The Study Of The Green Chemistry Of Polyepoxysuccinic Acid As A Reverse Osmosis Scale Inhibitor

In the 20th century, chemistry created enormous material wealth and brought great revolutions for human survival. At the same time, human beings had paid huge prices of resources depletion and environmental pollution, as a consequence of ignorimg natural law and the limited self-regulation capacity of ecosystem. This curel realtity challenged the idea of traditional chemistry. "Eliminating the pollution from the source"-the concept of green chemistry was proposed and embraced by more and more chemists. Producing safer and more eco-fridenly chemical producs following the standards and protacals of green chemistry, developing energy-saving, non-toxic, pollution free chemical industry has become the goal for many chemists. This paper aims to study the widely recognized green scale inhibitor, Polyepoxysuccinic acid. From the property and the green chemistry design of the scale inhibitor, using both experiments and theoretical analysis, we carefully studied the synthesis and application of PESA in the reverse osmosis process.We employed synthetic method for PESA which is of atomic economy and environmental friendly on in term of the theory of green chemicals. Maleic anhydride without nitrogen and phosphorus pollution was chosen as the monomer, and water as the reaction medium without any organic solvents, the inorganic compound H2O2 as oxidant, Na2WO4 as catalyst, and solid NaOH as initiating agent. The optimal conditions of hydrolysis, epoxidation and polymerization of the synthetic process were identified through simple factor experiment and orthogonal experiment. In this case, the PESA product with high performances, less energy consumption and no waste has been realized. The optimal conditions of the epoxidation are that the reaction temperature is 70℃reaction time is 55 min, with 35% dosage of oxidizing agent H2O2 (30%),2.4% dosage of maleic anhydride and catalyst Na2WO4 and the dosage of maleic anhydride. The condition of polymerization is that the dosage of initiating agent is 0.34% maleic anhydride with polymerization temperature of 80℃, polymerization time of 2h, and pH of 7+/-0.5.The PESA was obtained under the optimal conditions above with the maleic anhydride monomer converting ratio of 89.1% and carboxyl content of 21.45%. The scale inhibition ratio of CaCO3 is above 96%. After tests and measurement, the products could meet all requirement of The Sector Standard of The Technical requirements of PSEA (HG/T 3823-2006), According to the standard method OECD301B, the biograduation ratio of PESA is above 77%. The effectiveness and applicability of PESA as a RO scale inhibitor were studied using both static and dynamic methods. 10mg/L PESA was added into the synthesized RO water with cation concentration of 40mg/L, 100mg/L and 200mg/L, respectively. According to the results, PESA showed multi-inhibitory performances with the average scale inhibition ratio of 90% to CaCO3, CaSO4, BaSO4 and SrSO4 which could easily deposit on the RO membrane.The dynamic scale inhibition performance of PESA in the RO system of both sea water and tap water was investigated under the full recycle operation mode. After ten cycles of experiments, the variations in water permeability and desalination ratios are within 5% after PESA treatment. In addition PESA is well compatible with with Fe and Al coagulants commonly used in RO system.Analysis of JSM-6360LV SEM images of CaCO3 crystals treated with PESA suggested that PESA could induce CaCO3 crystal deformation, damaging the crystal structure, thus prevent the growth of CaCO3 scale. Reacting with PESA can greatly increase the relative degree of super saturation of slightly soluble salts. We recognized that PESA had a verity of anti-scaling effects like separation, promotion in solubility by complexion, and crystal deformation on scale causing ions.We also compared the methods for evaluating scale inhibitors. Through conductometric titration, the relative saturation level of the slightly soluble salts was obtained which is used to evaluate the performance of scale inhibitor. The results show that Titration method gave essentially the same results as the precipitation of CaCO3, but was more repeatable. Compared with CaCO3 precipitation, conductometric titration can access the performance of the scale inhibitor more quickly and accurately, is easier to apply and more repeatable.