Technical Specifications
This grade family is available as 3 CheMost grades — the differences are in the columns below.
| Property | Unit | N50E | N50 | N50S | Test Method |
|---|---|---|---|---|---|
| Appearance | Brown transparent liquid | Brown transparent liquid | Brown transparent liquid | Visual | |
| Sodium Sulfonate | % | 53 | 53.5 | 53.5 | ASTM D3712 |
| Viscosity @ 100 °C | mm²/s | 30 | 40 | 50 | ASTM D445 |
| Molecular Weight | 430 | 480 | 500 | GPC | |
| Flash Point | °C | 180 | 180 | 180 | ASTM D93 |
| pH | 7.5 | 7.5 | 7.5 | — | |
| Base-Oil Solubility | Mineral Group I/II/III >20% | Mineral Group I/II/III >20% | Mineral Group I/II/III >20% | — |
* Typical values from batch production. Batch-specific COA available on request.
Technical content reviewed by the CheMost additives team · Specifications last reviewed
Molecular Structure
Molecular structure · sodium sulfonate
R–C₆H₄–SO₃Na (R = C₁₅–C₂₄ alkyl)
Sodium salt of a long-chain alkylaryl (petroleum) sulfonic acid; the monovalent Na⁺ cation keeps oil-in-water emulsions stable.
What Is Sodium Petroleum Sulfonate?
CheMost sodium petroleum sulfonate is an oil-soluble, high-molecular-weight rust inhibitor and emulsifier based on the sodium salt of natural (petroleum-derived) sulfonic acids. It is supplied as a brown transparent liquid with an effective sodium-sulfonate content above 50%, and is the standard surface-active additive for soluble and semi-synthetic metalworking fluids and for water-extendable rust-preventive systems.
Petroleum (natural) sulfonates are recovered as a co-product of the acid-treating of mineral oil and isolated as the sodium salt, which lowers viscosity for easier handling. The polar sulfonate head group adsorbs onto metal while the long alkylaryl tail keeps the molecule oil-soluble — giving the dual saponification/cleaning and film-forming behaviour stated on the data sheet. Because the cation is monovalent, sodium sulfonate keeps oil-in-water emulsions stable, whereas the divalent calcium, magnesium and barium sulfonates tend to break them; this is exactly why the sodium salt is the cation of choice for emulsifiable metalworking fluids.
CheMost offers three molecular-weight grades on a single ladder: N50E (MW ~430, the most hydrophilic emulsifying grade for metalworking fluids), N50 (MW ~480, the balanced general grade) and N50S (MW ~500, the highest-molecular-weight grade for the strongest rust film). The Technical Specifications table above lists all three side by side; the guidance below explains which to choose.
How Sodium Petroleum Sulfonate Works
Adsorbed protective film
The polar sulfonate head anchors to the metal surface and the non-polar alkylaryl tail packs vertically, forming a water-impervious monolayer that displaces moisture and blocks the oxygen and water needed for corrosion.
Emulsification of soluble oils
As an anionic surfactant the sulfonate stabilises oil-in-water emulsions; the monovalent sodium cation keeps the emulsion intact where divalent metal soaps would split it — making it the primary emulsifier for soluble cutting oils and semi-synthetic fluids.
Saponification & cleaning
The sulfonate carries saponification and detergency capacity that lifts particulate and residue from the metal surface — supporting cleanliness in metalworking and rust-preventive duty.
Molecular-weight ladder
Higher molecular weight gives a thicker, more durable hydrophobic film and better rust prevention (N50S); lower molecular weight raises hydrophilicity and emulsifying power for water-extendable fluids (N50E). All three grades hold 53–53.5% sulfonate at pH 7.5.
Choosing Between N50E, N50 and N50S
All three grades are the same petroleum sodium-sulfonate chemistry at 53–53.5% active (full numbers in the Technical Specifications above); they differ in molecular weight, which sets the balance between emulsifying power and rust-film strength.
N50E (MW ~430, viscosity 30 mm²/s) has the lowest molecular weight and the strongest hydrophilicity, so it is the emulsifier of choice in soluble and semi-synthetic metalworking fluids, where it also contributes lubricity and coolability. N50 (MW ~480, viscosity 40 mm²/s) is the balanced general-purpose grade for combined emulsification and rust protection. N50S (MW ~500, viscosity 50 mm²/s) is the highest-molecular-weight grade, giving the most durable hydrophobic film and the best stand-alone rust prevention for oil-based preventive and slushing systems. All three are soluble in Group I, II and III mineral base oils above 20%.
Applications
CheMost sodium petroleum sulfonate is used as the rust-inhibitor/emulsifier component in formulations targeting the duties below; the grade is matched to whether emulsification or rust-film strength dominates.
Soluble & semi-synthetic metalworking fluids
Primary emulsifier and corrosion inhibitor in soluble cutting oils and semi-synthetic coolants for cutting, drawing and grinding — N50E is the usual choice for its hydrophilicity and emulsion stability.
Rust-preventive & slushing oils
Forms the protective film in inter-process and storage rust-preventive oils on steel, cast iron and non-ferrous metals; the higher-MW N50/N50S give the most durable film.
Industrial & circulating oils
Provides rust protection in circulating and general industrial oils where a sodium sulfonate’s emulsion compatibility is preferred over a demulsifying barium grade.
Finished-fluid performance approvals belong to the fully formulated metalworking fluid or oil, not to an individual additive component.
Treat Rate
The data sheet specifies the product but not a per-application dosage, so the figures below are indicative, derived from the target system and our formulating experience — confirm the final level for your formulation.
