JP6542966B1 - Scale inhibitor and method for producing the same and method for preventing scale - Google Patents

Abstract

An object of the present invention is to provide a scale inhibitor which efficiently prevents scale formation in a digestion process in pulp production, a method for producing the same, and a method for preventing the scale.
The anti-scaling agent of a digestion process characterized by having a weight average molecular weight of 15,000 to 25,000 polyitaconic acid and / or polyitaconic acid salt, a method for producing the same, and a method for preventing the scale.
【Selection chart】 None

Description

  The present invention relates to a scale inhibitor used in a pulping and digesting process, a method for producing the same, and a method for preventing scale. In the present specification and claims, the digestion step includes the step of digesting the pulp with a digester as well as the step of recovering black liquor produced from the digester.

  At the time of pulp production, much calcium and silica are eluted from the wood which is the raw material, and calcium and silica are also supplied from the water used, so the concentration of calcium and silica in the water system is high, and the scale Is easy to generate. Above all, in the digesting process, pulping treatment is carried out at a high temperature of 100 ° C. or more using a strongly alkaline white liquor mixed with sodium hydroxide and sodium sulfide, and calcium salts and silicates contained in wood are white liquor Since it is easy to dissolve in, heat-exchange of the heater is achieved by attaching a scale containing calcium carbonate, for example, mainly calcium carbonate, to the inner wall of the digester and the screen of the accessory, heater, washer and screen wire. It causes various problems such as failure, reduced filtration and dewatering efficiency, and reduced washability.

  As a method of removing such adhesion scale, the operation is periodically stopped to mechanically separate and remove mechanically, or the piping and devices are immersed in the cleaning solution to circulate the cleaning solution to separate and remove the scale. It is This work is usually performed once every 3 to 6 months, and requires 1 to 2 days in one work. However, even if such adhesion scale separation and removal is performed regularly, scale adhesion may occur suddenly, causing problems such as dehydration failure due to pipe blockage and screen clogging, which hinders the operation, resulting in energy costs. Can lead to For this reason, adding a scale inhibitor to process water is also performed.

  Conventionally, it is known to add low molecular weight polyitaconic acid or its salts to process water as a scale prevention method of various processes. For example, Patent Document 1 describes that polyitaconic acid having a weight average molecular weight of 500 to 2000 and a salt thereof are added to an aqueous system to prevent scale. Further, Patent Document 2 shows that a mixed solution of polyitaconic acid and phosphonic acids is effective as a scale inhibitor for a paper pulp manufacturing process, and in particular, it is shown that polyitaconic acid having a molecular weight of 500 to 5,000 is preferable. There is.

Japanese Patent Application Laid-Open No. 58-174295 JP 2011-52358 A

  However, when the present inventors used the above-mentioned conventional low molecular weight polyitaconic acid as a scale inhibitor in the digestion process of pulp production, they found a problem that a sufficient scale prevention effect could not be obtained. The present invention has been made in view of this conventional situation, and an object of the present invention is to provide a scale inhibitor capable of exhibiting a sufficient scale preventing effect even in a digestion step, a method for producing the same and a method for preventing the scale. There is.

  As a result of intensive studies to solve the above problems, the present inventors surprisingly found that high-molecular-weight polyitaconic acid, which was conventionally considered to be inferior in scale-preventing effect, prevents scale in the cooking process in pulp production. It has been found that it is preferable, and the present invention has been completed.

  That is, the scale inhibitor of the present invention is a scale inhibitor used in a digestion process in pulp production, and is characterized by containing a polyitaconic acid and / or a polyitaconate having a weight average molecular weight of 15,000 to 25,000. .

  The scale inhibitor of the present invention preferably further contains phosphonic acid and / or phosphonic acid salt. By coexistence of phosphonic acid and / or phosphonic acid salt, the scale preventing effect can be further improved.

  Moreover, it is preferable that the weight ratio of polyitaconic acid and / or polyitaconate and phosphonic acid and / or phosphonate is 9: 1 to 4: 6. The inventor has found in this range an excellent scale inhibition effect in the cooking process.

  Furthermore, in the scale inhibitor of the present invention, phosphonic acid and / or phosphonic acid salt can be 1-hydroxyethane-1,1-diphosphonic acid.

  In the scale inhibitor of the present invention, the degree of dispersion (Mw / Mn), which is the ratio of the weight average molecular weight Mw to the number average molecular weight Mn of polyitaconic acid and / or polyitaconate, is preferably 3 or less. Within this range of the degree of dispersion, an excellent scale preventing effect can be exhibited.

