In my country, industry is growing quickly, which means we’re using more water. Reusing water is now a key way to save our water supply. In fact, cooling systems that recycle water make up 70% to 90% of all the water used by industries. With the widespread use of scale inhibitors, in order to adapt to the application of various industries, many different types and properties of scale inhibitors have been produced.
1.what is a scale inhibitor?
Scale inhibitors are a type of agent that can disperse insoluble inorganic salts in water and prevent or interfere with the precipitation and scaling of insoluble inorganic salts on the metal surface.
2.What are the main components of reverse osmosis scale inhibitors?
Reverse osmosis scale inhibitors mainly include some natural dispersants, phosphonic acid, phosphonocarboxylic acid, phosphonosulfonic acid and polymers, and the vast majority of scale inhibitors currently used are polymers. They can disperse insoluble inorganic salts in water and prevent or interfere with the precipitation and scaling of insoluble inorganic salts.
In order to provide convenience for use and convenient purchase, we need to understand the types of scale inhibitors. The common classifications are mainly the following:
2.1 Polycarboxylic acid scale inhibitors and dispersants
Polycarboxylic acid compounds have good scale inhibition effects on calcium carbonate scale, and the dosage is also very small. Commonly used ones include polyacrylic acid PAA, hydrolyzed maleic anhydride HPMA, AA/AMPS, multi-polymers, etc.
2.2 Organic phosphonates
Organic phosphonates have a good effect on inhibiting calcium sulfate scale, but a poor effect on inhibiting calcium carbonate scale. It has low toxicity and is easy to hydrolyze.
2.3 Organic phosphonic acid scale inhibitors
Commonly used ones include ATMP & Amino Trimethylene Phosphonic Acid, HEDP & Etidronic Acid, EDTMPS, HEDP & Etidronic Acid, PBTCA, BHMTPMPA & Bis(Hexamethylene Triamine Penta (Methylene Phosphonic Acid)), etc., which have a good effect on inhibiting the precipitation or precipitation of calcium carbonate, hydrated iron oxide or calcium sulfate.
2.4 Polyphosphates
Commonly used polyphosphoric acids include sodium tripolyphosphate and sodium hexametaphosphate. Long-chain anions generated in water are easily adsorbed on tiny calcium carbonate crystals. At the same time, this anion is easy to replace with CO32-, thereby preventing the precipitation of calcium carbonate.
3. Performance of scale inhibitors
We know that scale inhibitors have a scale inhibition effect. The scale inhibition effect is due to the fact that they can prevent the growth of small carbonate crystals and distort the lattice, so that carbonates in the circulating cooling water will not form hard scale on the surface of the heat exchanger. At the same time, through the characteristics of the organic phosphates and other components in its organization to form a protective film with the metal, it can combine with the calcium ions in the circulating cooling water to prevent metal corrosion. This product works well in many pH situations. It helps stop scaling and corrosion in conditions between pH 7.0 and 10.0. This simplifies things for industrial production and prevents issues like corrosion or scaling that can occur if pH levels are off. The product’s carbonate hardness can get to roughly 680 mg/L, which means it’s good at preventing scaling.
4. Mechanism of action of scale inhibitors
First, they use complexation and solubilization. When the copolymer dissolves in water, it becomes a negatively charged chain. This chain makes a water-soluble mix with calcium ions, which boosts the solubility of inorganic salts and stops scale from building up. Second, they cause lattice distortion. Some parts of the molecule take up space on the inorganic salt nucleus or microcrystal. This messes with the crystal’s normal growth, slowing it down and cutting down on salt scale creation. Third, scale inhibitors create an electrostatic repulsion. Once the copolymer dissolves in water, it sticks to the inorganic salt’s microcrystals. This ups the repulsion between particles, keeping them from clumping together and maintaining a dispersed state. This action stops or lessens scale from forming. Because of these actions, scale inhibitors can spread out insoluble inorganic salts and prevent scale aggregation. This helps to prevent scale and has big future potential for industrial use.
5. The difference between reverse osmosis scale inhibitor and circulating water scale inhibitor
Due to the different situations faced by the two, the requirements for the two are different:
The operating environment of circulating water requires long-term and bacteria-resistant, and a large amount of polymer dispersant can be used to provide a dispersion effect on suspended matter to increase the scale inhibition effect. The circulating water system is large in volume and operates in the open air, so the purity of the agent is not high.
Since the reverse osmosis scale inhibitor has a short action time, the scale inhibitor is required to quickly react with the scaling ions, so it is required to be fast and efficient; in addition, due to the narrow internal channels of the membrane, if a polymer dispersant is used, it will cause greater problems; at the same time, the scale inhibitor process is a concentration process on the membrane surface. If the impurity content is high, it will also affect the stable operation of the system.
The significant advantage of a high concentration of scale inhibitor is that it can reduce transportation costs.
For single-agent scale inhibitors, the higher the concentration, the narrower its stable range. For compound scale inhibitors, due to the different stable ranges of each single agent, it is more difficult to increase the concentration of the product.
In addition, the higher the concentration of the scale inhibitor, the faster the speed of its change during storage, and the content of its impurities will increase accordingly.
