Preparation Of Environmentally Friendly Scale Inhibitor And Its Effect On The Crystallization Of Ca²⁺ In Water

The scale formed by the reaction of cations such as calcium and magnesium in industrial circulating cooling water with anions will adhere to the surface of the heat exchanger.It is not only reduced heat transfer efficiency,but also blocked pipes or causes corrosion under scale.This will increased equipment cleaning costs,shorten equipment life,and even lead to safety hazards in the production process.In industrial production,the formation of scale is generally inhibited by the addition of scale inhibitors.Chitosan oligosaccharide（COS）is an oligosaccharide product with higher solubility obtained by degrading chitosan（CTS）.It has a strong function and a wide range of sources,non-toxic and biodegradable.However,COS as a scale inhibitor lacks the carboxyl functional group that plays important role,and the scale inhibition effect is general.Functional groups are typically introduced into the COS or copolymerized with other polymers that containing functional group to enhance scale inhibition performance.Polyaspartic acid（PASP）is an excellent green water treatment scale inhibitor.However,PASP only contains carboxyl functional group,which has a general anti-scaling effect against calcium phosphate and at high Ca²⁺concentration.The polysuccinimide（PSI）is generally subjected to ring-opening reaction by modifying monomer that contained amino group to synthesize graft copolymer,and other functional groups that contained in the monomer are introduced into the side chain of the PASP.In this paper,CTS is first oxidatively degraded to synthesize low molecular weight COS.Then,it is polycondensed into PSI by high temperature using maleic anhydride and ammonia water,PASP is synthesized under alkaline conditions.COS@PASP and His@PASP were synthesized by ring opening reaction of PSI with COS and histidine（His）,respectively.The synthesized products were structurally characterized and tested their scale inhibition performance under different conditions by static scale inhibition experiments.When the molecular weight of COS falls below 3000,it has a good scale inhibition effect on calcium scale.And the lower the molecular weight,the better the scale inhibition effect.Although it can also have a certain scale inhibition effect under the conditions of high temperature,high Ca²⁺concentration and long heating time,the required COS dosage is large and cannot meet the industrial requirements.COS can change the crystal form and morphology of scale,and the interaction between them is strong.The scale inhibition performance of COS@PASP was significantly improved compared to COS.Its tolerance under high temperature,high Ca²⁺concentration and long heating time is significantly improved.COS@PASP can significantly change the crystal form and morphology of calcium scale at low concentrations.Therefore,COS@PASP has certain industrial application prospects.His@PASP has excellent inhibition effects against calcium carbonate,calcium sulfate and calcium phosphate.It is also well tolerated at high Ca²⁺concentration,and it can be used for high hardness circulating cooling water.His@PASP has a significant effect on the crystal form and morphology of calcium scale,and has high interaction energy with calcite.His@PASP is also an excellent corrosion inhibitor and dispersant.It can form a protective film on the metal surface to inhibit the corrosion.For the rust that has been generated,His@PASP can disperse it in the solution to avoid the influence on heat transfer.His@PASP also has good biodegradability and is a biodegradable green water treatment agent.