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Öğe Catalytic dissolution of two Turkish lignites in tetralin under nitrogen atmosphere: effects of the extraction parameters on the conversion(Elsevier Sci Ltd, 2001) Karaca, H; Ceylan, K; Olcay, ATwo Turkish lignites were extracted with tetralin in a batch autoclave under nitrogen atmosphere. Fe2O3, Mo(CO)(6), MoO3 or Al2O3 were used as the added catalyst. The isothermal extraction temperatures ranged from 325 to 425 degreesC, the starting nitrogen pressure ranged from atmospheric to 5 MPa, the isothermal extraction periods ranged from 0 to 120 min. After removal of char and solvent, the remaining products were separated into three fractions: preasphaltenes (benzene insolubles), asphaltenes (benzene soluble, n-pentane insolubles) and oils (n-pentane solubles) by successive extractions with benzene and n-pentane. The variations in the conversions and soluble product compositions were investigated with respect to the extraction conditions. The results indicate that the conversions of the lignites are low below 350 degreesC but high over 375 degreesC. The catalysts enhance mainly the oil formation, and the catalytic activities of Mo(CO)(6) and Fe2O3 are higher than the others. Lignite-impregnated catalysts show higher reactivity than the physically mixed catalysts. Increasing the extraction time and temperature affects the total conversion and soluble product composition. The gaseous product formation increases with the time at temperatures of 400 degreesC and above. (C) 2001 Elsevier Science Ltd. All rights reserved.Öğe The characterization of coal liquefaction products obtained under inert atmosphere and catalytic conditions. Part I: Insoluble products (chars)(Taylor & Francis Inc, 2005) Karaca, HIn this study, two types of Turkish lignite were liquefied under inert atmosphere and catalytic conditions. Catalyst was added to the reaction medium by physically mixing or impregnation. The products obtained at coal liquefaction were separated into two groups as soluble products with THF extraction and insoluble products (chars). The effects of various process parameters on the properties of chars were examined. The ash contents of chars were decreased significantly by increasing solvent to coal ratio and reaction temperature, and changed partially by pressure, catalyst type and concentration. Carbon, hydrogen and nitrogen contents of the chars decreases, but the sulphur and oxygen contents increase with increasing solvent to coal ratio, pressure, catalyst concentration, reaction time and reaction temperature. The fuel quality of chars obtained by catalyst impregnation method was determined to be much higher with respect to the catalyst physically mixing method.Öğe Chemical cleaning of Turkish lignites by leaching with aqueous hydrogen peroxide(Elsevier Science Bv, 1997) Karaca, H; Ceylan, KTwo Turkish lignites (Beypazari and Tuncbilek) were leached with the solutions of hydrogen peroxide in water or in 0.1 N H2SO4. The effects of some process parameters, such as concentration, time and temperature, on the removal of ash and sulphur have been investigated. The rate of ash and sulphur removal are relatively high in the first 30 min, but slow after 60 min of the reaction time. Depending on the type of lignite, the maximum reductions ranged from 30 to 70% in ash, from 70 to 95% in pyritic sulphur, and from 42 to 58% in total sulphur. A relatively small reduction (a maximum of 25%) was estimated for organic sulphur. The optimum process conditions were established as a hydrogen peroxide concentration of 15 wt.%, a temperature of 30 degrees C and a leaching time of 60 min. High peroxide concentration or high temperature did not result in an appreciable further reduction in ash and sulphur. Due to partial dissolution or oxidation of the lignites, some organic material losses occurred but no heating value loss was estimated. An overall kinetic approach was also applied for pyritic sulphur removal and the conversion data were analyzed by using both homogenous and heterogeneous reaction models.