Overbased Calcium Sulfonate (TBN 400)

Quick Specs

What Is Overbased Calcium Sulfonate?

Calcium sulfonate makes up 65% of the global detergent additive market. That's not a typo. Two out of every three detergent molecules added to engine oil are calcium sulfonate — and a large fraction of those are the overbased variety.

"Overbased" doesn't mean "too much base." It means the molecule carries roughly twenty times more metal than a stoichiometric neutral salt would. A neutral calcium sulfonate contains exactly enough calcium to balance the sulfonate acid groups — TBN around 30 or less. An overbased calcium sulfonate at TBN 415 packs in a massive surplus of calcium carbonate, dispersed as nanometer-scale particles inside a sulfonate shell.

Think of it as a reverse micelle.

The sulfonate molecules arrange themselves with their oil-soluble hydrocarbon tails pointing outward into the base oil. Their polar heads point inward, surrounding a core of amorphous calcium carbonate — particles smaller than 80 nanometers, fine enough that the whole assembly stays transparent and won't settle out during storage. This is what makes the chemistry work: the calcium carbonate core is the alkaline reserve, neutralizing acids on contact, while the sulfonate shell keeps the whole thing suspended and delivers surfactant-like detergency to keep metal surfaces clean.

Here's what matters for the formulator: CheMost-C400 delivers 415 mgKOH/g of TBN. That puts it in the "super high alkalinity" tier — TBN above 400 — which is the top of the calcium sulfonate range. You use this grade when you need maximum acid-neutralizing capacity per unit weight of additive, which is why it's the workhorse detergent in marine cylinder oils burning heavy fuel.

Calcium petroleum sulfonate product range — full grade comparison C30 to C500

Technical Specifications & Quality Control

Solubility

The TBN lands at 415, which sits between RB Products' CS 425 (the highest in the reference set at 425) and Lanxess C-402 at 405. Viscosity runs 100 mm²/s at 100°C — thinner than CN Lubricant's T107 (130) but heavier than Calcinate C-400CLR (75). Density at 1220 kg/m³ is on the denser side of the range, consistent with high CaCO₃ loading.

What you don't see in most competitor spec sheets: moisture content and mechanical impurities. We report both — 0.08% moisture (ASTM D95) and 0.03% mechanical impurities (ASTM D473). These aren't glamorous numbers. But they're the kind of data that tells you whether a batch was manufactured to tight tolerances or just shipped.

Every production batch of CheMost-C400 passes through infrared spectroscopy verification. The FTIR spectrum below is a typical batch scan — it confirms the characteristic sulfonate S=O stretching bands and the carbonate C-O absorption that together define the overbased calcium sulfonate structure.

If you're qualifying a new detergent supplier, ask for the FTIR. If they can't produce one, that's useful information. It tells you something about their QC regimen — or the lack of one.

Calcium Sulfonate Grease Applications

Here's the thing — if you search for "calcium sulfonate," most of what you'll find isn't about engine oil at all. It's about grease.

That's because overbased calcium sulfonate does something unusual. The same molecule that works as a detergent in crankcase oil can be thermally converted into a grease thickener — specifically, a calcium sulfonate complex thickener. The amorphous calcium carbonate in the overbased sulfonate converts to crystalline calcite during the grease-making process, and those calcite particles form the three-dimensional network that gives the grease its structure.

This dual identity matters for procurement. If you're buying overbased calcium sulfonate, you're buying either a detergent intermediate or a grease precursor — sometimes both, from the same drum.

Ca Sulfonate Grease vs. Lithium Grease

Lithium complex greases own about 60% of the market. But calcium sulfonate greases are gaining ground, particularly in applications where water washout or high temperatures kill lithium greases.

The dropping point difference isn't subtle. Calcium sulfonate greases stay in place at temperatures where lithium greases have already melted and run out of the bearing.

And because the calcite thickener itself provides some extreme-pressure protection — CaCO₃ acting as a solid lubricant at the contact zone — you get a measure of EP performance without necessarily adding a full EP additive package.

