WO1991005742A1

WO1991005742A1 - Descaling composition and methods of use

Info

Publication number: WO1991005742A1
Application number: PCT/US1989/004655
Authority: WO
Inventors: Allen C. Hieatt
Original assignee: Eden Technologies, Inc.
Priority date: 1989-10-17
Filing date: 1989-10-17
Publication date: 1991-05-02

Abstract

The present invention is directed to compositions and methods for removing water scale from surfaces and preventing redeposition. The composition comprises a hydroxycarboxylic acid, an alkanolamine and an alkali metal monocyclic aryl sulfonate. Heat-exchange systems utilizing water as heat-exchange medium are operated by incorporating a minor amount of this composition in the circulating water.

Description

DESCALING COMPOSITION AND METHODS OF USE

This application is a continuation-in-part of my co-pending U.S.A. application, Serial Number 195,851, filed May 19, 1988.

This invention relates to chemical compositions and methods of use thereof which are useful in removing and preventing reformation of water scale on various surfaces.

In an even more particular respect, the invention relates to such compositions which are especially adapted for use in heat-exchange systems utilizing water as a recirculating heat-exchange medium.

"Scale" is a general term which describes precipitates from aqueous fluids which deposit on surfaces in contact with water, .generally as a result of exceeding the limit of solubility of such materials in the water, e.g., by evaporation of the water or by otherwise concentrating these components. Such scale materials include compounds such as sulfates, oxides, carbonates, halides and the like. Examples include calcium carbonate and iron oxides.

To be effective, a descaling composition should break down components of scale. Primarily, the descaling composition should remove carbonates and sulfates.

A number of methods have been devised to prevent or remove scale. For example, Rubin, in U.S. Patent

No. 3,075,924 teaches a detergent composition which includes a long chain aliphatic sulfate and an alkylamine acetic acid.

SUBSTITUTESHEET Clark et al, in U.S. Patent No. 3,053,897, disclosed compositions for the removal of rust and scale. Clark teaches the use of triethanolamine in combination with an alkali and an aliphatic hydroxy acid. Clark also teaches the use of alkali metal salts of sulfonated fatty acids.

Conklin et al, in U.S. Patent No. 2,847,384, disclosed a descaling composition which includes a non-ionic wetting agent which is a mixture of polyoxythylene-propylene polymeric compounds with sodium xylyene sulfa'te.

Petroy, U.S. Patent No. 3,699,047, employed zinc ion in a scale inhibiting composition which may also include an alkyleneamine-acetic acid compound.

Monson, in U.S. Patent No. 2,589,195, disclosed an inhibiting scale composition which includes a triethanolamine which is reacted with an ethylene oxide to form an amine having a number of ethylene oxide units. The terminal hydroxy groups are acylated with a fatty acid.

Further examples of prior art descaling compositions are disclosed in the Abadi patents, U.S. 4,435,303 and 4,595,517.

As yet, however, such prior art does not provide economically effective methods for preventing scale formation, particularly in large industrial applications where recirculating water containing scale-forming components is used as a circulating medium in heat-exchange equipment, e.g., boilers, coolers, etc. Instead, the common approach in the prior art is to employ expensive and complicated deionizing and other water purification pretreat ent

BSTITUTESHEET processes to reduce the initial level of scale-forming components in the aqueous heat-exchange medium. Also it is common practice to bleed sizable quantities of the aqueous heat-exchange medium from the system to avoid build up of concentrations of the scale-forming components which exceed their solubility limits in the cooling or heating water. The water removed to control the concentration of scale-forming components in such heat-exchange systems is called "blowdown".

It would be highly desirable to reduce the amount of blowdown encountered in operating conventional heat-exchange systems, particularly evaporative cooling systems which utilize water as the heat- exchange medium, as the problem is disposing of the blowdown has become increasingly serious and the cost of the makeup water constitutes a significant cost element in the operation of such systems.

