SCALE REMOVAL COMPOSITION COMPRISING ALPHA-HYDROXY CARBOXYLIC ACID AND THICKENER

Abstract: A scale removal composition for removal of hard water scale from solid surfaces which includes an aliphatic alpha-hydroxy carboxylic acid, a natural or synthetic gum or polymer which is soluble in water at a pH of about 3 or less, water, and, optionally, sodium silicate.

Description: SCALE REMOVAL COMPOSITION COMPRISING ALPHA-HYDROXY CARBOXYLIC ACID AND THICKENER The present invention is directed to a composition and its use in removing scale f rom a surface . In one of its more specific aspects, the composition includes an al iphatic alpha-hydroxy carboxy lic acid, a water soluble gum or polymer and sodium silicate. The term "scal e" generally refers to the accumulated deposits commonly found on water-exposed surfaces . Frequently encountered scale is often made up of carbonates or sulfates of calcium, , sodium, potassium, or magnesium. The scale may al so contain metal oxides, grease, oil or dirt . The consistency of the scale may vary from brittle and porous to tough and dense . The function of a descalant or descal ing agent is to effectively remove these deposits. Scale can be removed by either mechanically detaching the accumul ation of deposits f rom the surf ace or by chemically treating the accumulation. A possible method for chemical treatment involves exposing the scale to a strong inorganic acid solution, e. g. hydrochloric, hydrofluoric or phosphoric acid . However, these acids are toxic and are difficult to handl e . U. S. Patent No. 3 ,294 ,689 to Pierce discloses a composi tion for removing heavy metal ions from an aqueous solution. The composi tion consists of a polyhy droxyl amine and one or more water soluble alpha- hydroxy acids at a base pH, particularly for removal of ferrous, cupric, nic elous, al uminium and cadmium cations and combinations of cations, such as ferrous and f erric ; ferric and manganous ; fer ric, ferrous. manganous and cupric ; and ferric, manganous, cupric , zinc and nickelous cations. U . S. Patent 3 , 308, 065 to Lesinski discloses a method for removing scale from metal surfaces . The method involves treating the scale with an aqueous alkal ine , saline solution containing at least one ammonium, amine or hydrox al yl amine salt of nitrilotriacetic acid, N-2-hydroxyethylamino diacetic acid, and alkylenepoly- 10 amine poly car bo y lie acid or mixtures thereof . U. S. Patent No. 3 ,699 , 047 to Petrey discloses a cooling system corrosion inhibi tor which comprises a divalent metal ion such zinc, cadmium and mixtures thereof, a - _ chel ating agent and a modif ied l ignosulf onate polymeric material. The chelating agent may be an alkylphos- phonic acid or salt thereof , a poly carboxy lic acid compound, such as ethylenediaminetetraacetic acid, nitrilotriacetic acid, hydroxyalky ltetraacetic acids 20 and sugar-acid chelates, such as sodium heptagluconate as di scussed in U . S. Patent No. 3 ,256 , 203 to Robertson et al . However, there remains a need for a descalant which may be used primarily for removal of alkali metal carbonate 25 residues formed from hard water which can remove such scales relatively quickly, effectively and safely without harm to the surface or to the worker. The present invention is directed to a descaling 30 composition consisting essentially of an aqueous solu¬ tion of aliphatic carboxylic acid of 2 to 6 carbon atoms having an alpha-substituted hydroxyl group and a natural gum or synthetic polymer which is water soluble at a pH of about 3 or below, optionally comprising also 35 sodium silicate. The acid content of the composition is within the range of from 5 to about 70 percent by weight of the composition, the gum or polymer is within the range of 0.1 to 5 by weight of the composition, and the ratio by weight of sodium silicate to acid is from about 0 to 0.6. A preferred acid is alpha- hydroxyacetic acid, which may be present in the composition at a concentration in the range of 10 to 35 percent by weight. Preferred gums are xanthan or tragacanth in an amount in the range of 0.05 to 2 percent by weight of the composition. Xanthan gum powder or granules coated with glyoxal is readily dispersible in water. A further preferred composition is one in which the acid is alpha-hydroxyacetic acid, the gum is xanthan, the acid concentration is in the range of from about 5 to about 35 percent by weight of the composition, the gum content is in the range of from about 0.2 to about 0.3 percent by weight of the composition, and the ratio by