GB2104384A - Soluble trichlorocyanuric acid composition and its production - Google Patents

Abstract

A trichlorocyanuric acid composition having increased water solubility consists essentially of finely ground trichlorocyanuric acid and an alkaline salt, preferably sodium carbonate, in the form of homogeneous granules. The composition is made by mixing the finely powdered ingredients, shaping the mixture under pressure and comminuting the product.

Description

SPECIFICATION Soluble trichlorocyanuric acid composition and its production The present invention pertains to trichlorocyanuric acid compositions, particularly to such compositions having improved water solubility.

Trichlorocyanuric acid is a well-known chlorine releasing compound which finds extensive application as a sterilizing agent in a variety of bleaching, sanitizing and detergent formulations. A particular and distinct advantage of trichlorocyanuric acid stems from its high available chlorine content, being 91.5% for the pure compound, although the commercial material may assay a few percent lower.

The dosage needed to produce a desired level of available chlorine for disinfection purposes is thus much less than with other commercial chlorine bleaches. Disadvantages of trichlorocyanuric acid are its high reactivity in the presence of contaminants and low water solubility - about 1.2 9/100 ml.

The storage stability of trichlorocyanuric acid has been considerably extended by mixing it with certain alkaline salts as disclosed in U.S. Patent 2,607,738 to Hardy. Further improvements aimed at retarding decomposition in the presence of moisture were realized by adding an arylsulfonamide to the compositions of Hardy in accordance with U.S. Patent 3,002,931 to Symes.

Although the storage stability of trichlorocyanuric acid has to a large extent been ameliorated, the low water solubility of the material continues to be an obstacle to its further commercial development.

One area of use for which trichlorocyanuric acid finds extensive application is in the sterilization of water in swimming pools. The procedure commonly followed is to circulate the pool water through a chlorine dispensing chamber containing tablets of trichlorocyanuric acid. As the tablets dissolve, chlorine is released into the water. The rate of dissolution is extremely slow but is sufficient to provide 1 to 2 ppm of chlorine. A three inch tablet will maintain this chlorine level for about a week in an average size home pool.

When the water in the pool is fairly clean, a few ppm of chlorine serves to keep the water free of algae and other deleterious microorganisms. In time, however, there is an accumulation of organic matter in the pool from various sources such.as perspiration, dirt, dust, air-borne particles and vegetable litter, for example, leaves and pollen. Eventually the organic content builds up to a point at which the level of chlorine provided by the trichlorocyanuric acid tablet is insufficient to control the growth of algae and bacteria. When this occurs, a supplemental chlorinating agent must be added directly to the pool in an amount sufficient to oxidize the suspended and/or dissolved organic matter not removed by the pool's filter system and thereby restore the sanitary condition of the water. Such treatment is known in the trade as superchlorination and is promoted by the rapid solubility, that is chlorine release, of the chemical agent.

Examples of chlorinating agents commonly employed as superchlorinators include aqueous sodium hypochlorite, calcium hypochlorite, sodium dichlorocyanurate and its dihydrate. These materials have not, however, proved entirely satisfactory, particularly from the standpoint of the home pool owner. Calcium hypochlorite because of its relatively low cost is the choice of many pool owners. On the other hand, its use is attended with numerous disadvantages and problems. These include: (1) high alkalinity which promotes precipitation of insoluble calcium compounds resulting in cloudy water, plugging of filters and heaters and scale deposition on pool surfaces; (2) slow rate of solubility; (3) moderately poor storage stability; (4) high reactivity, particularly in the presence of oxidizable substances; (5) build-up of dissolved solids such as calcium chloride; (6) susceptibility to rapid dissipation of residual chlorine in the presence of sunlight. Aqueous sodium hypochlorite is objectionable in that it contains low levels of available chlorine. Other serious objections are its very limited storage stability, very high pH and susceptibility to rapid dissipation of residual chlorine in the presence of sunlight.

Sodium dichloroisocyanurate is essentially free of the aforelisted drawbacks except that it can present a fire hazard on contact with combustibles. The dihydrate of sodium dichloroisocyanurate is both safe and effective as a superchlorinator but is expensive in terms of available chlorine.

It has been proposed to superchlorinate swimming pools with trichlorocyanuric acid since its high available chlorine content of about 90% exceeds by far that of any of the commercial active chlorine compounds. Thus far, efforts to implement such proposals have not led to practical results. The principal difficulty lies with the low water solubility of trichlorocyanuric acid and its even lower rate of solubility. When added to a swimming pool, the trichlorocyanuric acid merely falls to the bottom without appreciable dissolution.

