Nitrogen Atom Positioning Effect of Grafted Modified Polyaspartic Acidbased Antiscalants on the Inhibition of Calcium Scale

Two new yet structurally similar scale inhibitors (PASP-AAB and PASP-AAA), have been successfully synthesized through ring-opening reaction of polysuccinimide (PSI) with cheap (4-[(2-aminoethyl)amino]-4-oxobutanoic acid (AAB) or glycylglycine (AAA). Static antiscaling experiments imply both of them could dramatically improve the antiscaling efficiency on CaSO4 and CaCO3 scale, better than that of PASP. More essentially, the slightly different position of nitrogen atom substituent on the side chain of PASP-AAB and PASP-AAA enables the former efficiently inhibit the gypsum scale at very low concentration (2 mg/L). In addition, our results indicate the antiscaling performance of PASP-AAB at 4 mg/L could maintain the 100% efficiency against CaSO4 scale for at least 7 days, better than that of some reported polymer-, and phosphorus-based commercially available industrial antiscalants. Detailed mechanism studies reveal that the better calcium scale inhibition performance of PASP-AAB than that of PASP-AAA should be attributed to the easier formation of seven-membered chelation ring of side chain with Ca2+ when nitrogen atom was arranged outside of the ring. The unprecedented nitrogen substitution effect disclosed in this work provides a new perspective for understanding the structure-activity relationship of the grafting-modified polymeric inhibitor, meaningful for developing other novel green scale inhibitors.