The scale inhibitor of the present invention is a method for producing the scale inhibitor of the present invention,
It is characterized in that it contains polyitaconic acid and / or polyitaconic acid salt obtained by polymerizing itaconic acid using ammonium persulfate as a polymerization initiator.

  The method for preventing scale of the present invention is characterized in that the antiscalant of the present invention is added to the process water of the digestion step in pulp production. Thereby, it can prevent that a scale adheres to piping etc.

The scale inhibitor of the present invention is used in the digestion step in pulp production. Here, pulp production means production of wood pulp and non-wood pulp, and does not include production of waste paper pulp produced from waste paper. Specifically, it refers to the production of kraft pulp, sulfite pulp, soda pulp and the like. In these pulp production, as a digestion step, wood (or non-wood) chips are boiled in a chemical solution in a digester to remove lignin, and the pulp is dispersed in the chemical solution. The chemical solution is separated, concentrated and incinerated for recovery (black liquor recovery process), but in this specification, the black liquor recovery process is also included in the digestion process.
Therefore, the scale inhibitor of the present invention is used to remove scales not only for these pulp digests but also for equipment and facilities with which process water in black liquor recovery is in contact. As such equipment / equipment, specifically, chip bin and chip transport device and residual heat device, white liquor supply line, digester (inner wall of digester), digester extraction strainer and extractor line of digester, extracted digester again A heat exchanger and a cooking liquid circulation line for use as a cooking liquid, filters of an extraction line and a circulation line, piping, a liquid feed pump (feeder) and the like can be mentioned.

  The process water in the present invention refers to the white liquor of the cooking process, the cooking liquor in the digester, the infiltration zone of the digester, the cooking liquor extracted from the cooking zone and the washing zone, and the extracted cooking liquor as cooking liquor again And the temperature is 100.degree. C. or higher.

  The scales targeted by the present invention include scales of calcium compounds such as calcium carbonate, calcium phosphate, calcium silicate, calcium sulfate and calcium oxalate, or composite scales containing calcium compounds as main components. By applying the anti-scaling agent and the anti-scaling method of the present invention, the formation and adhesion of the scale are hindered, and even when it is attached, it becomes an amorphous scale that is easy to remove.

  It is essential that the polyitaconic acid and / or polyitaconic acid salt used in the present invention have an average molecular weight of 15,000 or more and 25,000 or less, and when itaconic acid is produced according to the radical polymerization method of the polymerizable ethylenic compound. An aqueous solution containing 10 to 40% by weight of itaconic acid is heated to 50 to 90 ° C., and ammonium persulfate is added as a polymerization initiator to polymerize.

  Examples of polyitaconic acid salts used in the present invention include alkali metal salts of polyitaconic acid, and examples of alkali metal salts include sodium salts and potassium salts. Other salts include, for example, ammonium salts of polyitaconic acid, partially neutralized salts such as amine salts, and completely neutralized salts.

  As the polymerization initiator used in the present invention, generally, azobis compounds such as azobisisobutyronitrile (AIBN), azobis-2,4-dimethylvaleronitrile, sodium persulfate, potassium persulfate, ammonium persulfate, peroxide Hydrogen, cumene peroxide, di-tert-butyl hydroperoxide and the like can be used, and from the viewpoint of preventing the formation of scale, the initiator used is preferably ammonium persulfate. Moreover, when adjusting a dispersion degree, you may add a chain transfer agent as needed. Specific examples of the chain transfer agent include thiol-based chain transfer agents such as mercaptoethanol, 2-mercaptopropionic acid, 3-mercaptopropionic acid and n-dodecyl mercaptan; carbon tetrachloride, methylene chloride, bromoform, bromotrichloroethane and the like. , Halides; secondary alcohols such as isopropanol and glycerin; phosphorous acid, hypophosphorous acid, and salts thereof (sodium hypophosphite, potassium hypophosphite, etc.); sulfite, bisulfite, dithione Acid salt, meta bisulfite, sulfite, thiosulfate (specifically, sodium bisulfite, potassium bisulfite, sodium dithionite, potassium dithionite, sodium metabisulfite, potassium metabisulfite etc.) Can be mentioned. Although the addition amount of the chain transfer agent is not particularly limited, it is preferably 1 to 10 g with respect to 1 mol of all the monomer components. The molecular weight of the obtained polymer can be measured by high performance liquid chromatograph or the like.

