What Is the Process of Recycling Oil?

Recycling oil generally involves collecting used oil, removing water and contaminants, and then either re-refining it through vacuum distillation and hydrotreating to produce high-quality base oils or processing it into industrial fuels; used cooking oil follows a different path, typically being converted into biodiesel via transesterification. Broadly, the goal is to reclaim value while preventing pollution, with modern facilities producing lubricants that can meet the same performance specifications as those made from crude oil.

The Core Process: Re-refining Used Motor Oil

Most “oil recycling” in the automotive and industrial context refers to re-refining used lubricating oil. This closed-loop pathway turns drain oil back into base oil stock suitable for blending into new lubricants. Contemporary re-refiners employ high-vacuum distillation, hydrotreating, and polishing steps to remove water, fuels, soot, metals, and degraded additives, yielding base oils comparable to virgin Group II/III stocks.

The following list outlines the typical industrial steps used to re-refine used motor oil, from collection to finished products.

1. Collection and acceptance testing: Used oil is gathered from service centers, fleets, and municipal drop-offs. Samples are screened for water, antifreeze, solvents, PCBs, and metals to ensure the feedstock meets regulatory and process limits.
2. Pre-treatment (settling and dewatering): Gross water and free contaminants separate in tanks; demulsifiers and heat may be applied to break water/oil emulsions.
3. Filtration and centrifugation: Fine particulates (soot, wear metals) are removed by filters, centrifuges, or both, reducing solids load before thermal processing.
4. Vacuum distillation: Under high vacuum, light ends (fuel, water) are stripped; then the oil is fractionated into base oil cuts. Heavy residues (“vacuum bottoms”) exit as a separate stream.
5. Hydrotreating/hydrofinishing: Distillate base oil cuts are treated with hydrogen over catalysts to remove sulfur, nitrogen, and oxygen, saturate aromatics, and improve color, stability, and odor.
6. Polishing/finishing: Some plants use clay or adsorption media to further improve color and remove trace impurities; spent media is managed under environmental controls.
7. Blending and quality control: The re-refined base stocks are tested (viscosity, V.I., volatility, oxidation stability) and blended with additive packages to meet API/ACEA/ILSAC specifications for engine or industrial oils.
8. Byproduct handling: Light fractions can be used as process fuel; vacuum bottoms may be routed to asphalt extenders or other permitted uses; separated water is treated to meet discharge limits.

Together these stages convert contaminated used oil into reliable base oils while isolating and responsibly managing byproducts, minimizing waste and emissions.

What Gets Removed—and Why It Matters

Used oil contains a mix of contaminants that must be taken out to restore performance and protect engines and equipment. The list below summarizes the major impurities and their origins.

• Water and antifreeze: Enter via leaks or improper handling; cause corrosion and poor lubrication.
• Fuel dilution and light hydrocarbons: From blow-by in engines; reduce viscosity and flash point.
• Soot and carbonaceous solids: Combustion byproducts that thicken oil and abrade parts.
• Wear metals (iron, copper, lead): From engine and machinery wear; catalyze oil degradation.
• Additive degradation products: Oxidized, nitrated species that affect stability and deposits.
• Salts and dirt: Environmental contamination that promotes corrosion and deposits.
• Chlorinated solvents or PCBs (prohibited): Dangerous contaminants screened out to meet regulations.

Removing these substances restores the lubricant’s protective properties, enabling the re-refined oil to perform on par with products derived from crude.

Alternative Pathways for Waste Oil

Not all collected oils are re-refined into base stocks. Depending on composition and local infrastructure, several legitimate pathways exist, each with distinct technologies and end products.

• Re-refining to base oil (closed loop): Highest-value pathway for used motor and industrial oils; produces Group I/II/III base stocks for new lubricants.
• Reprocessing into industrial fuel: Heavier waste oils can be cleaned and blended into on-spec fuel for kilns, boilers, and some marine applications under emissions controls.
• Transformer oil regeneration: In-service electrical insulating oils can be dehydrated, degassed, and adsorbed (e.g., with fuller’s earth) to restore dielectric strength and extend life.
• Used cooking oil to biodiesel: Filtered fats/oils/grease (FOG) are esterified/transesterified with methanol and a catalyst to produce fatty acid methyl esters (FAME) and glycerin co-product.

These pathways diversify recovery options, ensuring more oil-derived materials are kept in productive use while meeting technical and regulatory requirements.

Energy, Emissions, and Quality

Re-refining used lubricants typically consumes substantially less energy than producing base oils from crude, while avoiding upstream extraction impacts. Modern re-refined lubricants can meet the same API/ACEA performance categories as virgin products when blended with appropriate additives. Facilities operate under strict environmental permits governing air emissions, wastewater, and byproduct management.

Regulation and Compliance

In the United States, used oil is managed under EPA standards (40 CFR Part 279), which set rules for storage, transportation, burning, and re-refining; mixing used oil with hazardous solvents can trigger stricter hazardous waste rules. In the European Union, used oil falls under the Waste Framework Directive, with Member State regulations prioritizing regeneration (re-refining) where feasible. Cross-border shipments are controlled by the Basel Convention.

How to Prepare Oil for Recycling (Consumer Guide)

Households and small businesses play a critical role in keeping oil recyclable. The steps below help ensure your used oil can be safely collected and processed.

1. Drain used oil into a clean, sealable container (avoid mixing with antifreeze, brake cleaner, or solvents).
2. Cap the container tightly and label it “Used Oil.”
3. Collect used oil filters separately; drain them for at least 12–24 hours.
4. Take oil and filters to an authorized collection site (auto parts stores, service centers, municipal depots).
5. Keep receipts or logs if required by local programs, and never pour oil on the ground or into drains.

Following these steps maintains the value of the material and keeps it eligible for the highest-value re-refining pathways.

What About Contaminated or Mixed Oil?

If oil has been mixed with solvents or unknown chemicals, alert the collection site; special testing and handling may be needed. Do not attempt to burn or dispose of contaminated oil yourself.

Outcomes and Byproducts

From a typical re-refining operation, the primary outputs are multiple cuts of base oil, light hydrocarbons usable as process fuel, and heavy residues suitable for asphaltic applications or other controlled uses. Water is treated to discharge standards. Overall yields vary by feedstock and technology, but a majority of the incoming used oil can be recovered as valuable products.

Summary

Recycling oil centers on removing contaminants from used oils and either re-refining them into high-quality base stocks or converting them into other useful products like industrial fuels or biodiesel. The process—collection, dewatering, filtration, vacuum distillation, hydrotreating, and finishing—delivers lubricants that meet modern performance standards while saving energy and preventing pollution. With proper consumer handling and strong regulatory oversight, oil recycling closes the loop on a vital industrial material.

Is 10 year old oil still good?

On average, conventional motor oil lasts about five years on the shelf in unopened containers. Semi-synthetic and synthetic motor oils will last seven to eight years.

How much does AutoZone charge to recycle oil?

Bring your used oil and batteries to your local AutoZone and we’ll recycle them for FREE!

How do they recycle oil?

Used oil can be re-refined into lubricants, processed into fuel oils, and used as raw materials for the refining and petrochemical industries. Additionally, used oil filters contain reusable scrap metal, which steel producers can reuse as scrap feed.

Does Walmart use recycled oil for oil changes?

Oil. So with conventional you get 3,000 miles max life you get 5,000 full synthetic you get 6,000 at Walmart you will not come up to the numbers. You get conventional they say 3,000.