Synthetic calcium sulfonate is a type of lubricating oil additive that is composed primarily of calcium and sulfonate moieties. It is a kin to barium sulfonate, but calcium sulfonate will generally provide better performance in high-detergency applications. It serves as a dispersant, detergent, corrosion inhibitor, and antioxidant in lubricating oils. Additionally, it prevents rust and corrosion of engine components, keeps engine parts clean and free of dirt, and ensures stable viscosity of the oil.
Synthetic calcium sulfonate is a speciality lubricant additive that is often used as a corrosion inhibitor in high-temperature applications. It helps to reduce oxidation, prevent rust and has a high thermal stability. It is usually used in combination with other additives to extend the lubricant’s lifetime.
Synthetic calcium sulfonate is a type of calcium salt made by reacting calcium oxide or calcium hydroxide with sulfonic acid. It is commonly used as a detergent additive in various industrial applications, including lubricants, metalworking fluids, greases, and engine oils.
Synthetic calcium sulfonate acts as a detergent by helping to remove dirt, rust, and other contaminants from surfaces. It also provides anti-corrosion properties and helps to protect metal surfaces from wear and tear.
🧪 What Is Synthetic Calcium Sulfonate?
Synthetic calcium sulfonate is a type of oil-soluble detergent and corrosion inhibitor commonly used in lubricant formulations, greases, and metalworking fluids. It is made by neutralizing synthetic alkyl aryl sulfonic acids with calcium, followed by an overbasing process in some cases to produce products with high Total Base Numbers (TBNs), such as TBN 250–400.
🧬 Structure and Chemistry
- General formula:
R–Ar–SO₃⁻Ca⁺(where R is a synthetic alkyl chain, typically linear or branched C14–C24) - In overbased forms, colloidal CaCO₃ particles are suspended in oil and encapsulated by calcium sulfonate.
🏭 Types of Synthetic Calcium Sulfonates
| Type | Description | Use Case |
|---|---|---|
| Neutral calcium sulfonate | Just neutralized sulfonic acid (TBN ~0–30) | Rust prevention, dispersant |
| Overbased calcium sulfonate | Excess Ca reacted with CO₂ → forms CaCO₃ (TBN 200–400) | Engine oils, marine oils |
| Calcium sulfonate complex | Used in high-performance greases with added thickeners | Greases with superior EP/rust |
🧪 Key Properties
| Property | Range/Typical Values |
|---|---|
| TBN | 0–400 mg KOH/g |
| Calcium content | 1–15% |
| Sulfonate content | 5–30% |
| Appearance | Clear amber to hazy brown |
| Solubility | Oil-soluble |
| Stability | Excellent thermal & hydrolytic stability |
🔬 Synthesis Overview
Step 1: Sulfonation
If starting from synthetic alkylbenzene:R–Ph + SO₃ → R–Ph–SO₃H
Step 2: Neutralization
React with calcium base:R–Ph–SO₃H + Ca(OH)₂ → (R–Ph–SO₃)₂Ca + H₂O
Step 3: Overbasing (optional)
React excess calcium base with CO₂ in presence of a promoter and oil to form overbased product:Ca(OH)₂ + CO₂ → CaCO₃ (colloidally dispersed)
⚙️ Applications
🛢️ In Lubricants:
- Engine oils (TBN 250–400) to neutralize acids
- Marine oils (high-BN formulations for HFOs)
- Rust-preventive oils and hydraulic fluids
🧴 In Greases:
- Calcium sulfonate complex greases with superior:
- Water resistance
- Load-carrying (EP)
- Corrosion resistance
🔧 In Metalworking Fluids:
- Acts as a rust inhibitor and emulsifier
✅ Advantages
- Excellent detergency
- Strong acid neutralization (in overbased form)
- Superior rust and corrosion protection
- Good thermal and oxidative stability
- Biodegradable options available with certain sulfonate types
Some key benefits of synthetic calcium sulfonate as a detergent additive include:
- Cleaning performance: Synthetic calcium sulfonate has excellent cleaning power, enabling it to effectively remove stubborn dirt and contaminants from surfaces.
- Anti-wear and anti-corrosion properties: Synthetic calcium sulfonate forms a protective layer on metal surfaces, preventing corrosion and reducing wear and tear. This helps to extend the life of equipment and machinery.
- Thermal stability: Synthetic calcium sulfonate has good thermal stability, enabling it to remain effective at high temperatures typically found in industrial applications.
- Compatibility: Synthetic calcium sulfonate is compatible with a wide range of base fluids and other detergent additives, making it versatile for use in various formulations.
Overall, synthetic calcium sulfonate is a crucial ingredient in formulating high-performance detergents for industrial applications. Its cleaning power, anti-corrosion properties, and thermal stability make it an effective additive for improving the performance and lifespan of equipment and machinery.