Synthesis Of Polyepoxysuccinic Acid Derivatives And Their Performance For Scale And Corrosion Inhibition

Polyepoxysuccinic acid(PESA) is a kind of environmentally-friendly scale and corrosion inhibitor. Its performance for scale inhibition, corrosion inhibition and dispersion, however, is worse than the chemicals containing phosphorus because its structure is simple. Modification into its structure is an effective way to improve its comprehensive performance. In this work, some functional groups were introduced into the side chain of PESA and two PESA derivatives separately based on thiourea(CSN) and L-cysteine(LCY) were obtained and thus their comprehensive performance for scale and corrosion inhibition was improved.The two PESA derivatives, CSN-PESA and LCY-PESA, were syntheized by condensation of PESA separately with CSN and LCY. The suitable synthesis reaction conditions were determined based on the evaluation of the scale inhibition efficiency of CSN-PESA and LCY-PESA. The structures of the two derivatives were characterized by means of FTIR and NMR, and their molecular weights were measured by viscosity method.The performance of CSN-PESA and LCY-PESA for the inhibition of calcium carbonate scale, calcium sulfate scale, and calcium phosphate 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. Then the dirtiness resistance and the dynamic scale inhibition efficiency of the two derivatives were measured by dynamic simulation experiments. The results showed that the dirtiness resistance decreased at the dosage of 0.5 mg·L-1 and 1.0 mg·L-1 of CSN-PESA and LCY-PESA and that the dynamic scale inhibition efficiency of CSN-PESA and LCY-PESA separately increased about 10 % and 15 % compared with PESA. Their biodegradability was evaluated by the shaking-bottle incubating test and the results showed that the two derivatives belong to easily degradable chemicals.The performance of CSN-PESA and LCY-PESA for A3 steel corrosion inhibition was studied by weight-loss and electrochemical methods. The results showed that both CSN-PESA and LCY-PESA were the mixed-type corrosion inhibitors based on inhibiting cathodic corrosion reaction and they formed adsorption films on the surface of A3 steel for the protection of A3 steel surface. Moreover the corrosion inhibition efficiency of CSN-PESA and LCY-PESA is better than PESA. The collected calcium carbonate scale samples were characterized by SEM,FTIR and XRD techniques and the results showed that the two derivatives can induce the crystal lattice deformation and cause dispersion of calcium carbonate, damaging the crystal structure and preventing the growth of calcium carbonate scale and dispersing the tiny crystal in solution.The corrosion inhibition mechanism of CSN-PESA and LCY-PESA was studied based on thermodynamic analysis, kinetics analysis and quantum chemistry calculation. The results showed that the two derivatives were physically and chemically adsorbed on A3 steel surface and followed the Langmuir adsorption isothermal equation.The adsorption Gibbs free energies of CSN-PESA and LCY-PESA are-33.69 kJ·mol-1 and-34.16 kJ·mol-1 respectively.The S atoms and N atoms of CSN-PESA and LCY-PESA have important impact on electron density to the highest occupied molecular orbital(HOMO) and the lowest empty molecular orbital(LUMO), so the energy gaps between HOMO and LUMO(ΔE) of CSN-PESA and LCY-PESA are smaller than that of PESA, and the effect of inhibiting metal corrosion of CSN-PESA and LCY-PESA are better than that of PESA as well as the effect of inhibiting metal corrosion of LCY-PESA is more better than that of CSN-PESA.