GB2082600A

GB2082600A - Acrylic terpolymers

Info

Publication number: GB2082600A
Application number: GB8122102A
Authority: GB
Original assignee: Chemische Fabrik Stockhausen GmbH
Current assignee: Stockhausen GmbH and Co KG
Priority date: 1980-07-18
Filing date: 1981-07-17
Publication date: 1982-03-10
Also published as: FR2486949A1; IT1137294B; NO812461L; IT8122962A0; FR2486949B1; DE3027236A1; DE3027236C2; GB2082600B

Abstract

Novel polymers of a) 2-acrylamido-2- methylpropanesulphonic acid, b) acrylamide and/or methacrylamide, and c) acrylic acid and/or methacrylic acid especially salts thereof with, e.g., alkali ammonia, and amines are especially effective as treating agents for the prevention and/or removal of coating and encrustation on industrial plant apparatus such as boilers, turbines and pumps. The preferred polymers and salts comprise from 0.5 to 50% by weight of component (a), from 5 to 40% by weight of component (b) and have a molecular weight within the range of from 1,000 to 10,000.

Description

SPECIFICATION Acrylic terpolymers -This invention relates to terpolymers of 2-acrylamido-2-methylpropanesulphonic acid, acrylamide (and/or methacrylamide) and acrylic acid (and/or methacrylic acid), especially in the form of their salts, more especially their alkali and ammonium salts, processes for the manufacture of such terpolymers and methods of preventing encrustations in aqueous systems by their use.

The use of water-conveying systems in industrial plant in the presence of salts which tend to form deposits that are not readiiy soluble presents a number of problems.

Deposits and the formation of coverings cause a reduction in the efficiency and life of plant so that, for reasons of economy, cleaning with acid must be carried out at regular intervals. The manner in which the deposits are formed varies.

On the one hand they may be an accumulation of products of oxidation, caused by metal corrosion, and on the other hand they may be sparingly soluble alkaline earth compounds. The latter originate mainly from the bicarbonates dissolved in the service water as a result of increase in temperature, or increase in concentration caused by evaporation of water. In the majority of cases the problem is the removal of calcium/magnesium carbonates, sulphates and silicates. This formation of coatings is known as "boiler scale formation".

In the past there has been no lack of attempts to prevent the damaging deposits by the use of complex formers and/or sequestering agents. Whether this happened as a result of an improvement of the solubility of the salts or as a result of influencing the crystal growth was of no importance. Consequently, the following terms are to be found, interalia for the substances porposed as additives: boiler scale inhibitors, anti-boiler scale formers, anti-precipitation agents, anti-nucleation agents and dispersing agents.

Compounds that have proved especially advantageous are those which when added to the water even in lower than stoichiometric amounts prevent the harmful formation of coatings.

These properties are exhibited in particular by alkali polyphosphates, such as sodium tripolyphosphate and hexametaphosphate, but in aqueous solution these are quickly substantially decomposed as a result of hydrolytic action and they have therefore been replaced by products based on organic substances, of which the following can be mentioned: polyaminoalkylene phosphonates (German OS 25 39 687), alkali salts of low-molecular polyacrylic acid (US-PS 3514 376, U-PS 4008 164), hydrolysed polyacrylamide (US-PS 343 730, US-PS 4001 161, US-PS 4085 045), hydrolysed polyacrylonitrile (US-PS 3492 240) and low-molecular copolymers of acrylic acid and/or methacrylic acid and/or acrylamide with water-sosiuble esters of unsaturated acids (German OS 2 461 164), such, for example as acrylic acid glycol esters.The molcular weights of these polymer products are between 500 and 100,000, preferably between 1,000 and 12,000.

Acrylamide/acrylic acid copolymers with an asymmetrical molecular weight distribution have also been proposed as boiler scale inhibitors (US-PS 4072 607 and German OS 2802 709).

The use of the above-mentioned polymer products as boiler scale inhibitors in aqueous liquids has not, however, taken into account the problem of iron corrosion, although it is precisely this problem which is becoming important in the field of high-grade machines such as turbines, steam generators, pumps and condensers.

The present invention is based on our observation that low-molecular weight copolymers of 2-acrylamido2-methylpropanesulphonic acid, acrylamide and/or methacrylamide and acrylic acid and/or methacrylic acid, especially in the form of their alkali and ammonium salts, prevent boiler scale formation and also reduce iron corrosion.

The present invention accordingly provides a polymer comprising units derived from - a) 2-acrylamido-2-methylpropanesulphonic acid b) acrylamide and/or methacrylamide, and - c) acrylic acid and/or methacrylic acid.

