Solvent extraction is a powerful technique used to recover high-quality base oil from used lubricants. But not all waste oils are equally suitable. The success of the process—and the quality of the end product—depends heavily on the type and condition of the oil you feed into the system.

In this article, I’ll walk you through the best types of used oils for solvent extraction, what makes them suitable, and what to avoid.

Why Solvent Extraction?

Solvent extraction is ideal for removing:

• Aromatics
• Asphaltenes
• Oxidation byproducts
• Additives and metal impurities

The goal is to isolate and recover Group I or Group II base oils that can be reused or sold, rather than burned or discarded.

Best Types of Used Oils for Solvent Extraction

Here are the most compatible waste oils based on actual plant performance:

1. Used Engine Oil

• Source: Vehicles, diesel engines, generator
• Contains carbon, metal particles, additives
• Very common and widely available
• Works well after pre-treatment (filtration + dehydration)
• Yield: 60–75% base oil recovery (varies by technology and condition)

1. Used Hydraulic Oil

• Source: Construction, manufacturing, heavy machinery
• Low additive content
• Highly stable base stock, ideal for extraction
• Fewer contaminants = higher base oil yield
• Yield: Up to 80% high-grade base oil

1. Used Gear Oil / Transmission Oil

• High-viscosity, additive-rich
• Contains sulfur, phosphorus, and EP agents
• Still usable after solvent pre-cleaning
• May require de-sulfurizationor blending

1. Used Transformer Oil (Mineral Oil Type)

• Stable, light fraction oil
• Usually low in sludge
• Great for extracting high VI base oils
• Needs PCB testing before use (for old batches)

1. Blended Industrial Lubricants

• Mixed origin, including synthetic blends
• Feedstock must be tested and classified
• Acceptable if mineral base oil dominates

Used Oils to Avoid (or Use with Caution)

Used Oil Type	Base Oil Yield	End Product Notes
Used Engine Oil	60–75%	Slightly darker base oil
Hydraulic Oil	70–80%	Light color, high VI
Gear Oil	55–65%	Higher sulfur, thicker
Transformer Oil	75–85%	Light, clean output
Mixed Lubricants	50–70%	Variable results

Key Properties That Determine Suitability

Base Stock Type:
– Mineral oils = ideal
– Synthetics = variable

Additive Load:
– Lower additive oils are easier to extract
– Dispersants and detergents increase difficulty

Sludge Content:
– More sludge = more solvent usage and waste

Water and Emulsion:
– Must be removed before extraction to prevent yield loss

Heavy Metal Content:
– Increases the need for chemical pre-treatment

Pre-Treatment Required Before Solvent Extraction

To make used oil suitable for solvent extraction, basic pre-treatment steps include:

• Gravity settling or centrifugation
• Filtration(down to 5–10 microns)
• Water separation
• Optional: vacuum dehydration

This preparation increases yield, extends solvent life, and improves end-product purity.

Solvent Extraction Yield by Oil Type (Typical Range)

Used Oil Type	Base Oil Yield	End Product Notes
Used Engine Oil	60–75%	Slightly darker base oil
Hydraulic Oil	70–80%	Light color, high VI
Gear Oil	55–65%	Higher sulfur, thicker
Transformer Oil	75–85%	Light, clean output
Mixed Lubricants	50–70%	Variable results

Why It Matters

Choosing the right feedstock means:

• Less solvent usage
• Higher base oil recovery
• Lower waste output
• Faster ROI for your plant

Whether you're running a small batch unit or a continuous solvent extraction plant, feedstock matters more than almost anything else.

Start Recovering High-Quality Base Oil Today

We design and build solvent extraction plants that handle a wide variety of waste oil types. Our systems are built for:

• High base oil yield
• Flexible feedstock input
• Solvent recovery and reuse
• Environmental compliance