An integrated approach to waste tire pyrolysis for value-added products: process optimization and a comprehensive economic study for scalability†

Abstract

The improper disposal of waste tires poses significant environmental risks to land, water, and air, leading to health hazards. Previous studies on waste tire pyrolysis predominantly focused on liquid fuel production or carbon black, with limited emphasis on the comprehensive analysis of char, liquid, and gas yields. This study investigates the pyrolysis of waste tires to produce these valuable products, emphasizing their potential applications across various domains. Experiments were conducted in a 10 kg reactor, varying feedstock amounts from 1 to 10 kg, temperatures from 573 to 1173 K, and heating rates between 10 and 30 K min⁻¹. Char formation decreases with rising temperature until stabilizing, gas yield increases to a maximum before becoming constant, and oil yield initially increases slightly before declining or stabilizing with further temperature increase. Detailed characterization of feedstock and pyrolysis products was performed, including scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) for char, Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) for oil, and GC for gas to understand their properties and applicability in various fields. Optimal yields of char (27.61%), oil (46.34%), and gas (26.05%) were achieved at 5.5 kg feedstock, 873 K, and a heating rate of 20 K min⁻¹. A detailed cost analysis showed payback periods of 1.5 years, 1.7 years, and 1.85 years at discount rates of 10%, 20%, and 30%, respectively, with an internal return rate (IRR) of 18%. The crossover of net present value (NPV) from positive to negative marked the threshold, highlighting an industrial-scale economic focus rarely addressed in earlier studies. Sensitivity analysis confirmed the economic feasibility and suitability of the process for industrial applications, aligning with the objectives of the UN Sustainable Development Goals 2030.