JPH11131381A - Corrosion inhibitor for digester and / or black liquor canister in kraft pulp manufacturing process and method of inhibiting corrosion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corrosion inhibitor effective for suppressing corrosion of a digester and a black liquor concentrator in a kraft pulp manufacturing process, and a corrosion inhibitor method using the same. SOLUTION: One or more unsaturated carboxylic acid monomers selected from acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride and alkali metal salts and ammonium salts thereof, 1 selected from 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, and alkali metal salts and ammonium salts thereof.
The unsaturated sulfonic acid-based monomer is composed of at least 70 to 99 mol% of the unsaturated sulfonic acid-based monomer and 1 to 30 mol% of the unsaturated sulfonic acid-based monomer. A corrosion inhibitor for a digester and / or a black liquor concentrator in a kraft pulp manufacturing process, characterized by containing a water-soluble copolymer, A method for inhibiting corrosion of a digester and / or a black liquor concentrator added in the range of 1 to 100 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a corrosion inhibitor for a black liquor concentrator for concentrating a digester and / or a cooking liquor (hereinafter referred to as "black liquor") in a kraft pulp manufacturing process of the paper and pulp industry. The present invention relates to these corrosion control methods.

[0002]

2. Description of the Related Art Kraft pulp is made by boiling wood chips as a raw material in a cooking liquor containing sodium hydroxide and sodium sulfide at a high temperature and a high pressure to elute ligulin contained in the wood. It is manufactured by The cooking liquor is used by diluting white liquor, in some cases with black liquor, and has a cooking temperature of about 170 ° C. The composition of the white liquor is approximately sodium hydroxide 55 to 100.
g / L, 18 to 45 g / L of sodium sulfide, and 10 to 30 g / L of sodium carbonate (all in terms of Na ₂ O). On the other hand, the waste liquid after digestion is called black liquor, and sodium hydroxide, sodium sulfide, sodium carbonate, sodium polysulfide, sodium sulfate, sodium thiosulfate,
It contains inorganic salts such as sodium sulfite and sodium chloride.
After being concentrated to 75%, it is incinerated in a recovery boiler. As described above, the digester and the black liquor concentrator are exposed to an aqueous solution containing a large amount of salts at a high temperature, and cause severe corrosion of the material of the apparatus, particularly carbon steel.

[0003] Therefore, as a means for suppressing this corrosion, a method such as stainless steel lining or passivation of carbon steel by adding polysulfide has been adopted.

[0004]

However, even with the above-mentioned improved method, the corrosion of the digester and the black liquor can has not been satisfactorily suppressed, and a more effective corrosion control measure is desired. I have. An object of the present invention is to solve such an unsolved problem, and it is an object of the present invention to provide a corrosion inhibitor for a digester kama, a black liquor concentrating can in a kraft pulp manufacturing process, and a method for inhibiting these corrosions. .

[0005]

The inventor of the present invention intends to establish a method for suppressing corrosion in a digester kama and a black liquor can in a kraft pulp manufacturing process. As a result of intensive studies on a corrosion inhibitor exhibiting the following effects and a method for inhibiting the corrosion of digesters and black liquor cans using the same, it was found that a specific unsaturated carboxylic acid monomer and a specific unsaturated sulfonic acid monomer were used. The inventors have found that a water-soluble copolymer containing a monomer as a main component exhibits a high corrosion inhibiting effect, and have completed the present invention.

That is, the present invention relates to acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride and alkali metal salts thereof,
At least one unsaturated carboxylic acid monomer selected from ammonium salts, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid and alkali metal salts thereof, ammonium One or more unsaturated sulfonic acid-based monomers selected from salts as a main component, the unsaturated sulfonic acid-based monomer is 1 to 30 mol% of all monomers, and the weight average molecular weight is 5
A corrosion inhibitor for a digester and / or a black liquor concentrator in a kraft pulp manufacturing process, characterized in that the kraft pulp production process is characterized in that the kraft pulp is a corrosion inhibitor. A method for inhibiting corrosion of a digester in a kraft pulp production process, wherein 1 to 100 ppm of the corrosion inhibitor according to claim 1 is added to the digester white liquor in the production process. A method for inhibiting corrosion of a black liquor concentrate in a kraft pulp production process, which comprises adding 1 to 100 ppm of the corrosion inhibitor for a black liquor concentrate can according to claim 1 to black liquor in a kraft pulp production process. is there.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The water-soluble copolymer of the present invention can be obtained by polymerizing an unsaturated carboxylic acid (including its anhydride) monomer and an unsaturated sulfonic acid monomer as main components. Unsaturated carboxylic acid monomers include acrylic acid,
Methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride and at least one selected from alkali metal salts and ammonium salts thereof. Examples of the alkali metal salts include sodium salts and potassium salts. ,
Examples of the ammonium salt include salts with amines such as ammonia, monomethylamine, dimethylamine, monoethylamine, and diethylamine.

