Patent Application
20090214610
The invention is related to water purification systems, including systems employing polymers having pendant heterocyclic amine groups, such as polystyrene having pendant hydantoin and halogenated hydantoin groups, and to the compositions and methods for maintaining the polymers in a biocidally active state.
Heterocyclic N-halamine groups are known to have biocidal properties that can be utilized in water purification. Heterocyclic N-halamine groups that are attached to a polystyrene polymer are described in U.S. Pat. No. 5,490,983, to Worley et al. A crosslinked polystyrene polymer having similar pendant heterocyclic N-halamine groups is described in U.S. Pat. No. 6,548,054, to Worley et al. The crosslinked version of the polystyrene polymer is typically provided as “beads” or particles that do not have the problems associated with the powdered version of the polymer described in the '983 patent.
The beads are available from Vanson HaloSource of Redmond, Wash. A representative heterocyclic amine group described in both of these patents is a hydantoin group. When the hydantoin group has a chlorine or bromine atom bonded to one or both of the hydantoin nitrogen atoms, the hydantoin is biocidal. The '054 patent describes the creation of the biocidal halogenated polystyrene hydantoin (HPSH, an N-halohydantoinylated polymer) polymer from the nonbiocidal polystyrene hydantoin (PSH) polymer using a variety of free available chlorine sources (for example, sodium hypochlorite, calcium hypochlorite, sodium dichloroisocyanurate). Over time however, the biocidal HPSH polymer reverts to nonbiocidal PSH polymer as a result of depletion of the halogen atoms due to contact with biodemand in the medium being treated. PSH polymer, however, has the ability to be recharged or rehalogenated with a halogen to restore its antimicrobial properties.
The '054 patent describes recharging PSH polymer once the polymer has lost its biocidal efficacy by halogenating the PSH polymer using concentrated solutions of industrial strength liquid bleach. It has been determined that the levels of halogen in solution according to the '054 patent are of such a high concentration that when used in situ in a water treatment device, the subsequent purified water is rendered undrinkable and requires considerable post-treatment to remove the excess halogen to render the purified water drinkable.
One of the drawbacks of using HPSH polymer in water filters is that once the halogen is consumed from the HPSH polymer, the halogen must be either replaced by recharging the halogen-depleted PSH polymer, or the entire mass of PSH polymer must be discarded and replaced with fresh HPSH polymer. Until now, there was no practical alternative to either recharging or replacing the PSH polymer in a water treatment system. Replacing halogen-depleted PSH polymer with fresh HPSH polymer raises the capital and operating costs of the water treatment system. Recharging PSH polymer that has lost biocidal efficacy requires that the water treatment system be taken out of service. Off-line recharging of PSH polymer to HPSH polymer creates considerable down-time and system complexity.
Another short-coming of HPSH polymers is the drop in biocidal efficacy during use. As halogen is consumed from the HPSH polymer, the biocidal efficacy of the HPSH polymer drops below commonly required biocidal performance standards, such as the United States Environmental Protection Agency's (EPA) standards of 6 log removal of Klebsiella, and 4 log removal of poliovirus. While the drop in biocidal efficiency is expected as halogen is consumed by the biodemand, the speed with which this reduced effectiveness occurs creates several difficulties for the practical application of the HPSH polymer, such as in a water filter in the home or as an emergency water supply. Product designers and engineers wishing to apply HPSH polymer technology to commercial products must either increase the initial amount of HPSH polymer to achieve the desired performance life of the product or add complexity to the system by allowing for off-line rehalogenation of the PSH polymer.
U.S. Patent Application Publication No. 2005/0104034, to Bridges et al., incorporated herein expressly by reference, describes a tablet capable of delivering free available chlorine and/or free available bromine in water at a low concentration range. When water with low concentrations of chlorine or bromine is semi-continuously or continuously brought into contact with a biocidal N-halohydantoinylated polymer, the polymer is capable of sustaining the normal biocidal activity. However, the low concentration of halogen does not render the water undrinkable. The Bridges application also describes a method for replenishing halogens on the N-halohydantoinylated polymer while maintaining the N-halohydantoinylated polymer biocidally effective. While the Bridges application does provide a useful tablet and method, newer tablets are needed that elute a uniform concentration over a prolonged period of time that also have extended shelf life and are generally temperature stable. The present invention provides these advantages and has additional benefits.