  The weight average molecular weight of the polyitaconic acid and / or polyitaconic acid salt used in the present invention is essentially 15,000 or more and 25,000 or less, and exhibits an excellent scale preventing effect in this molecular weight range. When the weight average molecular weight is less than 15,000 or the weight average molecular weight exceeds 25,000, the scale preventing effect is insufficient. In the past, when using polyitaconic acid as a scale inhibitor, those with a low molecular weight of 500 to 5000 have been preferred (Patent Document 2), but scale prevention of polyitaconic acid in scale prevention in the cooking process of pulp production When used as an agent, it has been found that the weight average molecular weight is preferably 15,000 or more and 25,000 or less. Thus, in scale prevention in the cooking process of pulp production, although the reason why the scale prevention in the other processes and the suitable molecular weight range differ greatly is not clear yet, the temperature of process water in the digestion process is usually 100. It is presumed that the high temperature of at least ° C. is a factor.

  As the phosphonic acid and / or phosphonic acid salt used in the present invention, aminotrimethylenephosphonic acid (ATMP), 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP), diethylenetriaminepentamethylenephosphonic acid (DETPMP), Hexamethylenediamine tetramethylene phosphonic acid (HMDTMP), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC), and their water-soluble salts, and their water-soluble salts are sodium salts, potassium salts, ammonium salts And amine salts. The phosphonic acid and / or phosphonic acid salt used from the viewpoint of preventing the formation of scale is preferably 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP). Also, usually, these compounds are commercially available in the form of an aqueous solution.

  In the scale inhibiting agent of the present invention, when polyitaconic acid and / or polyitaconate is allowed to coexist with phosphonic acid and / or phosphonate, the weight of polyitaconic acid and / or polyitaconate and phosphonic acid and / or phosphonate is The ratio is preferably 9: 1 to 4: 6, more preferably 8: 2 to 6: 4.

  In the present invention, the degree of dispersion is the ratio of weight average molecular weight Mw to number average molecular weight Mn (Mw / Mn), and the closer this value is to 1, the more uniform the molecular weight distribution. In the scale inhibitor of the present invention, it is preferable that the polyitaconic acid and / or polyitaconate have a dispersion degree of 3 or less.

  The method for preventing scale of the present invention is a method for preventing scale of a cooking process in which the scale inhibitor of the present invention is added to the process water of the cooking process in pulp production. The anti-scaling agent may be diluted with water as needed for handling.

  Although the addition amount of the scale inhibitor of the present invention in the scale prevention method of the present invention differs depending on the generation degree of the scale, the operation condition of the apparatus, etc., it can not be determined uniformly. L, preferably 1 to 300 mg / L, more preferably 10 to 200 mg / L.

  The place of addition of the scale inhibitor of the present invention in the scale prevention method of the present invention may be directly added to the place or process where the scale is produced, or the process water upstream from the place and / or the circulating downstream You may add to the part. Addition is continuous addition or intermittent addition with a pump.

  In addition, when adding the scale inhibitor of the present invention, other polymers, surfactants, chelating agents, retention agents, pitch control agents, slime control agents, corrosion inhibitors, antiseptic agents, as long as the effects of the present invention are not impaired. You may add a foaming agent etc. simultaneously. In addition, the components of these additives can be blended into the scale inhibitor of the present invention as long as the effects of the present invention are not impaired.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

[Synthesis of polyitaconic acid and polyacrylic acid]
Polyitaconic acid (Synthesis examples 1 to 6), sodium polyitaconate (Synthesis example 10) and polyacrylic acid (Synthesis examples 7 to 9) were synthesized by the methods described below.

[Production of Synthesis Example 1]
60 g of itaconic acid and 270 g of water were added to a 500 ml four-necked flask with a glass reflux tube, a nitrogen vent tube, a dropping funnel and a stirrer, and a 48% aqueous sodium hydroxide solution was gradually added while cooling under stirring. . The amount of sodium hydroxide added is such that most of the produced polyitaconic acid is present as free acid. The solution was heated to 70 ° C., and 3.7 g of ammonium persulfate as a polymerization initiator was added under stirring while maintaining the solution temperature to start the reaction. After continuing the reaction for 6 hours, the temperature was raised to 90 ° C., maintained for another hour, and cooled to obtain polyitaconic acid of Synthesis Example 1. As a result of measuring the residual monomer concentration by ion chromatography, it was confirmed that the unreacted monomer was less than 0.1% by weight, and the reaction rate was substantially 100%.

