Method for Inhibiting Scale and Corrosion in Water Systems

The following illustrate that the combination of the polyacrylate and polymers of maleic acid or its derivatives together with an organo phosphonate and a chelant improve scale inhibition in aqueous systems.

The data in Table I illustrates (Examples A-E) that when all four (4) inhibitors of the composition were used in their ratios of about 1:1:1:0.36, the percentage of deposits in the system was substantially reduced as shown in Example A when compared to the baseline. Moreover, the amount of the deposit was substantially lower when comparing the data of Example A with Examples B through E wherein one of the four (4) components of the composition was omitted. Thus, it was found that the unique combination of the phosphonic acid with the acrylic polymer and the maleic acid polymer synergisically functioned with the chelant in sub-stoichiometric amounts to substantially improve water treatment with respect to corrosion and scale inhibition. While only three of the inhibitors of the composition were better than the baseline (as shown in Examples B, C, D, & E), the use of a combination of all four inhibitors was an improvement over not only the baseline but also the combination of only three (3) as shown by comparing Example A with Examples B, C, D, and E.

The data in Table I illustrates also the effectiveness of using the inhibitor composition of this invention in the ratio of approximately three (3.0) parts by weight of each of the organo phosphonates, the polyacrylic acid derivatives and the polymaleic acid derivatives with only about 1.0 part by weight of the chelant, e.g., an ethylenediamine tetraacetic acid tetrasodium salt.

As illustrated by the data in Table I, the addition of less than a stoichiometric amount of the chelant together with both polymers and the phosphonate enhances the effectiveness of the composition to inhibit the formation of mineral deposits in aqueous systems. The inhibitor composition of this invention keeps the scale-forming constituents suspended so the metal compounds or scale-forming materials will not adhere to the heat transfer surfaces, thereby yielding a cleaner heat transfer unit and more efficient use of energy. Moreover, it was found that in the event the chelant is present in an excessive amount, the excess will not promote corrosion but will prevent the inorganic ions, such as calcium, magnesium and other mineral salts, from depositing on the metal surfaces at temperatures as high as 212.degree. F. Previously, the addition of boiling water inhibitors was calculated on the use of exact or stoichiometric amounts of chelant together with polymers, phosphonates, etc. These prior procedures therefore required precise control of the chemical addition. For example, if the chelant were underfed, the metal ions would deposit on the surface, and with an overfeed the metal surface has a tendency to corrode and form insoluble products, e.g., iron salts, etc. that would redeposit in the system, and impairs the efficiency of heat transfer.

This invention, however, is designed to prevent the accumulation of an excessive amount of the chelant by using a combination of the acrylic and maleic polymers with the phosphonate which react with the feed-water minerals when added to the system in less than substoichiometric amounts. The inhibitor composition of this invention may be used as a dry powder and permitted to dissolve during the addition to the system. Generally, the inhibitor composition is solublized or used as an aqueous solution. These solutions may contain from about 0.01 to 75% by weight of the inhibitors, but preferably from abort 1 to 50% by weight. These solutions can be prepared by adding each of the four inhibitors in any order to water at ambient temperatures. The amount of the inhibitor composition added to the aqueous system is less than stoichiometric but is sufficient to inhibit scale and sludge formation depending on the quality of the water being treated. Generally, however, depending on the quality and source of the water, e.g., hardness, the inhibitor of this invention is added to the system in amounts ranging from about 0.01 to about 600 parts per million (ppm) and preferably from about 1 to about 200 ppm of water in the system.

In addition, the inhibitor composition of this invention may be used in combination with other known additives customarily employed in water treatment including, for example, such compounds as corrosion inhibitors e.g. the triazoles, biocides, and various other water-treating additives. The inhibitor is generally added to the makeup or feed water as the water enters the system and typically by means of a calibrated injector which delivers a pre-determined amount periodically or continuously to the water system.

While this invention has been described by a number of specific embodiments, it is obvious there are variations and modifications which can be made without departing from the spirit and scope of the invention as particularly set forth in the appended claims.