In addition the present invention provides alkali and ammonium salts or mixtures of alkali and ammonium salts of the above polymers, which polymers are obtainable by copolymerisation of the relevant monomers in aqueous solution in the presence of radical formers under normal pressure and can then be converted into the corresponding salts. The pH value during polymerisation can be selected as desired, for example by the addition of alkali.

The present invention also provides processes for the preparation of said polymers and their salts and also methods of treating substrates which employ them.

In the polymers of the present invention, the acrylamide and/or acrylic acid moities can be partially and/or completely be replaced by methacrylamide and methacrylic acid moities, respectively. However, for convenience only, the invention will now be described in more detail with reference to the former moities.

The terpolymers according to the invention contain from 0.5 to 50%, preferably from 1 to 10%, of 2-acrylamido-2-methylpropanesulphonic acid, from 5 to 40%, preferably from 10 to 20%, or acrylamide, the acrylic acid providing the balance and the figures relating to weight.

The molecular weights of the terpolymers according to the invention are between 500 and 20,000, preferably between 1,000 and 10,000. The molecuie weight distribution may be symmetrical or asymmetrical with several maxima.

The mean molecular weight was determined from the limit viscosity in 10% NaCI solution measured in a capillary viscometer. Provided that the contributions to the specific viscosith of the sulphonate-containing groups in the polymer chain are the same as those afforded by the carboxyl groups, the following formula is used: [ti] = 0.025 .

(Korotkina et al.: Zh. Prikl. Khim. 38, 2533 (1965)).

A preferred embodiment of the polymerisation comprises first of all placing a portion of the acrylic acid in the reaction vessel and heating it to the temperature required for carrying out the polymerisation. The remainder of the acrylic acid is mixed with the comonomers in a metering vessel and neutralised, or only partly neutralised, by the addition of alkali.

When polymerisation is complete, a liquid product with acid groups that are still free is obtained, which can be adjusted to the desired pH value by alkali and/or ammonia and/or amines.

Suitable amines are as follows: ethylenediamine, mono-, di- and trialkylamines with a linear and/or branched and/or cyclic alkyl radical having from 1 to 6 carbon atoms, such as methylamine, ethylamine, propylamine, isopropylamine and cyclohexylamine, hydroxyalkylamines having up to 6 carbon atoms, such as mono-, di- and triethanolamine, ispropanolamine and dimethylisopropanolamine.

The terpolymers according to the invention are distinguished by their dispersing power together with simultaneously prevailing corrosion-reducing properties with respect to iron and steel. As little as 2 ppm are adequate substantially to reduce the precipitation of calcium/magnesium carbonate from aqueous solutions.

The loss of action which occurs over a prolonged period is insignificant since the precipitates which are then produced are no longer able to form damaging deposits and can easily be removed by means of a filter.

It was also possible to observe that old deposits of calcium/magnesium carbonate were gradually redispersed as a result of the action of the terpolymer. The terpolymers according to the invention can be used in any aqueous system in which deposits, especially of alkaline earth carbonates, sulphates and silicates, are to be prevented. The following shall be mentioned by way of example: cooling water and hot water systems, boiling and vaporising units, heat exchangers, turbines and pumps.

Afurther possible use of the anionic terpolymers is in the oil-flooding of geological formations as anti-precipitation agents, and in the recovery of drinking water in sea water desalination plants by evaporation or high pressure osmosis.

The polymers are thermally stable up to temperatures of approximately 300"C. No reduction of action was observed after such a heat treatment.

Example 7 258 g of water, 3 g of acrylic acid and 12.0 g of hydrogen peroxide (35% strength) were placed in a reaction flask and heated to 90+2C. In another vessel, a mixture of 354 g of acrylic acid, 22.5 g of 2-acrylamido-2-methylpropanesulphonic acid and 220 g of acrylamide (30% strength in water) was partly neutralised with 270.2 g of sodium hydroxide solution (45% strength) and, while stirring, this solution was then introduced into the hydrogen peroxide-containing solution over a period of approximately 1 hour. 54 g of hydrogen peroxide (35% strength) and 12 g of hydroxylamine hydrochloride (dissolved in 40 g of water) were metered in through a second inlet pipe proportionally to the partly neutralised mixture. The temperature was constantly maintained at 90 + 20C.

When addition was complete, the mixture remained at this temperature for a further 4 hours. When the reaction mixture had cooled, the pH was adjusted to 8.5 with sodium hydroxide solution (45% strength).

There resulted an approximately 40% strength solution of the sodium salt of a terpolymer of acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid, M = c.2900 (polymer 1).