Additionally, it would be desirable to provide improved descaling compositions for use in a wide variety of end-use applications in which water conservation or waste disposal is a significant factor. For example, it would be highly desirable to achieve such results in the operation of direct heat- exchange systems such as automotive radiators, and the like. Also, reducing the solubility of scale-forming components in water is important in residential use, e.g., tub and tile cleaners and the like, and the metal scavenging effect of such compositions would provide desirable results in widely diverse products such as plant foods, medicines, etc.

Therefore, the principal object of the present invention is to provide an improved composition for solubilizing scale and scale-forming components in aqueous systems.

SUBSTITUTESHEET Another object of the invention is to provide methods for operating heat-exchange systems which reduce the amount of blowdown required to prevent scale formation.

Still other objects of the invention are to provide compositions for solubilizing scale-forming components in aqueous systems and utilizing such capabilities to. improve the qualities of various household, industrial and medical products.

Briefly, in accordance with the invention, a composition is provided which consists essentially of a hydroxycarboylie acid, an amine and a monocyclic aryl surfactant.

According to another embodiment of the invention, methods for removing water scale from surfaces are provided which include the step of contacting the surfaces with water containing a minor effective amount of this composition.

According to a more specific embodiment of the invention, a method is provided for operating a heat- exchange system which utilizes water as a heat- exchange medium. These methods include the step of circulating in the system a water heat-exchange medium containing scale-forming components and an effective amount of this composition, i.e., in an amount sufficient to maintain the scale-forming components in solution.

The composition of the present invention is in the form of a concentrate which can be further diluted as required by the particular end-use of the composition. The hydroxycarboxylic acids used in the practice of the invention have the structural formula

0

II HO-(C-R₁)-C-OH

wherein R^_^ is hydrogen, a branched or straight chain alkyl, cycloalkyl, or aryl substituent having one or more carbon atoms and forms a stable C-R. group which does not inactivate the carboxylic acid group. The preferred hydroxycarboxylic acid is hydroxyacetic acid wherein C-R, is a methane radical.

The alkonolamines used in the practice of the invention have the structural formula

R₂

I

HO-C-R,-N-R_K i ^{6 5} ^R3 wherein R_g is a branched or straight chain alkyl group having from 0-5 carbon atoms, and R₂, R-,, R. and R₅ are selected from the group consisting of hydrogen, a branched or straight chain alkyl group, a cycloalkyl group or aryl group, such that the cumulative electro¬ chemical effect of the substituent groups does not create an overly positive charge and negate the basicity of the alkanolamine. Preferred alkanolamines of this general formula consist of methanolamine and triethanolamine.

The alkalimetal monocyclic aryl sulfonates use in the concentrate composition include sodium and potassium salts of the sulfuriσ acids of tolerance and xylene, e.g. 2,3-dimethyl benzenesulfonate; 2,4- dimethylbenzenesulfonate; 2,5-dimethylbenzesulfonate; 3,4-dimethylbenzesulfonate, 4-ethylbenzemesulfonteand

SUBSTITUTESHEET the like. Sodium dimethyl benzene sulfonates and mixtures thereof are preferred.

The compositions of the invention can be prepared by dissolving the alkanolamine in a suitable solvent, suitably an aqueous alcoholic solvent, and then mixing the amine solution with the surfactant. The mixing steps are preferably carried out under high shear conditions until complete solution and reaction occurs.

Suitable alcohol solvents include those having the structural formula

^Rl HO-C IHET₂ i

^R3 wherein R,, R₂, R-, are each selected from the group defined above for R^Rg. Preferred alcohols of this general formula are methanol, ethanol, propanol and ethylene glycol.

In my previous co-pending U.S.A. application S/N 195,851, I described compositions in which the amine- sulfonate composition further reacted with. However, I have now determined that such further steps can be omitted. One may to obtain a useful, desirable product if t-he carboxylic acid is added directly to the composition.