Admittedly, some improvement in solubility characteristics can be realized by resorting to finely divided material but performance is at best minimal. And even if satisfactory superchlorination were achieved by this approach, use of finely powdered trichlorocyanuric acid would create clouds of airborne dust, thereby presenting a serious health problem to handlers and users of the product. Moreover, the undissolved trichlorocyanuric acid causes corrosion of metal and pitting of the tile and concrete. It can also produce bleach spots in the vinyl lining of aboveground pools, and can even attack the plastic itself.

Increased solubility as well as improved stability against loss of available chlorine of trichlorocyanuric acid has been achieved by mixing it with various alkaline salts as disclosed in the aforecited patents to Hardy and Symes. In fact, a tableted mixture of trichlorocyanuric acid and sodium carbonate has been substituted for the pure trichlorocyanuric acid in pool chlorinators to provide higher levels of chlorination. However, if the tablets are added directly to the pool, the sodium carbonate preferentially dissolves while most of the trichlorocyanuric acid settles out giving rise to the aforediscussed problem.

In according with the invention, trichlorocyanuric acid compositions having improved water solubility are prepared by first forming a homogeneous mixture of powdered trichlorocyanuric acid and an alkaline metal salt fol iowed by intimately and uniformly mixing them together in the substantially dry state.

The resulting homogeneous mixture is then formed into a shaped configuration by subjecting it to compaction. Enough pressure should be applied in order to bind the particles together with sufficient force whereby the shaped article does not crumble too readily during ordinary handling. The shaped articie is then crushed or ground and a granular fraction isolated as the final product. Generally satisfactory results are obtained with a roll press operated at about 10,000 Ib/in (1.75 MN/m). Compaction of powdered materials is a familiar technique in the art using standard equipment such as briquetting, piston or roller presses.

The trichlorocyanuric acid and alkaline metal salt should be of such fineness that the granules, produced from comminuting the compacted shapes, will be essentially homogeneous. That is, the particle size of the powdered mixture should be small relative to that of the granules to ensure that the latter will be of uniform composition. Generally speaking, the powdered mixture of the trichlorocyanuric acid and alkaline metal salt should at least pass through a 100 mesh sieve; all mesh sizes designated herein are U.S.A. Standard Series. The compacted shapes are comminuted and then sized to give the final granular product. In general, the granules will have a mesh size range of about - 1 0 to about + 60, preferably about - 20 to about + 40. Off-size material can be recovered and worked up into product, thus virtually eliminating material losses.

There are various alkaline salts which are suitable for providing trichlorocyanuric acid bleaching and sanitizing compositions having improved water solubility characteristics in accordance with the present invention. The alkaline salt should be substantially water soluble while having a pH below that at which trichlorocyanuric acid breaks down into tri chloroamine, which is unstable and can lead to violent decompositions or even explosions.

Alkali metal hydroxides are too basic for use in the compositions of the invention. Preferred alkaline salts are alkali metal salts and include sodium borate, sodium carbonate, sodium silicate, trisodium phosphate, tetrasodium pyro phosphate, sodium triphosphate, potassium carbonate, sodium bicarbonate, potassium bicarbonate and the like including mixtures thereof. Where the herein compositions are to be used as chlorinators for sanitizing swim ming pools, the preferred alkaline salts are the alkali metal carbonates since such compositions combine good solubility characteristics with high available chlorine. An especially preferred carbonate in this connection is sodium carbonate.

Generally speaking, the degree of solubilization of the trichlorocyanuric acid is dependent on the amount and type of alkaline salt.

Normally, the more alkaline salt that is used the greater the solubility of the granular product. In the preferred mixture of trichlorocyanuric acid and sodium carbonate useful sanitizing compositions can be realized where the weight percent of the trichlorocyanuric acid can vary between about 60 to 90%, depending on the ratio of available chlorine to solubility factor that is desired. For the chlorination of swimming pools, optimum results are obtained where the weight ratio of trichlorocyanuric acid to sodium carbonate is 75/25 and the mesh size of granules is from about - 20 to + 40. This product has a solubility of about 31g/100 ml and an active chlorine assay of about 67%; the material dissolves instantly when added to a swimming pool in amounts effective to chlorinate the water at the residual chlorine levels necessary to maintain and/or restore the sanitary condition of the pool.

The trichlorocyanuric acid/alkaline salt compositions of the invention are white, substantially stable, granular dry materials. They can be stored for long period of time and/or transported over considerable distances without appreciable decomposition. When dissolved in water, the ingredients of the mixture product a vigorous effervescence which hastens the rate of dissolution. The composition can be used as such or added to detergents, cleaners, sanitizers, bleaches or other formulations.

The invention is illustrated by the following examples, in which parts are by weight and mesh sizes U.S. standards.

