Terpolymers of maleic anhydride, scale prevention

Process for the preparation of maleic anhydride terpolymers and their use as anti-scale agents

The shortage of drinking water which exists in certain regions of the world is a problem whose solution is seen in sea water. The transformation of this water into fresh water by various desalination processes is however disturbed by a technological problem which results from the nature of the mineral salts contained in sea water. They are not very soluble in water and their precipitates can hinder the mechanism or the mode of execution of the particular desalination process which is used, these effects being, for example, sealing semi-permeable membranes in an osmotic process and reducing heat transfer in a distillation process This reduces the efficiency of the desalination process and ultimately disrupts operations to the point that desalination has to be stopped and that the The appliance must be cleaned or replaced.

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These salt precipitates are usually called tartar and the work done to prevent the formation of tartar has been based on the use of chemical agents, usually polymers, to prevent the production of scaling. _; , although some have contained surfactants. A common feature of most anti-scale agents is the very low ratio of agent to mineral salt which is necessary to limit and delay precipitation. It can therefore be deduced therefrom that the inhibitory effect is due to a complexation, on the growth site of the crystals, which has the effect of repelling the arriving nuclei, and not to a chelation of the mineral cations of the salt.

The most common polymers which one chooses to use as anti-scale agents are polymethacrylic acid, polyacrylic acid and polymaleic acid and their copolymers with monomers such as acrylamide and vinyl acetate . Some of the polymers more recently developed to inhibit scaling include hydrolyzed polymaleic anhydride (United States patent

No. 3,810,832); a copolymer of maleic anhydride and vinyl acetate (United States Patent No. 3,715,307); a hydrolyzed copolymer of maleic anhydride and a monoethylenically unsaturated monomer or mixtures of such copolymers (British Patent No. 1,414,918); copolymers and terpolymers of maleic anhydride (Netherlands Patent No. 75.06,874); polymers of acrylic acid (United States Patent No. 3,514,376); a methacrylic acid polymer (United States Patent No. 3,444,054); maleic acid copolymers (U.S. Patent No. 3,617,577); copolymers of styrene and maleic anhydride (United States Patent No. 3,289,734); and polyacrylic acid (U.S. Patent No. 3,293,152).

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A comparison of the nature of the polymer and of the anti-scale activity, on the basis of the indications given in the aforementioned patents, suggests that the lowering of the molar ratio of the maleic anhydride portion to the other monomer portions in copolymers or terpolymers thus formed reduces both the charge density and the anti-scale activity. For example, the results of inhibition of scale formation obtained for the polymers described in British Patent No. 1,414,918 cited above reveal that the activity against the precipitation of calcium carbonate decreases when the progression in the set of activities associated with the homopolymer of maleic anhydride, ranging from a copolymer of maleic anhydride and acrylamide to a terpolymer of maleic anhydride, vinyl acetate and ethyl acrylate. The same trend is apparent from a correlation between the anti-scale activities of the polymers described in the aforementioned Dutch patent No. 75 06 874. When the ratio of the maleic anhydride portion to the other portion of monomer in the test polymer formed according to the indications given in the aforementioned Netherlands patent decreases, the activity against precipitation of calcium carbonate also decreases. Thus, the literature teaches that the use of monomers consisting of non-carboxylic acids together with a monomer consisting of maleic anhydride to form a polymer of mixed composition results in a decrease in the anti-scale activity of this polymer compared to the anhydride hydrolysed polymaleic.

The process used in the preparation of the anti-scale polymer influences the nature of this polymer and its activity independently of the ratios in which the monomers are used; this is true for most polymers.

General processes for the preparation of scale inhibiting polymers are described in US Pat. Nos. 3,755,264 and 3,359,246, in addition to the processes described in the aforementioned patents. Although there is abundant information on how to prepare polymers of maleic anhydride and / or acrylic acid, these preparation processes often have uncontrolled rates of polymerization and are accompanied by the Tromsdorff effect, gelation and gumming of the polymers during polymerization, difficulties in adjusting the order of magnitude and the range of molecular weights of the polymer, with very long polymerization times and a lack of reaction safety.

If we consider the preparation methods and activity suggestions of the prior art, we are surprised by the discovery that the combined action of a composition of monomers, a temperature and a solvent of reaction in accordance with the present invention makes it possible to prepare a new type of granular terpolymer of maleic anhydride which has a limited molecular weight range and whose maleic anhydride content is low, while the anti-tartar activity is still close to that of hydrolyzed polymaleic anhydride. The new process can also be applied to the preparation of useful maleic anhydride copolymers, which are granular and easy to process.

The present invention provides a terpolymer, its hydrolyzed form and the alkali metal, amine and ammonium salts of the hydrolyzed form, a terpolymer which comprises (a) 30 to 55 mole% maleic anhydride, (b) 30 to 65 moles% i of acrylamide or methacrylamide and (c) 5 to 15 moles% of a third monomer chosen from styrene, α-methylstyrene, acrylates and alkyl methacrylates of which the alkyl group contains 1 to 8 atoms of carbon and a 1-alkene having

4 to 10 carbon atoms.

