Membrane scale inhibitor

Scale inhibitor is a type of chemical agent that can disperse insoluble inorganic salts in water, prevent or interfere with the precipitation and scaling of insoluble inorganic salts on metal surfaces, and maintain good heat transfer performance of metal equipment. In terms of mechanism of action, the role of scale inhibitors can be divided into three parts: chelation, dispersion, and lattice distortion. In laboratory evaluation experiments, dispersion is a remedial measure for chelation, and lattice distortion is a remedial measure for dispersion.

Functional characteristics of high-efficiency scale inhibitor for reverse osmosis

1. No additional acid is required, which can effectively prevent acidic substances from corroding equipment and other equipment.

2. The chelating effect is stable and can prevent metal ions such as iron and manganese from forming dirt on the membrane tube.

3. Suitable for various membrane tube materials.

4. The dosage is small, saving the cost of dosing and achieving the most economical scale inhibition control.

5. Strong scale inhibition ability, suitable for various water qualities, with good effect, can reduce membrane cleaning and extend membrane service life.

6. The efficacy and stability of this agent are far superior to sodium hexametaphosphate or pure polymer scale inhibitors.

chelation

The process of chelating a complex with a cyclic structure formed by the bonding of two or more coordinating atoms of a central ion and certain multidentate ligands that meet certain conditions is called chelation. The result of chelation is that scaling cations (such as Ca2+, Mg2+, etc.) react with chelating agents to form stable chelates, thereby preventing their contact with scaling anions and greatly reducing the probability of scaling. Chelation occurs according to stoichiometry, such as one EDTA molecule chelating one divalent metal ion.

The chelating ability of chelating agents can be expressed by their calcium chelation value. The chelating ability of typical commercial water treatment agents (the mass fraction of the active components of the following agents is 50%, and the chelating ability is calculated as CaCO3): amino trimethylene phosphonic acid (ATMP) -300 mg/g; Diethylenetriaminepentamethylphosphonic acid (DTPMP) -450 mg/g; Ethylene diamine tetraacetic acid (EDTA) -15 μ g; Hydroxyethylenediphosphonic acid (HEDP) -45 μ g/mL. In other words, 1 mg of chelating agent can only chelate less than 0.5 mg of CaCO3 scale. If calcium and magnesium ions with a total hardness of smm0FL need to be stabilized in the circulating water system, the required chelating agent is 1000m/L, which is economically unsustainable. It can be seen that the contribution of scale inhibitor chelation is only a small part of it. But in low to medium hardness water, the chelating effect of scale inhibitors still plays an important role.

Dispersing effect

The result of dispersion is to prevent the mutual contact and aggregation between scaling particles, thereby preventing the growth of scale. Scaling particles can be calcium and magnesium ions, scaling particles composed of thousands of CaCO3 and MgCO3 molecules, as well as dust, sediment, or other water-insoluble substances. Dispersants are polymers with a certain relative molecular weight (or degree of polymerization), and the dispersibility is closely related to the size of the relative molecular weight (or degree of polymerization). If the degree of polymerization is too low, the number of particles adsorbed and dispersed will be small, resulting in low dispersion efficiency; If the degree of aggregation is too high, there will be too many particles adsorbed and dispersed, causing the water to become turbid and even forming flocs (which act similarly to coagulants). Compared to chelation, dispersion is more efficient. Experiments have shown that 1 mg of dispersant can stabilize scale particles ranging from 10 to 100 mg in circulating water. In medium to high hardness water, the dispersing function of the scale inhibitor plays a major role.