Compositions – Water-softening or purifying or scale-inhibiting agents – Plant or organic material containing
Reexamination Certificate
2001-02-13
2004-06-01
Metzmaier, Daniel S. (Department: 1712)
Compositions
Water-softening or purifying or scale-inhibiting agents
Plant or organic material containing
C252S186290, C252S186360, C424S661000
Reexamination Certificate
active
06743372
ABSTRACT:
BACKGROUND
The present invention relates to compositions for water treatment based on biodegradable polymers containing repeating succinyl units, biocidal oxidizing agents and a substituted or unsubstituted amidosulphonic acid; their use in, and the process for, conditioning water of cooling circuits.
When natural waters are used for industrial purposes, for example as cooling water, the water used is changed physically and/or possibly also chemically specifically or unintentionally. Thus, for example in open recirculating cooling systems, temperature changes, concentration and a pH increase due to the discharge of carbon dioxide in the cooling tower are unavoidable.
Due to the concentration and increase in pH from the discharge of CO
2
, the concentration of hardness constituents, in particular calcium ions and carbonate ions, increases. If the natural waters were in equilibrium before use (lime-carbon dioxide equilibrium), an increase in concentration of the hardness constituents leads to supersaturation. To prevent scale deposition (encrustations), in particular on heat-transfer surfaces, treatment of the waters by addition of additives (“scale inhibitors”) is necessary.
A further, sometimes even the predominant, purpose of the use of additives in water treatment is protection of metallic materials against corrosion. For example, when unalloyed carbon steels are used in open recirculating cooling systems, adequate corrosion inhibition is desired, since the conditions prevailing in such systems (oxygen saturation, salt accumulation) lead to an acceleration of corrosion.
WO 97/39078 proposes the use of biodegradable polymers, such as, for example, polyaspartic acid, or other aspartic-acid-containing polymers in combination with biocidally acting oxidizing agents to condition water in, cooling circuits.
Descriptions are given, inter alia, of experiments in which 10 mg/l of polyaspartic acid having a molecular weight of about 3000 were tested in the presence of 0.4 mg/l of sodium hypochlorite for scale-inhibiting activity, and no decrease in scale-inhibiting activity was observed over the measurement period of 4 hours. When 0.4 mg/l of a mixture of sodium hypochlorite and sodium hypobromite in a weight ratio of 1:1 was added, 95% of the initial activity was still present after 4 hours.
Furthermore, in a cooling circuit having a cooling tower, the concentration of polyaspartic acid was tested without and with addition of 0.2 mg/l of chlorine in the form of sodium hypochlorite over one month: without chlorine addition, with daily doses of 20 to 50 mg/l of polyaspartic acid, a concentration of between 11 mg/l and 2 mg/l was established, and with chlorine addition a concentration of about 20 m/l was established.
A disadvantage of the mixtures of WO 97/39078 is the fact that the polymers used there react to a considerable extent with microbicides such as chlorine, bromine or halogen-releasing products, which is observable by a decrease in the biocide concentration.
It must be expected that owing to the reaction with the biocide, portions of polyaspartic acid are also destroyed, and that, as a result, the desired scale-inhibiting and/or corrosion-inhibiting activity is no longer achieved.
In many cases, although it would be possible to create a compensation at least to a certain extent by a higher dosage of the polyaspartic acid, the economic efficiency of the use of polyaspartic acid would suffer.
Therefore, the object of the present invention is to provide a composition for water treatment based on polymers containing repeating succinyl units, the components of which polymers remain stable over a long period, so that the use is economically justifiable, even in cooling circuits, especially in those having relatively long residence times.
DESCRIPTION
The object was achieved by means of the fact that polymers containing repeating succinyl units are mixed with biocidally acting oxidizing agents and, as stabilizer, unsubstituted or substituted amidosulphonic acid is added. The stabilizer here has the task of preventing or substantially reducing the reaction between polymer and oxidizing agent.
Although the use of ammonia, amines, amides or amidosulphonic acids as stabilizers for chlorine is disclosed by U.S. Pat. No. 4,711,724 and U.S. Pat. No. 3,170,883, and U.S. Pat. No. 4,642,194 describes the use of amidosulphonic acids and organic sulphonamides (EP-A 0 569 220) as stabilizers for specific phosphonic acids with respect to chlorine and U.S. Pat. No. 4,759,852 also with respect to bromine, the use of amidosulphonic acid and organic derivatives of amidosulphonic acid for stabilizing polyaspartic acid with respect to chlorine and bromine, has not previously been mentioned in the literature.
The high efficacy of amidosulphonic acid for stabilizing halogen with respect to polymers containing repeating succinyl units is surprising to those skilled in the art, since amide structures are present in the polymers themselves. The addition of a further amide should therefore give rise to the expectation of little activity. Surprisingly, by this means, the reaction between oxidizing biocide and polymer was considerably reduced.
The present invention therefore relates to the use of polymers containing repeating succinyl units, in particular polyaspartic acids, as compositions for water treatment in combination with a biocide and amidosulphonic acid H
2
NSO
3
H or organic derivatives of amidosulphonic acid, and to the use of these compositions for water conditioning of cooling circuits.
The polymers used according to the invention have repeating succinyl units having one of the following structures:
In addition, as a result of suitable reaction procedure and choice of starting materials, further repeating units can be present, e.g.
a) maleic acid units of the formula
b) maleic acid and fumaric acid units of the formula
The chemical structure is preferably analysed by
13
C-NMR, FT-IR and, after total hydrolysis, by HPLC, GC and GC/MS.
Many preparation processes produce not the pure acids, but initially the corresponding anhydrides, for example polysuccinimide (=PSI). Polymerization products of this type can be converted into a salt of PAA by reaction with a base in the presence or absence of water. This conversion of PSI polymers to PAA polymers takes place subsequently in a suitable apparatus by hydrolysis. Preference is given here to a pH between 5 and 14. Particularly preferably, a pH of 7 to 12 is selected, in particular by adding a base. Suitable bases are alkali metal hydroxides and alkaline earth metal hydroxides or alkali metal carbonates and alkaline earth metal carbonates, such as sodium hydroxide solution, potassium hydroxide solution, soda or potassium carbonate, ammonia and amines such as triethylamine, triethanolamine, diethylamine, diethanolamine, alkylamines etc. Particular preference is given, in addition to the free acids, to their Na, K or Ca salts.
The temperature during the hydrolysis is suitably in a range up to and including the boiling point of the PSI suspension and is preferably 20 to 150° C. The hydrolysis is carried out under pressure, if appropriate.
However, it is also possible to obtain the free polyaspartic acid by purely aqueous hydrolysis or treating the salt with acids or acidic ion-exchangers. The term “polyaspartic acid” (=PAA) for the purposes of the present invention likewise includes the salts, unless explicitly stated otherwise.
The final polyaspartic acid or the salts of polyaspartic acid are obtained by drying, preferably spray-drying.
Preferred polymers have a molecular weight, according to gel-permeation chromatography, of MW=500 to 10,000, preferably 700 to 5000, particularly preferably 1000 to 4500. Generally, the beta-form content is more than 50%, preferably more than 70%.
The concentration of the polyapartic acids to be used for the water treatment is usually approximately 0.5 to 100 mg/l of active compound in the aqueous phase, but mostly in the range from approximately 2 to 50 mg/l.
To achieve the object of the present in
Groth Torsten
Joentgen Winfried
Kleinstück Roland
Akorli Godfried R.
Bayer Aktiengesellschaft
Eyl Diderico van
Metzmaier Daniel S.
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