Biolubricants from waste cooking oil: A review of extraction technologies, conversion techniques, and performance enhancement using natural antioxidants.

Effective management of agricultural and industrial by-products is essential for promoting circular economic practices and enhancing environmental sustainability. Agri-food wastes and waste cooking oil (WCO) represent two abundant residual streams with significant potential for sustainable biolubricant production. Valorizing biomass and WCO aligns with Sustainable Development Goal (SDG) 7, as it improves energy efficiency through enhanced lubricant performance and reduced energy loss. Furthermore, this sustainable approach contributes to SDG 12 and SDG 13 by minimizing waste production and accumulation, thereby mitigating negative environmental impacts and climate change. This critical review addresses existing gaps in the production of biolubricants from WCO and the incorporation of natural antioxidants as versatile additives. It examines and compares various techniques for the extraction, chemical and physical modification, and characterization of WCO-derived biolubricants. Specific methods, including esterification, transesterification, and antioxidant incorporation, are evaluated for their effectiveness in converting WCO into biolubricants. The review also discusses the influence of residual bioactive compounds on oxidative stability and lubricating properties. While vegetable oils demonstrate superior friction-reducing capabilities compared to petroleum-based lubricants, their triglyceride structure often results in poor oxidative stability, limiting their practical applications. Modification strategies and antioxidant inclusion are proposed to enhance this stability. A comprehensive analysis of the physicochemical properties and tribological performance of biolubricants, both pre- and post-processing, is presented. This systematic evaluation of extraction and upgrading methodologies aims to facilitate the development and industrial adoption of sustainable biolubricants.