Mechanism of Scale Inhibitory Effect of Sequestering agent

The scale inhibition mechanism of Sequestering agent is quite complicated, and there are many explanations. I think the scale inhibition effect of chelating dispersants generally works through the following aspects:

1.Lattice Distortion

In the polycarboxylate chelating dispersant, polycarboxylate is a linear polymer compound. Except one end is adsorbed on the CaCO3 grains, the rest is around the grains, making it unable to grow and become smooth. Therefore, the grain growth is disturbed and distorted, the grains become finer, and the formed scale layer is soft and easily washed away by the water flow.

It has also been confirmed by experiments that the organic phosphonate in the chelating dispersant with organic phosphonic acid as the main component has a critical value effect (that is, a trace amount of the chelating dispersant can prevent the formation of scales), that is, only a few mg/l The organic phosphonic acid can prevent the precipitation of several hundred mg/l of calcium carbonate, and the organic phosphonic acid has better scale inhibition performance than polyphosphate (such as STPP). We have done tests, adding 5mg/l of chelating dispersant (organic phosphonate as the main component) in water with calcium hardness of 1375mg/l, after 120h at 90°C, the calcium hardness is 50% to 80%. No precipitation, but adding 5mg/l polyphosphate STPP under the same conditions is ineffective. Moreover, the organic phosphonate chelating dispersing agent has a good synergistic effect when used together with other agents (that is, when the total dose is unchanged, the effect of using each agent alone is not as good as the effect of mixing the two together). For example, the chelating dispersant is compounded with polyphosphate, compounded with polycarboxylate, etc., the effect is increased. In addition, organic phosphonate chelating dispersants have good corrosion inhibition performance at higher doses, and are non-toxic or extremely low-toxic agents, with good chemical stability, not easy to hydrolysis, high temperature resistance, and will not generate phosphate due to hydrolysis. This leads to environmental problems such as bacterial and algal overgrowth (eutrophication).

2.Increase the solubility and solubilization of scale-forming compounds

3.Electrostatic repulsion

After the molecule of chelating dispersant is ionized into anion in water, it has strong adsorption due to physical or chemical action, and it will adsorb to some slurry, pectin, oligomer, dye aggregate suspended in water On the particles of impurities such as dust, dust and other impurities, the surface of the particles has the same negative charge, so that the particles are electrostatically repelled to each other, preventing the particles from colliding and accumulating and growing, and the particles are suspended in the water in a dispersed state. The chelating dispersant with good performance can make the particles disperse in the water for a long time, even if the precipitation occurs, it can also slow down the sedimentation speed of the particles. , 85 ℃, can be maintained for 24h without deposition.

4. Dispersion

In addition to electrostatic repulsion, chelating dispersants (such as polyacrylic acid) have a dispersing and suspending effect, which can strongly disperse oligomers, dye aggregates, colloids, etc., so that they do not coagulate. The scale particles of the dispersant macromolecules produce steric hindrance, and the scale particles in the dispersed state are more difficult to collide and coagulate, and do not settle in the suspended water, and are easily washed away by water.

5.Cleaning effect

The molecules of the chelating dispersant chelate with metal ions (unscaled or on the scale body, in the scale body) to form three-dimensional scaled bicyclic or polycyclic chelates. These macromolecular complexes are loose It can be dispersed in water or into the scale body to make the scale body soft and easy to remove, so long-term use of chelating dispersant can play a role in removing the original scale. Due to the above reasons, the chelating dispersant has the function of scale inhibition and scale removal.