The invention also relates to a copolymer composed of (a) 30 to 70 mol% of maleic anhydride and (b) 30 to 70 mol% of acrylamide or methacrylamide. The terpolymer or copolymer is characterized by a relative viscosity of about 4 1.02 to 1.10 in dimethyl sulfoxide at a concentration of 0.5 g per deciliter; by a solubility of less than 0.10 g per g of solution (water) at room temperature and preferably by the almost complete absence of unreacted monomer.

The terpolymers of the present invention advantageously have a solubility of less than 0.06 g per g of solution (water).

A terpolymer is appreciated in the composition of which the third monomer is styrene, because of the favorable balance which exists between the anti-tartar activity and the hydrophobic character of its hydrolysed form. The monomers of this terpolymer are advantageously in the proportion of 30 to 50 mol% of maleic anhydride, 40 to 55 mol% of acrylamide and 5 to 15 mol% of styrene. Particularly preferred is a proportion of the monomers of 41 to 45 mol% of maleic anhydride, 45 to 49 mol% of acrylamide and 9 to 13 mol% of styrene. An advantageous copolymer contains 45 to 55 mol% of maleic anhydride and 45 to 55 mol% of acrylamide.

The present invention further relates to a method for preventing the formation of scale during the heating or desalination of water containing impurities capable of producing scaling, this water being sea water, boiler water, water containing calcium and magnesium cations and other forms of water containing similar impurities.

The process consists in mixing with this water the hydrolyzed form of a terpolymer or of an alkali metal, amine or ammonium salt of this terpolymer, the latter being composed of (a) at 55 mol% of anhydride maleic, (b) 30 to 65 mol% of acrylamide or methacrylamide and (c) 5 to 15 mol% of a third, monomer as defined above, so that the concentration of the hydrolyzed form or of the salt form of the terpolymer in water is at least two parts per million, the non-hydrolyzed terpolymer having the characteristics given above. An advantageous treatment method uses a terpolymer, the third monomer of which is styrene. An even more advantageous treatment method uses a terpolymer essentially formed from 41 to 46 mol% of maleic anhydride.

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that, 45 to 49 mole% acrylamide and 9 to 13 mole% styrene.

Another feature of the present invention resides in the process used to prepare the terpolymers and copolymers described above. This process allows the polymer to be isolated in the form of a granular precipitate rather than a gum, resin or oil, and has the effect that the resulting polymer is insoluble in water at the ambient temperature. It seems that this insolubility is the consequence of a transposition of the chemical structure of the polymer; but despite this point of view, insolubility is clearly related to the combined action of heat and solvent in the reaction process. This process most probably acts by forming a large number of imide portions along the central edge of the polymer, by causing the anhydride portion of the maleic anhydride fragments to recombine with the amide portion of the acrylamide fragments. The supposed imide portions are in turn responsible for the observed insolubility. Additional insolubility in the terpolymer series is due to the hydrophobic nature of the third monomer.

To obtain the desired insolubility in water at room temperature and the formation of a granular precipitate, it is necessary to use reaction temperatures of at least 120 ° C and a chain transfer solvent or mixture solvents of this type which tend to subtract free radicals, the polarity of which is greater than that of toluene, which participates in the polymerization chain reaction and which does not allow the swelling or the agglomeration of the polymer into particles which is formed.

The insolubility of the polymer in water can be exploited for its purification. Suspending the crude reaction polymer in cold water dissolves the water-soluble monomers leaving the polymer substantially free of unreacted monomer. This avoids possible contamination of the desalination operation by the residual monomer.

The compounds of the present invention have unexpected characteristics which presumably result from the presence of a large number of imide groups along the dorsal edge of the polymer and from the hydrophobic effect of the third monomer. It is essentially assumed that the imide groups along the polymer chain in the form of pentagonal and hexagonal nuclei and across the polymer chains in the form of bridges are created in the process of the present invention by recombination of the portions anhydride and amide of the polymer during its formation.

The novel character of insolubility in water at room temperature presented by the terpolymers of the invention can be produced just as well in the new copolymers of maleic anhydride and acrylamide using the process of the invention. The observation of this effect in the copolymers supports the hypothesis that the insolubility of one or other of the types of polymers of the present invention is mainly due to the presence of the imide portion and the effect Hydrophobic evidence of the third monomer of the terpolymer is an additional effect.

The reaction parameters necessary to achieve the desired transformation during polymerization are the high and similar molar amounts of the anhydride and acrylamide monomers, the temperature, the solvent and, in the case of the terpolymer, the mode of addition of the third. monomer. These parameters are decisive for the success of the operation and are the conditions necessary for obtaining the new insolubility character.

