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Demulsifier Additives
Demulsifier additives prevent the formation of a stable oil-water mixture or an emulsion by changing the interfacial tension of the oil so that water will coalesce and separate more readily from the oil. CheMost china manufacturers custom.
What Are Demulsifier Additives?
Demulsifier additives — also called demulsifying agents — are surfactants that accelerate the separation of water from oil. When a lubricating oil is contaminated with water — through steam leakage, condensation, or process ingress — the water disperses as fine droplets. Naturally occurring polar compounds can stabilize these droplets into a water-in-oil emulsion. Once emulsified, water cannot drain from the reservoir. Film strength collapses, corrosion accelerates, and oxidation rates multiply. Unlike emulsifiers, which create stable oil-water mixtures for metalworking fluids, demulsifiers do the opposite: they break emulsions so free water can be drained.
How Demulsification Works
A demulsifier molecule adsorbs at the oil-water interface: its polar head penetrates the water droplet surface while its lipophilic tail extends into the oil. This disrupts the rigid interfacial film that surrounds each droplet. Droplets collide, coalesce into larger drops, and settle under gravity — a process measured by ASTM D1401 (Water Separability of Petroleum Oils, 40 mL oil + 40 mL water at 54 °C or 82 °C). Industry equivalent SH/T 0191 is also widely used. A typical passing result is complete phase separation within 5 to 30 minutes.
Demulsifier Chemistry Types
Demulsifiers fall into several categories based on the charge of their hydrophilic group. For lubricating oil applications, non-ionic polyethers dominate because they are ashless, non-corrosive, and compatible with the full additive toolbox. The two primary polyether types are distinguished by their initiator chemistry.
| Type | Initiator | Characteristics | Typical Use |
|---|---|---|---|
| AP-Type (Amine-initiated Polyether) |
Polyethylenepolyamine | Multi-branched star-like structure. High interfacial contact area. Fast water drop. Effective on tight emulsions. | Crude oil dehydration, heavy emulsions, refinery desalting |
| SP-Type (Polyol-initiated Polyether) |
Propylene glycol or glycerol | Linear block copolymer (PO/EO). Sharp oil-water interface. Superior separated water clarity. Higher thermal stability. | Turbine oils, hydraulic fluids, gear oils, compressor oils |
Demulsifier vs. Emulsifier — What's the Difference?
These two additive types do opposite jobs, and confusing them causes formulation problems. Emulsifiers (common in metalworking fluids, soluble oils, and fire-resistant hydraulic fluids) lower interfacial tension to stabilize an oil-water mixture — they create a durable emulsion so the lubricant can carry water for cooling. Demulsifiers also lower interfacial tension, but their molecular structure is tuned to destabilize the oil-water interface, causing droplets to coalesce and the phases to separate. Using an emulsifier where a demulsifier is needed — or overdosing a demulsifier past its effective range — can trap water in the oil, accelerating rust and oxidation.
How to Select a Demulsifier
Demulsifier performance depends on the specific oil formulation and operating conditions. These four factors determine which chemistry and dosage will work:
- Base oil type. Mineral oils (Group I/II/III) respond well to both AP and SP polyethers. PAO and ester-based lubricants may require higher dosages or blended demulsifier systems — pre-testing is recommended.
- Emulsion severity. Light water haze can be resolved with SP-type alone at 0.02–0.05%. Tight, stable emulsions — especially those stabilized by asphaltenes or oxidized oil components — typically need AP-type or an AP+SP blend.
- Operating temperature. Demulsifier cloud point should be near or slightly below the system operating temperature. SP-types generally offer higher thermal stability than AP-types.
- Other additives present. Overbased detergents and some corrosion inhibitors can act as emulsifiers. Formulations heavy in these components may need higher demulsifier treat rates or synergistic blends.
Applications
| Application | Water Source | Consequence of Failure | Recommended Type |
|---|---|---|---|
| Turbine Oils | Steam leakage, gland condensation | Journal bearing corrosion, oil oxidation | SP-Type |
| Hydraulic Fluids | Condensation, process water ingress | Cavitation, valve sticking, corrosion | SP-Type |
| Industrial Gear Oils | Washdown, humid environments | Film strength loss, pitting, rust | SP-Type or AP+SP Blend |
| Engine Oils (Marine) | Coolant leaks, combustion water | Sludge, bearing corrosion, TBN depletion | AP+SP Blend |
| Crude Oil Dehydration | Formation water | Pipeline corrosion, refinery catalyst poisoning | AP-Type |
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CheMost Additives CO.,LTD
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