PYROLYSIS OF PETROLEUM OILY SLUDGE: A SUSTAINABLE APPROACH FOR WASTE VALORISATION AND ENERGY RECOVERY

Petroleum oily sludge (POS) is a hazardous waste generated during crude oil refining, storage, and transportation, containing hydrocarbons, water, sediments, and heavy metals that pose serious environmental risks. This study investigates pyrolysis as a sustainable method for POS treatment, focusing on the effect of residence time on product yield and quality. The sludge obtained from Kaduna Refining and Petrochemical Company Limited, Nigeria, was characterised using proximate and ultimate analyses, total petroleum hydrocarbon (TPH) determination, and SEM–EDS analysis. Results showed high moisture content (70%), high carbon content (85.3%), TPH of 86%, and a high lower heating value of 47.53 MJ/kg, confirming strong suitability for thermal conversion. Pyrolysis experiments were conducted in a fixed-bed batch reactor at 450°C with residence times of 30, 45, 60, 90, and 120 minutes. Pyro-oil yield increased from 0.34 g/g at 30 minutes to a maximum of 0.87 g/g at 90 minutes before decreasing to 0.61 g/g at 120 minutes due to secondary cracking reactions. Solid char yield decreased steadily from 0.70 to 0.48 g/g with increasing residence time. The flue gas contained high methane content (57.4 wt. %), indicating strong energy recovery potential. Solid char showed carbon enrichment (92%) and significant TPH reduction to 5.3%, confirming effective hydrocarbon conversion. Pyro-oil thermal properties showed that 90 minutes provided the best balance of fuel stability and safety. The study confirms pyrolysis as an efficient waste-to-energy strategy for sustainable refinery sludge management.