Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Conference Object Antioxidant, Antimicrobial and Cytotoxic Activities of Some Turkish Plant Extracts(John Wiley and Sons Inc., 2006) Altıok, Evren; Asbagh, L. Abbasi; Bulut, Çisem; Ülkü, Semra; Bayraktar, OğuzPlant extracts have been known to possess notable biological activity, including antioxidant, antimicrobial and cytotoxic properties. There is a growing interest in the use of natural products in the human food industries as consumer resistance to synthetic additives increases. These products can be used to improve human health. In vitro antioxidant, antimicrobial and cytotoxic activities of ethanol extracts of some plants from Urla region in Turkey were investigated. Plant materials were collected from Pistacia lentiscus, Vitex agnus-castus, Cistus creticus and Nerium oleander in October, November and December.Article Citation - WoS: 3Citation - Scopus: 5Adsorption Characteristics of Lead-, Barium- and Hydrogen-Rich Clinoptilolite Mineral(SAGE Publications Inc., 2003) Çakıcıoğlu Özkan, Seher Fehime; Ülkü, SemraThe carbon dioxide and water vapour adsorption properties of local clinoptilolite-rich material, both as the original and as lead-, barium- and hydrogen-rich forms, were examined. The lead- and barium-rich forms were prepared by treatment of the original clinoptilolite with Pb(NO3)2 and BaCl2 respectively, while the hydrogen-rich form was prepared by NH4Cl and heat treatment. Water and CO2 adsorption experiments were conducted in a volumetric system under static conditions, with low-pressure adsorption data being used for the characterization of the natural, Pb-rich, Ba-rich and H-rich clinoptilolite samples. Although the existence of barium-exchange was not noted, an appreciable decrease in CO2 adsorption was observed with the Pb-rich and H-rich forms due to a decrease in the electrostatic interaction between the surface and the adsorbate. Application of the Dubinin-Astakhov equation to the water adsorption data established the existence of micropores of different sizes that exhibited different adsorption mechanisms.Article Citation - WoS: 55Citation - Scopus: 60Effect of Regeneration Temperature on Adsorption Equilibria and Mass Diffusivity of Zeolite 13x-Water Pair(Elsevier Ltd., 2016) Sayılgan, Şefika Çağla; Mobedi, Moghtada; Ülkü, SemraThe adsorption equilibrium and mass diffusivity of zeolite 13X-water pair for different adsorption and regeneration temperatures were determined by a homemade volumetric system. The isotherms of the zeolite 13X-water pair were obtained by collecting pressure versus time data and applying ideal gas law. The effective diffusivity of the pair was calculated by using long term analytical solution of mass diffusivity based on Fick's law. The experimental study showed that the adsorption capacity of zeolite 13X-water pair was 23% (kg/kg), 21% (kg/kg) and 19% (kg/kg) when the adsorption temperature was 35, 45 and 60 °C respectively for the desorption temperature of 90 °C. Furthermore, the adsorption capacity increased from 22% (kg/kg) to 24% (kg/kg) when the desorption temperature was increased from 90 °C to 150 °C. It was observed that the present adsorption equilibrium results were compatible with the reported results in the literature. The mass diffusivity of the pair was found in the range of 4 × 10-9-6 × 10-8 m2/s for the long time period when the initial adsorptive pressure was 2000 Pa. The effective mass diffusivity depends on concentration and it was decreased with increasing adsorbate concentration.Article Citation - WoS: 3Citation - Scopus: 2Adsorption of No in Clinoptilolite-Rich Zeolitic Mineral by Concentration Pulse Chromatography Method(Elsevier Ltd., 2016) Narin, Güler; Ülkü, SemraThe equilibrium and kinetic parameters for NO adsorption in a clinoptilolite-rich natural zeolitic material from Turkey were determined using the concentration pulse chromatography method. Under the experimental conditions (carrier gas velocities and adsorption temperatures) the micropore diffusion resistance was found to be the mass transfer controlling step. Matching the first moment of the response peaks to the mathematical model the Henry's Law constants and heat of adsorption at zero loading were determined. The axial dispersion, external film, macropore and micropore diffusion coefficients, and activation energy for diffusion of NO in the micropores were calculated from the analysis of the second moments of the response peaks. For successive NO pulses without regeneration between the pulses, the retention times of the response peaks decreased and peak areas increased with the injection number indicating irreversible adsorption. The