As a result of measuring the weight average molecular weight of polyitaconic acid of Synthesis Example 1 by HPLC (high performance liquid chromatograph) set as the following conditions, the weight average molecular weight was 15,000.
Measuring instrument: LC-2000 Plus (manufactured by JASCO Corporation)
Pump: PU-2086 (manufactured by JASCO Corporation)
Detector: RI-2031 (manufactured by JASCO Corporation)
Column: Waters Ultra Hydrogel 250 (manufactured by Waters)
Eluent: 0.1 M NaNO ₃
Flow rate: 1.0 ml / min

[Production of Synthesis Example 2]
The polyitaconic acid of Synthesis Example 2 described in Table 1 was obtained by the same production method as in Synthesis Example 1 except that ammonium persulfate was changed to 3.1 g in order to adjust the molecular weight.

[Production of Synthesis Example 3]
Polyitaconic acid of Synthesis Example 3 described in Table 1 was obtained by the same manufacturing method as that of Synthesis Example 1 except that ammonium persulfate was changed to 2.0 g in order to adjust the molecular weight.

[Production of Synthesis Example 4]
Polyitaconic acid of Synthesis Example 4 described in Table 1 was obtained by the same manufacturing method as Synthesis Example 1 except that ammonium persulfate was changed to 4.6 g in order to adjust the molecular weight.

[Production of Synthesis Example 5]
Polyitaconic acid of Synthesis Example 5 described in Table 1 was obtained by the same production method as in Synthesis Example 1 except that ammonium persulfate was changed to 4.2 g in order to adjust the molecular weight.

[Production of Synthesis Example 6]
Polyitaconic acid of Synthesis Example 6 described in Table 1 was obtained by the same production method as in Synthesis Example 1 except that ammonium persulfate was changed to 1.5 g in order to adjust the molecular weight.

[Production of Synthesis Example 7]
The polyacrylic acid of Synthesis Example 7 described in Table 1 was obtained by the same production method as in Synthesis Example 1 except that itaconic acid was changed to acrylic acid.

[Production of Synthesis Example 8]
A polyacrylic acid of Synthesis Example 8 described in Table 1 was obtained by the same production method as in Synthesis Example 2 except that itaconic acid was changed to acrylic acid.

[Production of Synthesis Example 9]
A polyacrylic acid of Synthesis Example 9 described in Table 1 was obtained by the same production method as in Synthesis Example 3 except that itaconic acid was changed to acrylic acid.

[Production of Synthesis Example 10]
Sodium hydroxide of a neutralization equivalent was added to polyitaconic acid of the synthesis example 2, and sodium polyitaconate of the synthesis example 10 of Table 1 was obtained.

[Test method for preventing scale]
Example 1
In a 1 L pressure vessel, 800 ml of simulated cooking liquor (4% sodium hydroxide, 2% sodium carbonate, 4% sodium sulfide, 90% deionized water) was charged, sealed, and temperature raising was started while stirring. After the liquid temperature reached 150 ° C., 20 mg / L of polyitaconic acid of Synthesis Example 1 as a total of active ingredients was added to the simulated cooking liquor, and mixed with stirring. Next, calcium chloride was added so as to be 100 ppm as a calcium ion, stirring was continued as it was for 60 minutes, heating was stopped, and cooling was performed to room temperature to complete the test.

  The test solution after the scale prevention test was filtered with No. 5 C filter paper, and calcium hardness was calculated by the method of JIS-K0101.

The scale prevention ratio of Example 1 was calculated by the following equation, and the results are shown in Table 1. The calcium hardness was 0 when no scale inhibitor was added.
Scale prevention rate (%) = 1-((C-B) / (C-A)) x 100
A: Calcium hardness without addition of scale inhibitor (mg CaCO ₃ / l)
B: Calcium hardness at the time of the addition of the scale inhibitor of Synthesis Example 1 (mg CaCO ₃ / l)
C: Calcium hardness added (mg CaCO ₃ / l)

(Examples 2 to 4 and Comparative Examples 1 to 6)
The scale prevention test was carried out in the same manner as in Example 1 using polyitaconic acid of Synthesis Examples 2 to 6, sodium polyitaconate of Synthesis Example 10 and polyacrylic acid of Synthesis Examples 7 to 9. Table 1 describes the results of the scale inhibition test.

  The following is apparent from Examples 1 to 4 and Comparative Examples 1 to 6 shown in Table 1.

