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  • Author or Editor: L. Belkbir x
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Abstract  

Residual carbons from kerogen extracted from two Moroccan oil shales (from Timahdit and Tarfaya) were oxidized in air. The oxidations were studied by isothermal thermogravimetry. Several kinetic models for mechanisms of the reactions were tested to fit the experimental data. Oxidation of the residual carbon derived from Timahdit oil shale followed a two-third order reaction with an activation energy of 58.5 kJ mol–1, whilst that from Tarfaya oil shale was a half order reaction with activation energy of 64.1 kJ mol–1.

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Abstract  

Thermal analysis has been used to determine the impact of heating on the decomposition reaction of two Moroccan oil shales between ambient temperature and 500C. During pyrolysis of raw oil shale, the residual organic matter (residual carbon) obtained for both shales depends on the heating rate (5 to 40C min-1). Three stages characterize the overall process: the concentration of carbonaceous residue decreases with increase of heating rate, become stable around 12C min-1 and continue to decrease at higher heating rates. Activation energies were determined using the Coats-Redfern method. Results show a change in the reaction mechanism at around 350C. Below this temperature, the activation energy was 41.3 kJ mol-1 for the decomposition of Timahdit, and 40.5 kJ mol-1 for Tarfaya shale. Above this temperature the respective values are 64.3 and 61.3 kJ mol-1. The reactivity of Timahdit and Tarfaya oil shale residual carbon prepared at 12C min-1 was subject to a dynamic air atmosphere to determine their thermal behaviour. Residual carbon obtained from Tarfaya oil shale is shown to be more reactive than that obtained from Timahdit oil shale.

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Abstract  

Organic matter evolution and kinetics of combustion of Tarfaya and Timahdit oil shales have been examined by thermogravimetry (TG) and by differential thermal analysis (DTA). An agreement is observed between both techniques where it was found that combustion of organic matter occurs in two steps. Kissinger's method applied on experimental results gives an activation energy of the same magnitude for the first step of both oil shales (103 kJ mol–1) whereas the second is 148 kJ mol–1 for Timahdit and 118 kJ mol–1 for Tarfaya.The changes in specific surface area during thermal combustion of Timahdit and Tarfaya oil shales have been studied by thermogravimetric gas sorption balance and correlated with experimental results obtained on TG/DTA in air. For Timahdit oil shale oxidation products, specific surface areas calculated from nitrogen adsorption data shows a slight increase during the temperature domain of 280 to 430°C and after this temperature, they increase sharply. However, data obtained with Tarfaya oil shales shows a significant increase at the temperature of maximum oxidation of the first stage of combustion of organic matter.

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Abstract  

The gasification with carbon dioxide of residual carbons prepared from Timahdit and Tarfaya oil shale kerogens has been studied by thermal analysis techniques (TG and DTA) under heating rates varying from 5 to 48C min-1. The reactions obey first order kinetics. Activation energies have been calculated by several methods, such as Kissinger, Chen-Nuttall and Coats-Redfern methods, and are broadly comparable with literature data for similar carbons.

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