Didem Özçimen

Yildiz Technical University, İstanbul, Istanbul, Turkey

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Publications (16)22.65 Total impact

  • Didem Özçimen · Ayşegül Ersoy-Meriçboyu

    No preview · Article · Nov 2014
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    ABSTRACT: Ultrasonic irradiation is considered to be an effective way to increase the mass transfer between the immiscible liquid-liquid phases in a heterogeneous system leading to faster transesterification and higher yield, and saving excess methanol and catalyst. In this study, the transesterification of hazelnut oil with methanol and ethanol was performed in the presence of potassium hydroxide or sodium methoxide as a catalyst using two types of ultrasonic irradiation with a probe (20 kHz, 200 W) and a bath (35 kHz, 400 W), also a conventional production method was used. The reaction time, alcohol:oil molar ratio, catalyst type (KOH or NaOCH3) and catalyst amount (wt.% of oil) were studied as experimental parameters. The highest methyl ester conversion was obtained as 98.12%, by use of ultrasonic probe at a 5:1 methanol:oil molar ratio with KOH catalyst 1 wt.% of oil within 20 minutes reaction time at autogenous temperature. The application of ultrasonic irradiation by using a probe decreased the level of energy consumption, showing that this method may be a promising alternative to the conventional production method.
    Full-text · Article · Oct 2014 · International Journal of Green Energy
  • Sevil Yucel · Didem Özçimen · Pınar Terzioğlu · Serhat Acar · Can Yaman
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    ABSTRACT: 45S5 bioactive glass with chemical composition of 45 SiO2–24.5 Na2O–24.5 CaO–6 P2O5 (wt%) was synthesized through melting process using alkali extracted silica from rice hull ash, and commercial silica. Prepared bioactive glasses were characterized by incubation in simulated body fluid (SBF) to investigate their bioactivities and degradation. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), XRD and Vickers hardness measurements were obtained for all samples before and after incubation in simulated body fluid. The results showed that 45S5 bioactive glass produced with amorphous rice hull silica has a good bioactivity, so it can be used as an alternative to commercial silica for the production of the 45S5 bioglass.
    No preview · Article · Dec 2013 · Journal of Computational and Theoretical Nanoscience
  • Didem Özçimen
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    ABSTRACT: Biodiesel production generally involves the transesterification of vegetable and/or animal oils with alcohol and catalyst under conventional stirring with batch and/or continuous processes. In recent years, because of the economical causes, choosing efficient transesterification method for biodiesel production has become important. Using microwave method for the transesterification reaction supports high yields of highly pure products within a short time and a severe reduction in the quantity of by-products when compared to the conventional methods. In this study, transesterification of hazelnut oil was studied by using microwave-assisted method to examine reaction factors which affect the purity of the ester product, including the molar ratio of methanol to hazelnut oil, the amount of alkaline catalyst and the reaction time. The transesterification reactions were carried out by using hazelnut oil, methanol, and potassium hydroxide as the catalyst at 64 °C. A statistical design technique was applied by the use of a two-level factorial design matrix to interpret the experimental results. Empirical relations between the yield and the reaction conditions were developed. The experimental results indicated that microwave-assisted transesterification efficiently produced high yield of methyl esters in a short reaction time, showing that this method may be a promising alternative to the conventional method.
    No preview · Article · Aug 2013 · Journal of Biobased Materials and Bioenergy
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    Pınar Terzioğlu · Sevil Yucel · Taha M. Rabagah · Didem Özçimen
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    ABSTRACT: Wheat is a very important agricultural product, and is among the grains that has the highest sustenance value in the world. Every year large amounts of wheat hull is produced which has a low economic value. The present study aimed to characterize the structure of wheat hull and wheat hull ash obtained after burning wheat hull at 400 to 1000 degrees C for 5 h. This study also investigated the potential of wheat hull as a source for the production of silica xerogel. X-ray diffraction patterns, scanning electron microscope micrographs, the chemical properties, the particle morphology, particle size, surface chemistry of wheat hull, wheat hull ash, and its silica xerogels were determined by the use of various instruments and analysis techniques. A temperature of 700 degrees C was found to be the optimum ashing temperature with maximum amorphous silica content. The BET surface area of ashes ranged from 7.21 to 0.11 m(2)/g. The study demonstrated that silica xerogel powder with 93.9% silica content was obtained by the use of wheat hull after heat treating at 700 degrees C for 5 h.
    Full-text · Article · May 2013 · Bioresources
  • İsa Rahmanlar · Sevil Yücel · Didem Özçimen