Don't mix calcium sulfonate grease with lithium grease. The two thickener systems are chemically incompatible — calcium sulfonate's high alkalinity can react with the lithium soap, breaking down the grease structure. The result is usually a soupy, low-viscosity mess that leaks out of the bearing. If you're switching from lithium to calcium sulfonate grease, purge the old grease completely first.

The data from bench testing backs up what field experience shows. In four-ball EP testing on lithium 12-hydroxystearate grease, adding a sulfonate rust inhibitor alongside a standard EP additive dropped the wear scar from 0.73 mm to 0.47 mm — a 35% reduction. The sulfonate isn't just along for the ride; it's actively improving the EP film.

For grease manufacturers, CheMost-C400 at TBN 415 provides high thickener yield — roughly 20% more concentrated than standard 300 TBN grades. That means less additive volume needed to hit your target NLGI grade.

Engine Oil & Marine Cylinder Oil Applications

A word of caution: if you switch a vessel from HFO to VLSFO and keep using BN 70-100 cylinder oil, you risk over-alkalinity. Excess unreacted calcium carbonate on the liner can react with sulfate ash deposits to form hard calcium carboxylate soaps that abrade the liner surface. Match your cylinder oil BN to your fuel sulfur content.

The Acid Problem

Diesel fuel contains sulfur. When that sulfur burns, it forms SO₂ and SO₃. Those combine with water vapor in the combustion chamber to make sulfurous and sulfuric acid. These acids condense on cylinder walls and attack the metal.

Overbased calcium sulfonate stops this by neutralizing the acid before it does damage. The calcium carbonate core of the reverse micelle reacts with sulfuric acid on contact — CaCO₃ + H₂SO₄ → CaSO₄ + CO₂ + H₂O. One molecule of calcium carbonate neutralizes one molecule of sulfuric acid. The sulfonate shell, meanwhile, keeps piston ring grooves clean by dispersing soot and oxidation byproducts.

In passenger car and heavy-duty diesel engine oils, calcium sulfonate typically makes up 6-10% of the finished oil by weight. It's almost never used alone — it's blended with dispersants (usually PIBSA-succinimide types), ZDDP for antiwear, and antioxidants. The detergent is the alkaline backbone of the whole additive package.

Marine Cylinder Oils

This is where overbased calcium sulfonate does its heaviest lifting.

Two-stroke crosshead marine diesel engines — the kind that push container ships across oceans — burn heavy fuel oil containing up to 3.5% sulfur. The cylinder oil in these engines doesn't circulate. It's injected directly onto the liner surface by quill injectors, does its job once, and drains away. Every injection has to deliver enough alkalinity to neutralize the acid generated by that fuel at that moment.

The rough formula marine lubricant chemists use:

TBN = 0.35 × X × S × B / L

Where S is fuel sulfur content (%), B is fuel consumption rate (kg/h), L is cylinder oil consumption rate (kg/h), and X is an engine-specific coefficient (~0.15 for large crosshead engines).

The IMO 2020 sulfur cap changed the arithmetic. Before 2020, ships burning 3.5% sulfur HFO needed cylinder oils at BN 70-100. After 2020, with the global 0.5% sulfur cap on VLSFO, the most common cylinder oil grade shifted to BN 40-70. The treat rate of overbased Ca sulfonate adjusts accordingly — less additive needed for lower-sulfur fuel — but the additive itself is the same.

Treat Rate Guide

Corrosion Protection & Industrial Applications

Overbased calcium sulfonate protects metal through two mechanisms operating simultaneously.

The sulfonate anion adsorbs onto iron and steel surfaces, forming a densely packed hydrophobic monolayer. The long alkylbenzene chains orient perpendicular to the surface, creating a physical barrier that water and oxygen can't easily penetrate. This is physisorption — the same mechanism that makes neutral sulfonates effective rust inhibitors.

