Properties of Hydroxyethylamino-di(methylene phosphonic acid) (HEMPA)

Hydroxyethylamino-di(methylene phosphonic acid) (HEMPA) is an organophosphonic acid whose most notable property is superior tolerance to dissolved iron compared to common phosphonates like HEDP and ATMP, alongside effective chelation, scale inhibition, and corrosion inhibition.

Core Identity

Chemical Name: [[(2-Hydroxyethyl)imino]bis(methylene)]bisphosphonic acid

Synonyms: HEMPA, EABMP, Ethanolamine bis(methylenephosphonic acid)

Key Performance Properties

Exceptional Iron Tolerance: This is HEMPA's standout feature. In standardized tests with 10 ppm Fe³⁺, HEMPA retained about 71% of the phosphonate in solution. By contrast, HEDP retained only 12%, ATMP/NTMP 8%, and EDTMP less than 5%. This makes it particularly suitable for water systems with high levels of dissolved iron, such as oilfield produced water and cooling systems.

Scale Inhibition: It functions as a threshold scale inhibitor. In calcium carbonate tests (2.5 ppm active dose), HEMPA achieved 55% inhibition without iron and maintained 42% inhibition even with 10 ppm Fe³⁺ present—a performance drop of only 13 percentage points. Research also confirms it effectively inhibits gypsum crystallization by extending induction time and slowing crystal growth, with performance improving as pH rises from ~4 to ~7.

Corrosion Inhibition: It acts as a corrosion inhibitor for metals, particularly effective on unalloyed steel.

Chelation: It exhibits h3 chelating ability, sequestering metal ions to prevent them from interfering with system performance.

Typical Applications

Oilfield Water Treatment: Especially for systems with high dissolved iron and calcium content.

Industrial Water Systems: Cooling water, boiler water, and desalination applications.

Detergents and Soaps: Used as a chelating agent in formulations.

Metal Treatment: Metal cleaning and surface treatment processes.

Form and Handling

Commercial Form: Typically supplied as an aqueous solution (e.g., 50% or 60% active acid content).

Appearance: Colorless to light yellow transparent liquid.

Storage: Store in a shady, dry place; typical shelf life is 12 months.

Safety: It is acidic. Avoid contact with eyes and skin; if contact occurs, flush with plenty of water.

Note: Some supplier pages list the formula as C₆H₁₆NO₈P₂, but the more consistently cited and chemically plausible formula across technical sources is C₄H₁₃NO₇P₂ with a molecular weight of ~249 g/mol.