JPH0420005B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to new copolymers of itaconic acid and acrylic or methacrylic acid, a process for their preparation and their use as scale inhibitors. Aqueous systems containing dissolved inorganic salts are commonly used in operations such as heating, cooling and evaporative distillation involving heat transfer. This salt often becomes insoluble during this operation and deposits as scale on the heat transfer surfaces, resulting in reduced heat transfer and accidental equipment failure. Generally, inorganic scale salts include alkaline earth or other metal cations such as calcium, magnesium, iron and lead,
and from anions such as bicarbonate, carbonate, hydroxide, sulfate and phosphate. Many factors influence scale formation, including:
Examples include the PH of the water, the nature of dissolved salts, and the operating temperature. Many additives have been proposed as inhibitors of inorganic scale adhesion. Of particular interest are additives known as marginal scale control agents, which exhibit scale inhibition at extremely low additive concentrations of 1 part per million or less. Included in this critical scale control agent are homopolymers of acrylic and methacrylic acid and copolymers with such as maleic anhydride and fumaric acid. Although these additives have been shown to be effective at critical concentrations, their manufacture is generally expensive and poses problems of solvent contamination of the polymer product.
Use a non-aqueous solvent system. Therefore, there remains a need for effective critical scale control agents that can be produced simply and inexpensively, such as in aqueous solvent systems. The (meth)acrylic acid/itaconic acid copolymer is
In the past they have been produced in aqueous systems, but the use of such copolymers as scale inhibitors has not been published. Thus, U.S. Patent No.
The (meth)acrylic acid/itaconic acid copolymer of No. 3,308,067 is used as a detergent builder, while that of U.S. Pat. No. 3,366,509 is intended as a sizing agent;
And the copolymers of US Pat. No. 3,507,647 are used in lithography processes. UK application issued
G2054548A shows the use of (meth)acrylic acid/itaconic acid copolymers in the removal of boiler scale. Boss Marvel (Both
Marvel), J.Org.Chem., 24, 599 (1959) and Nagai, Polymer Chemistry, 17, 748.
(1960) describes a method for producing (meth)acrylic acid/itaconic acid polymers, but does not describe the uses of the resulting copolymers. All of these published processes involve conventional copolymerization using an aqueous medium and standard initiator systems that yield relatively high molecular weight copolymers. It is therefore a primary object of the present invention to provide a new process for the preparation of substantially homogeneous, controlled low molecular weight (meth)acrylic acid/itaconic acid copolymers which are particularly effective as critical scale inhibitors. It is. Substantially homogeneous low molecular weight copolymers of acrylic or methacrylic acid, or mixtures thereof, with itaconic acid are now prepared by separately and controlledly introducing (meth)acrylic acid monomers and polymerization initiators. It has been found that it can be easily produced by adding it to an aqueous solution of itaconic acid monomer. Accordingly, the present invention entails a process for producing a substantially homogeneous (meth)acrylic acid/itaconic acid copolymer having a number average molecular weight of 500 to 7000; 10 mole percent itaconic acid monomer in the presence of 5 to 90 mole percent acrylic or methacrylic acid monomer and 5 to 20 mole percent polymerization initiator, based on the total amount of the two monomers; Temperature 80 or more
contacting in an aqueous medium at 120°C for 2 to 8 hours, wherein the acrylic or methacrylic acid monomer and at least half the initiator are separately and essentially continuously in the medium during said period. Added to itaconic acid monomer in solution. In a preferred embodiment of this process, 95 to 60 mole percent itaconic acid monomer is copolymerized with 5 to 40 mole percent methacrylic acid monomer;
And the initiator is a redox system. Preferably, the itaconic acid monomer and 2 to 25 percent initiator are first dissolved in an aqueous medium, the remaining initiator is introduced during the polymerization period, and the resulting copolymer solution is After this addition 10 to 120
Hold at polymerization temperature for minutes. In a particularly preferred embodiment of this method, 5 to 40
The mole percent of methacrylic acid monomer is 1 to 2 mole percent of sodium persulfate and 6 mole percent of methacrylic acid monomer.
