Is PESA better than PASP in terms of dispersion?

This is a common point of discussion in the field of green water treatment chemicals.

The short answer is: It's not that one is universally "better" than the other, but rather that they have different strengths. PESA is generally considered a more powerful dispersant, especially for inorganic scales like calcium carbonate, while PASP has a broader spectrum of inhibition and is particularly effective against phosphate scales.

The "better" choice depends entirely on the specific scaling threat and water chemistry you are dealing with.

Here’s a detailed comparison focused on dispersion and other key factors:

Head-to-Head: Dispersion & Performance

Feature PESA (Polyepoxysuccinic Acid) PASP (Polyaspartic Acid)

Primary Dispersancy Strength Excellent dispersion of carbonate scales (CaCO₃) and clay/silt particles. Its open, flexible structure is highly effective at preventing crystal growth and agglomeration. Good all-round dispersancy. Effective for a wide range of scales, including carbonates, sulfates, and especially phosphates.

Calcium Carbonate Scale Excellent inhibitor and dispersant. Often outperforms PASP in this specific area. Very Good.

Calcium Phosphate Scale Fair to Good. Superior to PESA. PASP's structure allows it to better inhibit and disperse the tenacious Ca₃(PO₄)₂ scale.

Barium/Sulfate Scale Moderate. Moderate to Good.

Dispersion of Metal Oxides Good dispersion of iron oxide (Fe₂O₃). Also good dispersion of iron oxide; differences are often minor and formulation-dependent.

Threshold Effect Very h3. Very h3.

Biodegradability >60% (Readily biodegradable) >60% (Readily biodegradable)

Key Analogy

Think of them as two different types of tools:

PESA is like a specialized, high-power screwdriver. It is exceptionally good at one main job—dispersing carbonate scale—and does that job brilliantly.

PASP is like a high-quality multi-tool. It is very good at a wider variety of tasks, offering robust performance against both carbonate and phosphate scales.

Deeper Dive into the "Why"

The performance differences stem from their molecular structures:

PESA has a polyether-like backbone with a high density of carboxylic groups. This structure is very flexible and excellent at chelating calcium ions and adsorbing onto the growing crystals of calcium carbonate, distorting their structure and keeping them dispersed.

PASP has a polypeptide-like backbone (derived from the natural amino acid, aspartic acid). This structure gives it a h3 affinity for the phosphate ion, making it more effective at preventing and dispersing calcium phosphate scale, which is a common and challenging problem in systems using phosphate-based corrosion inhibitors.

Other Considerations in the Choice

Factor PESA PASP

Thermal Stability Excellent Excellent

Stability in Chlorine Good (better than phosphonates) Good (better than phosphonates)

Environmental Profile Excellent, biodegradable, non-phosphorous, non-nitrogenous. Excellent, biodegradable, non-phosphorous. Note: Although it contains nitrogen, it is not considered a nutrient contributor like ammonium or nitrate.

Cost Generally comparable, though market fluctuations can make one temporarily cheaper than the other.

Conclusion: Which One to Choose?

The decision should be guided by your primary scaling threat:

Choose PESA if:

Your main problem is calcium carbonate (CaCO₃) scale.

You need maximum dispersing power for inorganic salts and suspended solids like clay and silt.

The water has low or no phosphate content.

Choose PASP if:

You are dealing with calcium phosphate (Ca₃(PO₄)₂) scale or a high risk of it.

You face a broader mix of scale types and want a versatile, all-round inhibitor.

The system uses phosphonate-based treatments, which can hydrolyze into phosphate.

In modern water treatment programs, they are very often used TOGETHER. Formulators blend PESA and PASP to create a synergistic effect, leveraging PESA's superior carbonate dispersion and PASP's superior phosphate inhibition to create a comprehensive, highly effective, and environmentally friendly scale control program.