On the other hand, the unsaturated sulfonic acid monomer is 2-
Acrylamide-2-methylpropanesulfonic acid, 2-
Methacrylamide-2-methylpropanesulfonic acid, and at least one selected from alkali metal salts and ammonium salts thereof. Examples of the alkali metal salts include sodium salts and potassium salts, and ammonium salts include ammonia. , Monomethylamine, dimethylamine, monoethylamine, diethylamine and the like.

[0010] In the water-soluble copolymer of the present invention, the unsaturated sulfonic acid-based monomer accounts for 1 to 30 mol% of the entire monomer.
It is 5 mol%, more preferably 5 to 20 mol%.
Unsaturated sulfonic acid monomer is 1 to 30 mol% of all monomers
In addition, the effects intended by the present invention are not sufficiently exhibited, and are not practical.

The water-soluble copolymer of the present invention does not prevent inclusion of other unsaturated compounds as long as the effects of the present invention are not impaired.

The water-soluble copolymer of the present invention has a weight average molecular weight of 500 to 20,000, preferably 10 to 20,000.
00 to 15,000, more preferably 2,000 to 1
It is 0000. If the weight-average molecular weight is less than 500 or greater than 20,000, the corrosion-preventing effect is reduced and is not practical.

These constituents, composition ratios and molecular weights have been determined as optimal ranges as a result of the studies of the present inventors, and some of them have some effects outside this range, but from an economical point of view. It is not efficient.

The method for producing the polymer of the present invention is not particularly limited. For example, an unsaturated carboxylic acid monomer and an unsaturated sulfonic acid monomer may be used in a free state or in an alkali metal. It is carried out by subjecting to a polymerization reaction as a salt or an ammonium salt. Maleic acid,
Itaconic acid may each be subjected to the polymerization reaction as an anhydride.

The polymerization initiator used in the polymerization of the present invention is:
Although it does not limit the present invention because it varies depending on the polymerization conditions, any substance capable of decomposing under the polymerization conditions to generate free radicals may be used, such as sodium persulfate, hydrogen peroxide, chlorine peroxide, and butylhydrogen. Examples include peroxides such as peroxides and azo compounds such as azobisisobutyronitrile. The amount of the polymerization initiator used depends on the type of polymerization initiator used and the polymerization conditions. For example, in the case of hydrogen peroxide, the amount is 0.5 to 10 mol%, preferably 1 to 5 mol%, based on the amount of the unsaturated monomer. is there.

As a solvent used in the polymerization, water is preferably used, but an organic solvent such as alcohols and dioxane can be used alone or in a water-organic solvent mixed system.

The polymerization temperature is preferably from 80 to 110 ° C.
If the polymerization is carried out at a temperature lower than 80 ° C., a large amount of unreacted monomers may remain, which is not preferable.

When the corrosion inhibitor of the present invention is applied, the amount of the additive added is 1 to white liquor for inhibiting corrosion of the digester.
From 100 ppm, preferably from 2 to 80 ppm, more preferably from 5 to 50 ppm, and more preferably from 1 to 100 ppm, preferably from 2 to 80 ppm, more preferably from 5 to 50 ppm, based on the black liquor for inhibiting corrosion of the black liquor concentration can. It is 50 ppm. Addition amount is 1 for both digesters and black liquor cans
If it is less than ppm, the effect intended by the present invention is not sufficient,
Addition of more than 100 ppm has a sufficient effect, but does not improve the effect in proportion to the amount added, which is not preferable from an economic viewpoint.

The method of adding the corrosion inhibitor of the present invention to a digester or a black liquor concentrator is not particularly limited. Is added during. In the case of a black liquor concentrating can, it is convenient in operation to add it directly into the black liquor concentrating can or into the liquid discharged from the pulp digester and entering the black liquor concentrating can. The corrosion inhibitor of the present invention is also effective in controlling the scale mainly composed of calcium carbonate. Therefore, when it is added to the circulating white liquor of the pulp digester, it can be advantageous that not only the scale of the digester but also the corrosion can be suppressed. However, the corrosion inhibitor added to the white liquor circulating in the digester adheres to the pulp and is sent to the papermaking process, and the concentration of the corrosion inhibitor remaining in the liquor entering the black liquor concentrator becomes extremely low. It needs to be added directly to the liquor or into the liquor from the pulp digester to the black liquor canister.

Further, as long as the original object of the present invention is achieved, there is no limitation on the use of additives of other optional components.

