WO2004072327A1

WO2004072327A1 - Composition and method for removing and/or preventing scaling of elements in processing equipment

Info

Publication number: WO2004072327A1
Application number: PCT/EP2004/050134
Authority: WO
Inventors: Jacobus Cornelis Van Kaam
Original assignee: EXEL HENDRIKUS GERRIT
Current assignee: EXEL HENDRIKUS GERRIT
Priority date: 2003-02-17
Filing date: 2004-02-16
Publication date: 2004-08-26
Anticipated expiration: 2005-08-17

Abstract

The invention pertains to a descaling composition for use to elements in.processing equipment comprising a) 2-30 wt.% of sulfamic acid or a salt thereof, b) up to 10 wt.% of a glycol ether, c) 0.01 to 1.0 wt.% of mercaptobenzotriazole or a salt thereof as corrosion inhibitor, d) optionally an indicator having a pKa 3-4, e) optionally up to 5 wt.% of a buffer, f) 0 to 10 wt.% of a gelling agent, g) 0 to 5 wt. % of a nonionic surfactant, and h) water to complete the composition to 100 wt.%. The invention further relates to a raethod for removing and/or preventing scaling of elements in processing equipment, such as heat exchangers, condensers, vacuum waste systems, oil drill equipments, and piping systems.

Description

COMPOSITION AND METHOD OR REMOVING AND/OR PREVENTING SCALING OF ELEMENTS IN PROCESSING EQUIPMENT

The invention pertains to a descaling composition and a method for removing and/or preventing scaling of elements in processing equipment, comprising the introduction of said composition. The treatment of cooling water for various purposes is a problem, which appears in industrial equipment of many industries, which includes condensers, heat exchangers, power plants, refineries, oil drill equipment, vacuum waste drain systems, piping systems, diesel engines, compressors, and air conditioning systems. The following problems may occur in varying degrees in each of these types of systems: control of scale deposits, corrosion of metals, and biological growths.

The most common type of water-formed deposit encountered in these systems is calcium carbonate, which results from the breakdown of calcium bicarbonate that is naturally present in all raw waters. Calcium carbonate has a relatively low solubility, and this solubility decreases with increase in temperatures.

In addition to the temperature factor, the solubility of calcium carbonate is also determined by the pH conditions maintained in the system and by the total minerals present. Another deposit likely to be encountered in cooling water systems is calcium sulfate. In many cooling water installations, it is common practice to add sulfuric acid to the water to control scale deposits of calcium carbonate. Normally, sufficient acid is added to bring the pH of the water to the range of about 6 to 6.5. Although calcium sulfate, which is produced by the reaction of the carbonate with sulfuric acid, is much more soluble than the carbonate, it is entirely possible to exceed the solubility of calcium sulfate in the circulating cooling water and have that compound precipitated as a scale. Calcium phosphate is also precipitated, particularly where treating methods using polyphosphates are employed and high orthophosphate and calcium concentrations exist.

Iron-containing deposits ^' can result either from relatively high concentrations of iron being present in the water supply or by active corrosion taking place in the system.

Some water supplies also contain relatively large concentrations of silica, which may result in the deposition of this material along the surfaces. Wood surfaces of cooling towers are frequently presented with the problem of microorganism growth. For example, algae and bacteria from the water and the air as well as fungi attach themselves to the wooden surfaces of the tower and result in the formation of a slime, which in many instances poses as difficult a problem as scale deposits. The presence of slime interferes with normal flow in piping, normal heat transfer in heat exchangers as well as accelerates the rotting of the wood.

Vacuum (toilet) waste line systems are also well known to suffer from blockages caused by hard-scale formation. This deposit consists mostly of phosphate and magnesium. This deposit is not, as commonly stated a variant of calcification, but is mainly magnesium phosphate, which is a major component of urine stone.

