Quick answer: A deoiler — also called a reverse demulsifier or reverse emulsion breaker — is a water-soluble chemical that removes dispersed oil from produced water. Where a conventional demulsifier breaks water-in-oil emulsions to dehydrate crude, a deoiler does the opposite: it breaks oil-in-water emulsions to clean the water. It works mainly by charge neutralisation and flocculation — typically a cationic polymer neutralises the negative charge stabilising the fine oil droplets, letting them coalesce and flocculate into larger droplets that separate readily in a hydrocyclone or flotation unit. Deoilers are how produced water is brought below its oil-in-water discharge limit.
Key figures at a glance
- Deoiler = reverse demulsifier: water-soluble, breaks oil-in-water (O/W) emulsions
- vs conventional demulsifier: oil-soluble, breaks water-in-oil (W/O)
- Mechanism: charge neutralisation (cationic polymer) + flocculation
- Works with: hydrocyclones and flotation (DAF/IGF)
- North Sea/OSPAR produced-water limit: 30 mg/l dispersed oil (monthly average)
On the water side of a facility, the goal is the mirror image of crude treatment: get the oil out of the water, down to a legal discharge concentration measured in milligrams per litre. Deoiler chemicals are what make that possible on emulsified produced water. This is the informational explainer for how they work; the product and service detail lives on the deoilers service page, so this focuses on mechanism and application.
What a deoiler / reverse demulsifier is
A deoiler is a water-soluble treatment chemical that coalesces and separates oil dispersed in water. The names describe the same function from different angles: ‘deoiler’ (it removes oil from water), ‘reverse demulsifier’ (it breaks the reverse — oil-in-water — emulsion), and ‘reverse emulsion breaker’. It is dosed into produced water or oily effluent to drive residual oil out so the water can be discharged or reinjected within spec.
How it differs from a conventional demulsifier
The two are opposites, matched to opposite emulsions:
- Conventional demulsifier — oil-soluble, breaks water-in-oil emulsions, works in the continuous oil phase, and dehydrates crude (lowering BS&W).
- Deoiler / reverse demulsifier — water-soluble, breaks oil-in-water emulsions, works in the continuous water phase, and cleans produced water (lowering oil-in-water concentration).
This maps directly onto the emulsion-type distinction: the continuous phase determines which chemistry is needed, as set out in the emulsifier-vs-demulsifier guide.
Mechanism: charge neutralisation and flocculation
Fine oil droplets stay dispersed in water partly because they carry a surface electrical charge (usually negative) that makes them repel one another. A deoiler — commonly a cationic (positively charged) polymer — neutralises that charge, removing the repulsion so droplets can approach and coalesce. The polymer also bridges droplets together into larger flocs. These larger, coalesced oil droplets and flocs then rise or are removed easily by the downstream physical stage, whereas the original fine droplets would have passed straight through. Charge neutralisation plus flocculation is the essence of how a deoiler works.
Where deoilers are used (produced water, refinery effluent)
Deoilers are used wherever oil must be taken out of water to meet a discharge or reuse spec:
- Produced water on oil and gas facilities — the largest application, cleaning water for overboard discharge or reinjection.
- Refinery and petrochemical effluent — removing oil ahead of wastewater treatment.
- Slop and interface streams — recovering oil and clarifying water from tank and separator bottoms.
They typically work in concert with hydrocyclones and flotation (DAF/IGF), which physically remove the coalesced oil the deoiler creates.
Dosing and monitoring
Deoiler performance depends on getting the dose and the chemistry right for the water. The product is selected and its dose optimised by testing on the actual produced water (charge and droplet character vary between fields), then injected with enough mixing and contact time ahead of the separation stage. Performance is tracked with an oil-in-water monitor or laboratory analysis against the discharge limit (mg/L) — under-dosing leaves oil in the water, while over-dosing wastes chemical and can even re-stabilise the dispersion. Monitoring closes the loop between dose and result.
Dosing and monitoring a deoiler to a discharge limit
A deoiler only delivers if its dose is matched to the water it is treating, because the charge and droplet character of produced water vary between fields and over the life of a well. The product — commonly a cationic polymer — is selected and dose-optimised on the actual water, then injected with enough mixing and contact time ahead of the hydrocyclone or flotation stage that physically removes the coalesced oil. Too little deoiler leaves oil in the water; too much wastes chemical and can re-stabilise the dispersion, so there is a genuine optimum rather than a ‘more is better’ curve.
Performance is judged against the discharge limit. In the North Sea and wider OSPAR area, the standard for dispersed oil in produced water discharged to sea is 30 mg/l as a monthly average, and operators track this with an oil-in-water monitor or laboratory analysis. Watching the trend, not just spot values, catches a drifting dose or a changing water before it becomes an exceedance.
Because the deoiler and the physical separation stage work as a pair, tuning them together — dose, mixing, and residence time against the measured oil-in-water result — is what reliably keeps produced water within its permit.
How a deoiler fits the produced-water train
A deoiler is not a standalone solution; it is the chemistry that makes the produced-water train’s physical stages reach their discharge limit. On its own, a hydrocyclone or flotation unit removes dispersed oil well but struggles with the fine, charge-stabilised droplets that a tight oil-in-water emulsion carries. The deoiler neutralises the charge and flocculates those droplets into larger ones that the hydrocyclone or flotation cell can then remove — so the chemical and the equipment are a matched pair.
That pairing shapes where the deoiler is injected: upstream of the physical stage, with enough mixing and contact time for coalescence to occur before the stream reaches the separator. Inject too late and the droplets have not grown; inject with too much shear afterwards and they can be re-dispersed. The dose is optimised against the measured oil-in-water result at the outlet, not set once and forgotten.
Understood this way, the deoiler is the enabling step that lets a produced-water system meet a limit like the OSPAR 30 mg/l standard reliably, rather than intermittently. It is the difference between a train that passes on a good day and one that holds spec through the changes a maturing field brings.
Frequently asked questions
What is a deoiler chemical?
A deoiler is a water-soluble chemical (a reverse demulsifier) that removes dispersed oil from produced water by neutralising the charge on the oil droplets and flocculating them into larger droplets that separate easily. It brings produced water below its oil-in-water discharge limit.
How is a deoiler different from a demulsifier?
A conventional demulsifier is oil-soluble and breaks water-in-oil emulsions to dehydrate crude. A deoiler (reverse demulsifier) is water-soluble and breaks oil-in-water emulsions to clean produced water. They are opposite chemistries for opposite emulsions.
How do deoilers clean produced water?
By charge neutralisation and flocculation: a cationic polymer neutralises the charge keeping fine oil droplets apart, so they coalesce and floc into larger droplets. A hydrocyclone or flotation unit then removes those larger droplets, lowering the oil-in-water concentration to spec.
Related Rodanco resources: See Rodanco’s deoilers / reverse demulsifiers overview and water clarifiers page.
Where Rodanco fits: Rodanco supplies deoilers, reverse demulsifiers, and water clarifiers, selected and dose-optimised on your produced water to meet discharge limits. See our Deoilers / Reverse Demulsifiers and Water Clarifiers pages, or discuss a produced-water target through the Rodanco contact page.