Used oil re-refining is the process of restoring used oil to new oil by removing chemical impurities, heavy
metals and dirt. Used Industrial and automotive oil is recycled at re-refineries. The used oil is first tested
to determine suitability for re-refining, after which it is dehydrated and the water distillate is treated
before being released into the environment. Dehydrating also removes the residual light fuel that can
be used to power the refinery, and additionally captures ethylene glycol for re-use in recycled antifreeze.
Next, industrial fuel is separated out of the used oil then vacuum distillation removes the lube cut
(that is, the fraction suitable for reuse as lubricating oil) leaving a heavy oil that contains the used oil's
additives and other by-products such as asphalt extender. The lube cut next undergoes hydro treating,
or catalytic hydrogenation to remove residual polymers and other chemical compounds, and saturate
carbon chains with hydrogen for greater stability.
Final oil separation, or fractionating, separates the oil into three different oil grades: Light viscosity
lubricants suitable for general lubricant applications, low viscosity lubricants for automotive and industrial
applications, and high viscosity lubricants for heavy-duty applications. The oil that is produced in this step
is referred to as re-refined base oil (RRBL).
The final step is blending additives into these three grades of oil products to produce final products with
the right detergent and anti-friction qualities. Then each product is tested again for quality and purity
before being released for sale to the public.