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    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, A
    Two 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.
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    Kinetic rate models for dissolution of Turkish lignites in tetralin under nitrogen or hydrogen atmospheres
    (Elsevier Science Bv, 1998) Ceylan, K; Olcay, A
    The reaction kinetics of the dissolution of two Turkish lignites have been investigated. The dissolution products were separated into pseudo-components such as preasphaltenes, asphaltenes and oils by successive solvent extractions. Reaction mechanisms have been proposed and tested to estimate the rates of formation of these products. The proposed mechanisms are based on the assumptions that the reactions are irreversible, pseudo-first order with respect to the reacting species, and their rate constants obey linear Arrhenius behavior. The product distributions data have been assessed by a simple simulation program, The results indicated that certain simple kinetic models represent the data well and the prevailing mechanism changes slightly with temperature. The estimated energy of activation for dissolution changes from 54 kJ/gmol to 185 kJ/gmol depending on the lignite and the suggested reaction model. The results suggest that conversions of lignites to preasphaltenes and gases are slower than the conversion of preasphaltenes and asphaltenes to oils. Published by Elsevier Science B.V.