HOW DOES A BASE OIL SOLVENT EXTRACTION PLANT WORK?

How Does a Base Oil Solvent Extraction Plant Work?

How Does a Base Oil Solvent Extraction Plant Work?

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If you're considering setting up or investing in a base oil solvent extraction plant, it's important to understand how the process works from start to finish. This method is one of the most effective ways to recover Group I or Group II base oils from used lubricants, extending the life cycle of valuable hydrocarbons while reducing waste.

In this guide, I’ll walk you through the step-by-step process, technology involved, output quality, and what makes solvent extraction a reliable solution for used oil recycling.

What Is Solvent Extraction in Base Oil Recycling?

Solvent extraction is a chemical process used to remove impurities from used oil—such as:


  • Aromatic hydrocarbons

  • Asphaltenes

  • Additives

  • Oxidation products

  • Metals and carbon residue


By selectively dissolving unwanted components, the process leaves behind clean, reusable base oil.

How a Solvent Extraction Plant Works — Step by Step

Here’s a breakdown of the process stages in a typical solvent extraction system:

  1. Pre-Treatment and Filtration


Used oil first undergoes:

  • Solid particle removal(via filters or centrifuge)

  • Dehydration(vacuum or heat) to remove moisture

  • Optional: demulsificationto break oil-water emulsions


This step protects the equipment and increases yield.

  1. Solvent Mixing (Extraction Phase)


A selective solvent—commonly MEK (methyl ethyl ketone), furfural, or propane—is added to the pre-treated oil.

  • The solvent dissolves undesirable aromatic compounds

  • Base oil remains undissolved or lightly soluble


The mixture is agitated for full contact.

  1. Phase Separation


Once the solvent has extracted impurities, the mixture separates into two layers:

  • Extract phase(solvent + impurities

  • Raffinate phase(base oil + minimal solvent)


Separation is typically done in a settler or extractor column.

  1. Solvent Recovery


Solvents are recovered from both phases using vacuum distillation or flash evaporation, and recycled back into the system.

  • Solvent in the raffinate is removed to isolate base oil

  • Solvent in the extract is recovered for reuse


This step keeps the operation cost-effective and eco-friendly.

  1. Polishing and Finishing


Final steps may include:

  • Clay treatmentfor color improvement

  • Filtrationto remove trace residues

  • Optional hydro-treatment(if higher base oil grade is needed)


The end product is clean, re-usable Group I or Group II base oil, ready for blending or resale.

Common Solvents Used in Base Oil Extraction



























Solvent Type Use Case Pros Notes
MEK (Methyl Ethyl Ketone) Widely used Efficient, affordable Needs recovery unit
Furfural Deep aromatics removal High selectivity Toxic, needs careful handling
Propane Light oils Environmentally safer Lower yield with heavy oils

Output Quality of Extracted Base Oil

Typical properties of recovered base oil:

  • Viscosity Index (VI):85–105

  • Color:5–3.5 (ASTM scale)

  • Sulfur Content:<0.1%

  • Ash:<0.01%

  • Water Content:<0.05%


With optional hydrogenation or clay polishing, base oil can meet industry specifications for:

  • Automotive lubricants

  • Industrial oils

  • Metalworking fluids


What Contaminants Are Removed?

The extraction process removes:

  • Aromatics

  • Additive residues

  • Heavy metals

  • Oxidation sludge

  • Varnish-forming compounds


What remains is a stable and clear hydrocarbon base, suitable for re-refining or blending.

Why Use Solvent Extraction for Base Oil Recovery?

Compared to pyrolysis or basic distillation, solvent extraction offers:

  • Higher purity output

  • Lower environmental impact

  • Better solvent recovery efficiency

  • Reusability of solvents and reduced waste


For operations targeting Group I or Group II base oil production, this process remains the industry standard.

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