I have further determined that alcohol used to dissolve the amine is largely dissipated during the exothermic mixing with the sulfonate. Substantial alcohol remaining in the concentrate composition does not materially increase the effectiveness of the product. The volume percentage of the hydrocarboxylic acid to the total mixture is in the range of about 25-60%, preferably about 35-45%. The efficacious ratio of hydrocarboxylic acid to alhauolamine is in the range of 0.7 - 10, preferably about 2.0 - 3.5.

In use, the aqueous chemical composition of the present invention is added to water in a recirculating aqueous system. Aqueous systems which are non- recirculating may be recirculated to increase the rate of reaction. If a relatively higher reaction rate is not required, non-recirculating systems may remain so. Solutions of about 0.5% to 5%, preferably from 0.5% to 1.0% by volume, of the present invention to water are usually sufficient to maintain a previously cleaned aqueous system. To clean a scaled and/or rusted aqueous system, solutions of up to 50%, by volume, of the aqueous chemical composition in water may be employed. Higher concentrations and higher reaction temperatures increase the rate of the descaling and antioxidizing reaction. It has been found, however, that concentrations in excess of 50% by volume do not exhibit statistically significant further increases in reaction rate.

To further illustrate the preferred practice of the invention, the following examples are presented.

SUBSTITUTESHEET EXAMPLE 1

A dilute ethanol-water solvent is prepared by agitating a mixture of water and ethanol (0.015% by volume) . To this ethanolic aqueous solvent is added an equal volume of triethanolamine and the resultant mixture is agitated for an additional 30 minutes at room temperature and pressure, resulting in complete solution of the amine. To this amine solution is added about 30% by volume of sodium xylene sulfonate and shear agitation is continued for an additional approximately 30 minutes. The reaction begins at room temperature but the temperature of the reaction mixture rises to approximately 100°F during this mixing period. To this mixture is added about 40% by colume of hydroxyacetic acid and mixing is continued for an additional 10 minutes.

UTESHEET EXAMPLE 2

For use in residential evaporative cooler, equal parts of the concentrate of Example 1 and water are mixed in the evaporative cooler sump.

SUBSTITUTESHEET EXAMPLE 3

For use in an industrial cooling tower, from about 0.5 to 1.0% by volume of the composition of Example 1 is added to the recirculating water in the system.

EXAMPLE 4

A suitable residential tub and tile cleaning solution is prepared by physically admixing the following components in the indicated percentages by volume.

COMPONENTS PERCENTAGE

Water 56

Concentrate 33

Butylcellosolve .05 Monoethanolamine 10.95

Cherry scent trace

SUBSTITUTESHEET EXAMPLE 5

A suitable buffered descaling composition is prepared by physically admixing the following components in the indicated percentages by volume.

COMPONENTS PERCENTAGE

Hydrochloric acid 70

Product of Example 4 30

Cherry scent trace

EXAMPIiE 6

COMPONENTS PERCENTAGE

Sulfuric acid 70

Product of Example 1 30

SUBSTI

Claims

C l a ims : _14"

1. A composition comprising:

(a) a hydroxycarboxylic acid having the formula

HO-(C-R₁)-C-OH

(b) an alkanol mine having the formula

and

(c) an alkali metal monocyclic aryl sulfonate;

wherein R-i-R₅ are substituents selected from the group consisting of hydrogen straight chain alkyl, cycloalkyl or aryl groups, R_g is a branched or straight chain alkyl group having 0-5 carbon atoms, and R is such a substituent which does not inactivate the carboxylic acid group.

2. A method for removing water scale from a surface, comprising contacting said surface with water containing an effective amount of the concentrate composition of Claim 1.

SUBSTITUTESHEET

3. A method for reducing the rate of deposition of water scale upon a surface in contact with water containing scale forming components, said method comprising incorporating into said water from about 0.15 to about 1.0 percent by volume of the concentrate composition of Claim 1.

4. The method of operating a heat-exchange system using water as the heat-exchange medium, comprising circulating in said system water containing scale- forming components and an amount of the composition of Claim 1 effective to maintain said components in solution.