reversibly adsorbed NO could be desorbed by purging with an inert gas at the adsorption pressure and temperature. Temperature programmed desorption profile obtained by heating the NO saturated adsorbent to 400 °C under inert flow revealed presence of multiple irreversibly adsorbed species in NZ with different thermal stabilities. Desorption of these species was not achieved during the heating up to 400 °C which makes the natural zeolitic materıal suitable for NO storage rather than for cyclic adsorptive separation processes.Article Citation - WoS: 60Citation - Scopus: 66Preparation and Characterization of Calcium Stearate Powders and Films Prepared by Precipitation and Langmuir-Blodgett Techniques(American Chemical Society, 2010) Gönen, Mehmet; Öztürk, Serdar; Balköse, Devrim; Okur, Salih; Ülkü, SemraThe preparation of calcium stearate (CaSt2) using precipitation and Langmuir-Blodgett techniques was investigated in this study. While sodium stearate and calcium chloride were used in the precipitation process, calcium stearate nanofilms were produced from stearic acid and calcium chloride in sodium borate buffer with the Langmuir-Blodgett technique. Fourier transform infrared (FTIR) spectroscopy indicated carboxylate bands at 1577 and 1543 cm-1 in equal intensity in the powder form, but the films had a higher intensity 1577 cm-1 band than the 1543 cm-1 band. This showed the calcium ions associated with the COO- ions in the monodendate and bidendate structures in powders, and it was mainly in the bidendate structure in films. While characteristic peaks of CaSt2 at 2θ values of 6.40° and 19.58° were obtained in the X-ray diffraction (XRD) pattern of the dried powdered product, no sharp peaks were present in the 13 layer CaSt2 film. From scanning electron microscopy (SEM) micrographs, it was seen that calcium stearate powder had lamellar structure and the average particle size was 600 nm. The AFM picture of the CaSt2 film indicated the surface was not smooth with a peak to valley distance of 6 nm. © 2010 American Chemical Society.Article Citation - WoS: 17Citation - Scopus: 23Synthesis of Zinc Borate by Inverse Emulsion Technique for Lubrication(Springer Verlag, 2011) Atakul Savrık, Sevdiye; Balköse, Devrim; Ülkü, SemraLubricating oil additives based on boron compounds are promising materials for lubrication due to their tribological advantages such as antiwear efficiency, good film strength, and high temperature resistance. This article deals with the preparation of zinc borate particles that are well dispersed and colloidally stabilized in mineral oil. This method starts with preparing two inverse emulsions (water-in-oil) with sorbitan monostearate (Span 60) as a surfactant, light neutral oil as a continuous phase, and the aqueous solutions of borax decahydrate (Na2B4O7·10H 2O) and zinc nitrate (Zn(NO3)2·6H 2O) as the dispersed phases. The produced particles were zinc borate crystals having both rod-like and spherical morphologies, and the diameters of spherical particles were changing between 20 and 30 nm. FTIR spectra of the obtained particles showed the characteristic peaks of trihedral borate (B(3)-O) and tetrahedral borate (B(4)-O) groups as well as the specific peaks of the sorbitan monostearate. TG showed 30.42% and 22.08% mass loss at 600 °C for the samples prepared by inverse emulsion and precipitation techniques, respectively. The endothermic peak at 50 °C is observed due to the melting of sorbitan monostearate and the heat of melting is evaluated as -3.50 J/g. Tribological studies revealed that sorbitan monostearate not only outperformed as a dispersing agent of inorganic particles, but also it proved to be an anti-wear agent. Zinc borate produced by precipitation decreased the wear scar diameter from 1.402 to 0.639 mm and the friction coefficient from 0.099 to 0.064. The inverse emulsion was effective in decreasing wear scar diameter and the friction coefficient by lowering them to 0.596 and 0.089 mm, respectively.Article Citation - WoS: 23Citation - Scopus: 25Microcalorimetric Investigation of Water Vapor Adsorption on Silica Gel(Springer Verlag, 2011) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraWater vapor adsorption on silica gel was investigated using Tian-Calvet-type microcalorimetry. Differential heat of adsorption data was obtained. The setup of microcalorimetry was used volumetric system to determine adsorption isotherms of water vapor-silica gel. The Langmuir model was used in the interpretation of the adsorption data. The Clausius-Clapeyron diagram was also given. Effective mass diffusivity of water vapor in the silica gel particle as a function of temperature was also determined. The silica gel, which