The temperature required for the reaction process is at least 120 ° C and this temperature can be obtained by operating under pressure when solvents are used which boil at fairly low temperatures at atmospheric pressure. The upper limit of the temperature range depends on the possibility of adjusting the reaction rate and the reflux temperature of the solvent or mixture of solvents, provided that the solvent or mixture of solvents which is used boils. at a temperature above 120 ° C. The temperature used is advantageously the reflux temperature of the solvent and it is usually between 125 and 150 ° C.

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Ί

The reaction time parameter varies according to the particular raw materials used. The progress of the polymerization can be followed by observing the precipitation of the polymer into fine granular particles and the polymerization is substantially completed when the precipitation ceases. The total duration is usually in the range of 1 to 10 hours and the most frequently observed period is approximately 2 hours.

The solvents used in the process of the present invention are reactive solvents; in other words, they play a role in the stages of chain propagation and termination in the polymerization. These are alkylbenzenes such as toluene, xylene, mesitylene, ethylbenzene and propylbenzene, as well as aliphatic ketones and cycloalkyl ketones such as methyl ethyl ketone, acetone, 4-methyl-2-pentanone, cyclohexanone, dibutyl ketone, dipropyl ketone and other similar organic aromatic and ketone liquid solvents. The process uses a mixture of the aromatic solvent and the ketone solvent in ratios of 15 to 85% by weight of ketone solvent to 15 to 85% by weight of aromatic solvent. The proportions chosen in a given case depend on the nature of the particular polymer which is formed. But in general, these reports guarantee the absence of agglomeration or swelling of the polymer during its formation.

An advantageous mixture of chain transfer solvents is a mixture of approximately equal amounts of xylene and methyl isobutyl ketone.

Any free radical initiator capable of triggering a radical reaction can be used in the process. Representative examples of initiators include di-tert-butyl peroxide, benzoyl peroxide, azobisisobutyronitrile, dicumyl peroxide and dilauroyl peroxide. Although the weight ratio of the initiator to the monomer varies depending on the particular monomers used, the range is usually 2 to 20% by weight based on the total monomers.

In accordance with these reaction parameters, a terpolymer of the present invention is formed by putting all

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first in contact 30 to 55 mol% of maleic anhydride with 303 65 mol% of acrylamide or methacrylamide in the reaction solvent chosen. The mixture is heated to the appropriate temperature and the free radical initiator, and the third monomer defined above in a proportion of 5 to 15 mol%, each dissolved in the reaction solvent, are then added to the reaction mixture, preferably at a rate chosen so that the reaction is completed in a period of 15 to 180 minutes. The usual addition time is about 30 to 60 minutes.

To form a copolymer of the invention, 30 to 70 mol% of maleic anhydride are brought into contact with 30 to 70 mol% of acrylamide or methacrylamide as described above with respect to the terpolymers, except that the 'the third monomer is omitted.

The reaction is preferably carried out in an inert atmosphere, for example in a nitrogen atmosphere.

The reaction mixture is preferably kept under stirring for the entire duration of the reaction, for example by mechanical stirring or by injection.

The polymer can be isolated by any of the known conventional techniques available in the art. The usual method consists in concentrating the reaction medium by evaporation, filtration, then suspension of the filtered solid matter in cold water to dissolve the unreacted monomer. The polymer is thus obtained substantially free of unreacted monomer. Other methods include washing the filtered reaction material with organic solvents such as ether, tetrahydrofuran, chloroform, carbon tetrachloride and similar organic solvents, non-hydroxyl and non-polar.

The polymer is then prepared for application against the formation of scale by hydrolysis in water at reflux. The transformation of the insoluble polymer into a soluble hydrolyzed polymer usually requires a period of 6 to 10 hours. Alternatively, the polymer can be hydrolyzed by stirring with 0.1 to 4M aqueous sodium hydroxide solution at temperatures of 25 to 100 ° C.

The alkali metal and ammonium salts of the hydrolyzed terpolymer can be formed by adding an alkaline base, ammonia or an organic amine to the aqueous solution of the hydrolyzed terpolymer or by directly using the base to hydrolyze the non-terpolymer hydrolysis. The subsequent evaporation of the water makes it possible to isolate the desired salt from the terpolymer, or else this salt can be used directly in aqueous solution, without isolating it. Common alkaline bases include sodium hydroxide, potassium hydroxide and

Lithium hydroxide. Ammonia bases and the usual amines include ammonium hydroxide, ammonia, monoalkylamines, dialkylamines and trialkylamines having 1 to 5 carbon atoms per alkyl group, pyridine, morpholine and lutidine.

The hydrolyzed terpolymers of the invention and the corresponding salts can be used to prevent the formation of tartar during the heating or desalination of water containing impurities capable of forming tartar, such as those which are present in sea water. , boiler water water containing calcium and magnesium ions and other forms of water containing similar impurities. The solid hydrolyzed terpolymer or its salts can be introduced directly into water containing the impurities capable of forming tartar, so that the concentration in water is at least two parts per million. Alternatively, the hydrolyzed terpolymer or its salts can be introduced into water containing impurities capable of forming tartar using a concentrated aqueous solution, so that the water contains a concentration of at least 2 parts per million .