Common methods for removing the hereinbefore mentioned scaling from, for instance piping systems, heat exchangers, cooling systems and the like, comprise treatment with strong acids and high-pressure cleaning. A serious disadvantage of both methods is the requirement of dismantling the production unit, resulting in substantial economical losses. Particularly in larger plants production stop ( ' Turn-around' ) must be planned a long time in advance, sometimes up to two years, after which the plant may be dismantled for weeks. Since this type of work is for specialist contractors, specialists such as isolation, scaffolding, welding, cleaning, and health & safety experts, must be hired, adding to the costs. Moreover, both methods provide considerable amounts of environmental unfriendly residues that are difficult to remove or not biodegradable. In the acid method the equipment is flushed with the acid or the metal parts are immersed in an acid bath. Some materials, however, are not resistant to these strong acids. In the high-pressure method water is pressed through a nozzle having a usually 0.2 mm diameter opening at a pressure of up to 2,500 bar. Such extremely high pressures are dangerous and for safety reasons not longer acceptable in many cases.

Improvements of these methods have been search for. In Chinese patent application No. CN 1,253,171 an efficient cleaner for centralized air conditioners was disclosed from sulfamic acid, citric acid, hydroxy ethidene diphosphonic acid and diethyl thiourea. Said cleaner can be diluted into a cleaning liquid, which flows through centralized air conditioner, heat exchanger and boiler pipeline to remove rust and dirt. In British patent application No. GB 898,820 and French patent application No. FR 2,630,728 a better cleaning composition comprising phosphate-containing molecules or phosphoric monomers was attempted to obtain. However, it was found that none of these prior art cleaner can be used for all purposes and they were found not be equally effective on multi-metals, composites, rubbers and plastics.

Australian patent application No. AU 9,151,482 discloses a method of descaling a solar collector, which contains metal pipes by using an aqueous composition containing sulfamic acid. To sequester dissolved metal tolutriazole may be added to the composition. It was however found that such compositions are rather aggressive and affect metal parts, leading to substantial corrosion (weight loss) of such treated metal. French patent application No. 2,469,450 describes a toilet cleaner comprising an acid, particularly sulfamic acid or citric acid, and optionally an undefined corrosion inhibitor. Specific acid - corrosion inhibitor compositions that are effective as descalers and not damaging to the surface to be treated, have not been disclosed.

Other references disclosing descalers are, for instance, German patent application No. DD 226,908, which only discloses compositions containing mixtures of organic acids without the use of a corrosion inhibitor, and US patent application No. US 4,522,738 disclosing a toilet bowl cleaner comprising an envelope containing an acidic and a basic material whereby carbon dioxide is generated. The acid material, which can be sulfamic acid, but preferably is citric acid, is used in a composition that serves a different purpose than the presently claimed descalers, and which moreover does not comprise a corrosion inhibitor.

US patent No. US 4,765,921 discloses cleaning compositions for industrial and sanitary installations comprising a water-soluble polymer and a strong acid. The strong acid may be phosphoric acid, phosphonic acid, hydrochloric acid or sulfamic acid. The composition may optionally contain a corrosion inhibitor. Specifically disclosed compositions comprise phosphoric acid or hydrochloric acid and benzotriazole. The above prior art compositions have the disadvantage that they insufficiently remove scaling or that they are too aggressive and affect the materials to be cleaned. Further, none of the known compositions have been mentioned to be suitable for cleaning industrial equipment without dismantling said equipment.

Thus it is an object of the invention to provide a method of preventing and removing scaling, rust, and other deposits, preferably without dismantling the equipment, and not having other adverse effects on the equipment and/or process, which is effective in different materials, such as multi-metals, rubber, plastic, composites, and wood. It is another objective to provide a cleaning composition of which the activity can be monitored during the cleaning process to enable suitable replenishment of such composition when the activity becomes too low.

The present invention provides a composition that meets the requirements of monitoring and a composition that is effective when used on various materials. Thus the invention relates to a descaling composition for use to elements in processing equipment comprising: a) 2-30 wt.% of sulfamic acid or a salt thereof, b) up to 10 wt.% of a glycol ether, c) 0.01 to 1.0 wt . % of mercaptobenzotriazole or a salt thereof as corrosion inhibitor, d) optionally an indicator having a pKa 3-4, e) optionally up to 5 wt.% of a buffer, f) 0 to 10 wt.% of a gelling agent, g) 0 to 5 wt . % of a nonionic surfactant, and h) water to complete the composition to 100 wt.%.