When polyitaconic acid having a weight average molecular weight of 15,000 to 25,000 as in Examples 1 to 3 was used, the scale prevention ratio of calcium carbonate was as high as 60% or more. On the other hand, even when it is polyitaconic acid as in Comparative Examples 1 to 3, when the weight average molecular weight is less than 15,000 and more than 25,000, the scale prevention ratio is 35% or less. Moreover, even if the weight average molecular weight is 15,000 to 25,000 as in Comparative Examples 4 to 6, in the case of polyacrylic acid, the scale prevention ratio is 30% or less, and it is a polyitaconic acid having a weight average molecular weight of 15,000 to 25,000. Only, the unique effect of the present invention that a high scale prevention effect is obtained is clarified.
Further, it was found from the comparison between Example 2 and Example 4 that even when sodium polyitaconate is used instead of polyitaconic acid, a good scale preventing effect can be obtained.

[Synthesis of polyitaconic acid]
Polyitaconic acid (Synthesis examples 11 to 13) was synthesized by the method shown below.

[Production of Synthesis Example 11]
Polyitaconic acid of Synthesis Example 11 described in Table 2 was obtained in the same manner as in Synthesis Example 2 except that ammonium persulfate as a polymerization initiator was changed to sodium persulfate.

[Production of Synthesis Example 12]
Polyitaconic acid of Synthesis Example 12 described in Table 2 was obtained by the same manufacturing method as that of Synthesis Example 2 except that ammonium persulfate as a polymerization initiator was changed to potassium persulfate.

[Production of Synthesis Example 13]
Polyitaconic acid of Synthesis Example 13 described in Table 2 was obtained in the same manner as in Synthesis Example 2 except that ammonium persulfate as a polymerization initiator was changed to azobisisobutyronitrile.

(Examples 5 to 7)
The scale prevention test was implemented similarly to Example 1 using the polyitaconic acid of the synthesis examples 11-13 which changed the kind of polymerization initiator. Table 2 describes the results of the scale inhibition test. As a control, Example 2 and Comparative Examples 2, 3 and 5 were described.

  The following is apparent from Examples 2, 5 to 7 and Comparative Examples 2, 3 and 5 shown in Table 2.

  When the polymerization initiator is changed as in Examples 2 and 5 to 7, the scale inhibition ratio of calcium carbonate is 50% or more in any of Comparative Examples 2, 3 and 5 using a polymer other than the present invention. In comparison, it showed high scale prevention effect. Among them, as in Example 2, in the case of polyitaconic acid using ammonium persulfate as the polymerization initiator, the scale prevention rate is 65%, and the scale prevention effect was most excellent. The scale preventing effect changed depending on the type of the polymerization initiator, and it was found that the scale preventing effect is excellent particularly when ammonium persulfate is used.

[Preparation of scale inhibitor]
According to the composition described in Table 3, the scale inhibiting agent used for Examples 8-16 and comparative examples 7-14 was prepared.

(Examples 8 to 16 and Comparative Examples 7 to 14)
In the same manner as Example 1, a scale prevention test was conducted. Table 3 describes the results of the scale inhibition test. In addition, Example 2 was described as a control.

  The following is apparent from Examples 2, 8 to 16 and Comparative Examples 7 to 14 shown in Table 3.

When phosphonic acid is further contained in the polyitaconic acid of the present invention (Example 2) as in Examples 8 to 14, the scale prevention ratio of calcium carbonate is 79% or more, which is higher than that of Example 2. It showed the effect. On the other hand, in Comparative Examples 7 to 12 in which the polymers other than the present invention contained phosphonic acid, the scale inhibition ratio of calcium carbonate was 50% or less. Further, when only phosphonic acid is used as in Comparative Examples 13 and 14, the scale prevention ratio of calcium carbonate is 0%, and the scale prevention effect is improved only when phosphonic acid is contained in the polyitaconic acid of the present invention. Unique synergy effect was shown.
Moreover, when the weight ratio of polyitaconic acid and phosphonic acid was 9: 1 to 4: 6 as in Examples 8 to 13, the scale prevention ratio was 86% or more. Furthermore, as in Examples 9 to 11, when the weight ratio is 8: 2 to 6: 4, the scale inhibition ratio is as high as 95%, which is shown to be preferable.
Also, from the comparison of Example 11 and Example 15, it was found that even when sodium salt of HEDP is used as the phosphonic acid instead of HEDP, the same good scale prevention effect can be obtained.
Furthermore, it was found from Example 16 that the combination of sodium polyitaconate and the sodium salt of HEDP also gave a good scale prevention effect.

