Thermo-oxidative characterization and kinetics of tar sands Mustafa Versan KOK * Department of Petroleum and Natural Gas Engineering, Middle East Technical University, Inonu Blv, 06531 Ankara, Turkey article info Article history: Received 4 October 2010 Received in revised form 16 June 2011 Accepted 20 June 2011 Available online 27 July 2011 Keywords: Tar sands Asphaltite Thermal analysis Kinetics abstract In this research, non-isothermal kinetics and thermal analysis of Gerçüs ¸ tar sand sample is studied by DSC (differential scanning calorimeter) and TG/DTG (thermogravimetry). Experiments were performed using three different mesh size (20e35, 35e50 and >50) of sample. Differential scanning calorimeter (DSC) curves revealed three reaction regions in the temperature range of 20e600  C. On the other hand, thermogravimetry (TG/DTG) curves of tar sand samples at different particle sizes demonstrated three stages of weight loss. Two different kinetic models (Coats & Redfern and Arrhenius) were used to determine the kinetic parameters of the samples and it was observed that the average activation energy values were between 17.5 and 26.6 kJ/mol, for reaction region-II and 126.2e160.1 kJ/mol for reaction region-III, respectively. In order to see the contribution of each region to the overall reactivity of the tar sand sample, weighted mean apparent activation energy of the samples are also determined. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Tar sands are naturally occurring bitumen-impregnated sands that yield mixtures of liquid hydrocarbon and that require further processing other than mechanical blending before becoming finished petroleum products. Tar sands are rocks (other than coal or oil shale) that contain highly viscous hydrocarbons that are unre- coverable by primary production methods. Thermo-analytical methods, such as TG/DTG (thermogravimetry), DSC (differential scanning calorimeter) and DTA (differential thermal analysis) have proved to play an important role in the characterization and combustion studies of fossil fuels, including tar sands [1e5]. Tonbul et al. [6] studied the thermal behavior of asphaltites using thermogravimetric analysis at atmospheric pressure. TG/DTG data of samples demonstrated two stages of mass loss. The first stage, called primary volatilization, occurred in the temperature range of 200e600  C. On the other hand, secondary gasification stage occurred, in the temperature range of 600e800  C. Kok et al. [7] studied the combustion characteristics and reaction kinetics of Silopi region asphaltites. Product gas analyses were used to deter- mine the atomic H/C ratio, relative reaction rate, activation energy and Arrhenius constant for each asphaltite sample studied. In the low temperature region, an early production of oil was observed where the volatiles within the asphaltite were released. Remaining heavy hydrocarbons caused the formation of high temperature oxidation region. Ballica [8] studied the oxidation of S ¸ ırnak asphaltite samples under isothermal conditions using a fixed-bed reactor in various temperature modes. The effect of heating rate on reaching final isothermal temperatures was inves- tigated. Kinetic parameters of the overall oxidation reaction for each heating rate were also determined. Kok [9] studied the non- isothermal combustion and kinetics of Silopi asphaltite samples by differential scanning calorimeter (DSC) and thermogravimetry (TG/DTG). In all the experiments, two reaction regions were observed. The first region was due to the evaporation of moisture in asphaltite sample. The second region was due to release of volatile matter and burning of carbon. Elbeyli [10] studied the pyrolysis properties and kinetic analysis of asphaltite samples by means of thermogravimetry (TG/DTG). Thermogravimetric curves showed that the decomposition proceeds through two steps. Coats-Redfern method was used to analyze the TG/DTG data for the determination of kinetic parameters for different heating rates. Hiçyılmaz and Altun [11] studied the S ¸ ırnak asphaltite samples by gravity and flotation methods. Combustion of raw and improved asphaltites was performed by non-isothermal thermogravimetric experi- ments. Activation energies were correlated with ash contents, calorific values, bum-out temperatures and sulfur contents of the samples. Al-Ottom et al. [12] studied the different parameters affecting the behavior of flotation of Jordanian tar sand utilizing a fluidized bed floatator. The effects of the addition of a flotation agent, NaOH, temperature and flotation time on the beneficiation of bitumen in the froth were investigated. It was found that the beneficiation factor in the froth increased with the increase of temperature and flotation time. Penner et al. [13] reviewed and * Orta Dogu Teknik Universitesi, Universiteler Mah., Dumlupinar Blv, No. 1, 06800, Cankaya/Ankara, Turkey. E-mail address: kok@metu.edu.tr. Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2011.06.042 Energy 36 (2011) 5338e5342