Storage-stable aqueous solutions of chlorine dioxide and methods for preparing and using them

Abstract

Stable, aqueous solutions of chlorine dioxide and methods for producing stable, aqueous solutions of chlorine dioxide are disclosed. Generally, the chlorine dioxide solutions of the invention are aqueous solutions containing about 1000 ppm by weight or less of total impurities and/or 10 ppm or less of manganese and iron combined. The aqueous chlorine dioxide solutions are storage stable for at least 90 days at 25° C. and maintain at least 75% of the initial chlorine dioxide concentration. Methods of preparing, using and transporting the chlorine dioxide solutions are also disclosed.

Claims

1. An aqueous chlorine dioxide solution containing about 1000 ppm by weight or less of total impurities, wherein the impurities are ions comprising: 1,000 ppm by weight or less of sodium ions; 200 ppm by weight or less of calcium ions; 1 ppm by weight or less of manganese ions; 100 ppm or less of magnesium ions; 100 ppm or less of sulfate ions; 100 ppm or less of nitrate ions; 1 ppm or less of potassium ions; 100 ppm or less of bicarbonate ions, and 100 ppm or less of iron ions, wherein the concentration of chlorine dioxide in the solution is at least 1000 ppm by weight, and wherein the aqueous chlorine dioxide solution retains at least 75% of the original chlorine dioxide after 90 days at 25° C. when stored in an amber glass bottle.

2. The aqueous chlorine dioxide solution according to claim 1, wherein the aqueous chlorine dioxide solution contains 300 ppm by weight or less of sodium ions.

3. The aqueous chlorine dioxide solution according to claim 1, wherein the aqueous chlorine dioxide solution contains 100 ppm by weight or less of sodium ions.

4. The aqueous chlorine dioxide solution according to claim 1, wherein the aqueous chlorine dioxide solution contains 10 ppm by weight or less of magnesium ions.

5. The aqueous chlorine dioxide solution according to claim 1, wherein the aqueous chlorine dioxide solution contains 10 ppm by weight or less of sulfate ions.

6. The aqueous chlorine dioxide solution according to claim 1, wherein the aqueous chlorine dioxide solution contains 10 ppm by weight or less of nitrate ions.

7. The aqueous chlorine dioxide solution according to claim 1, wherein the concentration of chlorine dioxide in the aqueous chlorine dioxide solution is at least 2000 ppm by weight.

8. A method for reducing bacterial, viral or fungal load comprising contacting an object carrying a bacterial, viral or fungal load with the chlorine dioxide solution of claim 1.

9. The method according to claim 8, wherein the object is selected from the group consisting of a surface of an animal, water, a hard surface, and food.

10. The aqueous chlorine dioxide solution according to claim 1, wherein the concentration of chlorine dioxide in the aqueous chlorine dioxide solution is at least 4000 ppm by weight.

11. The aqueous chlorine dioxide solution according to claim 1, wherein the concentration of chlorine dioxide in the aqueous chlorine dioxide solution is at least 6000 ppm by weight.

12. The aqueous chlorine dioxide solution according to claim 1, wherein the aqueous chlorine dioxide solution contains 10 ppm by weight or less of bicarbonate ions.

13. The aqueous chlorine dioxide solution according to claim 1, wherein the aqueous chlorine dioxide solution contains 10 ppm by weight or less of iron ions.

14. The aqueous chlorine dioxide solution according to claim 1, wherein the aqueous chlorine dioxide solution contains about 500 ppm by weight or less of the total impurities.

15. The aqueous chlorine dioxide solution according to claim 1, wherein the aqueous chlorine dioxide solution contains about 250 ppm by weight or less of the total impurities.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 provides a graphical representation of the dependence of ClO.sub.2 partial pressure versus concentration in water as a function of temperature.

(2) FIG. 2 provides a graphical representation of pure aqueous chlorine dioxide concentration when stored in amber glass bottles as a function of time and temperature with an initial chlorine dioxide concentration of about 4500 ppm.

(3) FIG. 3 provides a graphical illustration of the stability of aqueous chlorine dioxide solutions with 19% NaCl by weight at different temperatures in HDPE bottles.

(4) FIG. 4 provides a graphical illustration of the stability of chlorine dioxide solutions with 19% NaCl by weight and 4500 ppm chlorine dioxide in glass or PET bottles.

