Evaluation of a low-phosphorus terpolymer as calcium scales inhibitor in cooling water

Scale formation, e.g. precipitation of calcium carbonate and calcium sulfate, is a significant problem in cooling water system. For the control of calcium scale and in response to environmental guidelines, the novel low-phosphorus terpolymer was prepared through free radical polymerization reaction of acrylic acid (AA), oxalic acid-allypolyethoxy carboxylate (APEM), and phosphorous acid (H3PO3) in water with redox system of hypophosphorous and ammonium persulfate as initiator. The synthesized AA-APEM-H3PO3 terpolymer was characterized by Fourier transform infrared spectrometer (FT-IR) and H-1 NMR. The inhibition property of the low-phosphorus terpolymer towards CaCO3 and CaSO4 in the artificial cooling water was studied through static scale inhibition tests, and the effect on morphology of CaCO3 and CaSO4 was investigated with combination of scanning electron microscopy and X-ray powder diffraction analysis, respectively. FT-IR was also used to study the effect on morphology of CaCO3. It was shown that AA-APEM-H3PO3 exhibited excellent ability to control calcium scale, with approximately 90.16% CaCO3 inhibition and 96.94% CaSO4 inhibition at levels of 8 and 4mg/L AA-APEM-H3PO3, respectively. AA-APEM-H3PO3 also displayed ability to change the morphologies and crystal structures of CaCO3 and CaSO4 precipitates. The proposed inhibition mechanism suggests the surface complexation and chelation between the functional groups -P(O) (OH)(2), -COOH, and Ca2+, with polyethylene glycol segments increasing its solubility in water.