Sodium HEDP4 (tetrasodium hydroxyethylidenebisphosphonate, HEDP-Na4) and sodium HEDP2 (disodium hydroxyethylidenebisphosphonate, HEDP-Na2) are both sodium salt forms of HEDP, and they are distinctly different in a number of ways: -
The chemical structure and composition of

sodium HEDP4 is the product of the substitution of four acidic hydrogen atoms by sodium atoms in the molecule of HEDP, with the chemical formula C₂H₂O ₇P₂Na₄; HEDP2 sodium, on the other hand, is the product of the substitution of two acidic hydrogen atoms by sodium atoms in the HEDP molecule, with the chemical formula C₂H₄O₇P₂Na₂ . This structural difference gives rise to a range of different behavior in terms of chemical and physical properties . -Physical
Properties

In appearance, the solid state of sodium HEDP4 is usually a white powder, moisture-absorbent, easily soluble in water, convenient for transportation, and suitable for use in severe cold conditions; while sodium HEDP2 is usually a white crystal . In terms of solubility, both can be dissolved in water, but due to the different structure, at the same temperature, the same solvent conditions, their solubility will have a slight difference, but can meet most of the water treatment and other application scenarios on the dissolution and dispersion requirements. -Chemical
properties

from the acidity and alkalinity point of view, HEDP4 sodium 1% aqueous solution pH value of 10.0 - 12.0, alkaline; HEDP2 sodium is also alkaline, but the specific pH range and HEDP4 sodium there are differences. In terms of stability, HEDP2 sodium is still very stable at high pH, not easy to hydrolyze, not easy to decompose under general light and heat conditions, acid and alkali resistance, resistance to chlorine oxidation performance is better than other organic phosphoric acid (salt); HEDP4 sodium also has a better stability at 250 ℃ can still play a good corrosion and scale inhibition, but in some extreme conditions, the two stability will be different performance. - Application areas and effect differences

in the field of water treatment, both can form stable complexes with iron, copper, zinc and other metal ions, dissolve the metal surface oxides, scale and corrosion inhibition. But HEDP4 sodium is an excellent inhibitor of calcium carbonate scale, in the industrial circulating cooling water, low-pressure boilers, oilfield water injection and oil pipelines and other scenarios, to prevent the deposition of calcium carbonate scale effect is remarkable, so as to protect the normal operation of the system, reduce equipment corrosion and clogging; HEDP2 sodium, in addition to scale and corrosion inhibition, can be in water with the metal ions, especially calcium ions to form the hexacyclic chelating complexes, and therefore has a better scale inhibition effect and has obvious dissolution limitation effect. In addition to scale and corrosion inhibition, sodium HEDP2 can form hexacyclic chelates with metal ions in water, especially calcium ions, thus it has better scale inhibition and obvious solubility-limiting effect, and when it is used in combination with other water treatment agents, it shows ideal synergistic effect, and it has obvious advantages in the systems with complicated requirements on water quality and needing multiple water treatment agents. In the textile industry, HEDP4 sodium can be used as metal and non-metal cleaning agents, peroxide stabilizers and color-fixing agents in the printing and dyeing industry; HEDP2 sodium in addition to metal cleaning, but also commonly used in textile dyeing and color-fixing additives and other aspects.

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