Example 1 Sixty parts of trichloroisocyanuric acid (TCCA) powder that had at least 89% available chlorine and that passed through a 100 mesh screen were blended with 40 parts of finely powdered soda ash that passed through a 100 mesh screen. These powdered materials had roughly the same bulk density and showed no tendency to segregate after blending. The mixture was placed in a 1-inch (2.54-cm) die and compacted into a tablet using 20,000 pounds (90 kN) of pressure.

The resulting tablet was crushed and the particles screened to a size that passed through a 20 mesh screen but retained on a 40 mesh screen. When added to water, each particle effervesced and dissolved very rapidly leaving less than 10% as solids. These solids floated on the surface of the liquid and dissolved in a reasonable amount of time.

Example 2 The procedure of Example 1 was repeated but using 70 parts TCCA and 30 parts soda ash. The effect when added to water was similar to Example 1 with somewhat more undissolved solids left after the initial effervescence.

Example 3 The procedure of Example 1 was repeated using 80 parts TCCA and 20 parts of soda ash. When added to water, about 20% of solids sank to the bottom after effervescing and were slow to dissolve. This example shows that solubility falls off as the TCCA is increased above about 75%.

Example 4 The procedure of Example 1 was repeated using 90 parts TCCA and 10 parts of soda ash. Solubility results were similar to Example 4.

Example 5 Sixty parts TCCA that was material that passed through a 20 mesh screen but was retained on a 100 mesh screen were blended with 40 parts soda ash that was 90% retained on a 100 mesh screen. When compacted as in Example 1 and added to water, the mixture effervesced briefly but a large amount of slowly dissolving material sank to the bottom.

This example shows that solubility decreases with larger particle size of the TCCA and soda ash.

Example 6 TCCA (750 parts) of the same specification as Example 1 was blended with soda ash (250 parts) of the same specification as Example 1. The powders were blended in a Patterson-Kelley Co. cross-flow blender but could be blended in any commercial blender that gives homogenously mixed solids. The blended powders were then compacted between 2 rotating rollers in a commercially available compacting system from The Fitzpatrick Company. The blend is in a solid, compacted sheet at this time. The compacted sheet is then passed through a grinding mill also produced by The Fitzpatrick Company. The granular product from the grinding mill is screened to save the material that passes through a 10 mesh screen but is retained on a 60 mesh screen. The off-size material is reblended with powder and fed back to the compactor to be compacted into product. In this way, no product is lost. This product, when added to water, effervesces and dissolves very rapidly leaving less than 10% of solid which dissolves in less than one hour.

Claims (11)

1. A trichlorocyanuric acid composition having improved water solubility consisting essentially of a mixture of trichlorocyanuric acid and a metal salt that is alkaline and that does not react with the trichlorocyanuric acid to form trichloroamine, the mixture being in the form of homogeneous, compacted granules.

2. A composition as claimed in Claim 1 in which the mesh size of the granules (U.S.A.

Standard Series) is in the range 10 to 60.

3. A composition as claimed in Claim 1 or 2 in which the percentage by weight of trichlorocyanuric acid is from 25% to 75%.

4. A composition as claimed in any preceding claim in which the metal salt is sodium carbonate.

5. A composition as claimed in Claim 1 consisting essentially of a mixture of trichlorocyanuric acid and sodium carbonate, the particle size of the trichlorocyanuric acid and sodium carbonate being no larger than 100 mesh (U.S.A. Standard Series), compacted into homogeneous granules having a mesh size in the range 10 to 60, the percent by weight of the trichlorocyanuric acid in the granules being from 25% to 75%.

6. A method of producing a trichlorocyanuric acid composition having improved water solubility comprising; (a) forming a mixture of finely powdered trichlorocyanuric acid and a metal salt that is alkaline and that does not react with the trichlorocyanuric acid to form trichloroamine, (b) forming the mixture into a shaped configuration by compacting the mixture under pressure and (c) comminuting the product of (b) to provide homogeneous granules of trichlorocyanuric acid and the metal salt.

7. A method as claimed in Claim 6 in which the metal salt is sodium carbonate.

8. A method as claimed in Claim 6 or 7 in which the particle size of the trichlorocyanuric acid and the metal salt is no more than 100 mesh (U.S.A. standard).

9. A method as claimed in Claim 6, 7 or 8 in which the percentage by weight of the trichlorocyanuric acid in the mixture is from 25% to 75%.

10. A method as claimed in any one of Claims 6 to 9 in which the mesh size of the granules (U.S.A. Standard Series) is in the range 10 to 60.

11. A method as claimed in Claim 1 substantially as hereinbefore described in any one of Examples 1, 2, 3, 4, 5 and 6.