weight of sodium silicate to acid is in the range of 0.03 to 0.2. A particularly preferred composition is one in which the acid content is about 23 percent by weight of the composition and the ratio by weight of sodium silicate to acid is about 0.04. These composi¬ tions may be employed for removing scale from a surface by contacting a scale removing effective amount of the composition with the scale. These compositions are particularly preferred for removing metal carbonates of hard water from surfaces. The descaling composition may be prepared by (a) mixing a biopoly er gum or synthetic polymeric thickener which is water soluble at a pH of about 3 or below in water to obtain a homogeneous solution; (b) adding sodium silicate and (c ) dissolving an aliphatic carboxylic acid of 2-5 carbon atoms having an alpha-substituted hydroxyl group. The compositions of the present invention di ssolve or emulsify scale compositions composed primarily of metal carbonate residues of hard water at a rapid rate . In preparing the compositions of the present invention, the gum or thickener is dispersed or dissolved in water 10 after which the alpha-hydroxy carboxylic acid is added to obtain a fluid solution. In the case of alpha- hydroxyacetic acid, a 70 mol percent aqueous solution preferably is employed in making up the composition. , _ Gums which may be employed must be stable at a pH of about three and below because of the acidity of the alpha-hydroxy carboxylic acids . Gums generally are derived f rom natural sources and are well-known in the art. It has been found that particles or granules of 20 xanthan gum coated with glyoxal for ease in dispersing the particles in an aqueous medium is particularly usef l . Sodium silicate may also be added to the composition. Sodium silicate serves as a metal conditioner. Other 25 metal conditioners compatible with the ingredients may also be employed. Various colorants or odorants may also be employed to make a more commercially desirable product. Of course," these additional additives must be 30 compatible with the other ingredients. It has been found that the order of mixing influences the properties of the resulting composition. The preferred order of mixing is to add the gum or polymer to water and thoroughly mixing to obtain a dissolved 35 solution. Sodium silicate, if employed, and any colorants or odorants may be added at this stage. Finally, the alpha-hydroxy aliphatic carboxylic acid is added to the mixture with mixing until a homogenous solution is achieved. It is believed that the combination of the alpha-hydroxy carboxylic acid and the gum or polymer in aqueous solution enhances the reaction with the scale and removes the scale generally by dissolving it. At certain concentrations of acid and scale, however, a suspension of scale solids or even a paste forms which can be readily removed from the treated surface by washing with water. The composition of the present invention has the additional property of being substantially non-foaming. Thus, it may be used on pipes without clogging. The composition may be employed in removing scale simply by contacting the composition with the scale-contaminated surface. Scale may be removed from plumbing, boilers, coolers, heat exchangers, condensers, central heating systems, humidifiers, automobile engine radiators, piping found in engines and the like. Scale may be removed by adding the composition to the water flowing by or otherwise in contact with surfaces to be descaled. Because of little or no foaming, this method is particularly advantageous. The scale may also be removed by direct application by using brushes, sprayers or methods known in the art for cleaning metal and other surfaces. The present invention will be further illustrated by means of the following examples. It is to be under¬ stood, however, that these examples are merely for illustrative purposes and that the present invention is not meant to be limited thereby. EXAMPLE 1 To 500 ml of water was added two grams of xanthan gum which was dispersed in the water by mixing after the xanthan gums had dissolved; 250 ml of a 70 mol percent aqueous solution of alpha-hydroxyacetic acid was added and mixed until a uniform mixture was obtained. The resulting composition was tested for its ability to dissolve hard water scale having the following analysis in percentages by weight: carbonates - 56 percent; calcium - 33 percent; potassium - 4 percent; hydrogen (from moisture) - 4 percent; silicon dioxide - 2 percent; other - 1 percent. Four grams of scale in 