Corrosion Inhibition of a Green Scale Inhibitor Polyepoxysuccinic Acid

The corrosion inhibition of a green scale inhibitor, polyepoxysuccinic acid (PESA) was studied based on dynamic tests. It is found that when PESA is used alone, it had good corrosion inhibition. So, PESA should be included in the category of corrosion inhibitors. It is not only a kind of green scale inhibitor, but also a green corrosion inhibitor. The synergistic effect between PESA and Zn2+ or sodium gluconate is poor. However, the synergistic effect among PESA, Zn2+ and sodium gluconate is excellent, and the corrosion inhibition efficiency for carbon steel is higher than 99%. Further study of corrosion inhibition mechanism reveals that corrosion inhibition of PESA is not affected by carboxyl group, but by the oxygen atom inserted. The existence of oxygen atom in PESA molecular structure makes it easy to form stable chelate with pentacyclic structure.

Molecular Dynamics Simulation on Scale Inhibition Mechanism of Polyepoxysuccinic Acid to Calcium Sulphate

Molecular dynamics simulation has been performed to simulate the interaction between PESA and the （001） face of anhydrite crystal CaSO4 at different temperatures with the presence of various number of H2O molecules. The results show that PESA can effectively prevent the growth of CaSO4 scale at 323-343 K. At the same temperature, the binding energy between PESA and the （001） face of CaSO4 for systems with various number of H2O has the order of E-bind（OH2O）〉Ebind（200-400H2O）〉E, bind（lOOH2O）. For the same system at different temperatures the binding energies are close and are mainly contributed from the Coulomb interaction, including ionic bonds. The bonds are formed between the calcium atoms of anhydrite scale crystal and the Hydrogen bonds are formed between the O oxygen atoms of the carboxyl group of PESA. atoms of the carboxyl group of PESA and the H atoms of H2O. van der Waals interaction is conducive to the stability of the system of PESA, H2O, and CaSO4. The radial distribution functions of O（carbonyl of PESA）-H（H2O）, O（CaSO4）-H（H2O）, and O（CaSO4）-H（PESA） imply that solvents have effects on the anti-scale performance of PESA to CaSO4.

Determination of the dissociation constants of polyepoxysuccinic acid

The dissociation constants of polyepoxysuccinic acid(PESA)were investigated in this study.Based on the potentiometric titration and the BEST program,the dissociation constants of PESA were determined.Considering the complexity of the dissociation of PESA in aqueous solution,several models were constructed to simulate the dissociation process of PESA.By comparison,the dissociation constants of PESA were obtained with model 4.The species distribution of PESA in aqueous solution as a function of pH was also presented according to the experimental and calculation results.It showed that the H_(2)L model with five basic structure units to describe the dissociation of PESA was reasonable,and the relevant constants had less error and better matching between the experimental and calculation data.The corresponding values of pK_(ai) were 4.68 and 4.92,respectively,for H2L at 35℃ with ionic strength of 0.1 mol/L.