Study On Preparation And Scale Corrosion Inhibition Mechanism Of Polymer Of Chitosan Modified Polyaspartic Acid

Water pollution and shortage of water resources are some of the vital factors that restrict the sustainable development of human society and economy.At present,most of the used industrial circulating cooling water contains phosphorus compounds with organic phosphonic acid salt as the primary component.the phosphorus compounds is nutrient composition of bacteria and algae in the water.The circulating cooling water discharge containing phosphorus causes eutrophication,resulting in the destruction of the ecological environment.Therefore,the development of a phosphorus-free corrosion inhibitor has become a crucial problem in the field of water treatment.Hence,to develop a novel environmentally-friendly,non-phosphorus corrosion inhibitor to replace the traditional phosphorous scale inhibitor,we used chitosan（CS）modified polyaspartic acid（PASP）to synthesize PASP-CS and analyzed the scale of PASP-CS corrosion performance,mechanism,and influencing factors.The main findings are as follows:（1）PASP was synthesized from maleic anhydride and urea.The intermediate product（EPASP）with amino group was synthesized by ethylenediamine and PASP,and then PASP-CS was obtained by CS and EPASP reaction.By optimizing the reaction conditions,the scale inhibition performance of CaCO₃ and Ca₃（PO₄）₂products under the influence of various factors was studied.The optimum synthesis conditions obtained are:The mass ratio of EPASP to CS is 2:1,The mass ratio of EPASP to 50%glutaraldehyde is 1:1,the optimum volume ratio of hydrochloric acid to acetic acid is 4:1,the reaction temperature is 40℃,and the reaction time is three hours.After comparison and analysis of the scale inhibition performance of the modified products PASP-CS,PASP and the mixture of PASP and CS,The results of the scale inhibition performance studies demonstrate that when PASP-CS dosage is10 mg/L,the scale inhibition rates of CaCO₃ and Ca₃（PO₄）₂ are 91.1%and 84.9%,respectively.Compared with PASP,the scale inhibition performance for calcium carbonate and calcium phosphate is increased by 14.8%and 17.5%respectively.we conclude that Chitosan modified polyaspartic acid greatly improved the scale inhibition efficiency of calcium carbonate and calcium phosphate.This is because chitosan contains numerous-OH groups.After modification,it can improve the stability of the polymer to two valence cations,and improve its ability of anti-hydrolysis and anti-gelling.（2）The performance of PASP-CS and Common scale inhibitor for the inhibition of calcium carbonate scale,calcium phosphate scale,and calcium sulfate scale,for stabilizing zinc ion and for dispersing ferric oxide was investigated using static state scale inhibition method.The results showed that CSN-PESA and LCY-PESA are much better than the common scale inhibitors in general.PASP-CS has good calcium tolerance and can be used for the high hardness water treatment.The scale inhibition performance is best for PASP-CS with-COOH and-OH groups in the molecules modified by chitosan.The scale inhibition performance of PASP and CS containing only-COOH and only-OH group is poor while PASP-CS has excellent scale inhibition performance for calcium phosphate.Using the scans of calcium and XRD after the addition of PASP-CS and Ca²⁺,it can be inferred that the carbonate ions in water carbonate and phosphate binding inhibited the process of PASP-CS.The formation of CaCO₃ is irregular and is no longer a diamond or a strip.The obtained crystals form a stratified distortion and the scale is loose and dispersed.The crystal structure of the generated calcium phosphate becomes distorted,irregular,and dispersed.（3）The inhibition performance results of PASP-CS indicate that the corrosion inhibition performance of the polymers modified by chitosan was better than that of the commonly used water treatment agents and the inhibition rate of PASP-CS increased by 24.7%compared with that of PASP.The polarization curve analysis shows that PASP-CS is an anode type corrosion inhibitor which can form an adsorption film on the surface of carbon steel and shows a good corrosion inhibition and protection ability for carbon steel.Scanning electron microscopy and XRD analysis demonstrated that after the addition of PASP-CS,a layer of adsorption film was formed on the surface of the metal specimen which prevented the corrosive ions from acting on the surface of the test piece leading to a good corrosion inhibition performance.The performance research through the PASP-CS application shows that it would maintain 15 mmol/L hardness and stable alkalinity within circulating cooling water system with about 10 mg/L PASP-CS dosage.The PASP-CS scale inhibition and corrosion inhibition performance is better than those of the low phosphorus corrosion inhibitor.（4）The scale inhibition mechanism of PASP-CS for calcium carbonate and calcium phosphate was simulated by molecular dynamics method.The results of the study show that PASP-CS and calcium scale crystals are attracted to each other and the binding energy of PASP-CS and calcium scale is greater than that of PASP and calcium scale.After the addition of water molecules in the simulation system,the simulation results coincide with the actual conditions and the existence of water molecules enhances the deformation energy of the polymer scale inhibitor.By comparing the simulation results with the simulation results of calcium carbonate and calcium phosphate,the common scale inhibitor compares well with the experimental results.The results show that the simulation results are consistent with the experimental results under aqueous conditions,suggesting that the simulation is feasible under aqueous conditions.The proposed method of molecular dynamics simulation can be used to quickly and accurately predict the scale inhibition effect of scale inhibitor on calcium carbonate and calcium phosphate under aqueous conditions.（5）PASP-CS and carbon steel are simulated by using molecular dynamics method.The results show that when the water molecules exist,the deformation energy of polymer and carbon steel surface decreases while those of calcite and hydroxyapatite increase,suggesting that the role of water molecules on different crystal faces is different.These phenomena completely illustrate the importance of the existence of water molecules in the development of the simulation system.The molecular dynamics simulation of commonly used inhibitors and carbon steel was performed and the simulation results were compared with the experimental results.The results show that the simulation results are consistent with the experimental results under aqueous conditions.Therefore,the method of molecular dynamics simulation can be used to quickly and accurately predict the corrosion inhibition effect of corrosion inhibitors on carbon steel under aqueous conditions.