Polyaspartic acid-capped (4-[(2-aminoethyl) amino]-4-oxobutanoic acid as an efficient and green gypsum scale inhibitor and its scale inhibition mechanism

Abstract

Two new yet structurally similar scale inhibitors (PASP-AAB and PASP-AAA), have been successfully synthesized through ring-opening reaction of polysuccinimide (PSI) with inexpensive (4-[(2-aminoethyl) amino]-4-oxobutanoic acid or glycylglycine. Static antiscaling experiments imply they could dramatically improve the antiscaling efficiency of gypsum, better than that of PASP. Moreover, the slightly different nitrogen atom position on the side chain of PASP-AAB and PASP-AAA enables the former efficiently inhibit the gypsum scale at low concentration (2.0 mg/L). In addition, our results indicate the antiscaling performance of PASP-AAB (at 4.0 mg/L) could maintain the excellent efficiency (>99 %) against gypsum for at least 7 days, better than that of some reported polymer-, and phosphorus-based industrial antiscalants. The very efficient gypsum scale inhibition property of PASP-AAB makes it as one of the very effective green antiscalants reported in the literature by now. Detailed mechanism studies reveal that the better calcium scale inhibition performance of PASP-AAB should be attributed to the easier formation of seven-membered chelation ring of side chain with Ca2+. 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.