Öğe Demineralisation of lignites by single and successive pretreatment(Elsevier Sci Ltd, 2003) Karaca, H; Önal, YIn this study, two Turkish lignites (Bolu-Mengen, Kutahya-Tuncbilek) were treated under atmospheric and reflux conditions with 10-30% NaOH, 10% HCl and 10% H2SO4 solutions, singly and/or successive treatments to determine the effects of this treatment on the mineral matter and acidic functional groups. Characterisation of the treated and untreated samples was by Fourier transform infrared spectroscopy. The process of successive pretreatment was found to be more effective than single steps in terms of demineralisation and removal of carboxylate structures. During NaOH treatment, the first of successive steps, salts soluble in acid but not in water were determined. In successive demineralisation steps with 30% NaOH and 10% HCl, a low level of 3.3% ash was obtained for the Tuncbilek lignite. In addition, during the pretreatment, most of the Ca and K were exchanged with Na. (C) 2003 Elsevier Science Ltd. All rights reserved.Öğe Desulfurization of fuel by leaching using H2O2 and H2SO4(Taylor & Francis Inc, 2005) Karaca, H; Yildiz, ZIn this research, different concentrations of H2O2 and H2SO4 solutions were used in order to remove the sulfur from high sulfur contented No. 6 fuel oil. In desulphurization experiments, reaction temperature, reaction time, and the concentration of H2O2 and H2SO4 were varied in a range of 20-50 degrees C, 30-150 min, 5-35%, and 0.05-2.00 N, respectively. The ratio of reagent/fuel oil was taken as 10/1 and the stirring speed as 1,000 rpm. According to the results obtained, considering the desulphurization and the organic structure of the fuel, the most appropriate method was found as the H2O2 leaching method. It was barely determined that the highest desulphurization was achieved by H2O2/0.1N H2SO4 leaching method. The optimum process parameters for H2O2 leaching method were found as a concentration of 15%, reaction temperature of 30 degrees C, and reaction time of 60 min; and for H2SO4 leaching method were found as concentration of 0.1 N, reaction temperature of 30 degrees C, and reaction time of 150 min. It was observed that by increasing the reaction temperature, reaction time, and reagent concentration, the carbon and hydrogen contents of the fuel decreased considerably and on the contrary the oxygen content increased very rapidly. A partial decrease of nitrogen content was also observed.Öğe Desulphurization kinetics of number 6 fuel oil via a chemical method(Taylor & Francis Inc, 2005) Karaca, H; Yildiz, ZIn this research, desulphurization of number 6 fuel oil by the H2O2/H2SO4 method was studied. The effects of reaction temperature and reaction time on desulphurization were examined. Also, kinetic approximation for desulphurization was carried out. It was determined that the maximum desulphurization was performed at conditions of reaction temperature of 40 50 degrees C and reaction time of 150 min. The total sulfur content of the fuel oil sample was reduced from 2.78 to 0.68% at the reaction temperature of 50 degrees C and reaction time of 150 min. As the degree of desulphurization increased, the higher heating value decreased at higher reaction temperatures and reaction times. As a result of kinetic approximation, it was found that the order of the reaction was approximately 0.96 and the rate constant, k = 5.84 (*) 10(6) exp(-65.08/RT), for desulphurization of fuel oil by chemical method.Öğe Determination of optimum process parameters in desulphurization of fuel oil(Taylor & Francis Inc, 2005) Yidiz, Z; Karaca, HIn this research, desulphurization of number 6 fuel oil (residue fuel oil) by chemical methods was studied. Besides, factors like reaction temperature, reaction time, concentration, and stirring speed were examined to determine the effects of various process parameters on desulphurization and on higher heating value. According to the results obtained, the optimum values of process parameters were determined as H2O2 concentration of 15%, reaction temperature of 40 degrees C, reaction time of 60-150 min and stirring speed of 1,000 rpm. Under these conditions, the sulphur content in the fuel oil sample was reduced from 2.78 to 2.29%-1.54% approximately. The degree of desulphurization increased, but higher heating value decreased seriously at high levels of H2O2 concentration, reaction temperature, reaction time, and stirring speed. Some fuel oil samples that are pretreated with H2O2/0.1 N H2SO4 were extracted successively with acetone, ethanol, ethylene glycol, and hydrogen peroxide. In conclusion, the sulphur content decreased approximately from 2.29 to 1.08%. Partial decrease determined in the higher heating value of the sample at the end of extraction.