PESA Scale Inhibitor Modifications: Enhancing CaCO3 & CaSO4 Inhibition

I. Comparative Performance of PESA and Traditional Scale Inhibitors

The inhibitory effects of PESA on CaCO3 crystal formation and growth were compared with those of hydrolyzed polymaleic anhydride (HPMA), polyaspartic acid (PASP), and polyacrylic acid (PAA). The order of inhibitory effect, from greatest to least, was PESA > PASP > HPMA > PAA.

The solution containing PESA exhibited the smallest average volume particle size of CaCO3 crystals and the highest Ca2+ concentration in the final solution. The analysis shows that because PESA can form four Ca-O bonds with Ca2+, the number of bonds formed is the largest and the interaction is the strongest, thus hindering the growth of crystals and achieving a better scale inhibition effect.

II. Enhancing PESA Performance through Functional Group Modification

(1) Introducing -NH2 to Enhance Adsorption Capacity

The electronegativity of −NH2 is large, making it easier to adsorb scaling cations, thereby increasing the adsorption, dispersion and chelation capacity of the scale inhibitor molecules for scaling cations. −NH2 was introduced to synthesize thiourea epoxysuccinic acid (CSN-PESA). The scale inhibition rate of CSN-PESA for CaCO3 reached 96.1%, which was 22.1% higher than that of PESA. The reason is that the new polar group −NH2 was introduced into CSN-PESA, which enhanced the electrostatic adsorption and chelation capacity for Ca2+, reduced the combination of cations and anions, destroyed the formation of crystals, and achieved the effect of improving the scale inhibition rate.

(2) Introducing -COOH to Strengthen Chelation and Lattice Distortion

−COOH has both chelation and solubilization effects on scaling cations and lattice distortion. Increasing the number of −COOH groups in PESA is beneficial to improving the scale inhibition rate of PESA. PESA was modified with itaconic acid to obtain itaconic acid-epoxysuccinic acid (IA-PESA). At 50°C and a dosage of 6 mg/L of IA-PESA, the scale inhibition rate of IA-PESA for CaCO3 scale and CaSO4 scale was close to 100%.

By exploring the scale inhibition mechanism of IA-PESA, it was found that more −COOH makes it easier for CaCO3 crystals to transform from dense calcite to loose vaterite, causing lattice distortion and making the scale easier to be washed away by water.

(3) Introducing -CO-NH- for Improved Biodegradability and Adsorption

The −CO−NH− group can not only improve the biodegradability of the scale inhibitor PESA, but also improve the adsorption and dispersion capabilities, which is beneficial to the chelation of scaling cations. L-arginine-polyepoxysuccinic acid (Arg-PESA) was synthesized by introducing —CO—NH— into L-arginine. At a dosage of 6 mg/L, Arg-PESA achieved 100% scale inhibition for CaCO3 and over 80% for Ca3(PO4)2.

III. Advanced Copolymerization Methods and Multicomponent Derivatives

Several PESA derivatives, synthesized by copolymerizing various organic compounds and introducing various modified groups, exhibit excellent scale inhibition performance.

• LC-T-PESA: Prepared by a ternary copolymerization method, it achieved a 99% scale inhibition rate for CaCO3 at 10 mg/L. The synergy of −CO−NH−, −SO3H, and −COOH groups transforms scale from regular calcite to irregular, fluffy vaterite.

• ESA/IA/SMAS: The synthesized epoxysuccinic acid-oxalic acid-allylethoxycarboxylate exhibited a CaSO4 scale inhibition rate of 99% at a dosage of only 4 mg/L, demonstrating exceptional efficiency for sulfate scale.