinoptilolite rich natural zeolites in the recovery of whey proteins by adsorption/desorption, and in the bioconversion of whey, lactose source, to lactic acid were investigated. The possibility for the utilization of natural zeolite deposits of Turkey; and whey, by-product of cheese manufacturing, in the production of high value added chemicals is important from both economical and environmental concerns. Natural zeolites with a particle size range of 75-150 .m were prepared and characterized. Aqueous protein solution, whey powder solution and whey were treated with the natural zeolites and dealuminated zeolites. Batch adsorption studies were performed and uptake data were collected. Equilibrium adsorption isotherms were analysed by Langmuir and Freundlich isotherms. Langmuir isotherm fits the experimental data better. Furthermore, experiments were conducted to see the effects of temperature, initial adsorbate concentration, solid/liquid ratio, agitation speed, pH, particle size and dealumination in adsorption process. The adsorption mechanism was analysed with adsorption kinetics models; and considering the effects of particle size, agitation speed and temperature external film diffusion, surface diffusion and surface reaction were found as effective. The effects of the natural zeolite on the pH, elemental composition and the adsorption tendency of the lactose-lactic acid in the fermentation media were also investigated; and the results were compared with the sythetic ones. Natural zeolites were found as an alternative inexpensive mineral source for the fermentation.
  • Doctoral Thesis
    Adsorptive Characteristics of Aflatoxin B1 in the Presence of Purified Clinoptilolite Rich Mineral and Lactobacillus Plantarum S2
    (Izmir Institute of Technology, 2012) Bulut Albayrak, Çisem; Ülkü, Semra
    The human diet contains a wide variety of natural carcinogens. Aflatoxin B1 (afB1) is the most toxic and most prevalent compound. Both probiotic lactic acid bacteria and clinoptilolite rich zeolite mineral have potential to eliminate this toxin. This study was planned in order to investigate adsorptive characteristics of afB1 by local purified clinoptilolite rich mineral (PNZ) and probiotic strains which were isolated from different natural sources (fermented cabbage, boza ) in the present work. PNZ and isolated strains were characterized by using several physical, chemical and biological techniques. Adsorption characteristics of both probiotic lactobacilli and PNZ were investigated in simulated gastrointestinal solutions. The chosen probiotic strain was identified as L. plantarum .The studies indicated that, both L. plantarum S2 and PNZ can eliminate afB1 in the phosphate buffer solution. They are more effective when they were used together (45% for L. plantarum S2, 32% for PNZ, 86%for L. plantarum S2 and PNZ together). AfB1 adsorption equilibrium data were best represented by Sips isotherm model for PNZ, whereas by Langmuir isotherm model for L. plantarum S2. Thermodynamic studies implied that afB1 adsorption by mineral and L. plantarum S2 was physical adsorption. Experiments with different temperatures showed that afB1 adsorption by PNZ was exothermic but afB1 adsorption by lactobacilli was endothermic. Adsorption kinetics were analysed by diffusional models and reaction models for afB1 adsorption by PNZ mineral. Both film diffusion and /or intra particle diffusion were effective on adsorption kinetics depending on the experimental conditions (Temperature, pH, agitation speed, etc).