(5) FIG. 5 provides a graphical representation of the stability of aqueous chlorine dioxide solutions having an initial chlorine dioxide concentration of 3000 ppm with sodium chloride at different concentrations and temperatures. 3000 ppm chlorine dioxide and 2600 ppm NaCl are approximately equimolar concentrations, such as would be produced in Reaction 1, if the reaction were carried out at perfect stoichiometric conditions.

(6) FIG. 6 provides a graphical illustration of the stability of aqueous chlorine dioxide solutions having an initial chlorine dioxide concentration of 3000 ppm and containing various concentrations of MgCl.sub.2.

(7) FIG. 7 provides a graphical illustration of the stability of aqueous chlorine dioxide solutions having an initial chlorine dioxide concentration of 3000 ppm and containing various concentrations of CaCl.sub.2.

(8) FIG. 8 provides a graphical illustration of the stability of aqueous chlorine dioxide solutions having an initial chlorine dioxide concentration of 3000 ppm and containing various concentrations of Na.sub.2SO.sub.4.

(9) FIG. 9 provides a graphical illustration of the stability of aqueous chlorine dioxide solutions having an initial chlorine dioxide concentration of 3000 ppm and containing various concentrations of NO.sub.3 ions.

(10) FIG. 10 provides a graphical illustration of the stability of aqueous chlorine dioxide solutions having an initial chlorine dioxide concentration of 3000 ppm and containing various concentrations of Mn ions.

(11) FIG. 11 provides a graphical illustration of the stability of aqueous chlorine dioxide solutions having an initial chlorine dioxide concentration of 3000 ppm and containing various concentrations of K ions.

(12) FIG. 12 provides a graphical illustration of the stability of aqueous chlorine dioxide solutions having an initial chlorine dioxide concentration of 3000 ppm and containing various concentrations of HCO.sub.3 ions.

(13) FIG. 13 provides a graphical illustration of the stability of aqueous chlorine dioxide solutions having an initial chlorine dioxide concentration of 3000 ppm and containing various concentrations of Fe ions.

DETAILED DESCRIPTION

(14) New storage-stable solutions of chlorine dioxide and methods for cleaning water for use in oil or gas production are disclosed herein.

(15) As used herein, the term “stable” refers to the storage stability of an aqueous chlorine dioxide solution, i.e., its resistance to chemical degradation.

(16) As used herein, the term “ready to use” means an aqueous chlorine dioxide solution that does not need to be produced for immediate use at the point of use. A ready to use aqueous chlorine dioxide solution may be produced at a remote location and transported to the point of use, such as an oil or gas well. For example, the ready to use aqueous chlorine dioxide solution can be stored for 90 days or more at a temperature of at least 25° C. and lose less than 25% of its initial chlorine dioxide concentration.

(17) Unless stated otherwise, measurements in ppm refers to parts per million by weight.

(18) The aqueous chlorine dioxide solutions according to the present disclosure can be prepared by contacting the pure water with ultra-pure chlorine dioxide. Any method for contacting the water with chlorine dioxide gas can be used so long as the gas dissolves in the water and the process does not introduce undesirable impurities into the solution. For example, this may be accomplished by bubbling the gas through the water. Alternatively, a counter-current packed column contactor can be employed such that water trickles down from the top of the column over packing while gas flows upward from the bottom of the column and chlorine dioxide solution drains from the bottom of the column.

(19) Any suitable pure water can be used. Suitable water lacks substantial quantities of impurity that causes the shelf life of the aqueous chlorine dioxide to deteriorate below a desired shelf life. Suitable water can include deionized, distilled or water prepared by reverse osmosis or by a combination of these methods.

(20) U.S. Pat. No. 5,234,678, incorporated herein by reference, discloses a simple and safe method for producing high purity chlorine dioxide gas. This process involves the reaction of a solid granular sodium chlorite with dilute chlorine gas according to Reaction 1. Unlike liquid phase production methods, the product resulting from this process does not contain significant quantities of sodium chlorite, sodium chlorate, or substantial quantities of sodium chloride, since these materials do not form gases to any appreciable extent. Tests by an independent lab have shown that the chlorine dioxide gas produced from this process can be over 99.95% pure. Systems for generating ultra-pure chlorine dioxide gas are available from CDG Environmental, LLC of Allentown, Pa.

