The synthesis of TBN 400 super high-base calcium sulfonate involves a complex overbasing process, where alkaline earth metal (typically calcium) is reacted with sulfonic acid or sulfonate detergent, carbon dioxide (CO₂), and a promoter in the presence of oil and base stock solvents. This process produces a highly basic, colloidal calcium carbonate dispersed in an organic sulfonate matrix.
🧪 Overview:
- TBN: Total Base Number (~400 mg KOH/g), very high alkalinity
- Purpose: Neutralizes acidic byproducts in engines and enhances detergent properties in lubricants
- Main functional group: Calcium alkylbenzene sulfonate with overbased CaCO₃ micelles
🔬 Step-by-Step Synthesis Process
🔹 1. Sulfonation (if starting from alkylbenzene)
If sulfonic acid isn’t available:
- Alkylbenzene + SO₃ or chlorosulfonic acid → Alkylbenzene sulfonic acid
🔹 2. Neutralization
Convert sulfonic acid to calcium sulfonate:R–SO₃H + Ca(OH)₂ → R–SO₃Ca + H₂O
- Use calcium hydroxide or calcium oxide
- Performed in mineral oil or base oil, under heating (80–120°C)
🔹 3. Overbasing (Carbonation Process)
Excess calcium base (Ca(OH)₂ or CaO) is added along with:
- CO₂ gas: Reacts with Ca(OH)₂ to form colloidal CaCO₃
- Promoter (surfactant or alcohol like methanol, butanol, or phenol derivatives): Helps form and stabilize micelles
- Oil: Serves as dispersing medium
Key reaction:Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
- Reaction temperature: 50–100°C
- Control pH and CO₂ feed rate to prevent CaCO₃ precipitation
- Aim is to form amorphous or crystalline calcium carbonate micelles encapsulated by sulfonate groups
🔹 4. Filtration and Finishing
- Remove water and solids by vacuum distillation
- Optional: Add antioxidants or dispersants
- Final product is a clear or slightly hazy brown liquid in oil, with TBN ~400
⚙️ Key Inputs and Ratios (Typical):
| Component | Approx. Proportion (by weight) |
|---|---|
| Alkylbenzene sulfonic acid or salt | 10–20% |
| CaO / Ca(OH)₂ | 8–12% |
| Promoter (alcohol/phenol) | 1–5% |
| CO₂ gas | Controlled feed (~2–6 hrs) |
| Base oil / solvent | Balance |
📌 Critical Parameters:
- Temperature: 80–120°C (during carbonation)
- CO₂ flow rate: Must be controlled to prevent CaCO₃ precipitation
- Water removal: Vacuum drying needed to avoid destabilization
- Stability: Requires good dispersion of CaCO₃ micelles
🧴 Final Product Characteristics (TBN 400 Grade):
| Property | Typical Value |
|---|---|
| Appearance | Clear to hazy brown fluid |
| TBN | ~400 mg KOH/g |
| Sulfur content | 1.0–1.5% |
| Calcium content | 12–15% |
| Oil-soluble | Yes |
| Ash content (sulfated) | High (metal-based) |
Super high base synthetic calcium sulfonate is an additive widely used in lubricating oils with excellent detergency, dispersibility and antioxidant properties. The preparation of TBN400 calcium sulfate involves the following key steps, the purpose of which is to increase the base number and maintain the stability of the product.
Raw material composition
- Sulfonic acid:
- Commonly used alkylbenzene sulfonic acid, alkyl sulfonic acid or olefin sulfonic acid.
- The source can be natural or synthetic.
- Alkaline component:
- Calcium hydroxide (Ca(OH)₂) or calcium oxide (CaO).
- Accelerator:
- Methanol, ethylene glycol or other low molecular alcohols.
- Carbon dioxide (CO₂):
- Used for carbonation reaction.
- Base oil:
- As a reaction medium, it is usually a low viscosity base oil.
- Water:
- Provide a uniform reaction environment.
- Co-solvent:
- Aromatic hydrocarbons or esters to promote the dispersion of reactants.
Synthesis process flow
- Sulfonation reaction
- Dissolve alkylbenzene or other alkylated products in base oil.
- Use sulfuric acid or fuming sulfuric acid for sulfonation to generate sulfonates.
- Control the reaction temperature at 50-70°C to avoid excessive sulfonation and the formation of by-products.
- Neutralization reaction
- Add sulfonic acid to the reactor and neutralize it with calcium hydroxide or calcium oxide to generate calcium sulfonic acid.
- Control the reaction temperature at 60-80°C and stir evenly to ensure complete neutralization.
- Alkalization reaction
- Add excess calcium hydroxide or calcium oxide to further increase the alkalinity.
- At the same time, add a small amount of promoter (such as methanol) to increase the solubility of calcium and the reaction efficiency.
- Carbonation reaction
- Pass carbon dioxide into the reactor to react with calcium-based substances to generate calcium carbonate particles.
- Control the carbonation reaction temperature at 60-90°C.
- Use dispersants and base oils to ensure that the generated calcium carbonate particles are evenly distributed to avoid precipitation.
- Dehydration and solvent recovery
- Heat the reaction mixture to 120-140°C to evaporate water and low molecular alcohol.
- Ensure product stability and uniformity.
- Filtration and refining
- Use high-efficiency filters to remove unreacted solid impurities and large particles.
- After refining, a clear and uniform ultra-high base synthetic calcium sulfonate is obtained.
Process parameter control
- Molar ratio of sulfonic acid to base:
- Usually 1:2 to 1:3 to ensure sufficient neutralization and alkalization.
- Carbonation pressure:
- Usually 0.2-0.5 MPa, too high may cause uneven crystallization of calcium carbonate.
- Stirring speed:
- 500-800 rpm to ensure uniform distribution of calcium carbonate particles.
- Reaction time:
- Neutralization reaction 1-2 hours, carbonation reaction 2-4 hours.
Product performance
- Total base number (TBN):
- Greater than 400 mgKOH/g.
- Appearance:
- Light brown to dark brown transparent liquid, no precipitation.
- Cleanliness:
- It can effectively neutralize the acidic substances generated by fuel combustion and keep the engine parts clean.
- Dispersibility:
- Evenly distributed in the base oil to ensure stability under high temperature conditions.
Precautions
- Control of accelerator dosage:
- Excessive accelerator dosage will lead to difficulty in subsequent dehydration.
- Carbonation gas flow rate:
- Too fast carbonization speed may cause particle aggregation, and the gas flow rate needs to be controlled.
- Environmental protection and safety:
- When using sulfuric acid and carbon dioxide, attention should be paid to the treatment of waste gas and waste liquid to meet environmental protection requirements.
By strictly controlling the process parameters, TBN400 ultra-high base synthetic calcium sulfonate can be widely used in fields such as internal combustion engine oil, marine oil and industrial lubricating oil, providing excellent protection and cleaning effects for the lubrication system.