Introduction

Packaging presents a major growth area where there has been an increasing demand for plastics and 52% of the plastics produced in India are utilized for packaging. Among the commodity plastics, polyethylene (PE) and polyethylene terephthalate (PET) are predominantly used in packaging. Low-density polyethylene (LDPE) is used in the manufacture of carry bags and PET is used in packaging beverages like soft drink and mineral water. PET in particular presents a major growth area in the years to come. Indian PET consumption has grown at an annual rate of 30% and the current PET consumption is estimated to be around 45,000 tonnes per annum . India will probably see a rise in waste generation from less than 40,000 metric tonnes per year to over 125,000 metric tonnes by the year 2030.

Themost commonways to treatment of the solidwaste are land filling, incineration and materials recycling. A life cycle assessment (LCA) tool is used to compare different alternativewaste treatment strategies. The simulationmodelOrware (organic waste research) used for the material and energy flows in waste management based on life cycle assessment (LCA) was used in the quantification of emissions, energy use and financial costs. The results suggest the environmental preference of recycling over incineration over land filling.

The quality of recycled product remains questionable if poor state-of-the-art technologies are employed for recycling. To overcome certain demerits of recycling and incineration, researchers across the world have focused on development of value added products from waste plastics such as activated carbon, liquid fuel and gaseous product and monomer recovery. Again, extensive research is going on to look for alternative energy sources. The application of novel alternative process, pyrolysis or catalytic degradation as a means of reusing scrap tyres and waste plastic, have recently been the subject of renewed interest. In this process waste plastic and tyres break down to give oil, high calorific value gaseous product and a residual solid carbon. There are some valuable aromatic (limonene, indene, styrene, xylene and naphthalene) chemicals found in the oil that can be used in the petrochemical industry [4–7]. The residual carbon is being upgraded to produce a high-grade activated carbon.

These processes reduce the NOx emission as well. Thermogravimetic analysis (TGA) is widely used technique to study the pyrolysis reaction kinetics. Kinetic study of pyrolysis is essential to understand the degradation mechanism; to know the rate of reaction and reaction parameters; and to predict the products distribution. This information is very important for proper selection of the reactor; optimization of the reactor design and operation. Several studies on thermal and catalytic degradation of plastics such as polypropylene (PP), polyethylene (PE), low-density ployethelene (LDPE) and polystyrene (PS) are reported in literature [9–24]. Catalysts used are MCM-41, ZSM-5, Fe-K/Al2O3, DeLaZSM-5, USY and Ni-REY. Degradation of PET in supercritical methanol was investigated to develop a chemical recycling process for waste plastic, where PET decomposed to its monomer dimethyl terephthalate and ethylene glycol [25]. TGA is utilized to investigate pyrolysis of individual waste component including PET in order to calculate the composition of an unknown waste mixture [26]. The dynamic thermogravimetric kinetics of poly(trimethylene terephthalate) samples with various molecular weights and PET under argon, air and nitrogen are analyzed by Freeman-Carroll, Friedman and Chang method and kinetics parameters are reported [27]. Martin-Gullon et al. [28] investigated the kinetics of thermal degradation of PET under strict pyrolysis conditions and with different proportions of oxygen by TGA, which follows two independent reactions. Vyazovkin andWight [9] reported model-free and model fitting kinetics of decomposition.

Acknowledging the increasing usage of PET day-by-day and understanding the underlying demerits associated with the commonly used incineration and recycling techniques, it has become necessary to study the usefulness of PET to produce value added products. Though a few literature references, discussed elsewhere, have dealt with the kinetic study of PET using either pure PET or PET from a mixture of solid waste, further study on the same is the need of the hour. In this present work we have studied the pyrolysis kinetics of PET. Thermal degradation kinetics of carbonated soft drinks PET bottles are studied using TGA. The results of kinetics investigation are presented in terms of an nth order kinetic model with values of kinetic parameters such as activation energy, frequency factor and order of the reaction.