Research article Activation energy distribution in pyrolysis of Thar coal, Pakistan Muhammad Nasiruddin Khan, 1 * Anila Sarwar 2 and Syed Kabir Shah 2 1 Department of Chemistry, University of Karachi, Karachi 75270, Pakistan 2 Fuel Research Centre, Pakistan Council of Scientific & Industrial Research, Karachi, Karachi 75280, Pakistan Received 6 August 2014; Revised 12 January 2015; Accepted 27 January 2015 ABSTRACT: Thermochemical decomposition of 16 samples of low-rank Thar coal has been investigated using non- isothermal thermogravimetric data under an inert environment. Rapid weight loss of volatiles was found in the regions of 164–233 and 473–503 °C. Kinetics of pyrolysis reaction showed that the volatiles released in three consecutive steps follow first-order reaction. The kinetic evaluation focuses on all the steps to estimate activation energy, pre-exponential factor and the contribution of each step to the overall reaction. The results showed that evaporation of moisture and low-temperature volatile compounds require 3.17–4.81 kJ mol À1 activation energy. The combustion of char required a higher amount of energy (10.86–36.11 kJ mol À1 ). The formation of secondary char required 10.34–24.00 kJ mol À1 energy. The results suggested that Thar coal has a substantial potential for gasification due to high volatile content and low activation energy. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd. KEYWORDS: activation energy; coal pyrolysis; kinetics; thermogravimetry INTRODUCTION Coal pyrolysis is important as it is the fundamental step of all coal conversion processes like combustion, carbonization, liquefaction, and gasification. [1–4] It not only controls the release of volatile products and reactivity of the non-volatile char in combustion and gasification processes but also sorts out the competitive yield of product species in liquefaction process. A number of kinetic-based models on coal pyrolysis have been proposed during the last few decades to design and scale-up of gasifiers. [5,6] However, the modeling of coal pyrolysis is considered comparatively complex because of the effects of residence time, final temperature, heating rate and pressure in parallel independent reactions. [7] Furthermore, a model is commonly appropriate for a particular system in specific conditions. Model-free isoconversional and model- fitting isothermal kinetic approaches are recommended for the prediction of coal behavior on heating. [8] The non-isothermal model-fitting kinetic approach was also adopted by a number of researchers because the achievement of temperature-resolved measurements is easier and faster. [8,9] Non-isothermal technique was used in the present study because it is highly sensitive to the experimental noise and no data have been lost to attain a preset temperature. The kinetics of pyrolysis reaction involves the measurements at slow and fast rates. The process depends on the temperature within a coal particle and the rate of heat transfer. Scott suggested coal heating at a low rate (10 °C min À1 ) to overcome the difficulty in rate measurements. [10] He elucidated that a coal particle has a uniform temperature throughout its volume when heated at a low heating rate. Therefore, the slow rate pyrolysis approach is considered more appropriate to study the kinetics of devolatilization reaction at laboratory scale. Thar coal, the largest coal reserve of Pakistan, is expected as the most potential future fuel to resolve the current energy crisis of the country. In view of the importance of its future utilization in combustion, gasification and liquefaction processes, a detailed insight study is highly desirable. Generally, the pyrolysis of coal is considered as a first-order reaction but it strictly depends on the nature of coal. [5,6] Not a single attempt has been reported so far for the modeling of pyrolysis of Thar coal. Therefore, the present study is aimed to evaluate the reaction mechanism of Thar coal pyrolysis through kinetic studies. The main objective of pyrolysis is to estimate the minimum energy required to convert coal into gaseous products. The pre- exponential factor was also evaluated to predict some *Correspondence to: Muhammad Nasiruddin Khan, Department of Chemistry, University of Karachi, Karachi-75270, Pakistan. E-mail: nasiruk@uok.edu.pk © 2015 Curtin University of Technology and John Wiley & Sons, Ltd. Curtin University is a trademark of Curtin University of Technology ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING Asia-Pac. J. Chem. Eng. 2015; 10: 297–306 Published online 3 March 2015 in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/apj.1875