HEMPA (Hydroxyethylamino-Di(Methylene Phosphonic Acid)) is a specialized organic phosphonate whose primary value lies in its exceptional tolerance to dissolved iron and its effectiveness against gypsum (calcium sulfate) scaling, distinguishing it from more common phosphonates like ATMP or HEDP.
Identity and Basic Properties
Chemical Identity: CAS Number 5995-42-6, with the molecular formula C₄H₁₃NO₇P₂ and a molecular weight of approximately 249 g/mol.
Synonyms: Also known as EABMP (Ethanolamine bis(methylenephosphonic acid)) .
Physical Form: Commercial products are typically acidic aqueous solutions, with safety precautions required due to acidity.
Key Performance Advantages
Superior Iron Tolerance: This is HEMPA’s most cited differentiating feature. In standardized tests, HEMPA retained 71% of its active phosphonate in solution under an iron challenge, compared to only 12% for HEDP, 8% for ATMP, and <5% for EDTMP . This makes it suitable for water systems with elevated dissolved iron (e.g., oilfield produced water, cooling systems with corrosion byproducts) where conventional phosphonates may precipitate and lose efficacy.
Effective Gypsum Inhibition: A 2023 study found that at neutral pH (~7) and a dosage of ≥30 ppm, HEMPA completely suppressed gypsum (CaSO₄·2H₂O) precipitation. It works through multiple mechanisms: chelating calcium ions, adsorbing onto crystal surfaces, and incorporating into the crystal lattice to disrupt growth .
Primary Applications
Industrial Water Treatment: Used as a scale and corrosion inhibitor, particularly in systems with high dissolved iron or where gypsum scaling is a concern (e.g., cooling water, boiler water, desalination) .
Oilfield Applications: Suitable for oilfield water systems due to its compatibility with methanol/water solutions and its iron tolerance for produced water and injection water .
Specialized Industrial Processes:
Stainless Steel Treatment: Patented for use in formulations that simultaneously strip and passivate stainless steel surfaces, often combined with other phosphonates like ATMP and an oxidant .
Scale Control in Process Waters: Mentioned in patents for preventing scale in wet-process phosphoric acid production and as a component in nanoparticle-based scale inhibitor systems .
Handling and Storage
Safety: The product is acidic; avoid contact with eyes and skin. In case of contact, flush with plenty of water .
Storage: Store in a shady, dry place. The stated shelf life is generally 12 months .
Note: While HEMPA shows promise for gypsum control, most quantitative performance data (especially the iron tolerance comparison) comes from supplier technical literature or single studies. For critical industrial applications, it is advisable to validate performance with a sample under your specific water chemistry conditions.