This treatment can be carried out in a manner well known to those skilled in the art, in accordance with the methods used for the treatment of water. Thus, when conducting a discontinuous desalination operation, the anti-scale agent of the invention is introduced in portions. On the contrary, if a continuous desalination operation is carried out, the anti-scale agent can be continuously introduced into the water recycling line containing impurities capable of forming scale, or it can be added to the source which constitutes the food reserve for continuous desalination. Inhibition of the formation of

ΙΟ tartar in boilers is obtained in the same way. As is obvious to a person skilled in the art, the operations must be periodically interrupted in order to remove the concentrated impurities suspended by the anti-scale agent in the container or in the boiler. However, the cleaning operation usually consists of a simple emptying with rinsing of the container or of the boiler, instead of the painful cleaning which requires the elimination of a deposit of tartar.

The characteristic insolubility in water at room temperature of the terpolymers and copolymers of the present invention is shown in Table I. This insolubility was determined by stirring at room temperature for 3 hours a mixture of 25% of polymer and distilled water, then removing the liquid phase. The dissolved polymer is then separated from the liquid phase by lyophilization of the solution and this material and the insoluble polymer are dried in the oven at 25 ° over phosphorus pentoxide, under a vacuum of 0.1 mm of mercury for approximately 2 days. . The weights of dissolved polymer and insoluble polymer are compared for the balance of the masses and are chosen to express the solubility behavior in grams of dissolved polymer per gram of solution, for the particular composition involved. The polymer of method A which is chosen for comparison purposes is prepared according to the general method described in British Patent No. 1,414,918 cited above.

To demonstrate that the insolubility is not related to the duration, the terpolymer indicated in Table I is kept under stirring for 2 days in the manner and in the proportions indicated above. After 2 days of stirring at room temperature, the polymer is isolated in the manner indicated above and it has a solubility of 0.0408 g / g of solution.

A comparison (Table I) of the solubility behavior of the polymers of the invention with the corresponding behavior of the polymer of method A shows the considerable difference in the solubility characteristics of the polymers of the invention. The reason why the polymer of method A lacks insolubility in water is apparent from a comparison between its method of preparation and the method of the present invention (compare method A with example 8). The polymerization temperature is higher in the process of the invention (at least 120 °, compared to the range of 70 to 110 ° for process A) and a mixture of an aromatic solvent and a ketone solvent is there. used. As a result, the process of the invention meets the conditions necessary to create the novel character of insolubility in water at room temperature, which is assumed to be linked to the production of imide portions in the copolymers and terpolymers.

TABLE I

Insolubility of the polymer

<td> 15</td><td colspan="2">Composition of the polymer (mole% based on analysis)</td><td>Ire of</td><td>N® of 1'exemple</td><td>Solubility behavior (g of dissolved polymer per g of solution)</td>

<td></td><td>Maleic anhydride</td><td> •</td><td> 49</td><td> . 8</td><td> 0,058</td>

<td></td><td>acrylamide</td><td> •</td><td> 51</td><td></td><td></td>

<td></td><td>Maleic anhydride</td><td> •</td><td> 29</td><td> 10</td><td> 0,080</td>

<td> 20</td><td>acrylamide</td><td> •</td><td> 71</td><td></td><td></td>

<td></td><td>Maleic anhydride</td><td> • •</td><td> 46</td><td> 9</td><td> 0,073</td>

<td></td><td>methacrylamide</td><td> • •</td><td> 54</td><td></td><td></td>

<td></td><td>Maleic anhydride</td><td> •</td><td> 43</td><td></td><td></td>

<td></td><td>acrylamide</td><td> *</td><td> 46</td><td> 1</td><td> 0,050</td>

<td> 25</td><td>styrene</td><td> •</td><td> 11</td><td></td><td></td>

<td></td><td>Maleic anhydride</td><td> •</td><td> 58,4</td><td>process</td><td>total dissolution of</td>

<td></td><td>acrylamide</td><td> :</td><td> 41, 7</td><td>(AT)</td><td>polymer</td>

(The solubilities of the polymers of Examples 2 to 7 were less than 0.050 g / g of solution).

The scale inhibiting activity of the hydrolyzed terpolymers of the present invention was determined by measuring the amount of precipitate formed by heating under pressure of a normal artificial seawater solution to which the scale inhibiting terpolymer was added. . The procedure and the results are indicated in Example II and must be compared with two types of controls, one not containing the agent and the other using polymaleic acid (obtained according to the methods described in. British patent N® 1,414,918 cited above). These results demonstrate that, although the charge density of the hydrolyzed terpolymers of the invention has been reduced compared to that of polymaleic acid and that their hydrophobic character has been enhanced, the hydrolyzed terpolymers of the present invention display great activity anti-tartar which approximates that of polymaleic acid. It is presumed that the hydrolyzed terpolymers of the present invention involve in their mechanism of action a threshold of inhibition of the formation of tartar, for which the binding of the hydrolyzed terpolymer to the site of development of the crystallization nuclei inhibits the subsequent growth of the crystals on this site and the hydiophobic nature of the third monomer jLO contained in the bound terpolymer repels the water forming the polar cage which contains the solubilized mineral ions.

