Evaluation of maleic acid‐based copolymers containing polyoxyethylene ether as inhibitors for CaCO 3 scale

Synthesis, characterization and properties of a novel environmentally friendly ternary hydrophilic copolymer

A novel environmentally friendly scale inhibitor was synthesized by the free radical polymerization of itaconic acid (IA), acrylamide (AM), and sodium p-styrene sulfonate (SSS). The structures of the copolymers were characterized using FTIR, UV, and ¹H-NMR, which proved successful in obtaining the expected target structures. The synthesis conditions such as monomer ratio, initiator dosage, titration time, and reaction temperature were optimized by the static scale inhibition method, and the expected polymeric scale inhibitor with a competent scale inhibition performance was obtained. The copolymer conversions at different temperatures were obtained indirectly by bromination titration, and the relationship between the molecular weight of the polymer and the scale inhibition performance at different reaction temperatures was also investigated by GPC. The results showed that the copolymer had a good ability to control calcium carbonate scaling, and the inhibition rate of CaCO₃ reached 84.7% at a dose of 30 mg L^-1. The microscopic morphology and structure of calcium scales were analyzed by SEM, FTIR, and XRD, and it was concluded that the copolymer could change the crystallization path of calcium carbonate from stable calcite to vaterite. That could be dispersed in water. The proposed inhibition mechanism suggests that surface complexation between polymer functional groups and Ca²⁺ leads to excellent solubility of the complexes. These findings suggest that the prepared green copolymers have great potential for oilfield applications.

Stable Binding Conformations of Polymaleic and Polyacrylic Acids at a Calcite Surface in the Presence of Countercations: A Metadynamics Study

Elucidating the stable binding conformations of additives at the surface of CaCO3 crystals is essential to biomineralization, scale inhibition, and materials technology. However, accomplishing this by experimental means is rather difficult. In this study, molecular dynamics simulations based on a metadynamics approach were conducted to elucidate the stable binding conformations of a deprotonated polymaleic acid (PMA) additive and two deprotonated poly(acrylic acid) (PAA) additives with different polymerization degrees in the presence of various countercations at a hydrated calcite (104) surface. The simulated free-energy surfaces suggested the existence of several slightly different stable binding conformations for each additive. The appearance of these distinct binding conformations is speculated to originate from different balances of interactions between the additive, the calcite surface, and the countercations. The binding conformations and binding stabilities at the calcite surface were affected by the countercations, with Ca2+ ions producing a more pronounced effect than Na+ ions. Furthermore, the simulation results suggested that the binding stability at the calcite surface was higher for the PMA additive than for the PAA additives, and the PAA additive with a polymerization degree of 10 displayed a binding stability that was similar to or lower than that of the PAA additive with a polymerization degree of 5. The present simulation method provides a new strategy for analyzing the binding conformations of complex additives at material surfaces, developing additives that stably bind to these surfaces, and designing additives to control crystal growth.

Formation and Inhibition of Calcium Carbonate Crystals under Cathodic Polarization Conditions

The formation of CaCO3 crystals on the cathode surface and the scale-inhibition performance of scale inhibitor 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) on the cathode surface were studied by methods of solution analysis, gravimetric analysis, SEM, FTIR, and XRD techniques. They were then compared with the results of the formation and suppression of CaCO3 crystals in aqueous solution. PBTCA had a good solution-scale-inhibition performance and good lattice-distortion effects on CaCO3 crystals in solution, which could change the CaCO3 from calcite to vaterite and aragonite crystals. The solution-scale-inhibition efficiency exceeded 97% when the PBTCA concentration reached 8 mg/L. Under cathodic polarization conditions, the surface-scale-inhibition efficiency of the cathode and solution-scale-inhibition efficiency near the cathode surface both exceed 97% at polarization potential of −1V. The addition of PBTCA significantly reduced the amount of CaCO3 crystals formed on the cathode surface and had good surface and solution-scale-inhibition effect. However, the lattice-distortion effect of PBTCA on CaCO3 crystals disappeared on the cathode surface, and the resulting CaCO3 contained only calcite crystals. The high-scale-inhibition effect of PBTCA under cathodic polarization was mainly due to the inhibition of the formation of calcium carbonate crystals by PBTCA, and not because of the lattice distortion of CaCO3 crystals.