Particulate Dispersant Enhancement Using Acrylamide-Acrylic Acid Copolymers

There are a variety of commercially available particulate Fe.sub.2 O.sub.3 dispersants. The difficulty with these dispersants is that the dispersant activity is sensitive to the presence of soluble iron (Fe.sup.2+/3+). When soluble iron is present, as for example in cooling water, the dispersant activity of these particulate Fe.sub.2 O.sub.3 dispersants is strongly and negatively affected. In many cases, dispersant activity is completely inhibited.

My invention is the use of a low molecular weight copolymer consisting of 25% acrylic acid and 75% acrylamide to prevent interference by soluble iron of the dispersant activity of particulate Fe.sub.2 O.sub.3 dispersants. This copolymer, when used in conjunction with a particulate Fe.sub.2 O.sub.3 dispersant at a use level designed to provide a 1:1 ratio of copolymer to soluble iron, will prevent the inhibition of the performance of the particulate Fe.sub.2 O.sub.3 dispersant. The polymer may also increase the overall performance of the dispersant in a synergistic manner. It is anticipated that the polymer can be used to protect particulate dispersants for mud, silt, MnO.sub.2, Ca.sub.3 (PO.sub.4).sub.2, CaCO.sub.3, CaSO.sub.4, etc. from interference by soluble iron.

The copolymer has a preferred average molecular weight of 10,000 although it may vary from 1,000 to 20,000.

While these materials may be selected from a wide variety of compounds, the most commonly used dispersants are the low molecular weight homo and copolymers of acrylic acid. These acrylic acid-containing polymers usually contain at least 30% by weight of acrylic acid and, preferably, 50% by weight. The comonomer can be, for example, methacrylic acid, maleic acid, methylacrylate, acrylamide, vinylacetate, etc. A typical such material is described and claimed in U.S. Pat. No. 3,419,502, the disclosure of which is incorporated herein by reference. Another useful group of dispersants of this type are the acrylic acid vinyl sulphonate polymers. They generally contain from 5-25 mole percent of the vinyl sulphonate or its alkali metal (preferably Na) salts and from 95-75 mole percent of acrylic acid and its water-soluble alkali metal or ammonium salts. Preferably, the acrylic acid-vinyl sulphonate copolymers contain 10-20 mole percent of the vinyl sulphonate and from 90-80 mole percent of acrylic acid. The molecular weights of these classes of polymers range from as low as 500 to as high as 50,000. Molecular weight ranges of from 750-50,000 are preferred with a molecular weight range of approximately 900-15,000 being especially preferred. Ideally, the molecular weight will range from 1,000-6,000.

Other typical polymers or combinations that may be used as iron oxide dispersants in cooling water systems are set forth below in Table I.

To illustrate the efficacy of the invention, several laboratory tests were performed. The effect of soluble iron on decreasing the activity of several polymeric dispersants to disperse suspended Fe.sub.2 O.sub.3 is set forth below in Table II.

The various other benefits of the invention are self-explanatory and are set forth in Tables III, IV, and V below.

The test procedure used to generate the data in the Tables is set forth below.

One hundred (100) milligrams (mg) of Fischer reagent grade Fe.sub.2 O.sub.3 iron oxide powder is washed into a 1500 ml beaker with 1000 ml of synthetic Chicago Tap water (SCTW) that contains the appropriate experimental treatment.

pH.about.8

110 ppm HCO.sub.3.sup.-1 as CaCO.sub.3

90 ppm Ca.sup.2+ as CaCO.sub.3

50 ppm Mg.sup.2+ as CaCO.sub.3

Conductivity 400 micromhos

In a typical experimental run, four experiments are run simultaneously in a four-place gang stirrer. The solutions in the beakers typically contain 1 ppm polymer acid form actives. The polymers may be identical or different. The gang stirrer is put on maximum speed (.about.150 rpm) and stirred for 2 or more hours--typically 2 hours. Readings are taken while stirring at .about.2.5 cm below the surface of the solution with a Brinkman PC/600 colorimeter using a 470 filter and a 2 cm probe light path. The readings are taken after one and two hours. Dispersancy is measured as a function of the amount of Fe.sub.2 O.sub.3 dispersed (resuspension values). With this set of conditions and using %T (Transmission) values instead of absorbance (A) for measurement, greater dispersancy is associated with low %T values.

The test is run as described above but with 1 or 3 ppm of soluble iron (Fe.sup.2+) added to the test solution from an acidic (pH-1) stock solution of 1000 ppm Fe.sup.2+ made from ferrous sulfate. Since the test solution will have a proportional drop in pH from the normal pH-8 to pH-6 or pH-3 (1, 3 ppm Fe.sup.2+ respectively), the solution pH is raised to pH-8 by the addition of a small amount of dilute NaOH with the gang stirrer in operation. In effect, because of the presence of oxygen and alkalinity, the ferrous iron is in situ converted to Fe.sub.2 O.sub.3. This procedure effectively simulates the precipitation of iron under many practical circumstances, as for example in cooling water. The result is a test solution containing 100 ppm Fe.sub.2 O.sub.3 and 3 ppm Fe.sup.2+ converted to Fe.sub.2 O.sub.3 and the appropriate amount of experimental treatments.