The following examples 1 to 11 only illustrate the present invention and are in no way limiting in nature (Example A is a comparative example).

. All temperatures are expressed in degrees

Celsius and this is ambient temperatures, unless otherwise specified.

The infrared spectra were measured on a Perkin-Elmer model IR-21 grating spectrophotometer and the values ​​are reproduced in microns.

The viscosity measurements which were used to calculate the molecular weight of the polymers were carried out by the conventional method using an Ubbelohde viscometer using a solution of 0.5 g of the polymer in 100 ml of 25 + dimethylsulfoxide. . 0,0l ° C. The viscosity measured is the relative viscosity (nu) which is defined by the relation nu = t / to in which _t is the flow time in seconds of the polymer solution and t is the flow time in seconds of the solvent.

Method A

Copolymer (A) of maleic anhydride and acrylamide prepared according to the process described in British Patent No. 1,414,918 cited above

A solution of 46.5 g (0.474 mole, 71.4 mole%) of maleic anhydride, 13.5 g (0.190 mole, 28.6 mole%) of acrylamide and 143.0 g of toluene are stirred and heating under nitrogen until the temperature has reached 70 ° C.

A solution of 12.0 g (20% by weight) of benzoyl peroxide in 70.0 g of toluene is then added to the solution obtained over a period of 5 minutes. The solution is then refluxed at 110-113 ° C for 6 hours. After cooling, the toluene solution is decanted from the resinous material which is purified by trituration with benzene. Copolymer A having a relative viscosity of 1.04 is obtained in a yield of 63%.

Composition of copolymer A determined by elementary analysis

58.4 mole% maleic anhydride

41.7 mole% acrylamide.

Example 1,

Terpolymer (1) of maleic anhydride, acrylamide and styrene

150.0 g (1.53 mole, 45 mole%) of maleic anhydride, 108.8 g (1.53 mole, 45 mole%) of acrylamide, 235.0 g of methyl isobutyl ketone and 235.0 g are charged of xylene in a round bottom flask with four tubes of 2000 ml capacity, equipped with a reflux condenser and a mechanical stirrer.

The apparatus is purged by passing a stream of nitrogen, then the flask is lowered into an oil bath maintained at 150 ° C. and as the reaction mixture warms up, a solution is formed. When a moderate reflux has been obtained, at a temperature of the reaction mixture of 126 to 130 °, the free radical initiator solution formed of 14.71 g of di-tert-butyl peroxide, 16.0 g of methyl isobutyl ketone and 16.0 g of xylene is added continuously at a rate chosen so that the addition is completed in 30 minutes. At the same time, a solution of the third monomer, consisting of 35.4 g (0.340 mole, mole%) of styrene, 29.0 g of methyl isobutyl ketone and 29.0 g of xylene is added continuously at a rate chosen so that the addition is completed in 60 minutes. During and after the addition of the third monomer, the polymer precipitates, forming a fluid reaction suspension. When the polymerization is substantially complete (2 hours), the polymerized mixture is allowed to cool to ambient temperature, it is filtered and the precipitate is washed with diethyl ether, then it is dried in the vacuum oven at 80 ° C for 17 hours. Alternatively, the precipitate can be washed with water and dried in a vacuum oven. Terpolymer 1 flowing powder, brown-yellow in color

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which is formed is obtained in a yield of 87.6% and has a relative viscosity of 1.04.

Composition of terpolymer 1 determined by elementary analysis:

moles% maleic anhydride moles% acrylamide moles% styrene.

Infrared spectrum (KBr): 2.94, 3.02, 5.42, 5.64, 5.80, 5.86, 6.05, 6.22 and 8.40.

The other terpolymers of the present invention can be prepared by the process of example 1 by replacing the monomers used in this example by the corresponding monomers, in the suitable ratio.

Example 2

Terpolymer (2) of maleic anhydride, acrylamide and styrene Terpolymer 2 is prepared by following the procedure of Example 1, using the monomers in the same molar percentage ratios, but replacing the ratio of the solvents of Example 1 with a ratio of 75% by weight of methyl isobutyl ketone for 25% by weight of xylene. Terpolymer 2 is obtained in a yield of 87.5% in a fluid powder of relative viscosity equal to 1.04.

Composition of terpolymer 2 determined by elementary analysis:

moles% maleic anhydride moles% acrylamide moles% styrene.

The infrared spectrum (KBr) is identical to that of terpolymer 1.

