HEDP (Hydroxyethylidene Diphosphonic Acid) | CAS 2809-21-4 – A High‑Performance Scale and Corrosion Inhibitor Essential to Water Treatment. It is a well-documented organophosphonic acid, with detailed chemical and safety information available from public databases such as HEDP (CAS 2809-21-4) chemical information.
In industrial water treatment systems—such as circulating cooling water, boiler water, and reverse osmosis (RO) or membrane separation systems—scale formation and corrosion are two of the most critical challenges affecting operational efficiency and equipment lifespan. HEDP (Hydroxyethylidene Diphosphonic Acid, CAS No. 2809-21-4) is a highly effective organophosphonic acid that has been widely adopted to address these challenges. Thanks to its excellent chelating ability, outstanding thermal stability, and cost‑effectiveness, it has become one of the most mature and reliable core products in the global water treatment chemical industry.
Contents
What Is HEDP?
HEDP, short for Hydroxyethylidene Diphosphonic Acid, is an organophosphonic acid compound containing two phosphonic acid groups (–PO3H2). Its molecular structure includes stable carbon–phosphorus (C–P) bonds and hydroxyl functional groups, which give HEDP exceptional chemical stability in aqueous solutions. Compared with conventional inorganic phosphates, HEDP is far less prone to hydrolysis and maintains excellent scale inhibition and corrosion control performance across a wide temperature and pH range.
Due to these structural characteristics, it can effectively chelate multivalent metal ions such as calcium, magnesium, iron, and copper at very low dosage levels. This prevents the formation and deposition of common scales such as calcium carbonate, calcium sulfate, and calcium phosphate.
Key Physicochemical Properties
- Chemical Name: Hydroxyethylidene Diphosphonic Acid
- CAS Number: 2809-21-4
- Molecular Formula: C2H8O7P2
- 外观 Colorless to pale yellow transparent liquid (industrial grade)
- Solubility: Completely soluble in water
- Stability: Excellent resistance to heat, hydrolysis, and oxidation
In practical applications, HEDP remains stable at temperatures up to 200 °C and performs effectively under acidic to mildly alkaline conditions. These properties make it particularly suitable for high‑concentration circulating cooling water systems and high‑temperature boiler water applications.
Mechanism of Action: How HEDP Works
The scale inhibition and corrosion control performance of HEDP is achieved through several complementary mechanisms:
- Threshold Effect: Effectively inhibits scale formation and crystal growth at concentrations far below stoichiometric levels.
- Crystal Lattice Distortion: Adsorbs onto crystal surfaces, interfering with normal crystal growth and producing softer, non‑adherent scale.
- Chelation and Dispersion: Forms stable complexes with Ca2+, Mg2+, Fe3+, and other metal ions, preventing precipitation.
- Protective Film Formation: Creates a dense protective layer on metal surfaces, reducing direct contact with water and dissolved oxygen.
Through these combined effects, HEDP delivers long‑term and reliable performance even under complex and challenging water quality conditions.
Typical Applications in Water Treatment
HEDP is widely used across nearly all industrial water treatment sectors, including the following key applications:
1. Circulating Cooling Water Systems
In circulating cooling water systems for power generation, steel production, petrochemical, and chemical industries, HEDP is commonly used as a core component in formulated scale and corrosion inhibitor programs. When combined with polymer dispersants such as polycarboxylates or copolymers, it enables higher cycles of concentration while reducing makeup water and blowdown requirements.
2. Boiler Water Treatment
HEDP performs effectively in low‑ and medium‑pressure boiler systems by inhibiting calcium carbonate and phosphate scale formation, while also providing supplementary corrosion protection for boiler metal surfaces.
3. Reverse Osmosis and Membrane Systems
In RO and nanofiltration systems, it can be used as a scale inhibitor or as part of pretreatment programs, particularly for feed water with high hardness or alkalinity. It helps extend membrane service life and significantly reduces cleaning frequency.
4. Industrial Cleaning and Metal Surface Treatment
Thanks to its strong chelating properties, HEDP is also widely used in industrial cleaning formulations, descaling agents, and metal surface treatment processes, including electroplating and passivation applications.
Environmental and Regulatory Advantages
As environmental regulations become increasingly stringent worldwide, the sustainability of water treatment chemicals has gained greater importance. HEDP is considered a low‑phosphorus, high‑efficiency product. Due to its low effective dosage and stable performance, it helps reduce overall phosphorus discharge. Moreover, it can be effectively blended with low‑phosphorus or phosphorus‑free polymers to support more environmentally responsible water treatment programs.
Why Choose Watercarechem?
As a professional supplier specializing in water treatment chemicals, Watercarechem offers high‑quality HEDP products with the following advantages:
- Consistent active content and excellent batch‑to‑batch stability
- Strict quality control and comprehensive technical documentation (TDS / MSDS)
- Suitable for a wide range of water qualities and application scenarios
- Extensive global market experience and support for customized solutions
Conclusion
HEDP (CAS 2809-21-4) is a proven, high-performance organophosphonic scale and corrosion inhibitor that plays an indispensable role in modern industrial water treatment programs. From circulating cooling water and boiler systems to membrane processes and industrial cleaning applications, HEDP consistently delivers reliable performance, long-term stability, and excellent cost efficiency.
Thanks to its wide applicability, low effective dosage, and strong technical foundation, HEDP is often selected as a core component in customized water treatment formulations designed for long-term operation and reduced total operating costs.
Request a Quotation or Technical Support
At Watercarechem, we do more than supply standard chemicals — we help our partners select the right product grade and dosage based on real operating conditions. Whether you are sourcing HEDP for cooling water treatment, boiler applications, RO membrane protection, or industrial cleaning, our technical team is ready to support your project.
- Available in different concentrations and customized specifications
- Stable quality with full TDS and MSDS support
- Experienced in export supply and international regulatory compliance
- Fast response for technical consultation and commercial quotations
Contact us today to request a quotation, technical datasheet, or application guidance for Hydroxyethylidene Diphosphonic Acid, (CAS 2809-21-4), our team will respond promptly.
Frequently Asked Questions (FAQ)
Q: What is the difference between HEDP liquid and powder? A: The liquid version is typically 60% concentration, making it easy to pump and automate. The powder version is usually 90%+ pure, making it ideal for transport to cold regions (to avoid freezing) or for use in solid chemical formulations.
Q: Can HEDP be used in drinking water treatment? A: While certain grades of HEDP can be used to clean drinking water pipes under strict dosage controls and local regulations, it is primarily recommended for industrial and commercial water systems.
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Last Updated on 2026-02-04 by system
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