Example 2 The polymerisation of acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid was carried out in the same manner as in Example 1 except that the amount of 2-acrylamido-2methylpropanesulphonic acid was increased to 45 g and accordingly the amount of acrylic acid was reduced by an equal molar amount.

The reaction mixture was subsequently adjusted to a pH of 8.5 with potassium hydroxide solution (40% strength). There resulted an approximately 40% strength solution of the sodium/potassium salt of a terpolymer of acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid, M = c. 3500 (polymer 2).

Example 3 Acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid were polymerised in the same manner as that described in Example 1 except that the amount of 2-acrylamido-2-methylpropanesulphonic acid was increased to 90 g and accordingly the amount of acrylic acid was reduced by an equal molar amount. The reaction mixture was then neutralised (pH 8.5) with ethylenediamine. There resulted an approximately 42% strength solution consisting of the sodium and ethylenediammonium salt of a terpolymer of acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid, M = c.3000 (polymer 3).

Example 4 Acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid were polymerised in the same manner as that described in Example 2. Neutralisation was then carried out with diethanolamine. There resulted an approximately 47% strength solution of the sodium/diethanolammonium salt of a terpolymer of acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid, M = c. 4300 (polymer 4).

Example 5 Acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid were polymerised in the same manner as that described in Example 2. Neutralisation was carried out with cyclohexylamine. There resulted a 47% strength solution of the sodium/cyclohexylammonium salt of a terpolymer of acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid, M = c. 4200 (polymer 5).

Example 6 After neutralisation with 131 g of sodium hydroxide solution (45% strength), 10.5 g of acrylamide, 198.5 g of acrylic acid and 1.05 g of 2-acrylamido-2-methylpropanesulphonic acid were polymerised in a reaction flask in the same manner as that described in Example 1. There resulted a 40% strength solution of the sodium salt of a terpolymer of acrylamide, acrylic acid and 2-acrylamido-2-methylpropanesulphonic acid (polymer 6).

Example 7 After neutralisation with 131 g of sodium hydroxide solution (45%strength),71g of acylamide, l3gof methacrylamide 21 g of acrylic acid and 105 g of 2-acrylamido-2-methylpropanesulphonic acid were polymerised in a reaction flask in the same manner as that described in Example 1. There resulted a 40% strength solution of the sodium salt of a terpolymer of acrylamide, acrylic acid and 2-acrylamido-2methylpropanesulphonic acid (polymer 7).

Example 8 After neutralisation with 131 g of sodium hydroxide solution (45% strength), 84 g of acrylamide, 85 g of acrylic acid 20 g of methacrylic acid and 21 g of 2-acrylamido-2-methylpropanesulphonic acid were polymerised in a reaction flask in the same manner as that described in Example 1. There resulted a 40% strength solution of the sodium salt of a terpolymer of acrylamide, acrylic acid and 2-acrylamido-2methylpropanesulphonic acid (polymer 8).

Polymers 6,7 and 8 were tested for sequestering action by the same methods as were used for polymers 1 to5.

Examination ofsequestering action of the polymers Polymers from Examples 1 to 8 were tested as boiler scale inhibitors by the following method: The polymer to be examined was added in a concentration of 2 and 5 ppm to 2000 ml of tap water that contained approximately 190 mg of calcium oxide/l. The siolution was heated to 90f 2DC by a heating bath in the course of 60 minutes.

When a temperature of 90"C had been reached, 20 ml of freshly boiled tap water (without addition) were added. Then, over a period of 6 hours, 50 ml samples were taken hourly and filtered through a Gooch crucible (type G 4). The calcium oxide content in the filtrate was determined complexometrically at a pH of 12 with murexide as indicator. The amount of calcium oxide contained in each solution has been quoted as a percentage of the initial amount of calcium oxide in the tap water (see table).

Polymer 1 was subjected to a heat treatment of up to 3000C to test the thermal stability. The subsequent examination of the dispersing action showed no difference from the untreated sample.

TABLE 1 The percentage of calcium oxide contained in tap water of a temperature of 90"C, based on the initial amount of calcium oxide, as a function of time.

Product none Polymer 1 Polymer2 Poly. 3 Poly. 4 Poly. 5 Concentration ppm (based on ppm dry substance) 0 0 2 5 2 5 2 5 2 5 2 5 Time (hours) 1 - 93 100 100 100 100 99 100 99 100 99 100 2 76 75 97 98 95 99 98 99 97 99 97 99 3 66 62 95 96 96 99 96 99 95 99 94 97 4 59 53 90 96 95 99 95 98 93 98 91 96 5 52 49 88 93 86 98 86 97 86 95 86 95 6 48 48 82 91 77 90 78 90 75 90 76 90 mg CaO/l tapwater 194 194 187 187 189 189 190 190 188 188 191 191 The percentage of calcium oxide in tap water of a temperature of 95"C, based on the initial amount of calcium oxide, as a function of time.