[Preparation of scale inhibitor]
The scale inhibitors used in Examples 17-20 were prepared according to the formulations described in Table 4.

(Examples 17 to 20)
In Examples 17 to 20, in the case of Example 1 using various phosphonic acids shown in Table 4 instead of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) used as the phosphonic acid in Example 11 Similar to the above, the scale prevention test was conducted. Table 4 describes the results of the scale inhibition test. In addition, the result of Example 11 is described as a control.

  From Examples 11, 17 to 20 shown in Table 4, the following is clear.

  As in Examples 11 and 17 to 20, the scale inhibition ratio of calcium carbonate was 80% or more regardless of which phosphonic acid was used. Among them, as in Example 11, when HEDP was used as the phosphonic acid, the scale inhibition rate was 95%, indicating that HEDP is particularly preferable.

[Synthesis of polyitaconic acid]
Polyitaconic acid (Synthesis example 14) was synthesized by the method shown below.

[Production of Synthesis Example 14]
Polyitaconic acid of Synthesis Example 14 was obtained in the same manner as in Synthesis Example 2 except that 1.1 g of 2-mercaptopropionic acid as a chain transfer agent was added to adjust the degree of dispersion. The weight average molecular weight and the degree of dispersion were measured, and the results are shown in Table 5.

[Preparation of scale inhibitor]
The scale inhibitors used in Example 22 were prepared according to the formulations described in Table 5.

(Examples 21 and 22)
In the same manner as Example 1, a scale prevention test was conducted. Table 5 describes the results of the scale inhibition test. In addition, the result of Example 2, 11 was described as a control.

  From Examples 2, 11, 21 and 22 shown in Table 5, the following is apparent.

When the degree of dispersion was 3 or less as in Examples 2 and 21, the scale prevention ratio of calcium carbonate was 65% or more in all cases, and showed a high scale prevention effect. Among them, as in Example 21, when the degree of dispersion is 2 or less, the scale prevention rate is 71%, and the scale prevention effect is most excellent. By the degree of dispersion, the unique effect of the present invention in which the scale prevention effect is changed is clarified.
Further, when phosphonic acid was added to polyitaconic acid as in Example 11 and Example 22, the scale prevention rate was improved to 95% or more, and a synergistic effect was shown.

By applying the scale inhibitor of the present invention and the method for producing the same and the method for preventing the scale to the digestion step in pulp production, scale formation can be efficiently prevented, so the frequency of operation troubles and shutdowns due to scale adhesion in the step It is possible to greatly reduce the energy consumption.

Claims (8)

A scale inhibitor used in the digestion process (but excluding green liquor production process) in pulp production,
A scale inhibitor comprising polyitaconic acid and / or polyitaconate having a weight average molecular weight of 15,000 or more and 25,000 or less obtained by polymerizing itaconic acid using ammonium persulfate as a polymerization initiator. The scale inhibitor according to claim 1, wherein polyitaconic acid and / or polyitaconate having a weight average molecular weight outside the range of 15,000 or more and 25,000 or less is not mixed. Furthermore, phosphonic acid and / or phosphonate is contained, The scale inhibiting agent of Claim 1 or 2 characterized by the above-mentioned. The scale inhibitor according to claim 3 , wherein the weight ratio of polyitaconic acid and / or polyitaconate to phosphonic acid and / or phosphonate is 9: 1 to 4: 6. The scale inhibitor according to claim 3 or 4 , wherein the phosphonic acid and / or the phosphonic acid salt is 1-hydroxyethane-1,1-diphosphonic acid. The dispersion degree (Mw / Mn) which is a ratio of the weight average molecular weight Mw and the number average molecular weight Mn of the polyitaconic acid and / or the polyitaconic acid salt is 3 or less. The scale inhibitor according to item 1. A method for producing the scale inhibitor according to claim 1, wherein
A method of producing a scale inhibitor, which comprises containing polyitaconic acid and / or polyitaconic acid salt having a weight average molecular weight of 15,000 to 25,000 obtained by polymerizing itaconic acid using ammonium persulfate as a polymerization initiator. . A scale preventing method in a cooking process characterized by adding the scale inhibitor according to any one of claims 1 to 6 to process water of a cooking process (but excluding green liquor manufacturing process) in pulp production.