Variable Reaction Order for Kinetic Modeling of Oil Shale Pyrolysis

Abstract

This work investigates kinetics of El-Lajjun oil shale pyrolysis. The kinetic data obtained from TG/DGA curves at heating rates 1, 3, 5, 10 and 30 °Cmin -1 to a final pyrolysis temperature 550 °C were employed assuming their second-order kinetics to determine apparent activation energy, 99-141.4 kJ/mol and frequency factor, 1.89•10 7 to 1.71•10 11 , for each heating rate using the Coats & Redfern method. The obtained values of apparent activation energies and frequency factor were modified through an equation to 112-179 kJ/mol and 3.95•10 7 -3.66•10 13 , respectively, to fit the developed kinetic equation.In this study, kinetic modeling of the pyrolysis process was performed using a newly developed variable reaction order. The variable reaction order was inferred directly from the experimental data and correlated with heating rate, h, (°Cmin -1 ), rate of conversion, dx dtand a constant equal with 8.314 (°C).The range of generated values of the variable reaction order varied between 1.99 and 1.85. Conversion of a sample was calculated basing on initial and final weight of the sample at the end of run. A satisfactory fit of the experimental data was obtained using the equation developed for a variable reaction order.

Pyrolysis and char oxidation characteristics of oil shales and coal in a thermogravimetric analyzer

“…The global reaction order of coal pyrolysis is determined to be higher than unity, and such a high value is a measure of complexity and multiplicity of the reaction mechanism. [28] The apparent activation energy based on the optimized reaction order of coal pyrolysis is found in good agreement with the values from literature. [29] On the other hand, the first stage of oil shale pyrolysis is predicted by two-step model in Figure 5.…”

“…From this work, the coal pyrolysis process can be predicted by three‐step reaction model as shown in Figure . The global reaction order of coal pyrolysis is determined to be higher than unity, and such a high value is a measure of complexity and multiplicity of the reaction mechanism . The apparent activation energy based on the optimized reaction order of coal pyrolysis is found in good agreement with the values from literature .…”

Determination of Selected Elements in Shale Oil Liquid

“…The structural distribution of sulfur in the distillate fractions of the obtained oil was investigated, to identify that the sulfur containing compound was basically composed of naphthenic rings in different combinations with aliphatic alkyls [4,5]. Several authors have studied Jordanian oil shale pyrolysis and some characteristics of the shale oil obtained were determined [6,7].…”

Variable Activation Energy Principle to Model Oil Shale Pyrolysis Kinetics

“…Numerous investigations on oil shale (OS) pyrolysis kinetics have been carried out [1][2][3][4][5][6][7][8][9]. These studies used experimental methods such as differential thermal (DT), thermogravimetric (TG), Rock-Eval, and triple quadrupole mass spectrometer (TQMS) methods, or a simple laboratory retorting system to predict the conversion of kerogen or rate of mass loss with pyrolysis temperature.…”

“…Kinetic modelling of oil shale or its demineralized kerogen is viewed from different perspectives. Several models [11][12][13][14] employed single activation energy value to estimate kinetic parameters, assuming a first order of reaction, whilst other methods [5,7,15] made use of the distribution of activation energy values over the entire range of pyrolysis process. The spread of activation energy values over the entire range of conversion characterizes the different, either primary or secondary, reactions of thermal cracking.…”