Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Biocides; animal or insect repellents or attractants
Reexamination Certificate
1997-09-02
2001-03-27
Levy, Neil S. (Department: 1616)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Biocides; animal or insect repellents or attractants
C504S133000, C504S212000, C514S241000
Reexamination Certificate
active
06207177
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a stable, gel-like slurry having a pH of about 6.5 to about 8.5 containing about 30 to about 40 wt % (dry basis) of a monosodium cyanurate monohydrate. It also relates to the preparation of that slurry and its use in swimming pools and other water systems.
Cyanuric acid (CYA) is used in swimming pool water at levels from 25 to 150 ppm (parts per million by weight) to stabilize hypochlorous acid from sunlight decomposition. CYA is added to swimming pool water upon start up of the pool with fresh water or on a routine basis by those customers who use forms of chlorine other than chlorinated isocyanurates to maintain desired CYA concentration.
CYA is typically in a dry (containing 6 wt % or less water), granulated form. Typical means of application are to broadcast over the pool or to slurry the granules in water and pour the slurry down the pool skimmer. CYA is very slow to dissolve and can take several days to dissolve if broadcast into a pool. Until the CYA has been dissolved for at least 24 hours the pool operator must be careful not to backwash the filter as this would flush the CYA granules out of the filter before they can dissolve in the pool water. The CYA is a weak acid (pH about 3.0) and usually the pool water pH must be adjusted after it has been added.
Slurries of pure CYA untreated with caustic tend to settle and form hard cakes that are typically difficult to resuspend, making them a poor choice as a commercial slurry product. A typical CYA slurry in a half gallon vessel takes several minutes of constant shaking to resuspend the solids. If settled with vibration (such as occurs in transportation) the solids are even more difficult to resuspend. In some cases, after prolonged storage, the cakes become hard and can be removed from the container only by breaking the container open and physically agitating the cake.
Attempts have been made to improve the performance of CYA by reducing its particle size or by adding a dispersant, such as surfactant, but were not successful. The addition of polymers to pure CYA results in a stable slurry, but the dispersant properties of the slurry are usually diminished and an additional chemical is introduced into the pool.
It is well known that monosodium cyanurate (MSCY) has some advantages over CYA because it is more soluble and has a more neutral pH. But the MSCY products proposed have all been dry formulations that are slower to dissolve than slurries and require more capital to manufacture. U.S. Pat. No. 4,233,444, for example, discloses making monoalkali metal cyanurate continuously in a two reactor system. This patent was mainly for the production of chlorinated isocyanurates, but it mentions that monoalkali cyanurates can be used for stabilizing chlorine-containing water if the metal cyanurates are recovered by centrifuging and drying. This technology, as well as other technology for producing dry MSCY, is not believed to be commercially practiced due to the large capital requirements required to make it, including two reactors, a centrifuge, dryer, and possibly other solids handling equipment, such as either a mill or a compactor and screening equipment.
SUMMARY OF THE INVENTION
We have discovered that MSCY monohydrate (MSCYH) can be produced in the form of a gel-like slurry that is stable and readily dissolves in water. The gel-like slurry of this invention is superior to conventional products for stabilizing chlorine in a swimming pool because, when poured into the pool, it easily disperses and dissolves within seconds, faster than either CYA or dry MSCY granules. Also, the product is close to neutral in pH, requiring less pH adjustment of the pool. The slurry of this invention remains in a pourable form over time and little or no shaking is required prior to its use.
The MSCYH slurry of this invention is thick and viscous, and exhibits pseudo-plastic properties that make it resistant to settling (dewatering); it is easily resuspended by shaking. Based on typical slurry behavior and prior work with CYA and alkali metal salts of CYA, these properties were not expected. The process for making the slurry requires only one mixing tank and therefore uses much less capital equipment than is required to produce conventional MSCY.
REFERENCES:
patent: 4233444 (1980-11-01), Doonan
patent: 4432959 (1984-02-01), Shimamura
patent: 5066408 (1991-11-01), Powell
Brookes Anne E.
Fuerle Richard D.
Levy Neil S.
Occidental Chemical Corporation
LandOfFree
Monosodium cyanuric acid slurry does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Monosodium cyanuric acid slurry, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Monosodium cyanuric acid slurry will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2526074