(21) Generally, the chlorine dioxide solutions of the invention are aqueous solutions containing about 2500 ppm or less of total impurities, more preferably 1000 ppm or less, more preferably about 500 ppm or less, even more preferably about 250 ppm or less and yet more preferably, about 100 ppm or less of total impurities.

(22) The aqueous chlorine dioxide solutions preferably contain at least 100 ppm chlorine dioxide. According to at least one embodiment, the aqueous chlorine dioxide solutions contain at least 1000 ppm chlorine dioxide, at least 2000 ppm chlorine dioxide, at least 3000 ppm chlorine dioxide, at least 4000 ppm chlorine dioxide, at least 6000 ppm chlorine dioxide, at least 8000 ppm chlorine dioxide, at least 10,000 ppm chlorine dioxide, or more. It can be appreciated however, that the concentration of dissolved chlorine dioxide will depend on the temperatures the solution is likely to experience.

(23) According to at least one embodiment, the aqueous chlorine dioxide solution contains 100 to 10,000 ppm chlorine dioxide, from 1000 to 8000 ppm chlorine dioxide, from 2000 to 8000 ppm chlorine dioxide, or from 3000 to 8000 ppm chlorine dioxide.

(24) In an embodiment the solution can be prepared by contacting chlorine dioxide gas with water where the chlorine dioxide gas can have a concentration in the range of about 1 to about 15% by volume in a gas, such as an inert gas, nitrogen or air. Preferably, the water contains about 1000 ppm or, more preferably, about 500 ppm or less of contaminants by weight. The chlorine dioxide gas can be contacted with water by any suitable method that does not introduce contaminants or result in excessive loss. For example, the gas can be bubbled through the water, such as with a sparger. Alternatively, the solution can be prepared in a packed column with a flowing gas and flowing water such that the flowing gas flows up through the column as water trickles down over the packing in the column and the dissolved chlorine dioxide solution can be collected as the effluent from the bottom of the column. Such columns and packing can be obtained from Koch Glitsch, Inc. of Wichita Kans., for example.

(25) In an embodiment the chlorine dioxide solutions can be stored at temperatures that may exceed at least 40° C., at least 25° C., or at least 20° C. In other embodiments, the chlorine dioxide solutions can be stored at temperatures below 40° C., below 25° C., below 20° C., below 15° C., below 10° C., and even below about 5° C. One of ordinary skill in the art will recognize that lower storage temperatures generally provide greater storage stability.

(26) The aqueous chlorine dioxide solutions can be stored in containers that minimize loss of chlorine dioxide. Preferably the containers are flexible containers and have a head space over the stored chlorine dioxide solution of about 1 percent of the volume of the container or less.

(27) Containers are also disclosed for holding chlorine dioxide solutions made of materials and with wall thickness such that the rate of chlorine dioxide loss from the container is reduced. In an embodiment, the container can be a glass bottle, ideally a bottle in which the glass is formulated to minimize transmission of ultraviolet light. In an embodiment the container can be made of a biaxially oriented polymer such as polyethylene terephthalate. In another embodiment, the container can be made from high density polyethylene (HDPE) such as is used in making plastic 55-gallon drums.

(28) Provided that such chlorine dioxide solutions are stored in flexible containers with no head space, they can be safely shipped and stored at concentrations that would otherwise be unsafe because the partial pressure of gas above the solution would be less than 1 atmosphere over a very wide range of concentrations and temperatures. Since the pressure on the outside of the container will always be 1 atmosphere (adjusted for altitude), bubbles of concentrated chlorine dioxide cannot form inside the container. If the flexible container is not completely filled, then the container can withstand thermal expansion of the liquid and even mild exothermic decompositions in stray bubbles, if such were to occur.

(29) Chlorine dioxide solutions can deteriorate by chemical degradation into chlorine, oxygen, chlorite, chlorate, or other decomposition products. Traditionally, it has been believed that this mechanism prevented long shelf life for chlorine dioxide solutions. The present invention is based in part on the surprising discovery that these decomposition reactions either do not occur or occur at very slow rates in solutions made of pure water and ultra-pure chlorine dioxide. Solutions made by reacting liquid reagents according to reaction 1 yield chlorine dioxide in addition to sodium chloride in an equimolar concentration, and possibly unreacted sodium chlorite and/or unreacted chlorine gas.