An aqueous solution of 95 to 60 mole percent itaconic acid monomer and 0.02 to 0.04 mole percent ferrous sulfate in 1 to 12 mole percent sodium bisulfite separately over 3 to 5 hours at normal pressure and reflux temperature. and add this solution to
Hold at temperature for 45 to 75 minutes. The present invention also provides substantially 5 to 90 mole percent acrylic or methacrylic acid units and 9
A substantially homogeneous copolymer comprising from 10 to 10 mole percent itaconic acid units and having a number average molecular weight of 500 to 7,000 is also entailed. The copolymer preferably has 5 to 40 mole percent methacrylic acid units and 95 to 60 mole percent itaconic acid units; it can be in the form of its alkali metal, ammonium or amine salts; and usually is this copolymer from 1 to
Exists as an aqueous solution containing 60% by weight. The invention further entails methods for preventing scale formation in water containing scale-forming impurities, such as seawater for seawater desalination processes.
The method consists of mixing an effective amount of the copolymer, preferably at a concentration of 0.5 to 10 ppm, with the water. The method may also preferably include adding something like sulfuric acid to the seawater in an amount to neutralize 55 to 85 percent of the bicarbonate alkalinity of the seawater. As described herein, the novel polymerization process of the present invention provides for the first time a virtually homogeneous,
Provides controlled low molecular weight copolymers. Moreover, these new copolymers exhibit improved scale inhibitor activity over prior art (meth)acrylic acid/itaconic acid copolymers, thereby reducing seawater flashing in the production of potable water. This means that they can be used more effectively when evaporating. Homogeneous copolymers are technically defined as compositions with narrow molecular weight distribution. This distribution is easily determined by analytical techniques such as high pressure liquid chromatography (HPLC) and is virtually monocentric for homogeneous copolymers. In contrast, heterogeneous copolymers have a characteristic binodal distribution, especially when the reactivities of the two monomers are very different, as is the case with (meth)acrylic acid and itaconic acid. . As determined by HPLC, the molecular weight distribution of the substantially homogeneous copolymers of the present invention is such that the ratio of weight average molecular weight (MW _W ) to number average molecular weight (MW _N ) is less than 3 and is substantially It is a single clause. In this method, 95 to 10 mole percent itaconic acid is combined with 5 to 90 mole percent of either acrylic acid or methacrylic acid in an aqueous medium, in the presence of a defined amount of polymerization initiator, and at a defined temperature and polymerization time. For copolymerization, the acrylic or methacrylic acid monomer and the initiator are added separately and simultaneously to the itaconic acid monomer. Acrylic acid and methacrylic acid are copolymerized with itaconic acid in virtually the same way and are therefore interchanged or mixed in this step.
For a given (meth)acrylic acid/itaconic acid molar ratio of copolymer, a product with virtually the same molecular weight and scale inhibitor properties can be provided. Since the process is carried out in an aqueous medium, considerable savings are realized in terms of solvent and processing costs, there is no problem of contamination of the product with solvents, and there is no problem of product isolation from the final reaction solution. The need is removed. The amount of water present during the polymerization is critical only to the extent that the reaction mixture remains in solution during the polymerization and is sufficiently concentrated to titrate the time and temperature process parameters. in this way,
Polymerization typically involves a monomer concentration that is slightly lower than the water solubility of both itaconic acid and the resulting copolymer;
Generally 0.75 to 100% water per gram of total monomer
gram range, would be carried out. Although the polymerization is preferably carried out in water alone, the presence of small amounts of water-soluble solvents is possible if desired. Any water-soluble free radical initiator can be used as the polymerization initiator in this step. Suitable initiators include persulfates such as sodium and potassium persulfates as well as redox systems. Redox systems such as ferrous sulfate/sodium persulfate/sodium bisulfite are preferred. The polymerization initiator must be present in an amount of 5 to 20 mole percent based on the total amount of monomers. All or at least half of the initiator is added separately from the (meth)acrylic acid monomer virtually continuously throughout the polymerization period. Preferably, 2 to 2 of the initiator