Example 3

Terpolymer (3) of maleic anhydride, acrylamide and styrene

Terpolymer 3 is prepared in accordance with the procedure of Example 1, replacing the proportions of the monomers of Example 1 with proportions of 55 mol% of maleic anhydride, 35 mol% of acrylamide and 10 mol% of styrene . The free-flowing granular terpolymer 3, of relative viscosity equal to 1.04, is obtained in a yield of 88.1%.

Composition of terpolymer 3 determined by elementary analysis:

50.98 mole% maleic anhydride 5 35.5 mole% acrylamide

13.4 mole% styrene.

The infrared spectrum (KBr) is identical to that of terpolymer 1.

Example 4

Terpolymer (4) of maleic anhydride, acrylamide and styrene

Terpolymer 4 is prepared by following the procedure of Example 1, using the monomers in the same proportions, but replacing di-tertiary butyl peroxide with dicumyl peroxide on an equimolar basis. A yield of 88 is obtained. 0.2% the granular terpolymer 4 of relative viscosity equal to 1.03 g.

Composition of terpolymer 4 determined by elementary analysis:

44.5 mole% maleic anhydride

44.6 mole% acrylamide 10.9 mole% styrene.

The infrared spectrum (KBr) is identical to that of terpolymer 1.

Example 5

Terpolymer (5) of maleic anhydride, acrylamide and 1octene

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183.4 g (1.871 mole, mole%) of maleic anhydride, 72.5 g (1.021 mole, 30 mole% of acrylamide, 215.0 g of methyl isobutyl ketone and 215.0 g of xylene are loaded into a flask. The apparatus is purged for 1.5 hours with nitrogen, then it is immersed in an oil bath maintained at 150 ° C. When a moderate reflux has been reached, at a reaction mixture temperature of 126 to 130 °, a solution of 31.3 g of dicumyl peroxide, 36.0 g of methyl isobutyl ketone and 36 is added dropwise over 1 hour. , 0 g of xylene. At the same time, a solution of 57.3 g (0.510 mole, 15 mole%) of 1-octene, 47.0 g of methyl isobutyl ketone and 47.0 g of xylene is added dropwise over half an hour. When the polymerization is substantially complete (4.0 hours), the reaction mixture is allowed to cool. The terpolymer is filtered into particles, washed with excess diethyl ether and dried in a vacuum oven at about 90 ° C. A free-flowing brown-yellow powder is obtained in 56% yield, which is terpolymer 5 with a relative viscosity equal to 1.04osité.

Composition of terpolymer 5 determined by elementary analysis:

50.9 mole% maleic anhydride 10 41.2 mole% acrylamide

7.85 mole% of 1-octene.

The infrared spectrum (KBr) is identical to that of terpolymer 1.

Example 6

Terpolymer (6) of maleic anhydride, methacrylamide and styrene;

Terpolymer 6 is prepared by the procedure of Example 1, replacing the acrylamide with methacrylamide in the same molar percentage ratio. A granular terpolymer 6 having a relative viscosity of 1.052 is obtained in a yield of 95%.

Composition of the terpolymer according to elementary analysis:

42.8 mole% maleic anhydride 25 46.7 mole% methacrylamide

10.3 mole% of styrene.

Example 7

Terpolymer (7) of maleic anhydride, acrylamide and alphamethylstyrene_

Terpolymer 7 is prepared according to the procedure ¹ procedure of Example 1 by replacing styrene with alphamethylstyrene, in the same molar proportion (%). A granular terpolymer 7 having a relative viscosity of 1.04 obtient is obtained in a yield of 89.4%.

Composition of terpolymer 7 determined by elementary analysis:

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44.5 mole% maleic anhydride

44.9 mole% acrylamide

40.9 mole% of alpha-methylstyrene.

Example 8

Copolymer (8) of maleic anhydride and acrylamide

150.0 g (1.53 mol, 50 mol%) of maleic anhydride are loaded, 108.7 g (1.53 mol, 50 mol%) of acrylamide, 224.0 g of 4-methyl-2- pentanone and 224.0 g of xylene in a round-bottom flask with four tubes of 2000 ml capacity, equipped with a mechanical stirrer, a nitrogen inlet tube, a cold water condenser and d 'a thermometer. The mixture is stirred at room temperature and under a stream of nitrogen for 15 minutes. Then, the apparatus is lowered into an oil bath maintained at 130 ° C. and, at 60 ° C., the solid components dissolve. When the solution is at moderate reflux, at a temperature of 126 to 130 °, a solution of 12.98 g (10% by weight) of di-tert-butyl peroxide, 16, is added dropwise over 30 minutes. 0 g of methyl isobutyl ketone and 16 g of xylene. After addition of the initiator, precipitation of the polymer takes place. After 1 hour, a second solution of 12.98 g of di-tert-butyl peroxide and 112.5 g of xylene is added dropwise to the medium during polymerization, over a period of 2 hours. The polymerization is allowed to continue for another 1 hour, then the dispersion-like mixture is allowed to cool to room temperature, the precipitate is filtered, washed with diethyl ether and dried in the vacuum oven at 90 ° C. Alternatively, the precipitate can be washed with water and dried in a vacuum oven. The free-flowing powder copolymer 8, the relative viscosity of which is 1.05, is obtained in a yield of 89.6%.

