Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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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: 14Citation - Scopus: 25Kinetic and Equilibrium Studies of Adsorption of Ss-Glucuronidase by Clinoptilolite-Rich Minerals(Elsevier Ltd., 2015) Demirbüker Kavak, Dilek; Ülkü, SemraThe adsorption of the bacterial β-glucuronidase (GUS) enzyme, which is thought to be responsible for the production of reactive metabolites related to some diseases and cancer development, by clinoptilolite-rich mineral was investigated. Batch experiments were performed to analyze of the effects of the clinoptilolite amount and particle size, initial GUS concentration, shaking rate, pH and temperature on the adsorption equilibrium and kinetics. Adsorption equilibrium data were interpreted in terms of Langmuir and Freundlich isotherms; and they were well represented by the Langmuir isotherm model. The percentage of GUS removal by the clinoptilolite-rich mineral was changed in the range of 9.4-54.4% depending on its initial concentration. The kinetic data were analyzed using external film diffusion, intraparticle diffusion, pseudo-first-order and pseudo-second-order models and both external film and intraparticle diffusion appeared to be effective in GUS adsorption. Thermodynamic studies indicated that GUS adsorption is exothermic, physical and spontaneous at the temperatures investigated (288-310 K)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.Article Citation - WoS: 12Citation - Scopus: 11A Parametric Study on Isobaric Adsorption Process in a Closed Adsorbent Bed(Elsevier Ltd., 2010) Gediz İliş, Gamze; Mobedi, Moghtada; Ülkü, SemraA numerical study on heat and mass transfer in an annular adsorbent bed filled with adsorbent granules for an isobaric adsorption process is performed. In order to reduce the number of independent parameters that influences heat and mass transfer in the bed, the governing equations and related initial and boundary conditions for the problem are non-dimensionalized and this yields two dimensionless parameters as G and Γ. The G dimensionless parameter is the ratio of heat of adsorption to sensible heat stored by adsorbent particle and Γ parameter compares mass diffusion within the adsorbent particle and heat diffusion in the radial direction of the adsorbent bed. The obtained results show that the total dimensionless time for an adsorption process can be reduced by increasing of Γ value. The total dimensionless time is independent from G for low values of Γ (i.e. Γ=105). The results also show that the instantaneous equilibrium model can provide accurate results only for an adsorbent bed with a low value of Γ (i.e. Γ=105). The present study is performed for Γ values from 105 to 1 and G value from 1 to 100. © 2010 Elsevier Ltd.Article Citation - WoS: 61Citation - Scopus: 66The Use of Metal Piece Additives To Enhance Heat Transfer Rate Through an Unconsolidated Adsorbent Bed(Elsevier Ltd., 2010) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraThe effects of metal piece additives on effective thermal conductivity and diffusivity of an unconsolidated adsorbent bed in which adsorbent is silica gel were investigated. The metal piece additives were copper, brass, aluminum and stainless steel with two different sizes as 1.0-2.8 mm and 2.8-4.75 mm. The effective thermal conductivity and diffusivity of the mixed bed were predicted by comparison of the experimental results with the solution of dimensionless heat conduction equation for the bed. The performed experiments showed that the addition 15wt% of aluminum pieces with sizes between 1.0 and 2.8 mm enhances the effective thermal diffusivity and conductivity of a pure silica gel bed by 157% and 242%, respectively. © 2010 Elsevier Ltd and IIR.Article Citation - WoS: 42Citation - Scopus: 60Pistacia Terebinthus Extract: as a Potential Antioxidant, Antimicrobial and Possible Ss-Glucuronidase Inhibitor(Elsevier Ltd., 2010) Demirbüker Kavak, Dilek; Altıok, Evren; Bayraktar, Oğuz; Ülkü, SemraIn this study, inhibition of Escherichia coli glucuronidase (GUS) by a plant extract of Pistacia terebinthus was investigated. P. terebinthus (from Karaburun region in Turkey) leaf extract exhibits various bioactivities, such as antioxidant, antimicrobial and cytotoxic property because of its flavonoid, phenolic and alkaloid contents. HPLC analyses were performed to evaluate the composition of the extract and main flavonoid compounds such as luteolin, luteolin-7-glucoside and apigenin-7-glucoside were detected in extract. GUS activity and kinetic data of the GUS were obtained by measuring rate of production of resulting fluorescent 4-methylumbelliferone (4-MU) and phenolphthalein fluorometrically and spectrophotometrically, respectively. Plant leaves showed higher antioxidant capacity as 85 TEAC (trolox equivalent antioxidant capacity) value and higher antimicrobial activity towards Staphylococcus aureus. 92.4% GUS enzyme inhibition was achieved with 8.3 μg ml-1 crude extract concentration, where IC50 value was found as 2.1 (±0.2) μg ml-1. Kinetic studies by nonlinear regression revealed that inhibition type caused by plant extract was mixed type (noncompetitive and competitive together). Km and Vmax values were 96.94 ± 9.68 nM and 7.81 ± 0.16 nmol min-1 mg-1, respectively. Inhibition constant (αKi) was found as 7.00 ± 0.93 nM having α value 2.17 ± 0.93. Our results may provide useful information regarding the inhibition of microbial GUS activity, preventing deglucuronidation and reducing possible cancer risk by bioactive P. terebinthus crude extract. © 2010 Elsevier B.V. All rights reserved.Article Citation - WoS: 62Citation - Scopus: 64Effects of Porosity on Heat and Mass Transfer in a Granular Adsorbent Bed(Elsevier Ltd., 2009) Demir, Hasan; Mobedi, Moghtada; Ülkü, SemraIn the present study, the mechanism of heat and mass transfer in an annulus adsorbent is handled. The heat and mass transfer equations for the adsorbent bed and the mass balance equation for the adsorbent granules are numerically solved to obtain the distributions of temperature, pressure, adsorptive density and adsorbate concentration in the adsorbent bed. The study is performed for the silica gel-water pair and for three different values of porosity as 0.1, 0.2 and 0.3. The distributions of temperature and adsorbate concentration are considerably influenced from the bed porosity. The adsorption period increases with the increase of the porosity value. The porosity affects the pressure and adsorptive density distributions at the beginning of the process and after a relatively short time, the averages of these dependent variables approach to the final equilibrium state.
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