25 percent is dissolved in an aqueous medium along with itaconic acid, after which the remaining initiator is introduced as an aqueous solution over the course of the polymerization. The concentration of initiator in the aqueous additive solution is typically 5 to 25 weight percent. The temperature and duration of polymerization influence the properties of the resulting copolymer. Therefore, during the monomer addition period of 2 to 8 hours, the polymerization is
Limited to a temperature of 120°C. Polymerization at normal pressure and reflux temperature is preferred. Since the presence of a minimum amount of monomer in the final product is desired, the final polymerization solution is generally cooled for a period of time after the addition period of (meth)acrylic acid monomer and initiator. is 10 or so
Hold at polymerization temperature for 120 minutes. By selecting the above reaction parameters within the specified ranges, virtually homogeneous (meth)acrylic acid/itaconic acid copolymers with number average molecular weights of 500 to 7000, preferably 1000 to 4000 can be easily produced. be done. Thus, lower molecular weights can be obtained by using higher amounts of initiator and shorter addition times, higher temperatures and more dilute solutions. Conversely, higher molecular weights are achieved in more concentrated solutions at lower temperatures using smaller amounts of initiator and longer addition periods. Preferred embodiments of this process include copolymerizing 5 to 40 mole percent methacrylic acid with 95 to 60 mole percent itaconic acid. In a particularly preferred method, 5 to 40 mole percent methacrylic acid, 1 to 2 mole percent sodium persulfate, and 6 to 12 mole percent sodium bisulfite, 3 to 5 mole percent
was added separately over a period of time to an aqueous solution of 60 to 95 mole percent itaconic acid and 0.02 to 0.04 mole percent ferrous sulfate at normal pressure and reflux temperature, and the polymerization solution was added, following this addition, to an aqueous solution of 60 to 95 mole percent itaconic acid and 0.02 to 0.04 mole percent ferrous sulfate; and 75 minutes at reflux temperature. A substantially homogeneous copolymer consisting essentially of 5 to 90 mole percent acrylic or methacrylic acid units and 95 to 10 mole percent itaconic acid units and having a number average molecular weight of 500 to 7000 is prepared by evaporation followed by evaporation. It can be isolated in solid form from the final polymerization solution by standard techniques such as drying. However, since the copolymer will normally be added to an aqueous system, the final polymerization solution will generally be diluted or concentrated as needed to isolate the copolymer product. It will be used without. This solution can also be neutralized to form an aqueous solution of the alkali metal, ammonium or amine salt of the copolymer. Suitable alkali metal bases for neutralization include sodium hydroxide, potassium hydroxide, and lithium hydroxide, while suitable ammonium and amine bases include ammonia, ammonium hydroxide,
mono-, di- and trialkylamines having from 5 carbon atoms, pyridine, morpholine and lutidine. Essentially homogeneous (meth)acrylic acid of the invention/
Itaconic acid copolymer is a general limit scale -
It has inhibitory properties and is particularly useful in preventing the formation of alkaline calcium and magnesium scales in processes such as evaporative desalination of seawater. In such applications, the copolymer is present in an amount effective to prevent scale formation, typically at levels of 0.1 to 100 ppm and preferably 0.5 to 100 ppm.
10ppm, added to the water being treated. In such additions, an aqueous copolymer solution of 1 to 60 weight percent of the copolymer or its equivalent salt can be metered directly into the stream being treated, but Preferably it is diluted with water to a concentration of 0.1 to 1 weight percent before addition. Evaluation of these substantially homogeneous, controlled, low molecular weight copolymers
They have been shown to be superior to prior art (meth)acrylic acid/itaconic acid copolymers. Other additives commonly used in combination with critical scale inhibitors are also effective with the novel inhibitors of this invention. Particularly useful are mineral acids,
In particular, sulfuric acid, by means of which a part of the bicarbonate alkalinity present in the seawater etc. to be desalted is neutralized, the degree of bicarbonate neutralization usually being between 30 and 85
percent, especially 55 to 85 percent. For example, foam control agents, corrosion inhibitors, and oxygen scavengers can also be utilized with these novel scale inhibitors. The following examples are merely illustrative and should not be construed as limiting the invention, the scope of which is defined by the appended claims. ing. Example 1 130.1 g (0.70 mol) itaconic acid and 5.95 g
(0.025 mol) of sodium persulfate in 300 ml with a stirrer, reflux condenser and nitrogen inlet.