Composition of the copolymer according to the elementary analysis:

moles% maleic anhydride moles% acrylamide.

Infrared spectrum (KBr): 2.94, 3.02, 5.43, 5.65 5.86, 6.02, 6.20 and 8.45.

The other copolymers of the present invention can be formed by synthesis in accordance with the procedure of Example 8, by replacing the monomers of Example 8 with the corresponding monomers, in the suitable ratio.

Example 9

Copolymer (9) of maleic anhydride and methacrylamide

The copolymer 9 is prepared by following the procedure of Example 6, but omitting to use styrene.

A freely flowing powder copolymer 9 with a relative viscosity equal to 1.05 is obtained in a yield of 85%.

Composition of the copolymer determined by elementary analysis:

moles% of maleic anhydride '54 moles% of methacrylamide.

Infrared spectrum: 2.96, 3.03, 5.45, 5.65, 5.80,

5.86, 6.02, 6.25 and 8.23.

Example 10

Copolymer (10) of maleic anhydride and acrylamide

The copolymer 10 is prepared in accordance with the procedure of Example 8, replacing the ratios of the monomers used in Example 8 with 25 mole% of maleic anhydride and 75 mole% of acrylamide. , 7% the freely flowing powdered copolymer 10, of relative viscosity equal to 1.10.

Composition of the copolymer according to the elementary analysis:

71.8 mole% acrylamide

28.2 mole% maleic anhydride.

Example 11

Anti-scale activity of the hydrolysed polymers of Examples 1 to 10

An artificial seawater is prepared by dissolving the following weights of mineral salts in one liter of distilled water: NaCl 26.5 g; MgC ^ 2.4 g; MgSO ^ 3.3 g ,; CaCl ^

1.1 g; KC1 0.72 g; NaHCO ^ 0.245 g; and NaBr 0.08 g.

For the conduct of the test, a 1.0 ml sample of an aqueous 0.1% solution of the hydrolyzed polymer is introduced into a beaker containing 166 ml of artificial sea water and a piece of Monel leaf. 2.5 cm side. The test beaker and a positive control beaker containing 166 ml of seawater, 1.0 ml of an 0.1% aqueous solution of polymaleic acid (prepared according to the process described in British Patent No. 1 414 918 cited above) and a square of Monel leaf

<img file="LU79281A1_D0009.tif" />

2.5 cm side are placed in an autoclave (of the pressure cooker type) containing a 10% aqueous solution of lithium chloride, which can be stirred. The autoclave safety valve is adjusted to a pressure of 0.7 bar so that the boiling point of the seawater sample is brought to 115 ° C and the autoclave is closed, then heated until steam begins to escape through the safety valve (20 to 30 minutes). Heating is continued for 45 minutes, then the autoclave is allowed to cool. When the internal pressure of the autoclave has dropped to atmospheric pressure, the control beaker and the test beaker are removed and cooled in a water bath to 25 ° C. The contents of each beaker are analyzed as follows. The Monel leaf is removed and rinsed with 50 ml of 6N hydrochloric acid to remove any scale that may have formed. The final volume of seawater is measured and the amount evaporated is calculated. The seawater is filtered through a 0.2 micron cellulose filter membrane to collect the precipitate formed and the acid used to wash the Monel sheet is passed slowly over the filter to dissolve the precipitate. The volume of acid solution is then measured and the quantity of precipitated calcium and / or magnesium compounds is determined, by titration with ethylenediaminetetraacetic acid of an aliquot of the acid washing liquor. A total of four test samples and four positive control samples are prepared and the means and standard deviations are calculated. The averages and standard deviations of the amount of water lost are also calculated.

This amount is calculated as a percentage of the total amount and is expressed as the percentage of evaporation. The means of the positive controls and their percentages of evaporation are compared with a curve of variation of the deposits of tartar as a function of the percentages of evaporation for a polymaleic acid which is of the same type and of the same origin as indicated in Table III. gives further. The comparison is used to ensure that nothing abnormal happened during the test.

The averages of the results of the anti-scale test carried out using each of the polymers of various examples of the present invention are reproduced in Table II and expressed in milli-equivalents of calcium / magnesium complexed by EDTA, the table also giving the results of a test on a null control (control without scale-resistant polymer). The percentage of evaporation is reproduced in Table II also giving the average scale.