The use of sulfamic acid and mercaptobenzotriazole as the corrosion inhibitor is essential to provide a composition that is equally effective in various materials and that does not seriously affect the surface of the materials to be treated. Such compositions may also comprise at least one of an indicator, buffer, gelling agent, and nonionic surfactant. Sulfamic acid is used in a quantity of 2-30 wt.%, preferably 10-20 wt.%, and more preferably about 15 wt.%. Sulfamic acid can be used as such, or as a salt such as sodium, potassium, ammonium salt, or HC1 salt.

Many corrosion inhibitors are known in the art and used for removing rust in cleaning compositions, such as mercaptobenzotriazole, phenylacridlne, sodium iodide, thiourea, sulfonated castor oil, arsenic oxide, sodium arsenate, calcium bicarbonate, polyphosphate, calcium hydroxide, sodium silicate, sodium chromate, sodium nitrite, sodium phosphate monobasic, morpholine, sodium phosphate monobasic, polyphosphate, hydrazine, ammonia, octadecylamine, borax, and mixtures thereof. It was found that only mercaptobenzotriazole, preferably β-mercaptobenzotriazole, in combination with sulfamic acid has the advantageous properties of this invention and appears to be sufficiently effective for removing and preventing scaling and rust in various materials. This corrosion inhibitor can be used in combination with an indicator to monitor the activity of the composition. It was found that only 0.01 to 1.0 wt.% of mercaptobenzotriazole, or a salt thereof such as sodium, potassium or ammonium salt is effective in the present composition. Preferably, 0.05 to 0.5 wt.%, more preferably 0.1 to 0.2 wt.% of mercaptobenzotriazole are used. Preferably, the ratio sulfamic acid : mercaptobenzotriazole is 30:1 to 3:1, more preferably about 10:1.

It is advantageous to use further an amount up to 10 wt.% of glycol ether as solvent and as freeze-point lowering additive. Suitable glycol ethers according to the invention comprise polyoxyalkylene glycols, polyoxyalkylene-polyamine condensation products and polyoxyalkylene glycol ethers, the polyoxyalkylene groups including ethoxy and/or propoxy groups. Most suitable glycol ethers include diethylene glycol, propylene glycol, and ethylene glycol.

Although not necessary for the cleaning and derusting effect, it may be advantageous to add small quantities of an indicator, preferably one that has a pKa value between about 3 and 4, and changes from a color to colorless or vice versa . Addition of such indicator enables (automatic) monitoring of the system, visually or spectroscopically. For instance, an indicator changing from colorless to a color when the pH rises above pH 4 shows that the solution running through the equipment needs replenishing with fresh composition of the invention when it is colored. Suitable indicators include but are not restricted to martius yellow, phloxine B, erythrosine B, benzopurpurin 4B, stains-all, methyl yellow, salycylic acid, 2, 4-dinitrophenol, tetrabromophenolphthalein ethyl ester, and bromophenol blue. Methyl yellow proved to be particularly useful. Indicators, as usual, are added in very small quantities, such as from 10^"6 to 10~² wt.% based on the total weight of the composition (about 1 to 10,000 ppm) . The composition may further contain a suitable buffer to keep the pH as constant as possible. Such buffers are well known in the art and comprise for instance oxalate, tartrate, phthalate, phosphate, borax, and calcium hydroxide buffers. Phosphate buffers, such as anionic phosphate ester buffers (for instance Triton® H66) are particularly suitable. The composition of the invention usually does not contain more than 5 wt.% of the buffer, usually about 0.1 to 1 wt.%.

The composition may further contain a gelling agent. The gelling agent works as a thickener for the composition, which for many applications such as toilet cleaners is an advantage. Up to 10 wt.%, preferably up to 5 wt.% of gelling agent may be present. Suitable gelling agent are known in the art, for instance (bio) polymers, carboxymethylcellulose, starch, polyamide, silicone polyamide, polysaccharide, hydrogel, and the like.