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    ABSTRACT: Alcoholysis of waste frying oil (WFO) was studied by using microwave irradiation to examine alcoholization reaction factors which affect the purity of the ester product, including the molar ratio of methanol to WFO, the amount of alkaline catalyst and the reaction time. The alcoholysis reactions were carried out by using WFO, methanol and sodium hydroxide as the catalysts at 64 °C. In order to characterize the reaction conditions for methyl ester production, a series of experiments were carried out with methanol/WFO molar ratios between 6 and 18, and catalyst/WFO weight ratios between 0.5 and 1.5%. The results showed that the most important parameter affecting the reaction is the amount of sodium hydroxide. The best catalyst amount was found as NaOH 1% from the WFO. A higher methyl ester purity was obtained in 1–3 min. In the presence of 1% of NaOH molar ratios varying from 6:1 to 18:1 in 3 min of reaction time, the purity of methyl ester was 93.83–97.20%. However, difficulties were observed in separation process above 9:1. The experimental results indicated that microwave-assisted alcoholysis efficiently produced pure methyl esters in methyl ester quality in a short reaction time. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.
    No preview · Article · Sep 2012 · Asia-Pacific Journal of Chemical Engineering
  • E. Yiğit · M. N. Sarıdede · D. Özçimen
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    ABSTRACT: Laboratory flotation tests were carried out on the SO2 leaching residues of zinc concentrates of Mt. Isa lead–zinc concentrator. In the evaluation of these tests grades, recoveries and separation index values of the metallic elements are used. Separation index value of a metallic element is a new concept proposed in this paper and is useful in the evaluation of any concentration process. In the bulk concentrates obtained after flotation tests, the grades, recoveries, and separation index values of silver were around 900–1000 ppm, 18–20%, and 17–19, respectively.
    No preview · Article · Jan 2012 · Mineral Processing and Extractive Metallurgy Review
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    ABSTRACT: Bone matrix consists of organic and inorganic components. Organic phase mainly contributes to flexibility of bone while inorganic phase being responsible for the rigidity and hardness of the bone. Due to the biocompatibility of ceramics many forms of them have been used as the bone replacement and as the repair material. Hydroxyapatite which also exists in the natural structure of bone is one of those ceramics used as a component of bone cement. In order to modify the physical properties of prepared bone composite structures, some additives are included within the structure. In this study, a silicate material is included as an inorganic filler together with hydroxyapatite. Bis-GMA and HEMA were used as organic matrix. The prepared composites were than immersed in SBF and FTIR, SEM, hardness analyses were performed on the samples before and after the immersion. The results were reported in later part. It was observed that the precipitation of hydroxyapatite occurred after the immersion of samples in SBF and the hardness values were increased for each sample.
    Preview · Article · Oct 2011 · Key Engineering Materials
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    ABSTRACT: Since phenols and phenolic compounds in many industrial wastewaters are toxic organic contaminants for humans and aquatic life, to remove these compounds via the most efficient way is very important for environmental remediation treatment. In this context, almost all of the isotherm models (Freundlich, Langmuir, Temkin, Redlich–Peterson, Sips, and Khan) for adsorption in the literature were applied to explain the adsorption mechanism of 4-chlorophenol on activated carbon in this study. Also theoretical modeling data were obtained using model equations; interpolation and analysis of variance were made to compare data by using statistics software. In addition, the thermodynamic and kinetic studies for adsorption mechanism were included in the article. The adsorption of 4-chlorophenol on activated carbon fits well to the pseudo-first-order kinetic model than the pseudo-second-order, intraparticular diffusion and Bangham models. It is also indicated that 4-chlorophenol adsorption by granular activated carbon would be attributed to a type of transition between physical and chemical adsorption rather than a pure physical or chemical adsorption process. As a result, an environmental remediation problem and the adsorption mechanism on activated carbon that can be regarded as a solution to this problem are described and explained using the mathematical models and calculations in this study.
    No preview · Article · Jun 2011 · Environmental Modeling and Assessment
  • Didem Özçimen · Ayşegül Ersoy-Meriçboyu
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    ABSTRACT: Activated carbons prepared from hazelnut shells and apricot stones were used as adsorbents for the removal of copper(II) ions from aqueous solution. Adsorption studies were carried out by varying the initial metal ion concentration, the temperature and the pH. The amount of Cu(II) ions adsorbed increased with increasing temperature, pH and initial Cu(II) ion concentration. The equilibrium data were analyzed using the Freundlich and Langmuir isotherms. The parameters of the isotherm models were determined for two activated carbons; it was found that the Freundlich model showed a better fit of the adsorption data than the Langmuir model. The physical and chemical properties of hazelnut shell and apricot stone activated carbons were determined for comparative purposes.
    No preview · Article · Dec 2010 · Adsorption Science and Technology
  • Didem Özçimen · Ayşegül Ersoy-Meriçboyu
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    ABSTRACT: Apricot stone, hazelnut shell, grapeseed and chestnut shell are important biomass residues obtained from the food processing industry in Turkey and they have a great importance as being a source of energy. In this study, the characteristics of bio-oil and biochar samples obtained from the carbonization of apricot stone, hazelnut shell, grapeseed and chestnut shell were investigated. It was found that the biochar products can be characterized as carbon rich, high heating value and relatively pollution-free potential solid biofuels. The bio-oil products were also presented as environmentally friendly green biofuel candidates.