[0021]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

[Production of Polymer] Production of Polymer-G: To a 500 mL five-necked flask, 34.0 g (0.35 mol) of maleic anhydride and 50 g of water were added, and a 50% aqueous sodium hydroxide solution was added thereto. The maleic anhydride was dissolved slowly to adjust the pH to 6. The atmosphere in the flask was set to a nitrogen gas atmosphere, and the solution was heated to 90 ° C.
While stirring, 4.2 g of sodium persulfate from the dropping funnel
In 50 g of water and 10.7 g of acrylic acid
(0.15 mol), 11.0 g (0.053 mol) of 2-acrylamido-2-methylpropanesulfonic acid in 50 g of water
Were slowly added dropwise. After dropping, stirring was further continued at 90 ° C. for 3 hours to obtain a water-soluble copolymer aqueous solution. When the residual monomer concentration was measured by ion chromatography, there was no unreacted monomer,
It was confirmed that the reaction rate was substantially 100%. As a result of gel permeation chromatography measurement, the molecular weight was 5,500.

The effect of the present invention was evaluated by using the obtained aqueous solution of the water-soluble copolymer as it was.

Similarly, various polymers were obtained by changing the ratio of each component. Table 1 shows the compositions of the polymers used in the examples and comparative examples.

For comparison, the following compounds, which are known as corrosion inhibitors for cooling water systems, were similarly used.

Compound V: sodium hexametaphosphate (manufactured by Yoneyama Chemical Industry) Compound W: 1-hydroxyethylidene-1-diphosphonic acid (manufactured by Nippon Monsanto, trade name: Dequest 201)
0)

[0027]

[Table 1]

[Evaluation of Corrosion Inhibition Effect] A Corrosion Inhibition Test in Circulating White Liquor of Continuous Digester in Paper Mill A 100 L of the circulating white liquor was placed in a glass beaker, and a predetermined amount of a corrosion inhibitor was added while stirring to dissolve uniformly. I let it.
After transferring this test solution into a stainless steel autoclave, the weight and surface area of the mild steel (JIS) were measured in advance.
G 3141 SPCC-SB) Insert the test piece,
It was left still in an oil bath at 75 ° C. for 24 hours. Next, the autoclave was immersed in tap water and quenched, the test piece was taken out, and the corrosion products on the surface were removed with a nylon scrubber, followed by washing with water and drying.

The weight difference between the test pieces before and after the test was measured and converted to the corrosion rate. The results are shown in Table 2.

[0030]

[Table 2]

B Corrosion Inhibition Test of Multi-Effect Black Liquor Concentration Canister in Paper Mill at 100% of the concentrated black liquor was placed in a glass beaker, and a predetermined amount of a corrosion inhibitor was added and uniformly dissolved with stirring. . After the test solution was transferred to a stainless steel autoclave, a mild steel (JIS G 3141 SPCC-SB) test piece whose weight and surface area had been measured in advance was put therein, and allowed to stand in an oil bath at 120 ° C. for 24 hours.
After the autoclave was immersed in tap water and quenched, the test piece was taken out, the corrosion products were removed with a nylon scourer, then washed with water and dried. The difference in weight between the test pieces before and after the test was measured and converted into a corrosion rate for evaluation. The results are shown in Table 3.

[0032]

[Table 3]

From the results shown in Table 2, the corrosion inhibitor of the present invention is:
Table 3 shows the corrosion caused by white liquor in the digester.
It can be seen from the results that each has an extremely high inhibitory effect on corrosion caused by black liquor.

[0034]

According to the present invention, if the corrosion inhibitor and the method for inhibiting corrosion in the digester and the black liquor canister of the kraft pulp production process of the present invention are applied to the process, the corrosion can be continuously suppressed and the life of the apparatus can be extended. The operation can be greatly extended and stable operation can be performed safely for a long period of time. In addition, since the corrosion inhibitor of the present invention does not contain heavy metals and phosphorus, it can be applied without causing any pollution problem in the surrounding environment.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08F 222/02 C08F 222/02 222/04 222/04

Claims (3)

[Claims] 1. An unsaturated carboxylic acid monomer selected from acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride and alkali metal salts and ammonium salts thereof. , 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, and alkali metal salts and ammonium salts thereof.
At least one kind of unsaturated sulfonic acid-based monomer as a main component, the unsaturated sulfonic acid-based monomer is 1 to 30 mol% of all monomers, and has a weight average molecular weight of 500 to 20,000. A corrosion inhibitor for a digester and / or a black liquor concentrator in a kraft pulp manufacturing process, characterized by containing a certain water-soluble copolymer. 2. The corrosion inhibitor according to claim 1, which is present in an amount of 1 to 100 ppm based on the digester white liquor in the kraft pulp production process.
A method for suppressing corrosion of a digester in a kraft pulp manufacturing process, characterized by adding. 3. The black liquor concentrating can of claim 1 is added to the black liquor in the kraft pulp production process in an amount of 1 to 10%.
A method for suppressing corrosion of a black liquor concentrate in a kraft pulp manufacturing process, characterized by adding 0 ppm.