The composition may further contain 0 to 5 wt.% of nonionic surfactant, preferably 0.05 to 0.50 wt.%. Nonionic surfactants are well known in the art, for instance from ethyleneoxide to a fatty oxyalcohol, particularly with 12 to 18 carbon atoms, More particularly oxyalcohol-ethoxylate containing 2 to 50, preferably 6 to 8 mole of ethyleneoxide per mole of alcohol. Other nonionic surfactants are (C1-C20) alkylphenols or polypropoxylated or polyglycerolated fatty acids, having a fatty chain comprising, for example, from 8 to 18 carbon atoms, and it being possible for the number of glycerol groups to range in particular from 2 to 30. There may also be mentioned copolymers of ethylene and propylene oxide, condensates of ethylene and propylene oxide with fatty alcohols; polyethoxylated fatty amides preferably having from 2 to 30 mol of ethylene oxide, polyglycerolated fatty amides comprising on average 1 to 5 glycerol groups and in particular 1.5 to 4; polyethoxylated fatty amines preferably having 2 to 30 mol of ethylene oxide; ethoxylated fatty acid esters of sorbitan having from 2 to 30 mol of ethylene oxide; fatty acid esters of sucrose, fatty acid esters of polyethylene glycol, (C6-C24) aikyl polyglycosides, derivatives of N- (C6-C24) aikyl glucamine, amine oxides such as (C10-C14) alkylamine oxides or N- (C10-C14) acylaminopropylmorpholine oxides; and mixtures thereof.

The composition is completed to 100 wt.% by adding water to the composition. The water used may be tap water, but usually demi- (or deionized) water is preferred.

The invention further relates to a method for removing and/or preventing scaling of elements in processing equipment having metal elements, comprising the introduction of the hereinbefore mentioned composition to the equipment, bringing the composition in contact with the metal elements of the equipment, and maintaining the contact for a sufficient time to remove or prevent scaling.

The method can be used at any suitable temperature at which the composition is fluid. Preferably the elements are brought in contact with the composition at a temperature of about 5 to 100° C. The method is preferably performed in a way wherein the step of removing and/or preventing scaling is done without dismantling the equipment. This is one of the main advantages of the present method, since the production process needs no interruption. Further, hardly any residue is formed, and minor quantities of residue are relatively harmless and biodegradable, and can be removed by the normal sewage system. Preferably, the composition of the invention, or a diluted solution thereof, is continuously or semi-continuously pumped through the equipment, thereby preventing scaling, rust formation, and the like, and simultaneously removing such scaling, rust, that may be formed during the period that the composition was not circulated through the equipment. For those reasons the composition is particularly suitable for heat exchangers, condensers, vacuum waste systems, oil drill equipments, and piping systems.

The invention is further illustrated by the following examples.

Example 1

15 wt.% of sulfamic acid were dissolved in warm deionlzed water. Methyl yellow (0.0001 wt.%) was slowly dissolved in diethylene glycol(1.0 wt.%). The anionic phosphate ester buffer (Triton® H66; 0.4 wt.%), the nonionic surfactant octylphenoxytolylethoxyethanol (0.4 wt.%), and mercaptobenzotriazole (MBT; 0.15 wt.%) were mixed together. When all ingredients were completely dissolved, the mixture was added to the sulfamic acid solution after which the diethylene glycol with the methyl yellow indicator was added. Finally, deionized water was added up to 100 wt.%

The same composition was made with the exception that sulfamic acid was replaced by acetic acid, hydroxy acetic acid, or inhibited mineral acids. None of these compositions were both effective and safe on multi-metals. Further, many of these acids led to considerable gas and/or heat formation. The composition was experimentally used to clean in situ a vacuum toilet system. The system showed a hard scale build-up of 2-3 cm. The composition was pumped around slowly in a closed loop system. After a sequence of 8 hours the hard scale was completely dissolved, without attacking the metals, seals and other materials. No heat or gas was formed.

