Can DTPMP•Na7 be used with HEDP?

Yes, DTPMP·Na7 and HEDP can be, and often are, used together. In fact, they are considered to have a synergistic effect, meaning their combined performance is better than the sum of their individual effects.

However, successful use depends on the specific application and water conditions. Here’s a detailed breakdown:

Synergistic Benefits of Using DTPMP·Na7 with HEDP

Enhanced Scale Inhibition (Broad-Spectrum Control):

HEDP: Excellent against carbonate scales (like CaCO₃) and moderately effective against sulfate scales (like CaSO₄). It is known for its "threshold effect," where a small amount can inhibit a large amount of scale.

DTPMP·Na7: Outstanding against sulfate scales (CaSO₄, BaSO₄) and highly effective for controlling phosphate scales (e.g., calcium phosphate). It has a very high calcium tolerance and chelating capacity.

Combined Effect: By using them together, you get a broader spectrum of scale inhibition, effectively controlling both carbonate and sulfate scales across a wider range of pH, temperature, and ion concentration.

Improved Corrosion Inhibition:

Both are phosphonates that aid in corrosion inhibition by helping to form a stable, protective film on metal surfaces (primarily on carbon steel, in conjunction with other ions like Ca²⁺ and Zn²⁺).

Using them together can contribute to a more robust and persistent protective film.

Metal Ion Stabilization:

Both are excellent at chelating (sequestering) multivalent metal ions like Ca²⁺, Mg²⁺, Fe³⁺, Cu²⁺.

DTPMP·Na7 has a particularly h3 affinity for iron and is very effective at preventing Fe²⁺/Fe³⁺ from precipitating as iron hydroxide (which can cause fouling and under-deposit corrosion).

Key Considerations and Potential Drawbacks

While synergistic, the combination isn't always a simple "more is better" situation.

Optimal Ratio is Critical:

The ideal blending ratio of HEDP to DTPMP·Na7 is not fixed. It depends heavily on the specific water chemistry:

Calcium Hardness

Alkalinity

pH

Temperature

The presence of specific scale-forming ions (e.g., high sulfate vs. high carbonate).

A common industrial formulation might use a ratio like 1:1 to 1:3 (HEDP:DTPMP), but laboratory testing or vendor guidance is essential for optimization.

pH Dependence:

Both products are most effective in a neutral to alkaline pH range (typically pH 7-9.5). In highly acidic conditions (pH < 2-3), they can begin to hydrolyze and lose effectiveness.

Compatibility with Oxidizing Biocides:

This is a crucial point. Both HEDP and DTPMP are susceptible to degradation by h3 oxidizing biocides like chlorine (Cl₂) and bromine.

DTPMP·Na7 is generally more oxidatively stable than HEDP. If you are using a chlorinated system, DTPMP will last longer. When combined, the HEDP component will degrade first, leaving the DTPMP to continue working.

If high levels of chlorine are present, a more stable alternative like a polymer (e.g., PVS, PAA) might be considered to work alongside them, or a dedicated antioxidant can be used.

Typical Applications for the Combination

This blend is very common in:

Industrial Cooling Water Systems: Where control of both carbonate and sulfate scales is critical, along with corrosion inhibition.

Reverse Osmosis (RO) Antiscalant Blends: To provide broad-spectrum protection against multiple types of scales.

Oilfield Water Flooding: Used in injection water to prevent scale formation in the reservoir.

Conclusion

Yes, DTPMP·Na7 and HEDP are highly compatible and are frequently used together in water treatment formulations. Their combination provides superior, broad-spectrum scale inhibition and contributes to corrosion control.

Best Practice: For any specific application, it is highly recommended to:

Conduct laboratory tests (e.g., static or dynamic scale loop tests) with your actual water source to determine the optimal blend ratio.

Consult with your water treatment chemical supplier who can provide pre-formulated blends and technical support based on extensive experience and formulation science.

Using them together is a standard and effective practice, but it requires careful formulation to achieve the best performance and cost-effectiveness.