Inhibition and biodegradability performance of modified polyepoxysuccinic acid as a scale inhibitor against calcium carbonate

Abstract

Scaling by calcium carbonate precipitation is one of the major challenges in circulating cooling water systems, which are used to transfer an amount of waste heat in industrial productive process. Calcium carbonate scale decreases the efficiency of heat transfer equipment, hinders the normal heat transfer process, and even causes the equipment layoff. Polyepoxysuccinic acid (PESA) is an environmentally friendly scaling inhibitor. In order to enhance the performance of its scale inhibition on calcium carbonate, a modified and new PESA inhibitor, epoxysuccinic acid-oxalic acid-allypolyethoxy carboxylate polyethoxy carboxylate (PEM), which contained carboxylic acid and ether groups, was synthesized. The structure of PEM was characterized, and the optimal synthesis conditions were obtained by single-factor experiments. Its scale inhibition performance was estimated with static scale inhibition methods, and the biodegradability of PEM was studied with shaking-bottle incubating test. The results indicate that when monomer ratio (n ESA :n APEM ) is 2:1, dosage of initiator is 6% and reaction temperature is 70°C. The polymer PEM exhibited more excellent scale inhibition property against CaCO 3 than PESA, and the comprehensive scale inhibition property of PEM is much better than the property of PESA. The scale inhibition efficiency of PEM against CaCO 3 was 95.60% when the dosage was 16 mg L –1 . PEM exhibited good biodegradability performance because degradation rates were more than 40% on day 10 and above 95% on day 28. The influence of PEM on formation of CaCO 3 was investigated using scanning electronic microscopy and X-ray powder diffraction. The inhibition mechanism reveals that PESA chain in PEM could react with Ca 2+ or crystal nucleus of CaCO 3 , affect the growth of CaCO 3 crystals, and then distort its crystal structure. Meanwhile, there are four elements, carbon (C), hydrogen (H), oxygen (O), and sodium (Na), in its structure, without phosphorous (P), nitrogen (N), and sulphur (S), which will lead to secondary pollution to water environment, indicating that PEM is an environment-friendly calcium scale inhibitor.