First-order estimate. For a soluble-oil concentrate, the sodium-sulfonate emulsifier/rust-inhibitor is typically a few percent up to about 10% of the oil concentrate, trimmed to the emulsion stability and cast-iron-chip / humidity rust result you require. In a finished water-dilutable fluid run at, say, 5% concentrate, that places the active sulfonate at well under 1% of the working fluid.
For context, in soluble and semi-synthetic metalworking fluids the sulfonate is one part of an emulsifier-plus-rust-inhibitor system that is itself a major fraction of the concentrate; in oil-based rust-preventive and slushing oils the sodium grade is usually blended with a stronger barium or calcium sulfonate for film strength. Lower-MW N50E is dosed toward the higher end for emulsification; higher-MW N50S toward rust-film performance.
Treat rates are indicative, not fixed dosages. CheMost can provide formulation and treat-rate support on request.
Formulating With Sodium Petroleum Sulfonate — Complementary Additives
Sodium sulfonate supplies emulsification and a first layer of rust protection; a balanced rust-preventive or metalworking package pairs it with additives that strengthen the film and round out performance:
Barium petroleum sulfonate
The divalent barium grade gives a stronger rust film and demulsibility; pairing the sodium emulsifier with a barium or calcium sulfonate is the classic neutral-plus-overbased rust-preventive blend.
Dinonylnaphthalene sulfonates (DNNS)
Barium and calcium DNNS add high-performance rust protection and water-displacement, complementing the petroleum sulfonate film in demanding preventive oils.
Overbased calcium sulfonate
Adds an alkaline reserve and detergency; the overbased calcium carbonate also absorbs acidic corrosion by-products, reinforcing long-term protection.
EP / antiwear additives
In metalworking fluids, sulfur- and phosphorus-type EP/antiwear additives carry the load at the tool edge while the sulfonate manages emulsion stability and corrosion.
The CheMost Sulfonate Rust-Inhibitor Family
Sulfonate rust inhibitors are distinguished by their cation, whose rust-prevention strength rises in the order Na < Mg < Ca < Ba. CheMost manufactures the family below; sodium (this page) is the emulsifying grade, the others trade emulsion compatibility for film strength:
| Product | Cation | Behaviour | Best for |
|---|---|---|---|
| Sodium petroleum sulfonate | Na (monovalent) | Emulsifying, emulsion-stable | Soluble/semi-synthetic MWF, water-extendable RP |
| Barium petroleum sulfonate | Ba (divalent) | Demulsifying, strongest film | Rust-preventive, slushing & sealing oils |
| Calcium DNNS (barium-free) | Ca (divalent) | High-performance, barium-free | Modern RP oils avoiding barium |
| Barium DNNS (overbased) | Ba (overbased) | Alkaline reserve + rust film | Severe-duty preventive coatings |
Documentation, Qualification & Regulatory Support
Standard documentation — Certificate of Analysis (COA, per shipment), Technical Data Sheet (TDS) and Safety Data Sheet (SDS, GHS/CLP) — is provided. The full TDS is available on request rather than as a public download. Additional support is available on request:
Regulatory documentation
REACH, TSCA and country-specific market-registration documentation support available on request.
Third-party inspection
SGS / Intertek / BV pre-shipment inspection can be arranged on request.
Custom grades & packaging
Custom molecular-weight grades and packaging — metal drum, IBC, ISO tank.
Formulation support
Grade selection and treat-rate guidance for your metalworking or rust-preventive formulation.
Packaging & Supply
CheMost sodium petroleum sulfonate is stocked and shipped worldwide, with a typical lead time of 1–15 days and a 36-month shelf life at ambient temperature. Samples and quotations are answered within 12 hours.
Packaging
200 kg metal drum · 1000 kg IBC tank.
Minimum order
1 drum or 1 IBC — no minimum order value.
Incoterms
FOB · CIF · EXW, to suit your freight arrangement.
Loading ports
All major Chinese ports.
Frequently Asked Questions
What is sodium petroleum sulfonate used for?
It is the sodium salt of natural (petroleum) sulfonic acids, used as a rust inhibitor and emulsifier in soluble and semi-synthetic metalworking fluids and in rust-preventive oils. The monovalent sodium cation keeps oil-in-water emulsions stable, which makes it the preferred sulfonate for emulsifiable fluids, while the adsorbed sulfonate film protects steel, cast iron and non-ferrous metals.
What is the difference between N50E, N50 and N50S?
All three are 53–53.5% petroleum sodium sulfonate; they differ in molecular weight. N50E (MW ~430) is the lowest-MW, most hydrophilic grade — the best emulsifier for metalworking fluids. N50 (MW ~480) is the balanced general grade. N50S (MW ~500) is the highest-MW grade, giving the most durable rust film for oil-based preventive and slushing systems.
Why choose a sodium sulfonate over a barium or calcium sulfonate?
Rust-film strength rises with the cation in the order Na < Mg < Ca < Ba, but the monovalent sodium cation is the only one that keeps an oil-in-water emulsion stable — divalent calcium and barium sulfonates tend to demulsify. So sodium is chosen where emulsification matters (soluble metalworking fluids), and barium or calcium where the strongest rust film and demulsibility are wanted (rust-preventive and slushing oils).
Is sodium petroleum sulfonate oil-soluble?
Yes — it is oil-soluble in Group I, II and III mineral base oils above 20%, and the lower-molecular-weight N50E grade is also water-extendable for soluble-oil emulsions. All grades are supplied as a brown transparent liquid at pH 7.5 with a flash point of 180 °C (ASTM D93).
How is it supplied, and how fast can I get a sample?
It is supplied in 200 kg metal drums and 1000 kg IBC tanks with a 36-month shelf life, and shipped worldwide. As a manufacturer and sourcing partner (Est. 2013), CheMost answers sample and quotation requests within 12 hours.