Sustainable waste mitigation and bioenergy potential of hazardous petroleum sludge: A co-pyrolysis study with pigeon pea stalk

The accelerating increase in global energy consumption and waste output needs novel approaches to renewable energy and the disposal of waste. The present work investigated the co-pyrolysis behavior of pigeon pea stalk (PPS) and hazardous petroleum sludge (PS) to assess their synergistic interactions and bioenergy potential. Further, this study examines the thermal breakdown rates, reaction mechanisms, and thermodynamic characteristics of PPS-PS mixes. Co-pyrolysis of pigeon pea stalk and petroleum sludge was performed in a thermogravimetric analyzer. FTIR and XRD analyses were employed to determine the functional groups and phases, respectively. The kinetic parameters were calculated using isoconversional techniques such as Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW), and Vyazovkin (VZK) methods. The average activation energy values varied by feedstock and blend across the OFW, KAS, and VZK methods. PPS had activation energy values of 157.8, 155.34, and 146.59 kJ mol^-1, while PS exhibited higher values of 195.01, 193.72, and 179.55 kJ mol^-1. For blends, 1PPS1PS showed activation energy values of 158.62, 155.87, and 147.62 kJ mol^-1, while 3PPS1PS had slightly higher values of 182.38, 181.16, and 170.82 kJ mol^-1. The highest activation energy values among blends were observed in 1PPS3PS, measuring 207, 206.87, and 192.05 kJ mol^-1. The results reveal significant synergy in PPS-PS blends, enhancing pyrolysis efficiency and fuel quality. Co-pyrolysis significantly reduced the activation energy compared to PS alone, facilitating a more efficient thermal decomposition process. Furthermore, the solid response mechanism during pyrolysis was investigated using Criado’s technique (Z-master plot). These findings present an innovative approach for combining agricultural biomass with hazardous petroleum sludge to improve energy recovery and enhance sustainable waste management.