Öğe Effects of coal liquefaction parameters on the removal of oxygen and the higher heating value of the soluble products(Taylor & Francis Inc, 2005) Karaca, HIn this study, effects of coal liquefaction parameters on the removal of oxygen, the higher heating value of char, and soluble products during the catalyst physically mixing or impregnation of the two Turkish lignites were investigated. According to the results, the effects on the higher heating value of char and the soluble products of the reaction parameters were almost similar for both lignites. In the case of catalysts physically mixing, the higher heating value of total soluble products of Beypazari lignite increased as a result of increase in solvent/coal ratio and temperature. In the case of the catalyst physically mixing and impregnation of Tuncbilek lignite, the higher heating value of char and the soluble products was observed to have increased considerably at 350 - 400 degrees C of the reaction temperature in 10 - 60 minutes of reaction time. According to the results of FT- I. R., it was observed that functional groups with oxygen ( carboxylic, carbonyl and etheric) were decreased or removed completely, depending on the liquefaction conditions.Öğe Effects of the reaction conditions on the distribution of sulphur among the products of the catalytic dissolution of Turkish lignites(Elsevier Sci Ltd, 2002) Karaca, H; Ceylan, KEffects of the process parameter on the distribution of the inherent sulphur among the products of the catalytic liquefaction of two Turkish lignites have been investigated. The dissolution reactions were carried out in tetralin at 350-425 degreesC under nitrogen atmosphere. Fe2O3, MO(CO)(6), MoO3 or Al2O3 were used as the added catalysts. The starting nitrogen pressure ranged front atmospheric to 5 MPa. the isothermal extraction periods ranged from 0 to 120 min, solvent/lignite ratio ranged from 1/1 to 6/1. After drying in vacuum, the char and the Soluble products were analyzed for their sulphur contents. The results indicate that the sulphur content of the Soluble products were generally lower than 1% and only a small portion (approximate to0.5-7%) of the initial total sulphur passed to the Soluble product. Most of the Sulphur was remained in the char or passed into the gaseous products. Besides the process conditions, the structures of sulphur in the original lignites strongly affect the partitioning of the sulphur among the products. (C) 2002 Elsevier Science Ltd. All rights reserved.Öğe Thermogravimetric analysis of pretreated Turkish lignites(Elsevier Sci Ltd, 1999) Ceylan, K; Karaca, H; Önal, YThe kinetics of nonisothermal pyrolysis of raw, demineralized or oxidized Turkish lignites have been investigated by thermogravimetry, differential thermal analysis and differential scanning calorimetry. The analyses were carried out in an inert atmosphere or in air atmosphere. The weight loss data indicate that pyrolysis characteristics of the lignites and the prevailing kinetic mechanism vary depending on temperature. The weight loss rates show essentially two regimes, and the major weight loss occurs in the range of 300 degrees C-650 degrees C. The results for the low temperature region (T < 200 degrees C) suggest that the weight loss may be represented by 1.2-1.4-th order of reaction with an activation energy of approximately 15-35 kJ mol(-1). The differential thermal analysis and the differential scanning calorimetry data gave similar values for the overall reaction order and activation energies for this temperature region. At the higher temperature region (T > 300 degrees C), 1.2-1.8-th order of reaction shows a good fit with the weight loss data. The values of the estimated activation energies for this region vary from approximately 40 to 85 kJ mol(-1) depending on the type of sample. However, the differential thermal analysis data suggest that the overall reaction order is around 1.0-1.2 and the effective activation energies vary approximately from 170 to 250 kJ mol(-1). (C) 1999 Elsevier Science Ltd. All rights reserved.
