Study On Synthesis And Mechanism Of Corrosion And Scale Inhibition Of Carboxyalkylthiosuccinic Acids

After the advanced stage of development of oilfield, water injection process is commonly adopted. In order to alleviate the problem of scale and corrosion in injection-production system, adding corrosion and scale inhibitor is needed. However, appropriate corrosion and scale inhibitors are rarely used in characters of high temperature, high pressure and high salinity of injection water, and contain phosphorus generally. Caboxyalkylthiosuccinic acids are new kinds of additives developed to meet environmental protection requirements. The synthesis of caboxyalkylthiosuccinic acids were earliest reported by France Elf Atochem S. A. Company in 1999 as a patent. However, Their performances, especially about corrosion and scale inhibitors were rarely researched both at home and abroad.This paper mainly studied caboxymethylthiosuccinic acid and caboxyethylthiosuccinic acid. Through thermodynamic estimating synthesis of carboxyethylthiosuccinic acid, the appropriate reaction temperature was obtained. Through experiments, the appropriate solution and catalyst were obtained. Eventually, caboxymethylthiosuccinic acid was prepared by mercaptoacetic acid and maleic acid, and carboxyethylthiosuccinic acid was prepared by 3-mercaptopropionic acid and maleic acid. The optimized reaction additions were as follows. Molar ratio of reacant was 1:1, solvent is water, catalyst was resin D301-R, and the reaction was carried at atmospheric pressure and reflux temperature. The yield of product was 84%, and its purity is 90% or so. A purification method was test out, and synthesized products were characterized by 1HNMR, IR, melting point determination and alkali-melting experiment.Two methods were adopted to evaluate the performances of scale inhibition of synthesized products. One was according to SY/T5673-93, the other was simulating some oilfield conditions. And performances of scale inhibition of some commonly used performances of corrosion and scale inhibition inhibitors and synthesized products were compared. The results showed that under the conditions of high temperature, high pressure and high salinity simulating some oilfield conditions, the scale inhibition rate was reached 90% when using 100mg/L purified caboxymethylthiosuccinic acid, better than commonly used POCA, HPMA and caboxyethylthiosuccinic acid. The influences of concentration, temperature, pressure and flow rate on performances of caboxymethylthiosuccinic acid were investigated. The experiments of caboxymethylthiosuccinic acid dissolving CaCO3 showed caboxymethylthiosuccinic acid had chelating effect of calcium. The scale samples of CaSO4 and CaCO3, prepared by adding different corrosion and scale inhibitors, were analyzed by SEM and XRD. The mechanism of CaSO4 scale inhibition by caboxymethylthiosuccinic acid was to cause distortion of crystal lattice, and the mechanism of CaCO3 scale inhibition by caboxymethylthiosuccinic acid was to cause chelating and solubilization effect.According to SY/T5273-2000, the corrosion inhibition performance of Caboxymethylthiosuccinic acid to A3 steel in simulated solution was evaluated. The results showed that the corrosion inhibition rate was 49.6% when using 100mg/L purified Caboxymethylthiosuccinic acid. And the influences of concentration and temperature were investigated. Through testing polarization curves and ac impedance of A3 steel in simulated solution before and after adding caboxymethylthiosuccinic acid, it showed that caboxymethylthiosuccinic acid belonged to hybrid type corrosion inhibitor, and its mechanism was mainly the coordination bonds formed by the molecule's S and the d orbitals of Fe, and forming absorption film on metal surface through interface transform and chelation.