(30) FIG. 2 shows the stability of solutions of pure chlorine dioxide at about 3000 ppmw in pure water at various temperatures. Even at 40° C., the solution retains about 90% or more of its starting concentration for more than 90 days. This is considered commercially acceptable.

(31) Permeation of chlorine dioxide through the walls of a container occurs with many forms of container materials. Common plastics such as polyethylene, polypropylene and polycarbonate are known to be permeable to chlorine dioxide. If solutions are packaged in containers of these materials, the concentration of the chlorine dioxide will slowly decrease as it diffuses into and through the walls of the container. This process can be substantially eliminated by selection of the appropriate materials with an appropriate thickness. Testing of chlorine dioxide loss rates can be used to identify suitable materials for storage containers. FIG. 3 shows the chlorine dioxide concentration decrease as a function of time at various temperatures in 500 mL HDPE (high density polyethylene) bottles. In FIG. 3 “A” and “B” represent the results from separate but identical studies. This study demonstrated that the rate of loss of chlorine dioxide is a strong function of temperature. One of the curves in FIG. 3 is for a thick-walled HDPE bottle where the wall thickness is similar to that used in 55 gallon HDPE drums. This study further demonstrates that the loss rate of chlorine dioxide diffusion through the thick wall container is slower than through the thin walled container. This study also demonstrates that the rate of loss in the thick-wall bottle is initially equal to that in the thin. It is possible that this is because the rate of loss is initially determined by the rate at which gas diffuses into the inner surface of the bottle which is relatively fast. That rate would be the same for thick bottles as for thin. As time goes by, the wall becomes “saturated” and diffusion into the inner wall equals diffusion out of the outer wall. In this case, diffusion is slower through the thick wall. Because loss of concentration by permeation through the container walls is a function of surface to volume ratio of the container, the rate of concentration loss through the walls of an HDPE 55 gallon drum or larger HDPE container is negligible compared to the concentration decay due to other factors.

(32) The effect of sodium chloride on the stability of chlorine dioxide solutions is very surprising. Although the shelf life of chlorine dioxide solutions can be affected by chemical “demand” in the water, sodium chloride would not theoretically exert any demand. It has been hypothesized that the presence of high levels of sodium chloride causes the reversal of Reaction 1 to re-form sodium chlorite and chlorine. Analysis of samples that have degraded because of the presence of sodium chloride shows the presence of significant quantities of chlorite ion, while none is detectable in the pure (unsalted) samples. However, the stoichiometry does not fully explain the amount of degradation apparent in FIG. 2. This demonstrates that additional factors are present that can lead to chlorine dioxide loss.

(33) In many commercial applications, a shelf life of just a few days is adequate. For these applications small HDPE containers can be used for storage of aqueous chlorine dioxide. Desirably containers such as large 5 gallon or 55 gallon drums or even larger HDPE containers can be used to store chlorine dioxide solutions. Such containers, prior to use, can be pre-treated by filling with a pre-treatment solution containing chlorine dioxide or with dilute chlorine dioxide gas prior to filling with solution. This saturates the walls with chlorine dioxide and greatly slows initial chlorine dioxide losses. Shelf-life can be further extended by storing and shipping the filled containers under refrigeration and minimizing exposure to light or ultraviolet radiation.

(34) Other types of plastic containers exhibit superior barriers to permeation by chlorine dioxide from aqueous solutions. FIG. 4 shows the decay in concentration of solutions made with distilled water and stored in 750 mL bottles made of biaxially oriented PET (polyethylene terephthalate) polymer. After an initial rapid rate of loss, the solution in PET bottles is almost as stable as that stored in glass. Thus, after adjusting for the initial concentration loss, this study demonstrates that a solution of chlorine dioxide is storage stable in PET bottles.

(35) The inventors have surprising discovered that certain contaminants have a significantly greater impact on the storage stability of aqueous chlorine dioxide solutions than others. To determine the impact of various contaminants, the inventors set up a series of experiments to test the effect of the contaminants at various concentrations. In each of the tests, the inventors prepared a chlorine dioxide gas that was more than 99% pure and greater than 99.97% chlorine-free with no detectable chlorine at the limits of detections. Because no other reagents or potential products are used to produce the chlorine dioxide gas, the product was determined to be substantially pure chlorine dioxide gas.

