Phosphonobutane-1,2,4-tricarboxylic acid (PBTC) is a high-performance phosphonate-based scale and corrosion inhibitor widely used in water treatment. Due to its excellent calcium tolerance, chlorine resistance, and thermal stability, it is often combined with other chemicals to enhance performance. Below are the most common drug/chemical combinations with PBTC and their applications:
1. PBTC + Corrosion Inhibitors
(1) Zinc Salts (Zn²⁺)
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Synergy: Forms a protective Zn-phosphate film on metal surfaces.
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Application: Cooling water systems (pH 6.5–9).
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Dosage: PBTC (5–15 mg/L) + Zn²⁺ (1–5 mg/L).
(2) Molybdate (MoO₄²⁻)
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Benefit: Environmentally friendly, non-toxic corrosion inhibition.
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Use Case: Closed-loop systems, potable water.
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Ratio: PBTC (10–20 mg/L) + MoO₄²⁻ (5–15 mg/L).
(3) Organic Azoles (TTA/BTA)
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Target: Protects copper alloys in heat exchangers.
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Dosage: PBTC (5–10 mg/L) + Tolytriazole (TTA, 1–3 mg/L).
2. PBTC + Scale Inhibitors
(1) Polyacrylic Acid (PAA) / Polymaleic Acid (HPMA)
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Function: Enhances dispersion of CaCO₃, Ca₃(PO₄)₂, and Fe₂O₃.
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Application: RO systems, boilers.
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Dosage: PBTC (5–15 mg/L) + PAA (2–10 mg/L).
(2) Phosphonates (HEDP/ATMP)
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Synergy: Broad-spectrum scale control (especially for silica and sulfate scales).
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Use Case: High-hardness cooling water.
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Ratio: PBTC + HEDP (1:1 blend, 10–30 mg/L total).
3. PBTC + Biocides
(1) Oxidizing Biocides (NaClO, ClO₂)
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Advantage: PBTC is highly chlorine-resistant, unlike ATMP/HEDP.
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Dosage: PBTC (10–20 mg/L) + NaClO (0.5–2 mg/L as Cl₂).
(2) Non-Oxidizing Biocides (DBNPA, Isothiazolinones)
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Benefit: Controls biofilm without degrading PBTC.
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Example: PBTC (15 mg/L) + DBNPA (5–10 mg/L).
4. PBTC + Surfactants (For Cleaning & Dispersancy)
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Purpose: Improves penetration into existing scales/biofilms.
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Combination: PBTC + Nonionic surfactants (e.g., Triton X-100).
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Use: Pre-cleaning of heat exchangers or membranes.
5. Industrial-Specific Blends
| Industry | Recommended Combination | Key Benefit |
|---|---|---|
| Cooling Towers | PBTC + Zn²⁺ + PAA | Scale + corrosion control |
| Oil & Gas | PBTC + HEDP + MoO₄²⁻ | High-TDS brine treatment |
| RO Desalination | PBTC + SHMP (sodium hexametaphosphate) | Antiscalant for membranes |
| Boiler Water | PBTC + HPMA + Ammonia (pH control) | Silicate scale prevention |
6. Incompatible Combinations
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High-dose Al³⁺/Fe³⁺: May form insoluble phosphonate salts.
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Strong reducing agents (e.g., NaHSO₃): Can degrade PBTC at high temps.
Conclusion: Optimal PBTC Blends
PBTC works best when combined with:
✅ Corrosion inhibitors (Zn²⁺, MoO₄²⁻, TTA)
✅ Scale inhibitors (PAA, HEDP)
✅ Biocides (DBNPA, isothiazolinones)
✅ Surfactants (for cleaning applications)
Key Advantages of PBTC Blends:
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Superior chlorine resistance (vs. ATMP/HEDP).
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Excellent calcium tolerance (up to 1,000 mg/L as CaCO₃).
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Stable at high temperatures (≤120°C).