Phosphonates have valuable properties other than strictly sequestering power and are sometimes the agents of choice because of these properties. They have the ability to deflocculate and suspend water insoluble materials in colloidal form and prevent re-deposition of suspended dirt particles during rinsing cycles. This ability makes them valuable when formulating CIP cleaners to the ethanol industry. Until water pollution became such a factor, almost every cleaning formulation contained phosphates.
Phosphonates also exhibit a “threshold effect” in that they can prevent the formation of calcium and magnesium carbonate precipitates in hard water even when present in relatively small amounts that are not stoichiometrically enough to fully sequester all the calcium and magnesium ions present.
In summary, the phosphonates act in five ways:
- The ability to chelate.
- The ability to inhibit scale.
- The ability to disperse.
- They do not degrade as temperature increases.
- They do not add to environmental damage sometimes associated with phosphates (inorganic). Commercial products are approved by UL for direct use in potable water for scale and corrosion control.
The right choice of product must be matched with pH range and the evaluation of water hardness.
Other choices, particularly with temperatures exceeding 185 degrees Fahrenheit, are copolymers. Polyacrylates should be used at 50 ppm in the final working solution. Polymers prevent scale from forming by disrupting the structure of newly-formed crystals. This phenomenon slows crystal growth and reduces the agglomeration of crystallites that have already formed. These polymers are effective at sub-stoichiometric concentrations, unlike chelating agents which must be used in stoichiometric concentrations to yield optimum results. These polymers are anionic molecules which absorb into suspended particles, imparting to them a greater negative charge. When this occurs the particles repel each other, resulting in greater dispersency. This was discussed earlier concerning the definition of dispersants.
There are several companies that produce a wide variety of products. These are generally sold by molecular weights. For CIP formulations, a molecular content between 4,000 and 5,000 is used in combination with high alkaline products. Care must be taken because of caustic’s high pH range and particularly with solubility.