(36) Pure water containing less than 1 ppm solid impurities was used to dissolve the chlorine dioxide gas and form the aqueous chlorine dioxide solutions at a concentration of 3000 ppm+/−5% chlorine dioxide as the initial starting concentration. The data in the figures is reported as % of starting concentration unless otherwise noted.

(37) All data on concentration of aqueous solutions were measured by amperometric titration as described in EPA Standard Methods. Serial dilution was used to adjust to the range of the analytical device.

(38) The accuracy of the analytical technique used is ±3%. Any variation of less than 3% is not considered significant. Apparent increases in concentration in a sealed container are attributable to measurement variability.

(39) Loss of less than about 25% of starting concentration after about 90 days at elevated temperature is considered to represent commercially acceptable shelf life. This is significantly better than the reported shelf life of other common disinfectants such as sodium hypochlorite at comparable temperatures.

(40) FIG. 2 shows the concentration of chlorine dioxide in distilled water in amber glass bottles as a function of time and temperature. FIG. 2 demonstrates surprising stability of aqueous chlorine dioxide solutions over the duration of the test. Further, the figure shows the temperature dependence of the chlorine dioxide loss within the range of 10° C. to about 40° C. In each case the solutions had a commercially acceptable shelf life. This data also shows that refrigerated solutions may have a shelf life of about a year or more. FIG. 2 includes data for chlorine dioxide solutions (4500 ppm chlorine dioxide starting concentration) in pure water with no added compounds.

(41) FIG. 5 shows the concentration of pure chlorine dioxide in amber glass bottles as a function of time and temperature at different low levels of contamination with sodium chloride (NaCl). These studies show that, these chlorine dioxide solutions retain about 90% or more of their starting concentration for at least about 90 days except for the sample with 100 ppmw concentration of NaCl. These studies also demonstrate that salt substantially increases the rate of chlorine dioxide decomposition in solution and the resulting solutions do not retain the target concentration of 90% starting concentration for at least 90 days.

(42) FIG. 5 also shows the effect of temperature and low levels of sodium chloride contamination on solutions of pure chlorine dioxide dissolved in otherwise pure water. Concentrations reported in the legend are concentrations of sodium ion. These samples were aged at 25 and 40° C. At 25° C. and up to 100 ppm NaCl, the samples were equally stable within the margin of error. At 100 ppm Na+ and 40° C. the chlorine dioxide deteriorated at a markedly higher rate.

(43) Similar tests were performed using MgCl.sub.2 (reported as concentration of Mg ion and shown in FIG. 6), CaCl.sub.2 (reported as concentration of Ca ion and shown in FIG. 7), Na.sub.2SO.sub.4 (reported as concentration of SO.sub.4 ion and shown in FIG. 8), nitrate ions (reported as concentration of NO.sub.3 ions and shown in FIG. 9), manganese ions (reported as concentration of Mn ions and shown in FIG. 10), potassium ions (reported as concentration of K ions and shown in FIG. 11), bicarbonate ions (reported as concentration of HCO.sub.3 ions and shown in FIG. 12), and iron ions (reported as concentration of Fe ions and shown in FIG. 13).

(44) The data shows that increasing ion concentrations generally leads to greater chlorine dioxide decomposition (i.e., lower storage stability) over time.

(45) This data indicates that 3000 ppm solutions of pure chlorine dioxide in water having less than 10 ppm contamination with alkali metal salts lose less than about 10% of their concentration in about 100 days at temperatures up to 40° C., while the same solutions having alkali metal salts at 100 ppm deteriorate at a much higher rate at 40° C. There is no statistically significant difference in the stability of the solutions at different temperatures and salt concentrations for temperatures of less than about 25° C. or concentrations of less than about 10 ppm. Only the combination of high temperature and high concentration accelerated decomposition. For much higher concentrations such as 1500-6000 ppm of salt, the loss of concentration was much higher than for salt concentrations of about 100 ppm or less, even at room temperature.

(46) Chlorine dioxide solutions made by reacting sodium chlorite with chlorine in aqueous solution, which produces high concentrations of sodium chloride, are much less stable than solutions made using pure chlorine dioxide and pure water.

(47) The data shown in FIGS. 5 to 13 shows that increasing contaminant concentrations leads to increased decomposition of the chlorine dioxide in the aqueous chlorine dioxide solutions.

