Glycerol in the Industrial Metalworking: A Critical Narrative Review of Benefits, Limitations, and Application Range for Waste Management and Sustainability

The global oversupply of glycerol from biodiesel production has prompted interest in its industrial valorisation. One emerging pathway is its use as a base fluid for metalworking, where both the spent fluid and the swarf would avoid hazardous-waste classification, while also lowering worker exposure compared with petroleum-based emulsions. This review synthesises academic and industrial evidence to critically assess glycerol’s potential through the combined lenses of tribology, thermal stability, occupational and environmental implications, and industrial feasibility. Available evidence indicates that glycerol offers biodegradability, non-toxicity, and boundary-lubrication capability, enabling metallic residues to be reclassified as recyclable rather than hazardous. However, neat glycerol undergoes viscosity loss and oxidative degradation above ~180–210 °C, with potential acrolein formation, restricting applicability to low-to-moderate temperature machining and selected carbide finishing. Sector-level analysis delineates feasible adoption windows across small/medium workshops, automotive finishing lines, heavy-machinery/shipbuilding cells, and limited aerospace applications. Glycerol therefore cannot be regarded as a universal substitute but as a selective, sustainability-oriented fluid whose industrial feasibility depends on thermal management, formulation control, and regulatory alignment. Within its defined application range, glycerol may support circular metalworking and waste-valorisation strategies where process conditions remain compatible with its limits. Keywords: glycerol, metalworking fluids, industrial waste management, thermal stability, corrosion resistance, circular economy