Journal of Hazardous Materials 166 (2009) 126–132 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat An algorithm for the kinetics of tire pyrolysis under different heating rates Augustine Quek, Rajashekhar Balasubramanian ∗ Division of Environmental Science & Engineering, Faculty of Engineering, National University of Singapore, Block EA #03-12, 9 Engineering Drive 1, Singapore 117576, Singapore article info Article history: Received 10 June 2008 Received in revised form 3 October 2008 Accepted 5 November 2008 Available online 21 November 2008 Keywords: Pyrolysis Kinetics Models Scrap Tire Thermal lag abstract Tires exhibit different kinetic behaviors when pyrolyzed under different heating rates. A new algorithm has been developed to investigate pyrolysis behavior of scrap tires. The algorithm includes heat and mass transfer equations to account for the different extents of thermal lag as the tire is heated at different heating rates. The algorithm uses an iterative approach to fit model equations to experimental data to obtain quantitative values of kinetic parameters. These parameters describe the pyrolysis process well, with good agreement (r 2 > 0.96) between the model and experimental data when the model is applied to three different brands of automobile tires heated under five different heating rates in a pure nitrogen atmosphere. The model agrees with other researchers’ results that frequencies factors increased and time constants decreased with increasing heating rates. The model also shows the change in the behavior of individual tire components when the heating rates are increased above 30 K min -1 . This result indicates that heating rates, rather than temperature, can significantly affect pyrolysis reactions. This algorithm is simple in structure and yet accurate in describing tire pyrolysis under a wide range of heating rates (10–50 K min -1 ). It improves our understanding of the tire pyrolysis process by showing the relationship between the heating rate and the many components in a tire that depolymerize as parallel reactions. © 2008 Elsevier B.V. All rights reserved. 1. Introduction It is estimated that worldwide, over one billion waste tires are generated annually [1]. Tires do not break down easily in the nat- ural environment. The vulcanized rubber consists of long chain polymers (isoprene, butadiene, and styrene-butadiene) that are cross-linked with sulfur bonds and are further protected by antiox- idants and antiozonants that resist degradation. In landfills, rubber tires tend to float to the top due to trapped gases, thus breaking landfill covers. Combustion of tires produces pollutants harmful to human health including polycyclic aromatic hydrocarbons (PAHs), benzene, styrene, phenols, and butadiene [2]. This has put undue demands on conventional disposal options of scrap tires such as landfills and incineration. Consequently, there is an urgent need for the recycling of scrap tires, especially recovery of valuable resources from this car- bonaceous material. Pyrolysis is a feasible method for recovering valuable products such as char, activated carbon, oil and gas from scrap tires [3]. Pyrolysis can be thought of as the thermal breakdown of organic polymers into simpler molecules in the absence of air. Various processes are thought to occur that occur simultaneously such as thermal depolymerization, decomposition, and gasification ([3], and references therein). However, although several fundamen- ∗ Corresponding author. Tel.: +65 6516 5135; fax: +65 6516 5266. E-mail address: eserbala@nus.edu.sg (R. Balasubramanian). tal studies on pyrolysis of scrap tires have been carried out over the years ([3], and references therein), the mechanisms involved in the pyrolysis process are not completely understood yet. Modeling the kinetics of the tire thermal degradation pro- cess can provide insights into the mechanisms responsible for tire pyrolysis and predict potential difficulties in a pyrolysis reactor. Earlier studies have built pyrolysis models based on data obtained from thermogravimetry techniques [3], which measures the sam- ple mass loss with time and temperature. One method is to assume a single peak and apply only one set of kinetic parameters [4–8]. For example, Kore ˇ novaˇ ı et al. modeled the overall pyrolysis of scrap tires as a single reaction proceeding in two stages [8] using the Arrhenius equation. However, their thermogravimetric (TG) data, showed two maxima in the rate of mass loss for tire pyrolysis. They attributed these two points to lower molecular mass compounds release in the first stage and aromatic and heavier hydrocarbons in the second [8]. The fact that tire pyrolysis is a multi-stage, multi-component phenomenon is widely accepted [9–17]. The first stage of the pyrol- ysis is attributed to extender oils and softeners, the second stage to isoprene rubber or natural rubber (NR), butadiene (BR) and styrene- butadiene rubbers (SBR) [3,8,10,12,15–18]. Thus, a more realistic and popular approach is to model each major component of the tire sep- arately [9–15]. Each component is represented by a peak in the TG curve, to which the Arrhenius type equation can be fitted. This pro- duces one set of kinetic parameters for each component of the tire being pyrolyzed. The different sets of parameters thus give specific 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2008.11.034