2.0 gram increments were submerged in 100 mis of the solution at 22 degrees Celsius. The scale dissolved without a white film or emulsion over a period of two days. Little foam was observed which disappeared with the addition of 25 mis of water, and slight agitation. EXAMPLE 2 A 5 gallon ( 18 .925 liter ) batch of descaling solution was prepared by mixing 0.115 pounds ( .052 kilogram) of xanthan gum (sold under the trade name Kelzan) wi th 28.3 pounds ( 12 .83 kg) of water until a homogeneous solution was obtained. To the solution was added 0 .425 pounds ( 0.193 kg) of sodium sil icate and mixed until dissolved, followed by an addition of 14 .1 pounds (6 .4 kg) of 70 weight percent alpha-hydroxyacetic acid solution. The approximate composi tion in percentages by weight of each of the components is as fol lows : 65 .9% water ; 0 .3% xanthan ; 1% sodium silicate ; and 32.8% of a 70 weight percent alpha-hydroxyacetic acid solution. The concentration of hydroxyacetic acid on a water f ree basi s i s approximately 23 percent by weight weight of the composition . EXAMPLE 3 5 Three 200 ml batch solutions were prepared containing by weight 10 percent, 50 percent and 100 percent, respectively, of 70 weight percent alpha-hydroxyacetic acid, 0.2 weight percent of xanthan gum and sufficient water, if necessary, to make up 200 ml, and each tested Q for its ability to dissolve scale. The descaling solutions were kept at 22 degrees Celsius. Several pieces of scale 1 mm in thickness weighing from 1 to 1.5 grams were submerged in each of the three solutions. The composition of the scale was that of 5 Example 1. At the end of two days, the 10 percent acid solution had dissolved 0.4 g. of scale, the 100 percent solution had dissolved approximately 0.85 g., and the 50 percent solution had dissolved 2.4 g. scale. These results indicate that although all of the tested o concentrations are capable of dissolving scale, a 50 percent solution is more effective than a 100 percent solution, which, in turn, is significantly more effective than a 10 percent solution. 5 0 5

Claims: Ci_A __S 1. A descaling composition consisting essentially of a) an aliphatic carboxylic acid of 2 to 6 carbon atoms per molecule having an alpha- substituted hydroxyl group; b) a natural gum or synthetic polymeric thickener which is water soluble at a pH of 3 or below; and c) water; wherein the acid content is within the range of from about 5 to about 35 percent by weight of the composition, and the gum or thickener content is within the range of 0.1 to 5 percent by weight of the composition. 2. A composition according to Claim 1 wherein the acid is alpha-hydroxyacetic acid. 3. A composition according to Claim 1 wherein the gum is xanthan. 4. A composition according to Claim 3 wherein the xanthan is coated with glyoxal. A composi tion according to Cl aim 1 wherein the acid is alpha-hydroxyacetic acid, the gum i s xanthan coated with glyoxal , and the gum content i s in the range of 0 .2 and 0 .3 percent by weight of the composi tion. 6. A composition according to Claim 1 wherein the acid content is in the range of 10 to 35 percent by weight of the composition. A composition according to Claim 1 wherein the composition includes sodium silicate in an amount in the range of 0.03 to 0.2 parts by weight per part acid. A method for removing scale from a surface comprising contacting the scale with a scale removing effective amount of a composition as defined in Claim 1. 9. A method according to Claim 8 wherein the acid is alpha-hydroxyacetic acid, the gum is xanthan, the acid content is in the range of 5 to 35 percent by weight of the composition, and the gum content is in the range of 0.2 to 0.3 percent by weight of the composition. 10. A method according to Claim 9 wherein the compo¬ sition includes sodium silicate and the ratio by weight of sodium silicate to acid is about 0.04. 11. A method according to Claim 10 wherein the scale is a metal carbonate of hard water. 12. A descaling composition consisting essentially of a) alpha-hydroxyacetic acid; b) xanthan gum; c) water; and d) sodium silicate wherein the acid content of the composition is in the range of from about 10 to about 35 percent by weight on a water free basis; the gum content is within the range of 0.25 to 0.3 percent by weight; and the ratio of sodium silicate to acid is in the range of 0.03 to 0.2.

Inventors: ABADI KHODABANDEH, ABADI, KHODABANDEH
Applicants: ABADI KHODABANDEH, ABADI, KHODABANDEH
Application year: 1986
Main classification: C02F5
IPC codes: C02F5, C11D7, C23G1