Didem Özçimen

Yildiz Technical University, İstanbul, Istanbul, Turkey

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Publications (9)6.33 Total impact

  • 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.
    Asia-Pacific Journal of Chemical Engineering 09/2012; 7(5). · 0.80 Impact Factor
  • 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.
    Mineral Processing and Extractive Metallurgy Review 01/2012; 33(1):55-64. · 0.65 Impact Factor
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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.
    Key Engineering Materials 10/2011; 493-494.
  • 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.
    Renewable Energy. 01/2010;
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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.
    Fuel Processing Technology,. 01/2008; 89:858-863.
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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.
    Fuel Processing Technology. 01/2008;
  • 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.
    Renewable Energy 01/2004; · 3.36 Impact Factor
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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.
    Energy Sources 01/2001; 23(10). · 0.54 Impact Factor
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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.
    Environmental Modeling and Assessment 17(3). · 0.98 Impact Factor