High-Temperature-Resistant Scale Inhibitor Polyaspartic Acid-Prolineamide for Inhibiting CaCO3 Scale in Geothermal Water and Speculation of Scale Inhibition Mechanism

Abstract

An excellent high-temperature-resistant scale inhibitor, polyaspartic acid-prolineamide (PASP-Pro), was synthesized by polysuccinimide (PSI) and L-prolineamide (L-Pro), and then characterized by 1H-NMR and FTIR analysis. The inhibition performance of PASP-Pro on CaCO3 precipitation was studied at different temperatures through static tests; at the same time, the influence of PASP-Pro on the crystallization process of CaCO3 was investigated by combining the electrical conductivity test of CaCO3 solution with different CaCO3 scale characterizations. The suitable synthesis and evaluation conditions for PASP-Pro were obtained, and a possible multi-stage scale inhibition mechanism of PASP-Pro for CaCO3 scale was then suggested. PASP-Pro has better thermal stability and high-temperature scale inhibition performance (exceeds 87% after pretreatment at 150 °C) than PASP. In addition, PASP-Pro exhibited a promising anti-scaling property by inhibiting the crystallization of CaCO3; the induction period and the nucleation period of the CaCO3 crystallization process were prolonged nearly four times. It was found from XRD patterns that vaterite, an unstable crystalline phase, gradually emerged with the addition of the scale inhibitors, and the aragonite crystals are clearly observed in SEM images. Finally, the possible multi-stage scale inhibition mechanism of PASP-based inhibitors was proposed, including coating impurities, electrostatic repulsion, and inhibiting dehydration and rearrangement of CaCO3 crystallization.