Dissolved in 100 ml of distilled water in a round bottom flask.
The system was purged with nitrogen and the solution was heated to reflux under a nitrogen atmosphere. 25.8g (0.30mol)
of methacrylic acid and an aqueous solution of 17.9 g (0.075 mol) of sodium persulfate in 60 ml of water were added continuously to this refluxing solution using a syringe pump over a period of 5 hours. Once the addition was complete, the solution was refluxed (103°C) for an additional 60 minutes. The solution thus obtained was then distilled at atmospheric pressure to remove 30 ml of water and yield a concentrate of 239.7 g of an orange solution containing 584 weight percent solids. This is based on the combined weight of the monomer charge and sodium persulfate initiator.
Expresses product yield in weight percent. The molecular weight distribution and chemical homogeneity of the polymer product was determined using 1N sodium hydroxide solution at pH 7.4.
using an acetate-phosphate buffered eluent adjusted to
A set of three 25cm60Å u-Porasil
Determined by high pressure liquid chromatography (HPLC) on a gel permeation tube, the Porasil tube contains 1,2,3,4-butanetetracarboxylic acid and guddolerite (of known molecular weight). Goodrite) Calibrated with K732 and K752 polyacrylic esters. This analysis showed that the product was a homogeneous copolymer with a number average molecular weight of 1600 and a weight average molecular weight of 2940. Example 2 Various acrylic acids/
Example 1 Using itaconic acid and methacrylic acid/itaconic acid monomer ratios and varying mole percent of sodium persulfate initiator relative to total monomers
The manufacturing method was repeated. The result was a virtually homogeneous copolymer product having the numbers and weight average molecular weights indicated for each example. Example 3 68 ml of water was added to the reactor of Example 1, stirred;
0.08 g (0.3 mmol) of ferrous sulfate heptahydrate and 39.0 g (0.30 mole) of itaconic acid were charged. The reactor was purged with nitrogen and the resulting solution was heated to reflux (100° C.) while maintaining a positive nitrogen atmosphere. 3.69 g (15.0 mmol) in 38 ml of water
of sodium persulfate, 9.92 g (95.0 mmol) of sodium bisulfite and 50.4 g in 30 ml of water
(0.70 mol) of icy acrylic acid,
Added continuously over 3.5 hours to the refluxing solution. Once the simultaneous additions were complete, the solution was kept at reflux for an additional 60 minutes. The resulting yellow solution contained 52.8 weight percent solids and weighed 205.6 g, representing a yield of 105.2 weight percent based on the reactants charged.
HPLC analysis of the product solution showed that the product was a substantially homogeneous (meth)acrylic acid/itaconic acid copolymer with a number average molecular weight of 2210 and a weight average molecular weight of 4460. Itaconic acid/acrylic acid molar ratio 70/30 and
Repeating this process using redox initiators of 1.5 mole percent sodium persulfate, 9.5 mole percent sodium bisulfite, and 0.03 mole percent ferrous sulfate resulted in a number average molecular weight of 900.
A substantially homogeneous (meth)acrylic acid/itaconic acid copolymer with a weight average molecular weight of 1910 was obtained with a product yield of 68.2 weight percent. Example 4 123.5g (0.95 mol) of itaconic acid was added to 47.6g of itaconic acid.
