Chemistry: analytical and immunological testing – Condition responsive control
Reexamination Certificate
1997-12-16
2001-01-23
Warden, Jill (Department: 1743)
Chemistry: analytical and immunological testing
Condition responsive control
C436S103000, C436S104000, C436S175000, C436S178000
Reexamination Certificate
active
06177276
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method and apparatus for oxidizing phosphonates present in an aqueous solution and a method and apparatus for determining the concentration of phosphonates present in an aqueous solution. Methods and apparatus for monitoring, controlling and optimizing the concentration of phosphonates present in an aqueous solution also are provided.
BACKGROUND OF THE INVENTION
Phosphonates are compounds which are used in water treatment systems to control scale formation and corrosion. The concentration of phosphonates in the water must be maintained within specific limits in order to optimize and maintain the water treatment system's performance. Too little phosphonate in the water will lead to scale formation, while too much phosphonate may cause corrosion. Using more phosphonate than needed to prevent scale formation also is a waste of phosphonate.
Currently, the concentration of phosphonate present in the water of a water treatment system is typically measured in one of two ways. The most conventional method relies on the analysis of grab samples. That is, a sample of water is withdrawn from the system and analyzed by conventional manual techniques. For example, the phosphonate in the water sample is oxidized to phosphate using UV light and a chemical oxidizing agent such as potassium persulfate. The concentration of phosphate then is measured colorometrically, and correlated to the concentration of phosphonate present in the original sample. See Blystone et al.,
Internat'l Water Conference,
Pittsburgh, Pa. (1981). As used herein, the term “grab sample method” refers to the above-described method wherein a sample of water is withdrawn from the system and a chemical oxidizing agent is used in a wet bench laboratory analysis of the phosphate/phosphonate content. Grab sample methods are labor intensive, subject to human error, and take about 15 minutes for each grab sample. They cannot be automated readily because potassium persulfate is hazardous, not stable, and would have to be replaced as it is degraded.
Another method for determining the concentration of phosphonate present in the water of a water treatment system uses inert tracers. In this method, an inert tracer that can be easily measured spectroscopically, such as a fluorescent compound, is added to the system water in a fixed ratio to the amount of phosphonate added to the system water. The level of tracer in the system water is measured from time to time and correlated to the concentration of phosphonate present in the system water. U.S. Pat. No. 4,783,314 describes an example of this type of method. This tracer method suffers from several drawbacks. First, this method measures only the concentration of tracer in the system water, and assumes that the ratio of tracer to phosphonate remains constant throughout the system. Because phosphonate is an active ingredient (and may decompose, precipitate, or be adsorbed), whereas the tracer is inert, this assumption may not be a valid one. Second, because the level of phosphonate itself is not determined, errors resulting from a failure of this assumption are not detected. Phosphonates cannot be measured directly by this method because they are not easily detectable spectroscopically.
Accordingly, there is a need for a method for determining the concentration of phosphonate present in an aqueous solution that is simple, accurate, and subject to automation.
OBJECTS OF THE INVENTION
It is therefore one object of the present invention to provide a method and apparatus for oxidizing phosphonates that does not require a chemical oxidizing agent such as potassium persulfate.
It is another object of the present invention to provide a method and apparatus for determining the concentration of phosphonate present in an aqueous solution that is simple, accurate, and readily automated.
It is another object of the present invention to provide an automated method and apparatus for controlling the concentration of phosphonate present in an aqueous solution.
It is yet another object of the present invention to provide a method and apparatus for optimizing the concentration of phosphonate present in an aqueous solution.
In accordance with these and other objects, the present invention provides the following methods and apparatuses.
In accordance with one aspect, the present invention provides a method for oxidizing phosphonate in an aqueous solution, comprising (A) pumping the solution through a recirculating loop; (B) introducing ozone into the loop through a venturi injector; and (C) digesting the solution with ozone in a digestion chamber.
In accordance with another aspect, the present invention provides a method for determining the concentration of phosphonate present in an aqueous solution, comprising (A) reacting a first sample of the solution with ozone, thereby forming an oxidized first sample comprising phosphate; (B) measuring the concentration of phosphate present in the oxidized first sample; (C) measuring the concentration of phosphate present in a second sample of the solution; (D) subtracting the concentration of phosphate in the second sample from the concentration of phosphate in the oxidized first sample, and using this difference to determine the concentration of phosphonate present in the aqueous solution. Optionally, one or more computers are used to automate this method.
In accordance with another aspect of the present invention, there is provided a method for determining the concentration of phosphonate present in an aqueous solution, comprising (A) diverting a first sample of the aqueous into a recirculation loop; (B) introducing ozone into the loop through a venturi injector; (C) digesting the first sample with ozone in a digestion chamber; (D) recirculating the first sample through the recirculation loop until at least about 90% of the phosphonate present in the first sample is oxidized to phosphate; (E) introducing the oxidized first sample to a phosphate analyzer; (F) measuring the concentration of phosphate present in the oxidized first sample; (G) introducing a second sample of the aqueous solution into a phosphate analyzer; (H) measuring the concentration of phosphate present in the second sample; (I) subtracting the concentration of phosphate in the second sample from the concentration of phosphate in the oxidized first sample, and using this difference to determine the concentration of phosphonate present in the aqueous solution.
In accordance with another aspect of the invention, there is provided a method for controlling the concentration of phosphonate present in an aqueous solution, comprising (A) reacting a first sample of the aqueous solution with ozone, thereby forming an oxidized first sample comprising phosphate; (C) measuring the concentration of phosphate present in the oxidized first sample; (D) measuring the concentration of phosphate present in a second sample of the aqueous solution; (E) subtracting the concentration of phosphate in the second sample from the concentration of phosphate in the oxidized first sample, and using this difference to determine the concentration of phosphonate present in the aqueous solution; (F) comparing the concentration of phosphonate present in the solution to a predetermined target concentration; and (G) if the concentration of phosphonate present in the solution is less than the target concentration, increasing the concentration of phosphonate in the solution; or (G′) if the concentration of phosphonate present in the solution is more than the target concentration, reducing the concentration of phosphonate in the solution. Optionally, one or more computers are used to automate this method.
In accordance with another aspect of the invention, there is provided a method for continually optimizing the concentration of phosphonate in an aqueous solution contained in an apparatus, comprising (A) observing the apparatus for scale formation or corrosion; (B) if scale formation is observed, increasing a predetermined target concentration of phosphonate p
Richardson John
Trulear Michael G.
ChemTreat, Inc.
Foley & Lardner
Warden Jill
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