One embodiment of the present invention is a tablet containing benzoic acid and trichloroisocyanuric acid that is capable of achieving concentrations of free available chlorine that replenishes chlorine on N-halohydantoinylated polymers simultaneously while the N-halohydantoinylated polymers continue being biocidally effective against microorganisms in the water, and without rendering the water unsuitable for drinking due to high levels of chlorine. Accordingly, the tablet of the present invention obviates the need to recharge or replace the N-halohydantoinylated polymers. Additionally, the tablet of the present invention is less prone to decay at elevated temperatures and provides a uniform release rate of free available chlorine (FAC) when compared to tablets not having benzoic acid and trichloroisocyanuric acid. The present invention further provides a method to maintain a biocidally effective halogen charge on N-halohydantoinylated polymers without adversely affecting water quality and does away with the need to recharge or replace the N-halohydantoinylated polymers due to the tablet's ability to maintain N-halohydantoinylated polymers from becoming halogen depleted.
One embodiment of the present invention treats the N-halohydantoinylated polymers with low concentrations of free available chlorine by supplying the water to be treated by the polymers with chlorine. The chlorine is supplied by the trichloroisocyanuric acid in the tablet. The water with chlorine then contacts the N-halohydantoinylated polymers thereby maintaining the polymers biocidal. The chlorine in the water alone may not be sufficient to kill microorganisms, however, the N-halohydantoinylated polymers will be effective against many microorganisms. Free available chlorine refers to the chlorine in water that is available to bond with a nitrogen atom on a heterocyclic amine. In addition to maintaining N-halohydantoinylated polymers in a biocidally active state, the tablet is chemically stable at elevated temperatures, is compatible with the chlorine source; provides uniform time release profiles; meets chronic and acute toxicology limits to make long-term consumer consumption possible; and is cost-effective for commercial production. The useful life of the tablet is estimated, but not limited to, treating about 40 liters to about 1,000 liters of water.
The tablet includes trichloroisocyanuric acid (TCCA) and benzoic acid. While the present invention may be discussed in the context of a tablet, the use of the tem should not be construed to limit the invention. Any solid phase article may be rendered capable of providing similar benefits. In one embodiment, the tablet may include only TCCA and benzoic acid, or in another embodiment, the tablet may also include one or more compounds that may aid in manufacturing the tablet or add nutritional value to the water. Additional components, such as magnesium stearate that may be included for the purpose of facilitating manufacturing into tablets or other articles, are not considered to materially effect the release of free available chlorine from the tablet. The tablet, according to the invention, may release about 0.1 ppm (mg/L) to about 3 ppm (mg/L) chlorine in water at room temperature (approximately 20° C.) when tested in accordance with the testing procedure described below in association with
One embodiment is a tablet that includes the synergistic combination of benzoic acid and TCCA, and only those other compounds, such as magnesium stearate, that would not materially affect the basic characteristics of the tablet being temperature stable and capable of delivering substantially uniform levels of chlorine. In one embodiment, the tablet consists essentially of benzoic acid and trichloroisocyanuric acid. In another embodiment, the tablet consists essentially of about 4% to about 10% trichloroisocyanuric acid and about 90% to about 96% benzoic acid, by weight.
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
Benzoic acid, also known as benzenecarboxylic acid (C7H6O2) is widely used as an antimicrobial food additive and a flavor agent/adjuvant. Unexpectedly, benzoic acid when combined with TCCA has proven to be useful in methods for maintaining N-halohydantoinylated polymers in a biocidally effective state that eliminates the need to recharge the polymers. A benzoic acid and trichloroisocyanuric acid-containing tablet will also be useful when used with a water purification device as described in U.S. Patent Application Publication Nos. 2005/0098506 and 2005/0072729; both applications are incorporated herein expressly by reference.
In one embodiment, a tablet made in accordance with the invention, includes about 5% to about 5.5% by weight TCCA and about 94.5% to about 95% by weight benzoic acid. In one embodiment, the tablet is an about ½-inch diameter round tablet with sharp edges and has a total weight of about 450 mg to about 500 mg. Tablets having this shape were made using a lab carver press (Parr Pellet Press, Parr Instruments Co.) The hardness of the tablet is about 40 Newtons (measured using an Erweka type tester TBH30). Unless stated otherwise, the tablets described herein were made using the same lab carver press.