(48) According to at least one embodiment, the aqueous chlorine dioxide solution contains 100 ppm or less of metal impurities. In at least one embodiment, the aqueous chlorine dioxide solution contains 50 ppm or less of metal impurities, such as, for example, 25 ppm or less of metal impurities, or 10 ppm or less of metal impurities.

(49) In at least one embodiment, the aqueous chlorine dioxide solution contains 100 ppm or less of transition metal impurities, such as, for example, 50 ppm or less of transition metal impurities, 25 ppm or less of transition metal impurities, or 10 ppm or less of transition metal impurities.

(50) In at least one embodiment, the aqueous chlorine dioxide solution contains 100 ppm or less of alkali and alkaline metal impurities, such as, for example, 50 ppm or less of alkali and alkaline metal impurities, 25 ppm or less of alkali and alkaline metal impurities, or 10 ppm or less of alkali and alkaline metal impurities.

(51) The inventors have surprisingly discovered that the presence of manganese greatly affects the stability of aqueous chlorine dioxide solutions. As shown in FIG. 10, even small amounts of manganese ions (e.g., 10 ppm) can greatly diminish the storage stability of aqueous chlorine dioxide solutions. According to at least one embodiment, the aqueous chlorine dioxide solutions comprise 10 ppm or less of manganese, such as, for example, 5 ppm or less of manganese, or 1 ppm or less manganese.

(52) According to at least one embodiment, the aqueous chlorine dioxide solution contain 100 ppm or less of iron, such as, for example, 10 ppm or less of iron, 5 ppm or less of iron, or 1 ppm or less of iron.

(53) In at least one embodiment, the aqueous chlorine dioxide solution contains 10 ppm or less of iron and manganese impurities combined, such as 5 ppm or less iron and manganese impurities, or 1 ppm or less iron and manganese impurities.

(54) According to at least one embodiment, the aqueous chlorine dioxide solutions contain 1000 ppm or less of total impurities and/or 10 ppm or less of manganese ions. In at least one further embodiment, the aqueous chlorine dioxide solutions contain 1000 ppm or less of total impurities and 1 ppm or less of manganese.

(55) In at least one embodiment of the present invention, the aqueous chlorine dioxide solutions retain at least 75% of the original chlorine dioxide solution after 150 days at 25° C., such as at least 80% of the original chlorine dioxide solution or at least 90% of the original chlorine dioxide solution. In at least one embodiment of the present invention, the aqueous chlorine dioxide solutions retain at least 75% of the original chlorine dioxide solution after 90 days at 25° C., such as at least 80% of the original chlorine dioxide solution or at least 90% of the original chlorine dioxide solution

(56) According to at least one embodiment, the aqueous chlorine dioxide solutions retain at least 75% of the original chlorine dioxide solution after 90 days at 40° C., such as at least 80% of the original chlorine dioxide solution or at least 90% of the original chlorine dioxide solution.

(57) The storage-stable solutions of chlorine dioxide disclosed herein can be used in any number of applications. For example the solutions can be diluted and used in topical treatments by contacting human skin, nails, wounds, and lesions with an amount of the solution. Diseases can be selected from the group of diseases caused by bacteria, viruses, and fungi. The solutions can be used in various water treatment applications by contacting water with an amount of the solution to reduce the amount of viable bacteria, viruses or fungi. Such water can include potable water, waste water, or recirculating water as is found in cooling towers or other recirculating water systems, as well as water used in oil production. The solutions can also be used to treat hard surfaces such as food preparation surfaces or surfaces in houses or buildings to reduce bacterial, viral or fungal loads.

(58) Another aspect of the present invention relates to delivering chlorine dioxide to a location in need thereof. Aqueous chlorine dioxide solutions can be prepared as described above, such as, for example, by contacting chlorine dioxide gas with water to prepare an aqueous chlorine dioxide solution. The chlorine dioxide solution can be introduced into a container, such as those described above, and transported in the container to the location in need of chlorine dioxide. The chlorine dioxide may then be released from the solution for use, such as, by mixing the chlorine dioxide gas with a carrier gas and contacting an object to disinfect the object.

(59) The examples and embodiments disclosed herein are provided for purposes of illustration only and are not intended to limit the scope of the claims of the invention.