Lubrication science
Re-refined base oil: used oil made new again
Quick answer
How used lubricating oil is cleaned back to base oil, how it compares with virgin Group II, and where it is used.
What it is
Re-refined base oil is made from used lubricating oil. The refinery removes water, fuel, solids, metals and oxidised material and then treats the oil until it meets base oil specifications again. Used oil is not consumed by use. It is contaminated, and most of the contamination can be removed.
The process
| Step | What it does |
|---|---|
| 1. Collection | Used oil is collected and kept free of solvents and transformer oils with PCB. |
| 2. Pre-treatment | Settling and filtering remove water and solids. |
| 3. Dehydration | Heating removes water and light fuel ends. |
| 4. Vacuum distillation | Separates the usable oil from sludge, additive residue and heavy ends. |
| 5. Hydrotreating or hydrofinishing | Hydrogen treatment removes sulphur, nitrogen and oxidation products and restores colour and stability. |
| 6. Finished base oil | Blended and tested against the specification. |
Compared with virgin Group II (indicative)
| Property | Virgin Group II | Re-refined |
|---|---|---|
| Viscosity index | 95 to 120 | 90 to 115 |
| Saturates, % | 90 or more | 85 or more |
| Sulphur, % | 0.03 or less | 0.05 or less |
| Oxidation stability and seal compatibility | Good | Good with correct additives |
Where it fits
- Hydraulic, compressor, gear and slideway oils, and many greases.
- Engine oils and automotive fluids, where the finished product must meet the same approvals as virgin oil.
- Where a circular supply and a lower carbon footprint have value.
Cautions
- Quality depends on the feedstock and the process. Ask for test results, not only a claim.
- Approvals matter more than the source. Use only products that carry the approval your machine needs.
Takeaway. Re-refined base oil can meet the same specifications as virgin oil. Judge it by test data and approvals, as you would any other base oil.
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