The procedure of Example 1 is repeated, except that it is copolymerized with 4.3 g (0.05 mole) of methacrylic acid at 80° C. in the presence of (20 mole percent) sodium persulfate. The icy methacrylic acid and sodium persulfate (as a 10 weight percent aqueous solution) are all added continuously in separate streams over 8 hours. Once the addition is complete, continue heating for an additional 10 minutes. A substantially homogeneous low molecular weight (meth)acrylic acid/itaconic acid copolymer similar to the copolymer of Example 1 is obtained. Comparative Example 1 CSMarvel and THSheph-
erd) Journal Organic Chemistry, Volume 24, No. 599
(meth)acrylic acid/itaconic acid copolymer (65/35 acrylic acid/
Itaconic acid) was prepared in water. A copolymer with a number average molecular weight greater than 8000 as determined by HPLC was obtained in high yield. Comparative Example 2 A (meth)acrylic acid/itaconic acid copolymer (50/50 acrylic acid/itaconic acid and methacrylic acid/itaconic acid) was produced according to the process described in Example 1 of U.S. Pat. No. 3,366,509. did. The methacrylic acid/itaconic acid copolymer interferes with isolation and interferes with scale control testing. Formed a rubbery gel in water. Acrylic acid/itaconic acid copolymer is
It was obtained in virtually quantitative yield and had a number average molecular weight greater than 10000 as determined by HPLC. Example 5 The methacrylic acid/itaconic acid and acrylic acid/itaconic acid copolymers of each of the previous examples were tested in a laboratory single-stage flash evaporator using synthetic seawater to determine their scale control effectiveness. It was determined. How to operate and test laboratory evaporators, Desalination, 31, 279 (1979)
It was as described by Auerbach and Carrushers. Synthetic seawater was used in the Office of Saline containing an increased bicarbonate content of 0.25g/Kg to increase the potential for scale formation.
It was the ``Standard Synthetic Seawater Composition'' by Water). The copolymer concentration in this test was 3 parts per million based on active solids. The results of the tests are summarized in table. Percent attached scale is calculated from the equation: % attached scale = 200 x mmol attached scale/mmol bicarbonate in brine. Copolymers that give a lower "% Adhesion Scale" at a given usage rate will give superior efficacy.

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Claims (1)

[Claims] 1. 95 to 10 mole percent itaconic acid monomer and 5 to 90 mole percent acrylic or methacrylic acid monomer, based on the total amount of the two monomers mentioned above. contacting in an aqueous medium at a temperature of 80 to 120° C. for 2 to 8 hours in the presence of a mole percent polymerization initiator, during which time the acrylic or methacrylic acid monomers and at least half of the initiator are separately and essentially continuously added to said itaconic acid monomer in solution in said medium, comprising: a substantially homogeneous number average molecular weight 500;
to 7000 (meth)acrylic acid/itaconic acid copolymer. 2 of the itaconic acid monomer and the initiator
The method of claim 1, wherein between 25 percent and 25 percent of the initiator is dissolved in the medium and the remainder of the initiator is introduced over the period of time. 3. The copolymer solution obtained is maintained at the above temperature for 10 to 120 minutes after the above addition.
Or the method described in Section 2. 4. The method according to claim 1, wherein the initiator is a redox agent. 5. The method of claim 1, wherein 95 to 60 mole percent of itaconic acid monomer is copolymerized with 5 to 40 mole percent of methacrylic acid monomer. 6 5 to 50 mole percent methacrylic acid monomer, 1 to 2 mole percent sodium persulfate, and 6 to 12 mole percent sodium bisulfite separately at normal pressure and reflux temperature.
adding over a period of time to an aqueous solution of 95 to 60 mole percent itaconic acid monomer and 0.02 to 0.04 mole percent ferrous sulfate, and after the addition, holding the solution at temperature for 45 to 75 minutes;
A method according to claim 1. 7. A substantially homogeneous copolymer consisting essentially of 5 to 90 mole percent acrylic or methacrylic acid units and 95 to 10 mole percent itaconic acid units and having a number average molecular weight of 500 to 7000. 8. A copolymer according to claim 7, having from 5 to 40 mole percent methacrylic acid units and from 95 to 60 mole percent itaconic acid units. 9. An underwater scale consisting of a substantially homogeneous copolymer consisting essentially of 5 to 90 mole percent acrylic or methacrylic acid units and 95 to 10 mole percent itaconic acid units and having a number average molecular weight of 500 to 7000. Anti-forming agent. 10 an effective amount of a substantially homogeneous copolymer consisting essentially of 5 to 90 mole percent acrylic or methacrylic acid units and 95 to 10 mole percent itaconic acid units, and having a number average molecular weight of 500 to 7000. , mixing with seawater containing scale-forming impurities and further adding to said seawater sufficient sulfuric acid to neutralize 55 to 85 percent of its bicarbonate alkalinity. A method for preventing scale formation in seawater containing impurities that form.