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Time：2025-04-23 11:34:36 Reading volume：
The core principle of industrial oil purification technology is to separate pollutants (such as water, solid particles, gas, colloid and acidic substances) in oil by physical, chemical, or combined methods to restore the physical and chemical properties of oil. The purification processes of different industrial oils (hydraulic oil, gear oil, turbine oil, etc.) are different, but follow the following technical routes:
| Pollutants | Removal principle | Corresponding technology |
|------------------|-----------------------------------------------------------------------------|----------------------------------|
| Solid particles | Mechanical interception (screening, adsorption) | Filtration, centrifugation, magnetic separation |
| Free/emulsified water | Density difference separation (sedimentation, centrifugation), demulsification and coalescence, vacuum evaporation | Centrifuge, coalescence dehydration, vacuum oil filter |
| Dissolved water/gas | Reduce partial pressure to promote volatilization (vacuum), increase temperature to accelerate diffusion | Vacuum dehydration and degassing, thin film evaporation |
| Colloid/asphalt | Adsorption (polar materials) or solvent dissolution | White clay adsorption, solvent extraction |
| Acidic compounds | Neutralization reaction or adsorption | Alkaline washing, silica gel adsorption |
(1) Multi-stage precision filtration
- Principle: Gradually reduce the pore size of the filter element (e.g. 50μm→10μm→3μm), and capture particles through Brownian diffusion, direct interception and other mechanisms.
- Application: Particle contamination control of hydraulic oil and gear oil (ISO 4406 cleanliness standard).
(2) Centrifugal separation
- Principle: Use centrifugal force (≥3000g) to make dense water/solid particles settle outward, and the clean oil is discharged from the center.
- Formula: Separation efficiency ∝ (ρ<sub>p</sub> - ρ<sub>o</sub>)·ω<sup>2</sup>·r (ρ: density, ω: angular velocity, r: rotation radius)
- Application: High water emulsified oil (e.g. steel rolling machine oil).
(3) Vacuum dehydration and degassing
- Principle:
- Dehydration: Under vacuum degree ≤1kPa, the boiling point of water drops to ≈20℃, and the water evaporates when heated to 50-65℃.
- Degassing: Henry's law (gas solubility is proportional to partial pressure), vacuum reduces partial pressure and forces gas to precipitate.
- Application: Deep purification of turbine oil and transformer oil.
(4) Coagulation and separation
- Principle:
- Coagulation stage: Oil passes through the hydrophilic fiber layer, and tiny water droplets collide and merge into large water droplets (diameter >100μm).
- Separation stage: Large water droplets settle in the gravity field due to the density difference.
- Application: Demulsification (such as reducing the water content of turbine oil from 1000 ppm to ≤ 100 ppm).
(1) Adsorption refining
- Principle: The microporous structure of activated clay/silica gel (specific surface area ≥ 200m²/g) adsorbs polar molecules (acids, colloids).
- Process parameters: clay addition 3-5%, temperature 80-120℃, contact time 30-60 minutes.
- Application: Regeneration of waste lubricating oil (acid value drops from 1.5mgKOH/g to 0.1mgKOH/g).
(2) Acid-base refining
- Principle:
- Acid washing: sulfonation of colloid with concentrated sulfuric acid (generating sulfonic acid slag, which needs to be separated).
- Alkali neutralization: NaOH neutralizes the residual acid to generate saponified products (subsequent water washing and removal).
- Disadvantages: Produces hazardous waste (acid slag, wastewater), which is gradually replaced by the hydrogenation process.
(3) Solvent extraction
- Principle: Like dissolves like principle, propane/N-methylpyrrolidone (NMP) selectively dissolves hydrocarbons in the oil and discards impurities.
- Recovery rate: The base oil recovery rate can reach 85-90%.
1. Pretreatment: coarse filtration (100μm) → centrifugal dehydration (water content reduced from 5% to 0.5%).
2. Main treatment: vacuum dehydration (water ≤100ppm) → white clay adsorption (acid value ↓80%) → fine filtration (NAS 7 level).
3. Post-treatment: supplement anti-wear agent (such as ZDDP) → viscosity detection (ISO VG 46±10%).
| Equipment type | Technical points | Performance indicators |
|-------------------|------------------------------------------|----------------------------------|
| Vacuum oil filter | Vacuum degree ≤0.1kPa, heating power 0.1kW/L·h | Water ≤50ppm, gas content ≤0.1% |
| Centrifugal separator | Speed ≥5000rpm, processing capacity 2000L/h | Water removal efficiency ≥95% (when the initial water content is 1%) |
| Electrostatic oil purifier | Electric field strength 3-5kV/cm, flow rate 100L/min | 0.1μm particle removal rate ≥90% |
1. Oil type:
- Mineral oil: suitable for physical + adsorption purification.
- Synthetic oil (esters): avoid white clay adsorption (may remove useful additives).
2. Pollution degree:
- Mild pollution (water content <0.1%, number of particles <1000/mL): fine filtration is sufficient.
- Severe pollution (acid value >1mgKOH/g): chemical refining is required.
- Energy consumption: vacuum dehydration consumes about 0.5- 1.2 kWh/m³ of oil.
- Cost: physical purification costs ≈ 20-30% of new oil, chemical regeneration costs ≈ 50-70%.
- Recycling standard: GB 17145-2017 waste mineral oil recycling specification.
- Molecular distillation: separate components at 0.001-0.1Pa for high-end synthetic oil regeneration.
- Supercritical CO<sub>2</sub> extraction: no solvent residue, recovery rate > 95% (experimental stage).
By properly selecting the process, industrial oil can be recycled multiple times (3-5 times), reducing production costs and environmental load.
