Performance Evaluation and Development of Hydraulic Oil Formulated with Re-Refined Base Oil for Industrial Applications

This study reports the formulation, laboratory evaluation, and field validation of an ISO VG 46 anti-wear (HM- type) hydraulic oil blended from Group II re-refined base oil (RRBO) produced by vacuum distillation and high-pressure hydro treating of used lubricating oil. Five formulations were prepared at RRBO substitution levels of 0, 50, and 100 wt%, with progressive optimization of the additive system. Physicochemical characterization, oxidation stability (ASTM D943, D2272), hydrolytic stability (ASTM D2619), filterability (ISO 13357), demulsibility (ASTM D1401), air release (ASTM D3427), foaming (ASTM D892), corrosion (ASTM D665, D130), gear scuffing (FZG A/8.3/90), and vane pump wear (ASTM D7043, Vickers 35VQ25) were determined. A direct one-for-one substitution of virgin base oil with RRBO using an unmodified additive package produced a 41% loss of RPVOT life, a 42% reduction in D943 oxidation life, and failure of the ISO 13357-2 wet filterability criterion. Reformulation with a boosted aminic/phenolic antioxidant synergist system, a supplementary ashless amine-phosphate anti-wear component, a modified demulsifier, and a silicone-free polyacrylate defoamer recovered 94% of the reference RPVOT life and brought all parameters within DIN 51524-2 and ISO 11158 HM limits, with total 35VQ25 pump wear of 21.4 mg against a 90 mg limit. A 4,000-hour field trial on a 160-tonne injection moulding machine confirmed stable viscosity (−1.8% at 40 °C), TAN rise limited to 0.31 mg KOH/g, and ISO 4406 cleanliness maintained at 17/15/12. The optimized formulation delivered an estimated 18–24% reduction in base- fluid cost and a 52–67% reduction in cradle-to-gate greenhouse gas burden relative to virgin Group II.