Product Polymer 6 Polymer 7 Polymer 8 Concentration ppm based on dry 0 0 1 5 1 5 1 5 substance) Time (hours) 2 75 76 94 99 71 80 91 98 4 54 58 84 98 60 71 88 96 6 47 49 65 97 57 64 72 92 Examination ofanti-corrosion action of the polymers Polymers 1,2,3,4 and 5 were subjected to the following anti-corrosion test: 200 and 2000 mg amounts of common salt were dissolved in 200 9 of distilled water and 2 g of terpolymer (based on dry substance) were then added to these solutions.

Iron sheets (steel 37) were then exposed to the aqueous media for 24 hours.

In the samples without the addition of terpolymer there was viable rust formation after only 1 hour.

Rust formation was assessed in accordance with the following scale: 0 = no rust 1 = very slight rust formation 2 = slight rust formation 3 = medium rust formation 4 = medium-to-heavy rust formation 5 = heavy rust formation 6 = very heavy rust formation 0.5% NaCI NaCI Polymer 1 0 1 Polymer 2 0 1 Polymer 3 1 2 Polymer 4 0 0 Polymer 5 0 0 no addition 5 6

Claims

1. A polymer which comprises units described from a) 2-acrylamido-2-methylpropanesulphonic acid b) acrylamide and/or methacrylamide, and c) acrylic acid and/or methacrylic acid.

2. A polymer as claimed in claim 1, which has be prepared in aqueous solution in the presence of radical formation agents under normal pressure.

3. A polymer as claimed in claim 1 or claim 2, which comprises from 0.5 to 50% by weight of component (a).

4. A polymer as claimed in claim 2, which comprises from 1 to 10% of component (a).

5. A polymer as claimed in any one of claims 1 to 4, which comprises from 5 to 40% by weight of component (b).

6. A polymer as claimed in claim 5, which comprises from 10 to 20% by weight of component (b).

7. A polymer as claimed in any one of claims 1 to 6, which comprises from 10 to 94.5% of component (c).

8. A polymer as claimed in any one of claims 1 to 7, which has a molcular weight within the range of from 500 to 20,000.

9. A polymer as claimed in claim 8, which has a molecular weight within the range of from 1,000 to 10,000.

10. A salt of a polymer as claimed in any one of claims 1 to 9.

11. A salt as claimed in claim 10, which is an alkali salt, an ammonium salt, an amine salt or a mixture of any two or more thereof.

12. A process for the manufacture of a polymer as claimed in any one of claims 1 to 11, wherein a portion of the acrylic and/or methacrylic acid is heated to the polymerisation temperature and the other portion, after admixture with the other two components and before polymerisation of the total mixture is at least partially neutralised.

13. A process for treating a substrate which comprises applying to said substrate a polymer as claimed in any one of claims 1 toll.

14. A process as claimed in claim 13, which comprises a treatment to remove an encrustation or coating on said substrate.

15. A terpolymer of (meth-) acrylamide with (meth-) acrylic acid and a further copolymerisable monomer, characterised in that they have been produced by the copolymerisation of a) 2-acrylamido-2-methylpropanesulphonic acid, b) acrylamide and/or methacrylamide c) acrylic acid and/or methacrylic acid in aqueous solution in the presence of radical formers under normal pressure, and have optionally been converted by neutralisation with alkali, ammonia and/or amines into their alkali and/or ammonium salts.

16. Terpolymers according to claim 15, characterised by a content of a) from 0.5 to 50, preferably from 1 to 10% by weight of 2-acrylamido-2-methylpropanesulphonic acid b) from 5 to 40, preferably from 10 to 20% by weight of acrylamide and c) from 94.5 to 10% by weight of acrylic acid.

17. Process for the manufacture of terpolymers according to claim 15 or claim 16, characterised in that a portion of the acrylic acid is heated in the polymerisation vessel to the polymerisation temperature and the other portion, after mixing with the other two comonomers and before polymerisation of the total mixture, is at least partly neutralised.

18. A polymer as claimed in claim 1, substantially as described in any one of Examples 1 to 8 herein.

19. A process as claimed in claim 12, substantially as described in any one of Examples 1 to 8 herein.

20. A process for treating a substrate as claimed in claim 13, substantially as described herein.