The Synthesis And Scale Inhibition Mechanism Of Polyaspartic Acid As A Green Scale Inhibitor

Polyaspartic acid (PASP) is a typical of environmentally friendly scale inhibitor with a biodegradable polypeptide structure. Developing polyaspartic acid and its derivatives and extending their application have attracted worldwide attention. In this paper using maleic anhydride and ammonium hydroxide as raw materials, polyaspartic acid was synthesized by means of pyrocondensation polymerization. Then L-aspartic acid or Taurine was used to modify the polymer in order to enhance its inhibiting and dispersing property.The optimal reaction conditions of the synthesis of polyaspartic acid were determined through the single-factor experiments and orthogonal experiments as follows:the molar ratio of maleic anhydride and ammonia hydroxide was1:2.0, the pyrocondensation reaction time was3h at240℃, the concentration of sodium hydroxide was2mol.L-1, the dosage of sodium hydroxide was30mmol.The scale-inhibiting properties on CaCCO3of polyaspartic acid were studied by scale static beaker test, and the influence of the dosage of PASP, the test temperature and the concentration of Ca2+in experimental water on polymer scale inhibitor were investigated. The experimental results showed that the PASP’s inhibition ratio was73.54%with a dosage of llmg/L when the concentration of Ca2+in experimental water was240mg/L. PASP could be used as scale inhibitor in industrial circulating cooling water and oil-field circulated water especially. A-PASP had been synthesized using L-aspartic acid (ASP) to modify polyaspartic acid in order to improve the scale inhibition performance of PASP, while the A-PASP’s inhibition ratio was78.32%with a dosage of llmg/L under the same test condition. T-PASP had been synthesized using Taurine (SEA) to modify polyaspartic acid in order to improve the capacity of dispersion of PASP, so a dosage of hard scale greatly decrease and it was substituted lots of suspended scale in the conical vessel. The combined inhibitor showed the best scale inhibition performance when the concentration ratio of A-PASP to T-PASP was4:1.The surface structures of CaCO3scale were characterized by SEM and PASP’s scale inhibition mechanisms were studied. It showed that PASP has advantageous chelating and dispersive property, so PASP can hinder formation of CaCO3scale in the circulating cooling water. In addition, PASP make CaCO3scale become looser and difficultly deposit on the surface of the container and flow with the circulating water.