But overbased sulfonate adds a second layer. The colloidal calcium carbonate in the micelle core absorbs acidic corrosion initiators — HCl, SO₂, organic acids from oil oxidation — neutralizing them before they reach the metal. The sulfonate film blocks water. The carbonate core mops up acid.

Between the commonly available metal cations for sulfonate rust inhibitors, the effectiveness ranking is:

Barium > Calcium > Magnesium > Sodium

This correlates directly with ionic radius. Barium's large, polarizable ion (135 pm) binds tightly to the metal oxide surface and resists displacement by water. Calcium (99 pm) is next best. But barium sulfonates are being phased out globally due to heavy-metal regulations — which leaves calcium as the most effective eco-acceptable option. Magnesium and sodium sulfonates have their niches (magnesium for low-ash formulations, sodium for soluble-oil metalworking fluids), but for an oil-soluble rust inhibitor that stays put through humidity and salt spray, calcium sulfonate is the standard.

A customer once asked us why their slushing oil formulation performed inconsistently — sometimes passing 1000-hour humidity cabinet, sometimes failing at 200. Turned out they were using neutral sulfonate alone. Adding 30% overbased calcium sulfonate to the sulfonate component stabilized the film and bought them roughly triple the protection window. The CaCO₃ reserve was doing the work the neutral sulfonate film couldn't sustain on its own.

Formulation Guidance & Additive Compatibility

Treat Rate Ranges

Additive Compatibility

The general rule: overbased calcium sulfonate plays well with almost everything at typical treat rates. The only thing it actively dislikes is strong oxidizing agents — and those have no business being in a finished lubricant anyway.

Storage, Handling & Packaging

Overbased calcium sulfonate at TBN 415 is a viscous liquid at room temperature — roughly the consistency of cold honey. Below 15°C, it approaches a semi-paste and won't pump without heating.

This is not a defect. It's the physical consequence of packing that much calcium carbonate into the micelle structure. Higher TBN grades are always more viscous than lower TBN grades from the same manufacturer.

Storage Recommendations

Shelf life: 2 years from production date in sealed original packaging at recommended storage conditions. The product is non-flammable (flash point >190°C), non-explosive, and non-corrosive under standard industrial handling. If skin contact occurs, wash with soap and water.

Packaging & Ordering

Why CheMost C400

This isn't a generic "why choose us." It's why this specific product from this specific factory — CheMost-C400 from Jinzhou — performs consistently across marine cylinder oils, heavy-duty diesel formulations, and calcium sulfonate grease production. Request the TDS and a qualification sample.

Frequently Asked Questions

What is overbased calcium sulfonate?

Overbased calcium sulfonate is a highly alkaline detergent additive where excess calcium carbonate is dispersed as nanometer-scale particles (less than 80 nm) inside a sulfonate reverse micelle. The "overbased" designation means the metal-to-acid ratio far exceeds the stoichiometric neutral salt — typically 15-20 times higher. At TBN 415, CheMost-C400 contains roughly 20 equivalents of calcium per equivalent of sulfonate acid. This colloidal CaCO₃ core provides the alkaline reserve that neutralizes combustion acids in engine oil and, when thermally converted, serves as the thickener in calcium sulfonate complex grease.

What is overbased calcium sulfonate used for?

Two primary applications, one secondary. The first — and historically the original — is as a detergent additive in engine oils. Overbased calcium sulfonate neutralizes sulfuric acid from fuel combustion, disperses soot and sludge, and prevents high-temperature piston deposits. It's the alkaline backbone of most heavy-duty diesel and marine engine oil formulations, typically used at 3-10% treat rate in HDEO and up to 22% in high-BN marine cylinder oils. Calcium sulfonate makes up 65% of the global detergent market, and the majority of that volume is overbased.

The second major application is as a grease precursor. When overbased calcium sulfonate is heated and treated with a converting agent during grease manufacturing, the amorphous calcium carbonate converts to crystalline calcite — and those calcite particles form the three-dimensional thickener network. Lanxess, Kimes, and Seqens all market dedicated "grease feed" versions of overbased calcium sulfonate optimized for this conversion.

