Effect of degree of deprotonation of maleic anhydride‐allyl polyethoxy carboxylic acid copolymer on calcium scale

Abstract

AbstractA hydrophilic copolymer (MA‐APEA) containing carboxylic acid group and ethylene oxide group is synthesized from maleic anhydride (MA) and allyloxy polyethoxy carboxylic acid (APEA) in free radical polymerization and its structure is characterized using FT‐IR, 1H nuclear magnetic resonance spectrometer and gel permeation chromatographic techniques. Seven polymer solutions with different degrees of deprotonation are prepared by adding caustic solution to the polymer solution. Effects of the degree of deprotonation of the polymer on curbing calcium scale and the corrosion inhibition of low carbon steel are studied. Influences of the operating conditions on inhibition against CaCO3 scale by the polymer with different degrees of deprotonation are also investigated. Effects of the degree of deprotonation on CaCO3 deposits/precipitate are analyzed using scanning electronic microscope and X‐ray diffraction. The results show that different degrees of deprotonation of the polymer have different influences on different calcium scale and corrosion inhibition of low carbon steel. The performance of the polymer to withstand high alkalinity and high hardness and high temperature decreases with increase in the degree of deprotonation. The change in the degree of deprotonation influences the conversion of aragonite and vaterite to calcite, and hardly impacts the crystal morphology of CaCO3 crystals. MA‐APEA has proven to be an excellent calcium scale inhibitor.