    No preview · Article · Jun 2010 · Renewable Energy
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    Didem Özçimen · Ayşegül Ersoy-Meriçboyu
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    ABSTRACT: Carbonization experiments of grapeseed and chestnut shell samples having the average particle size of 0.657 mm and 0.377 mm, respectively, were performed to determine the effect of temperature, sweep gas flow rate and heating rate on the biochar yield. A statistical design technique was applied by the use of a two-level factorial design matrix to interpret experimental results. Carbonization conditions were selected according to a two-level factorial design matrix considering the following variables: temperature (723 K and 823 K), nitrogen gas flow rate (0 and 1000 cm3/min) and heating rate (5 and 20 K/min). Empirical relations between the biochar yield and the carbonization conditions were developed. To comment on the effect of parameters between the superior and inferior levels and to prove the accuracy of design equations from statistical design technique, biochar yields obtained at different conditions were also presented in the graphical way. It was found that temperature has the strongest effect on the biochar yields in comparison with nitrogen gas flow rate and heating rate. Biochar yields of grapeseed and chestnut shell were decreased with the increasing temperature, heating rate and sweep gas flow rate. A comparison between the fuel properties of waste materials and biochar products was also done.
    Full-text · Article · Nov 2008 · Fuel Processing Technology
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    ABSTRACT: Carbonization experiments of hybrid poplar samples were performed in a thermogravimetric (TG) analyzer to investigate the effect of carbonization conditions, such as heating rate, particle size and sweep gas flow rate on the biochar yield. During carbonization, samples were heated from room temperature to the temperature of 723 K in an inert atmosphere. A statistical design technique was applied by using a two-level factorial design matrix to elucidate the experimental results. It was obtained that the biochar yields of samples were changed depending on the carbonization conditions. Empirical relations between the biochar yield and the carbonization conditions were developed. Biochar yields of samples were decreased with the increasing heating rate and sweep gas flow rate and increased with the increasing particle size. Kinetic analysis of the carbonization TG curves was achieved by using three different methods of calculation; also, 19 different model equations of possible solid-state rate controlling mechanisms were considered. A computer program in BASIC which enables regression analysis was used to calculate kinetic parameters from experimental TG data. It was observed that the carbonization conditions and the method of calculation influenced the kinetic results obtained.
    Preview · Article · Sep 2008 · Fuel Processing Technology
  • Didem Özçimen · Filiz Karaosmanoğlu
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    ABSTRACT: New and renewable fuels are the major alternatives to conventional fossil fuels. Biomass in the form of agricultural residues is becoming popular among new renewable energy sources, especially given its wide potential and abundant usage. Pyrolysis is the most important process among the thermal conversion processes of biomass. In this study, the production of bio-oil and biochar from rapeseed cake obtained by cold extraction pressing was investigated and the various characteristics of biochar and bio-oil acquired under static atmospheric conditions were identified. The biochar obtained are carbon rich, with high heating value and relatively pollution-free potential solid biofuel. The bio-oil product was presented as an environmentally friendly green biofuel candidate.
    No preview · Article · Apr 2004 · Renewable Energy
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    ABSTRACT: The fixed bed atmospheric pressure pyrolysis and nitrogen swept pyrolysis of the rapeseed cake obtained from cold extraction press have been investigated. Experiments were performed in the Heinze retort at a 7°C min-1 heating rate, with a 500°C final temperature varying sweep gas velocity (50, 100, 150, 200, 250, 300 cm3 min-1) under nitrogen atmosphere. Liquid, gas, and char yields were determined, pyrolysis conversion was calculated, and liquid, char, and gas products were presented as an environmentally friendly fuel candidate.
    No preview · Article · Dec 2001 · Energy Sources
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    ABSTRACT: The fixed bed atmospheric pressure pyrolysis and nitrogen swept pyrolysis of the rapeseed cake obtained from cold extraction press have been investigated. Experiments were performed in the Heinze retort at a 7°C min-1 heating rate, with a 500°C final temperature varying sweep gas velocity (50, 100, 150, 200, 250, 300 cm3 min-1) under nitrogen atmosphere. Liquid, gas, and char yields were determined, pyrolysis conversion was calculated, and liquid, char, and gas products were presented as an environmentally friendly fuel candidate.
    No preview · Article · Jan 2001 · Energy Sources

Publication Stats

292 Citations
22.65 Total Impact Points

Institutions

  • 2010-2013
    • Yildiz Technical University
      • • Faculty of Chemical and Metallurgical Engineering
      • • Department of Bioengineering
      İstanbul, Istanbul, Turkey
  • 2001-2010
    • Istanbul Technical University
      • • Department of Chemical Engineering
      • • Faculty of Chemical and Metallurgical Engineering
      İstanbul, Istanbul, Turkey