The third application is corrosion protection, where the sulfonate film adsorbs onto metal surfaces and the carbonate core absorbs acidic corrosion initiators. In slushing oils, overbased calcium sulfonate at 0.5-5% treat rate can extend humidity cabinet protection from a couple hundred hours to over a thousand.

Is calcium sulfonate grease better than lithium grease?

Better at specific things. Worse at others. Calcium sulfonate grease has a dropping point above 260°C — lithium complex tops out around the same temperature but calcium sulfonate keeps its mechanical stability closer to its dropping point. It handles water washout far better than lithium, and the calcite thickener provides inherent EP protection that lithium greases need additive packages to achieve. But calcium sulfonate grease is generally more expensive, harder to manufacture, and has lower pumpability at low temperatures. For a steel mill roll neck bearing exposed to water spray and 200°C, calcium sulfonate is the right call. For a passenger car wheel bearing that sees moderate temperatures, lithium complex still works fine and costs less.

What is the difference between overbased and neutral calcium sulfonate?

Neutral calcium sulfonate contains exactly the stoichiometric amount of calcium — one Ca²⁺ per two sulfonate groups. TBN is typically 30 or below. It's primarily a rust inhibitor, forming an adsorbed monolayer on metal surfaces. Overbased calcium sulfonate contains a massive excess of calcium, present as colloidal CaCO₃ particles stabilized inside the sulfonate micelle. TBN ranges from 200 to 500. It functions as both a detergent (acid neutralization + deposit control) and, at TBN 400+, as a grease thickener precursor. Neutral sulfonate protects surfaces from water; overbased sulfonate does that plus neutralizes acids and cleans surfaces.

Can you mix lithium and calcium sulfonate grease?

Don't. Calcium sulfonate grease is highly alkaline and lithium complex grease contains lithium soap fibers that react with that alkalinity, breaking down the thickener structure. If you're switching grease types, purge the old grease completely from the bearing first.

Why is TBN important in calcium sulfonate detergents?

TBN — Total Base Number, measured by ASTM D2896 — tells you how much acid one gram of additive can neutralize. For marine cylinder oils, the relationship between fuel sulfur and required oil BN is well-established: fuel at 0.5% sulfur needs BN 5-10, 1-1.5% sulfur needs BN 10-20, 2.5-3.5% sulfur needs BN 40-70, and above 3.5% sulfur needs BN 70-100. The cylinder oil TBN formula is TBN = 0.35 × X × S × B / L, where S is fuel sulfur percentage, B is hourly fuel consumption, L is hourly cylinder oil consumption, and X is an engine coefficient (~0.15 for large crosshead engines). A calcium sulfonate with TBN 415 delivers roughly 4.15 mgKOH of acid-neutralizing capacity per gram, which means about 15-17 wt% treat rate to hit a finished oil BN of 70.

How should I store and handle overbased calcium sulfonate?

Store between 20°C and 45°C in the original sealed drum or IBC. For pumping and blending, heat to 60-80°C using electric drum heaters or a temperature-controlled warehouse. In cold climates where drums may have been stored below 15°C, allow 24-48 hours for full heat equilibration before attempting to pump. Do not use open flame to heat drums. The product has a 2-year shelf life in sealed original packaging. If the drum has been opened, use within 6 months and keep the container tightly sealed between uses. Moisture ingress will increase the water content and can destabilize the colloidal CaCO₃ dispersion.

Related Products

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Further Reading

Calcium sulfonate detergent — how it works and why TBN matters

Calcium petroleum sulfonate — applications and formulation guide

How overbased calcium sulfonate works

Calcium sulfonate grease — properties, compatibility, and manufacturing

Low-ash detergent alternatives — magnesium sulfonate in modern engine oils

Detergents and TBN boosters — full product category

ZDDP antiwear additives

Ashless dispersants

Lubricant antioxidants

Last updated: May 13, 2026