Copolymer of citric acid and glutamic acid as calcium scale inhibitor

Poly(citric acid-co-glutamic acid) (PCA-GLU) was prepared successfully by using citric acid and glutamic acid as monomers. The synthesized polymers were characterized by Fourier-transform infrared spectroscopy and size exclusion chromatography. The static scale inhibition method was utilized to test the performance of PCA-GLU. The polymerization conditions, such as reaction time, reaction temperature, catalyst dosage, and monomer ratio, were optimized to gain the high-performance scale inhibitor. The scale inhibition rate exceeded 95% in simulated CaSO4 fouling solution which initially contained 3,000 mg L-1 Ca2+ and SO42- ions when the dosage of the optimized polymer scale inhibitor was 10 mg L-1. The results of calcium ion titration experiments in static scale inhibition experiments showed that PCA-GLU can chelate with Ca2+ ions, increase the content of Ca2+ ions stayed in simulated water and reduce the amount of deposition of CaSO4 scale. The CaSO4 scale collected from the simulated water was observed by scanning electron microscopy and characterized by X-ray diffraction. PCA-GLU significantly inhibited the crystal growth of CaSO4 and distorted the lattice of the crystal. Therefore, PCA-GLU is a potent inhibitor of a highly-effective green CaSO4 scale.