Rerefining

Rerefining, or re-refining, is the industrial process of reclaiming spent lubricating oils by removing contaminants to recover high-quality base oil suitable for making new lubricants. Spent oils from automotive and industrial equipment are collected, filtered, and pretreated to separate water, sludge, and solids.

Different processes are used, but common steps include dehydration and solids removal; distillation to separate light ends and recover base oil; purification to remove polar and heavy contaminants, often by acid treatment, adsorption, bleaching clays, or solvent extraction; and refining steps such as hydrotreating to remove sulfur, nitrogen, and metals and improve stability and color. The treated oil may undergo vacuum distillation to meet target viscosity and volatility.

Finally, the base oil stock is finished by polishing and sometimes blending with additives to achieve specifications for use as a base oil in finished lubricants. Depending on the process and feedstock, rerefined oils can meet API Group II or III specifications or be used as process oils.

Rerefining is a form of recycling that reduces waste generation and energy use compared with producing base oil from crude, and it lowers emissions associated with used-oil disposal. It is practiced internationally by dedicated rerefiners as well as large refiners who operate used-oil streams.

Quality and regulatory standards govern permissible contaminant levels and performance characteristics of rerefined base oils and the finished products.