Chemical Properties of 2-Phosphonobutane-1,2,4-tricarboxylic acid, sodium salt (PBTC·Na4)

2-Phosphonobutane-1,2,4-tricarboxylic acid, sodium salt (PBTC·Na4) is an organophosphonate containing one phosphonate group and three carboxylate groups on a butane backbone. The coexistence of phosphonate and carboxylate groups provides h3 chelation, threshold scale inhibition and dispersion capacity for multivalent metal ions such as Ca²⁺, Mg²⁺, Zn²⁺ and Fe²⁺

Appearance & solubility

Commercial forms are

colourless to pale yellow transparent liquid

or

white crystalline powder

. It is highly soluble in water and miscible with water at normal temperature; solid powder is hygroscopic

pH property

1% aqueous solution is weakly alkaline, typical pH range

6.5–8.5

. Compared with acidic PBTC, the tetrasodium salt avoids h3 acidity and is easier for alkaline formulation systems.

Thermal stability

Excellent thermal stability, far better than conventional organophosphonates (HEDP, ATMP). It maintains good scale inhibition performance under high‑temperature, high‑hardness and high‑alkalinity water conditions, and is suitable for high concentration ratio cooling water systems

Oxidative stability / chlorine tolerance

Good resistance to oxidative degradation by chlorine‑based biocides (TCCA, sodium hypochlorite). It is not easily decomposed by residual free chlorine in water, so it can be used together with chlorine biocides in circulating water formulas

Chelation & scale inhibition characteristics

It works as a threshold inhibitor. It distorts calcium carbonate crystal lattices and disperses microcrystals to prevent scale deposition. It can stabilize zinc salts and keep zinc ions dissolved in water, showing good synergistic corrosion inhibition with zinc salts and copolymers

Chemical compatibility

Compatible with most common water treatment additives: zinc salts, acrylic dispersants, other phosphonates, non‑oxidizing biocides. It is widely used in cooling water, RO, textile auxiliaries and industrial cleaning formulationsLANXESS.

Hydrolysis & degradation

Stable under neutral and alkaline circulating water conditions. It belongs to low‑phosphorus organophosphorus and will slowly hydrolyze under h3 acid + high‑temperature long‑term conditions.