Example 2

Scale dissolving test

An amount of hard water scale (urine stone) was immersed for 4 hours in 500 ml of a 10 % v/v aqueous composition of the invention and in 500 ml of 10 % v/v of three aqueous compositions, which were comparative.

After 4 hours the solutions were filtered through a

Whatman nr.5 paper filter and the weight loss of the scale was measured. The following compositions were tested:

A: sulfamic acid/mercaptobenzotriazole (according to the invention)

B: sulfamic acid/phosphoric acid (comparative)

C: sulfamic acid/tolutriazole (comparative) D: sulfamic acid/benzotriazole (comparative)

The results are given in Table 1

Conclusion: The composition according to the invention (A) with regard to its descaling effect is comparable to a sulfamic-benzotriazole composition, but substantially better than a sulfamic acid/tolutriazole composition. Only the combination with corrosive phosphoric acid (see also Example 3) gives better descaling properties.

Example 3 The corrosiveness (material loss) of an acideous water based Descaler & Conditioner on mild steel was determined by using compositions with different types of corrosion inhibitors. Thus steel panels were totally immersed into composition A according to the invention and into comparative compositions B-D, after which a weight change measurement and visual qualitative determination of change were performed.

Tests were performed according to the standard ASTM method

ASTM F 483 (Total Immersion Corrosion Test for Aircraft Maintenance Chemicals) .

Test specimens were made from Carbon Steel (Symbol CklO) having the material specifications: Standard Nr. 1.1121 Din 17210; 1652 ISO 683 T.ll; T.18

The test solutions were compositions A-D as described in

Example 2.

The test specimens were immersed in triplo (samples 1-3) according to concentrations of Descaler & Conditioner MR50E with specified inhibitor package. The weight of the steel panels was determined after 7 days of total immersion of the panel in the composition. The results are given in Table 2:

Table 2:

Conclusions:

The composition according to the invention (A) is about 40 to 100 times better with regard to its anticorrosive effect compared with compositions B-D (comparative) . Composition B, which has a greater descaling effect than composition A (see example 2) is unacceptable for descaling pipelines due to its strong corrosive action.

Claims

Claims :

1. A descaling composition for use to elements in processing equipment comprising a) 2-30 wt.% of sulfamic acid or a salt thereof, b) up to 10 wt.% of a glycol ether, c) 0.01 to 1.0 wt.% of mercaptobenzotriazole or a salt thereof as corrosion inhibitor, d) optionally an indicator having a pKa 3-4, e) optionally up to 5 wt.% of a buffer, f) 0 to 10 wt.% of a gelling agent, g) 0 to 5 wt. % of a nonionic surfactant, and h) water to complete the composition to 100 wt.%.

2. The composition of claim 1 comprising 10-20 wt.% of sulfamic acid.

3. The composition of 1 or 2 wherein the glycol ether is selected from at least one of diethylene glycol, propylene glycol, and ethylene glycol.

4. The composition of any one of claims 1-3 wherein the composition comprises an anionic phosphate ester buffer.

5. The composition of any one of claims 1-4 wherein the composition comprises a nonionic surfactant.

6. The composition of any one of claims 1-5 comprising an indicator selected from martius yellow, phloxine B, erythrosine B, benzopurpurin 4B, stains-all, methyl yellow, salycylic acid, 2, 4-dinitrophenol, tetrabromophenol- phthalein ethyl ester, and bromophenol blue.

7. A method for removing and/or preventing scaling of elements in processing equipment having elements, comprising the introduction of the composition of any one of claims 1-6 to the equipment, bringing the composition in contact with the elements of the equipment, and maintaining the contact for a sufficient time to remove or prevent scaling.

8. The method according to claim 7 wherein the elements are brought in contact with the composition at a temperature of 5 to 100° C

9. The method according to claim 7 or 8 wherein the step of removing and/or preventing scaling is performed without dismantling the equipment.

10. The method according to any one claims 7-9 wherein the processing equipment is a heat exchanger, condenser, vacuum waste system, oil drill equipment, or piping system.