Scale buildup is a big problem in water treatment for things like cooling systems, desalination plants, and oil recovery. It lowers how well we can use and treat water. It can also harm machines and be unsafe. At present, the use of scale inhibitors to control scaling is the most economical and efficient technical approach. The use of phosphorus-containing scale inhibitors is gradually restricted. Copolymer scale inhibitors also have good scale inhibition performance, but studies have shown that copolymer scale inhibitors are difficult to be degraded by microorganisms, and long-term accumulation will also cause water pollution and endanger human health. Therefore, green and environmentally friendly scale inhibitors have become the research and development focus and hotspot of water treatment scale inhibitors.
Right now, both Chinese and foreign researchers are putting their energy into making green scale inhibitors based on polyaspartic acid & PASP and polyepoxysuccinic acid & PESA derivatives.
Synthesis of PASP and PESA and research and development progress of their modification technology
PASP forms when aspartic acid molecules join together, losing water in the process. Its many carboxyl and amino groups help it prevent CaCO3 and CaSO4 scale buildup. PESA is typically made from maleic anhydride, which goes through epoxidation and polymerization after combining with anions. The application of PASP and PESA as monomer green and environmentally friendly scale inhibitors in water treatment still has defects such as large dosage, high impurity content, and poor temperature resistance. Therefore, it is necessary to study the modification of PASP and PESA to overcome the above shortcomings.
Progress in the research and development of chemical modification technology
At present, the chemical modification of PASP and PESA is mainly carried out by ring-opening modification and copolymerization modification.
The ring-opening modification approach includes two main types: ring-opening copolymerization and ring-opening crosslinking. This method usually involves opening the ring structure of epoxysuccinic acid (PSI) or epoxysuccinic acid (ESA) intermediates. Then, specific functional groups are added, followed by either polymerization or crosslinking, to get a certain amount of scale inhibition. The copolymerization method is to use a reagent containing one or more functional groups to react with PESA or PASP to generate corresponding derivatives.
Table 2 presents data on the scale inhibition, dispersion, and biodegradability of chemically altered PASP and PESA derivatives from studies conducted in different countries over the last three years. Based on the information in Tables 1 and 2, adding functional groups to PASP and PESA monomers can address issues with CaSO4 scale inhibition, Ca3(PO4)2 scale inhibition, and Fe2O3 dispersion. Some of these resulting derivatives maintain good scale inhibition and dispersion even when calcium hardness and alkalinity are high. At the same time, by optimizing the spatial structure of the molecule during modification, it can be better degraded and utilized by organisms.
Future development direction
(1) Further optimize the spatial structure of PASP and PESA modified products. The scale inhibitor has a reasonable spatial structure, which can save the amount of raw materials used in the modification process. At the same time, it is recommended that for the modification of PASP and PESA, not only weak acid groups should be introduced, but also strong acid groups with strong hydrophilicity should be introduced, which can effectively prevent the weak acid groups from generating insoluble calcium gels.
(2) Improve the biodegradability of scale inhibitor molecules. By introducing some functional groups that are conducive to microbial degradation, such as hydrophilic amide groups, amino groups, and carboxyl groups, a better humidity environment is provided for microorganisms.
(3) At the same time, the development of scale inhibitors is not limited to the non-toxicity of the final product, but also requires attention to the selection of raw materials and the intermediate synthesis links, and the final impact on the ecological environment. Further improve the synthesis method, optimize the synthesis process, control pollution from the source, and expand the scope of industrial use.
Summary and Outlook
As people become more aware of the environment, the creation and use of eco-friendly and efficient scale inhibitors is a growing trend in water treatment. Polyaspartic acid and polyepoxysuccinic acid are often used because they are non-toxic, work well, and break down naturally. But, they don’t work as well in water with high alkalinity and hardness, and their scale inhibition abilities are limited, which restricts how widely they can be used. So, by opening the ring and copolymerizing PESA and PASP, introducing scale inhibition functional groups and changing the molecular spatial structure to make their scale inhibition more targeted, multifunctional and adaptable to complex water quality, modifying PESA and PASP to improve their performance in different water conditions has become a key area of study and a direction for future development.