was degassed under vacuum at 10 -7 mbar and 120 °C for 18 h, was found to adsorb 0.6, 0.98, 1.1, 1.4, 2, 3.5, 11, 13, and 14 wt% water vapor at 120, 110, 100, 90, 75, 60, 40, 35, and 30 °C, respectively. The diffusivities of water vapor inside the silica gel for short- and long-range periods were described using kinetics data as a function of temperature in the Arrhenius form.Article Citation - WoS: 23Citation - Scopus: 25A Dimensionless Analysis of Heat and Mass Transport in an Adsorber With Thin Fins; Uniform Pressure Approach(Elsevier Ltd., 2011) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraA numerical study on heat and mass transfer in an annular adsorbent bed assisted with radial fins for an isobaric adsorption process is performed. A uniform pressure approach is employed to determine the changes of temperature and adsorbate concentration profiles in the adsorbent bed. The governing equations which are heat transfer equation for the adsorbent bed, mass balance equation for the adsorbent particle, and conduction heat transfer equation for the thin fin are non-dimensionalized in order to reduce number of governing parameters. The number of governing parameters is reduced to four as Kutateladze number, thermal diffusivity ratio, dimensionless fin coefficient and dimensionless parameter of Γ which compares mass diffusion in the adsorbent particle to heat transfer through the adsorbent bed. Temperature and adsorbate concentration contours are plotted for different values of defined dimensionless parameters to discuss heat and mass transfer rate in the bed. The average dimensionless temperature and average adsorbate concentration throughout the adsorption process are also presented to compare heat and mass transfer rate of different cases. The values of dimensionless fin coefficient, Γ number and thermal diffusivity ratio are changed from 0.01 to 100, 1 to 10 -5 and 0.01 to 100, respectively; while the values of Kutateladze number are 1 and 100. The obtained results revealed that heat transfer rate in an adsorbent bed can be enhanced by the fin when the values of thermal diffusivity ratio and fin coefficient are low (i.e., α -=0.01, δ=0.01). Furthermore, the use of fin in an adsorbent bed with low values of γ number (i.e. γ=10 -5) does not increase heat transfer rate, significantly.Article Citation - WoS: 35Citation - Scopus: 36Ammonium sorption by Gördes clinoptilolite rich mineral specimen(Elsevier Ltd., 2011) Cansever Erdoğan, Beyhan; Ülkü, SemraExperimental and theoretical works were performed for the estimation of the effects of pH, initial concentration, agitation speed, particle size and temperature on the ammonium sorption by local clinoptilolite rich mineral specimen. The kinetic sorption data were analyzed using external mass transfer, intraparticle diffusion, pseudo first and second order kinetic models. Diffusion model results revealed that external film diffusion dominated at the very early stages of sorption process and then it was overcome by intraparticle diffusion. Pseudo-second order kinetic model correlated with the experimental data better than the pseudo first order kinetic model. Sorption isotherm model results indicated that the Langmuir isotherm fitted well to the experimental data. Thermodynamic parameters Gibbs energy change (δG), enthalpy change (δH) and entropy change (δS) were calculated. It was shown that the sorption process was exothermic and spontaneous. The value of the activation energy suggested that ammonium sorption by the clinoptilolite rich mineral specimen is likely due to physical interactions between the sorbent and the sorbate. Analysis of the cation exchange results revealed that ion exchange mechanism was not the only step which was effective in ammonium sorption.Article Citation - WoS: 23Citation - Scopus: 26Cr(vi) Sorption by Using Clinoptilolite and Bacteria Loaded Clinoptilolite Rich Mineral(Elsevier Ltd., 2012) Cansever Erdoğan, Beyhan; Ülkü, SemraBatch sorption experiments were performed in order to understand the potential value of local clinoptilolite rich mineral and its bacteria loaded form in Cr(VI) sorption. The results indicated that Cr(VI) sorption capacities of the sorbents were increased after bacteria loading and the clinoptilolite rich mineral is a promising material in Cr(VI) sorption. Zeta potential and Fourier Transform IR (FTIR) analysis were performed to explain the possible mechanism involved in the Cr(VI) sorption. The results revealed that non-electrostatic forces played a significant role rather than the electrostatic forces. The existence of non-electrostatic forces was confirmed by the FTIR results. © 2011 Elsevier Inc. All rights reserved.