  • Doctoral Thesis
    Nitrogen Monoxide Storage and Release Properties of Local Natural Zeolite for Biological Applications
    (Izmir Institute of Technology, 2009) Narin, Güler; Ülkü, Semra; Ülkü, Semra
    In this thesis, nitrogen monoxide (nitric oxide, NO) adsorption, storage and release properties of the local clinoptilolite-rich natural zeolite and its modified forms were investigated. The zeolite particles (75-150 .m, 150-250 .m) were prepared through treatment of the natural zeolite with NaCl and consecutively with aqueous metal (Co2+, Ag+, Cu2+, Fe3+) salt solutions under different conditions. The prepared zeolites were characterized in terms of particle size and morphology, density, mineral and elemental composition, dehydration behavior, porosity, surface area, and infrared spectroscopic characteristics. The total adsorption capacities of the zeolites for NO were calculated from the breakthrough curves obtained at 30 oC on a dynamic adsorption system and found to be in the range of 5.5-8.5 mmol/g. NO was adsorbed in the zeolites reversibly and irreversibly. The total adsorption capacity was mainly contributed from the irreversible adsorption. The irreversible adsorption capacity was related to the type and amount of metal cation in the zeolite. The temperature-programmed desorption (TPD) profiles provided information about the desorption kinetics of the NO species formed on the zeolite surface upon the adsorption. The bands detected in the DRIFTS spectra upon admission of NO were assigned to reversibly and irreversibly adsorbed NO species. The unmodified and iron-sorbed zeolites gained antibacterial activity against E. coli after NO loading. The unmodified zeolite also exhibited antibacterial activity against B. subtilis after NO loading. The NO-loaded unmodified zeolite also exhibited complete bactericidal activity upon contact with both bacteria cells. The unmodified and copper-sorbed zeolites exhibited similar NO release kinetics.
  • Doctoral Thesis
    Recovery of Phytochemicals (having Antimicrobial and Antioxidant Characteristics) From Local Plants
    (Izmir Institute of Technology, 2010) Altıok, Evren; Ülkü, Semra
    The objective of the present work was to assess the selective isolation of polyphenols from olive leaf and grape skin, which are supplied from the main local plants. The effects of extraction conditions on the types and amounts of polyphenolic compounds and selective separation of them by adsorption were investigated. The batch adsorption and dynamic column studies were performed by silk fibroin and clinoptilolite. Kinetic models were used to determine the mechanism of adsorption. Dynamic column models were applied to optimize the operating parameters. The biological activities of isolated fractions from the crude extracts were determined by analyzing their antioxidant, antimicrobial and cytotoxic activities. Recovered trans-resveratrol significantly inhibited all pathogenic microorganisms. However, higher concentration of grape skin crude extract is required to achieve same inhibition. Although grape skin extract did not have any effect on prostate and breast cancer cells, trans-resveratrol has very significant inhibition effect.
  • Doctoral Thesis
    Inhibition of Microbial Ss-Glucuronidase by Natural Zeolites and Their Effects on Cancer Prevention in Human Intestinal Systems
    (Izmir Institute of Technology, 2010) Demirbüker Kavak, Dilek; Ülkü, Semra
    Bacterial β-glucuronidase (GUS) enzyme has an important role in the production of reactive metabolites related to some diseases and cancer development. In this thesis, health promoting role of clinoptilolite rich zeolite mineral was proposed to act as a potential inhibitor and as adsorbant of GUS and also to have cytotoxic effect towards cancer cells. Therefore inhibition and adsorption mechanism of GUS by clinoptilolite rich mineral and its cytotoxicity towards cancer cells were investigated. Additionally, another potential inhibitor; casein and their interactions with GUS and clinoptilolite rich mineral were revealed. Results showed that GUS activity was inhibited by either casein or clinoptilolite rich mineral and both of them acted as mixed type inhibitors. Additionally, it was found that clinoptilolite rich mineral was a potential adsorbent for GUS. Results showed that removal percentages of proteins were 9.4-54.4 % and 36.5-77.3 % for GUS and casein, respectively and depended on their initial concentrations. Equilibrium studies showed that both adsorptions were exothermic and physical and kinetic models implied that external fluid film or skin resistance, and intraparticle diffusion might be effective for GUS and casein adsorption, respectively. In cytotoxicity tests, clinoptilolite rich mineral (25mg/ml) inhibited approximately 50 % of the Caco-2 cell proliferation. This high inhibition was not observed for MCF-7 cells where inhibition was found to be 20-30 %. Flow cytometric results for both cell lines indicated that total apoptosis percentage in overall population was low compared to control sample. This result was also confirmed by cell cycle analyses.