Valorization of Biomass-Derived Nanomaterials for the Closed-Loop Regeneration of Waste Lubricants

Abstract

This work demonstrates the first use of hierarchically porous carbon nanosheet (CNS) and cellulose nanofibril (CNF) aerogels derived from coconut shell and wood biomasses, respectively, for the solvent-free regeneration of waste engine oils. The nanomaterials were produced via controlled pyrolysis (500°C) followed by KOH nanoactivation (1.5:1 w/w) and high-shear delamination. Their surface chemistry (FTIR), nanomorphology (TEM), specific surface area (BET, up to 914 m² g⁻¹) and pore size distribution (2–50 nm) were correlated with the decontamination efficiency of light and heavy waste oils. After a single pass through a CNS/CNF hybrid filter, the viscosity, flash point, ash content, total acid number (TAN) and sediment content approached the virgin-oil specifications. Coconut-shell CNS delivered the largest performance gain (TAN ↓44%; ash ↓48%; flash point ↑40 °C), whereas wood-derived CNF
aerogels conferred high mechanical strength and rapid oil wicking. Life cycle metrics indicate a 43% reduction in CO₂-eq emissions compared with those of commercial acid‒clay rerefining. The results advance circular-economy lubricant technologies based entirely on renewable nanomaterials.