To compare the anti-tartar activity of the test polymers with that of the positive control, namely polymaleic acid, it is necessary first to determine the incidence of the degree of evaporation on the tartar deposit. Assuming that the positive control is polymaleic acid and that the percentage of evaporation is mainly a function of the apparatus and the test conditions and not of the identity of the anti-scale agent, this determination was made. by repeatedly testing polymaleic acid as an anti-tartar agent under the experimental conditions defined above. In each test, the deposited amounts of tartar falling in each 0.6 unit percent evaporation increment were averaged from a 12% evaporation and the standard deviation of each average was calculated. These averages and the corresponding ranges of evaporation are presented in Table III.

Using the results of Table III, the behavior of the polymers of the examples as anti-scale agents was compared with the behavior of polymaleic acid. After the choice of the increment of the range of evaporation percentages in Table III in which the percentage evaporation of the polymer of the example in question is situated, the average scaling of the increment chosen in the range is compared. in Table III with the average scale given by the sample for the polymer of the example in question, in Table II. If the average scaling value of the sample of the polymer in the example in question is lower than the corresponding average scaling value for polymaleic acid, the polymer of the example has greater anti-scale activity than l polymaleic acid. When considering this comparison, one must take into account the spread of the average scaling values ​​for the sample and the average scaling values ​​for polymaleic acid in order to appreciate the merits of the poly21 mothers of the examples as anti-tartar agents, compared to the merits of the positive control, i.e. polymaleic acid.

TABLE II

<td> 5</td><td>Activity</td><td colspan="3">scale inhibitor of the polymers of the examples</td><td colspan="2">hydrolysed</td>

<td></td><td>Example No. of</td><td></td><td colspan="2">Medium scaling</td><td colspan="2">Evaporation</td>

<td></td><td>polymer (poly-</td><td></td><td>with the</td><td>samples</td><td colspan="2">average</td>

<td></td><td>hydrolyzed mother</td><td></td><td>(Meq)</td><td>difference</td><td> (%)</td><td>difference</td>

<td> 10</td><td></td><td></td><td></td><td>type</td><td></td><td>type</td>

<td> *</td><td> 1</td><td></td><td> 0,102</td><td> 0,028</td><td> 15,1</td><td> 1,5</td>

<td></td><td> 2*</td><td></td><td> 0,158</td><td> 0,039</td><td> 13,6</td><td> 1,8</td>

<td></td><td> 3</td><td></td><td> 0,080</td><td> 0,008</td><td> 13,0</td><td> 0,6</td>

<td></td><td> 4</td><td></td><td> 0,079</td><td> 0,028</td><td> 13,6</td><td> 0,6</td>

<td> 15</td><td> 5*</td><td></td><td> 0,143</td><td> 0,023</td><td> 15,4</td><td> 1,4</td>

<td></td><td> 6</td><td></td><td> 0,149</td><td> 0,046</td><td> 14,9</td><td> 1,6</td>

<td></td><td> 7</td><td></td><td> 0,073</td><td> 0,026</td><td> 12,3</td><td> 0,7</td>

<td></td><td> 8*</td><td></td><td> 0,149</td><td> 0,015</td><td> 15,3</td><td> 1,2</td>

<td></td><td> 9</td><td></td><td> 0,110</td><td> 0,060</td><td> 15,9</td><td> 1,2</td>

<td> 20</td><td> 10</td><td></td><td> 0,115</td><td> 0,032</td><td> 15,5</td><td> 2,4</td>

<td></td><td>Void witness</td><td></td><td> 0,200</td><td> 0,005</td><td> 15,0</td><td> 2,4</td>

<td></td><td colspan="2">* The amount</td><td colspan="4">of scale with the samples and the</td>

<td></td><td>amount of tartar</td><td colspan="5">with the positive control (polymaleic acid)</td>

<td></td><td>filed during</td><td>of the</td><td colspan="3">tests for these examples were</td><td>abnormally</td>

<td> 25</td><td>slightly high;</td><td colspan="3">so for the polymer</td><td colspan="2">of example N ° 2</td>

<td></td><td colspan="3">the average amount of tartar</td><td>filed for 1 '</td><td colspan="2">polymaleic acid</td>

<td></td><td>during this test</td><td colspan="2">particular</td><td>was 0.127</td><td>; for the</td><td>polymer</td>

<td></td><td colspan="2">N ° 5, it was 0</td><td colspan="2">, 148 and for the polymer</td><td colspan="2">No. 8, she was</td>

0.15.

³⁰ TABLE III

Scale deposit depending on the percentage of evaporation, when polymaleic acid is used as an anti-scale agent

<td>Range of evaporation percentages</td><td>Average amount of tartar found (Meq)</td><td>medium difference</td>

<td> 12,0-12,6</td><td> 0,065</td><td> +0,013</td>

<td> 12,6-13,2</td><td> 0,075</td><td> +0,003</td>

<td> 13,2-13,8</td><td> 0,081</td><td> +0,007</td>

<td> 13,8-14,4</td><td> 0,106</td><td> +0,010</td>

<td> 14,4-15,0</td><td> 0,117</td><td> +0,009</td>

<td> 15,0-15,7</td><td> 0,119</td><td> +0,004</td>

The