Abstract:

In order to solve the problem that polyaspartic acid (PASP) has poor scale inhibition effect at high Ca²⁺ concentration and poor effect of dispersing iron oxide, tyrosine (Tyr) was grafted to the side chain of PASP by ring-opening modification of the intermediate polysuccinimide (PSI). An environmentally friendly scale inhibitor of tyrosine-polyaspartic acid copolymer (Tyr-PASP) was synthesized and possessed a plurality of functional groups such as carboxyl group, amino group, amide group and phenolic hydroxyl group. The static scale inhibition experiment proved that Tyr-PASP possessed a better scale inhibition ability than PASP. When the molar ratio of n(Tyr):n(PSI)=1:1, Tyr-PASP showed the best scale inhibition effect against CaCO₃, and the inhibition efficiency reached up to 100% with a mass concentration of 4 mg/L. At 5 mg/L, the inhibition efficiency against CaSO₄ also achieved 100%. After the addition of Tyr-PASP, the crystal form of scale changed from stable calcite and aragonite to unstable vaterite, and the morphology became loose. Molecular dynamics simulations show that the binding between Tyr/PASP and calcite is exothermic and the binding energy is much higher than that of conventional adsorption energy. Electrostatic forces play a major role in the binding between Tyr-PASP and calcite. In addition, the dispersion effect of Tyr-PASP on iron oxide is also significantly improved.

Key words: tyrosine-polyaspartic acid copolymer, scale inhibition, crystal form, dispersion, molecular dynamics simulation