In another embodiment, a tablet made in accordance with the invention, includes about 9% to about 5.5% by weight TCCA and about 91% to about 94.5% by weight benzoic acid. The tablet is an about ½-inch diameter round flat face tablet with a beveled edge and has a total weight of about 600 mg to about 700 mg. Tablets having this shape were made using a commercially available pilot tabletting unit (Kilian single punch station Model #SP300). The hardness of the tablet is about 40 to 80 Newtons (Erweka TBH30).
In another embodiment, a tablet made in accordance with the invention, includes about 4% to about 10% by weight TCCA and about 90% to about 96% by weight benzoic acid.
A tablet made according to the invention provides free available chlorine at concentrations of about 0.1 ppm to about 4 ppm (mg/L) in flowing water at about room temperature (20° C.).
Quite unexpectedly, a tablet including benzoic acid and TCCA is stable at elevated temperatures. Temperature stability means that a tablet does not substantially lose the capacity to provide free available chlorine after being subjected for periods of time to a temperature higher than room temperature. Demonstration of this feature is shown in
Quite unexpectedly, another advantage of a tablet having benzoic acid and TCCA is the ability of the tablet to provide a uniform concentration of FAC in the water. Uniform as used herein may include slight variations of the instantaneous readings of FAC over the elution profile of the tablet, however, the overall elution profile is generally within an upper and a lower boundary, so that any instantaneous reading of FAC does not deviate substantially from a median value. Demonstration of this feature is shown in
Benzoic acid has other advantages, for example, it was found that lubricants, such as magnesium stearate, commonly used in many formulations are not required when using benzoic acid and TCCA. No picking [?] or other common tabletting manufacturing problems were encountered using benzoic acid alone with TCCA. While not intending to be bound by theory, it is speculated that the lubricity provided by benzoic acid alone is similar to other lubricants.
Referring to
The FAC measurements of a tablet containing benzoic acid, TCCA, and magnesium stearate are again shown in
As demonstrated above in Examples 4 and 5, the amount of TCCA and the size of the tablet are not the determinative factors in creating a tablet that provides an acceptable FAC elution profile. As demonstrated by the results shown in
Free available chlorine elution tests were conducted on several other tablet formulations varying the amounts of, and even eliminating either the TCCA and/or the benzoic acid component. Surprisingly, no other halogen source combined with benzoic acid provided an adequate elution profile as compared to the elution profile of the benzoic acid/TCCA tablet. Surprisingly, no other excipient combined with TCCA provided an adequate elution profile as compared to the elution profile of the benzoic acid/TCCA tablet, as discussed above.
All of the tablets of Table 1 were made using a Carver Press (Parr Pellet Press, Parr Instruments Co.) with a ½-inch die and punch identical to the one used to make the benzoic acid/TCCA tablet. Tablet (1) is similar to the tablet used in the temperature stability study discussed above. Tablet (2) is made from organic and inorganic chemicals known to be compatible with TCCA and have been used in the manufacture of tablets for other purposes. Tablet (3) uses an inorganic cementitious agent, calcium sulfate, commonly used to make plaster of paris. It was believed that tablet (3) would prevent the quick elution of TCCA from the tablet. Tablet (4) uses excipients common in the manufacture of a variety of tablets used for pharmaceuticals. Tablet (5) has a salt of benzoic acid, calcium benzoate, to test the comparison between the protonated carboxylic group (in benzoic acid) and a benzoic acid salt (calcium benzoate). Other benzoic acid salts such as sodium benzoate and magnesium benzoate were not considered appropriate, as these salts are readily soluble in water and display different properties than calcium benzoate and benzoic acid. As shown in
Of particular note is the comparison between tablet (1) and tablet (5).
Another advantage discovered with a tablet containing benzoic acid and TCCA is that the peak elution rate can be scaled up or down. As shown in
While the preferred embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 60/667,207, filed on Mar. 30, 2005, incorporated herein expressly by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2006/011860 | 3/30/2006 | WO | 00 | 8/18/2008 |
| Number | Date | Country | |
|---|---|---|---|
| 60667207 | Mar 2005 | US |
