Study On The Synthesis And Performance Of Polyaspartic Acid And Its Derivatives

With the rapid development of industry, the situation of corrosion and scaling in the industrial areas becomes more serious. The problem of corrosion and scaling is not only seriously affect industrial production, but also causes harm to the environment and arouses greater incidents, so people carried out extensive research on anti-corrosion and anti-scaling, and developed a lot of corrosion and scale inhibitors. With the heighten of people’s environmental protection awareness and environmental requirements become more stringent, the research of green efficient pharmaceuticals will be a hot spot in the field of industrial.Polyaspartic acid(PASP) is an environmentally friendly multi-functional polymer materials. It is not only biodegradable, but also have performances of chelation, dispersion and scale inhibition, and thus become popular research in the field of international water treatment. There are excellent scale inhibiting performances of polyaspartic acid on calcium carbonate and barium sulfate, but the scale inhibition for calcium phosphate is not obvious, so the application is subject to certain restrictions.The industry used to compound to get the better scale inhibiting effect. At presenet, the corrosion inhibiting performance of polyaspartic acid at home and abroad has made great progress, but is still not satisfactory as organophosphorus inhibitor in the treatment of highly mineralized water. So domestic and foreign scholars had modified polyaspartic acid, making it for ideal performance of water treatment agent. In this paper, the intermediate product polysuccinimide was synthesized by catalytic polymerization with L-aspartic acid as raw material in liquid phase, and then the main chain of polyaspartic acid were introduced several new functional groups by the method of open-loop, synthesized polyaspartic acid and its derivatives. Performance of scale inhibition, corrosion inhibition and biodegradability of the synthetic products were studied.In this paper, research work is as follows:1.The intermediate product polysuccinimide was synthesized by catalytic polymerization with L-aspartic acid as raw material and phosphoric acid as a catalyst in liquid phase. The effects of three factors on the synthesis and anti-scale ability of barium sulfate are investigated, which include polymerization temperature, the polymerization time, the molar ratio of phosphoric acid and L-aspartic acid. An L9(33) orthogonal experiment is carried out. The results show that each factor impact degree on anti-scale ratio from big to small is the polymerization temperature, the molar ratio of phosphoric acid and L-aspartic acid, the polymerization time in turn. The optimum condition of synthesis is confirmed:the molar ratio of phosphoric acid and ASP is0.18, the polymerization temperature is180℃, polymerization time is90minutes. Under this condition to verify experiment, the scale inhibiting efficiency for barium sulfate is83.2%.2.The main chain of polyaspartic acid were respectively introduced four new functional groups of single and double hydroxyl group, carboxyl group, sulfonic acid group by the method of open-loop, synthesized polyaspartic acid and its derivatives.The structure of these products were characterized by FT-IR. Characteristics absorption peaks in the infrared spectra showed that the polymer intermediates contained imide structure, and that the hydrolyzate contain amide groups and related groups. So we can be inferred that the obtained products are the target product of polysuccinimide and poly aspartate and its derivatives.3.By the test of static scale inhibition, scale inhibiting performance of the synthesized product were studied. After the new functional groups were grafted in PASP, the performance of scale inhibition for Ca3(PO4)2could significantly be improved, but reduce the performance of scale inhibition for BaSO4and CaCO3. Under the same conditions, the order of scale inhibiting performance for BaSO4and CaCO3all are PASP>PASP-ASP>PASP-SEA>HPAP>DHPAP, and the order of scale inhibiting performance for Ca3(PO4)2are DHPAP>PASP-SEA>HPAP>PASP-ASP>PASP.4.In this paper, the method of the static weight-loss was employed to research corrosion inhibiting performance of the synthetic products. The results show that compared with PASP, PASP derivatives which grafted these types of functional groups, could improve the corrosion inhibiting performance. The order of corrosion inhibiting efficiency to A3steel of five kinds of synthetic products are PASP<PASP-SEA<PASP-ASP<HPAP<DHPAP. Grafted di-hydroxyl group derivative has the best effect of corrosion inhibition, and the ratio of corrosion inhibition can reach92.8%when the dosage is100mg·L-1. Its corrosion inhibition performance increased50%more than that of polyaspartic acid in experiment.5.Biodegradability of PASP and its derivatives were studied. The results show that these types of product are biodegradable. The biodegradation rate of PASP and its derivatives gradually increased with time prolonged, the order of biodegradability from large to small are PASP>PASP-ASP>DHPAP> PASP-SEA>HPAP. Moreover, within20days, biodegradation rate of PASP and PASP-ASP could reach up to60%, which belong to the substances that were readily biodegradable. But for PASP-SEA, HPAP and DHPAP, biodegradation rates were up to10%within8days, belong to the biodegradable substances, which the biodegradation rate of derivatives with di-hydroxyl group side chain was the lowest.6.Taking scale sample of CaCO3and BaSO4as the representative, we analysed mechanism of scale inhibition for BaSO4of the five kinds of product and scale inhibition for CaCO3of PASP were analysed by SEM, which were used as a basis to explore static inhibition mechanism of the scale inhibitor, and it was shown that scale inhibition mechanism are result of different composite mechanism.7.Application of steady-state polarization and electrochemical impedance spectroscopy to analysis the corrosion inhibition mechanism of the corrosion inhibitor. The result shows that the corrosion potential move toward direction of the positive potential compared to the blank solution when several different inhibitors were added in solution, and the polarization curve slope of cathodic and anodic have significant change, and polarization curve slope of the anodic gradually increased. It is indicated that corrosion inhibition of PASP and its derivatives to carbon steel is main to control the loss of e-reaction on the anode. So we can determine that PASP and its derivatives belong to anodic corrosion inhibitors.