JPH11131382A - Corrosion inhibitor for concentration vessel for black liquor in process for producing kraft pulp, and corrosion inhibition therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a corrosion inhibitor effective for inhibiting the corrosion of a black liquor concentration vessel in a process for producing a kraft pulp, and further to provide a method for inhibiting the corrosion of the vessel for concentrating the black liquor by using the corrosion inhibitor. SOLUTION: This corrosion inhibitor effective for inhibiting the corrosion of a black liquor concentration vessel in a process for producing a kraft pulp contains a water-soluble copolymer comprises a terpolymer composed of an acrylic acid component, a maleic acid component and a hypophosphorous acid component regulated so that the molar ratio of the acrylic acid component to the hypophosphorous acid component may be (1:3)-(3:1) and the percentage of the hypophosphorous acid component may be 1-20 mol.%, and having 500-10,000 weight average molecular weight as an active ingredient. The method for inhibiting the corrosion of the vessel for concentrating the black liquor comprises adding 1-100 ppm of the corrosion inhibitor to the black liquor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion inhibitor for a black liquor canister for concentrating cooking waste liquor (hereinafter referred to as "black liquor") in the kraft pulp manufacturing process of the paper and pulp industry, and a method for inhibiting the corrosion.

[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 as a main component under high temperature and high pressure to elute ligulin contained in the wood. Manufactured by pulping. The waste liquid after the digestion is called black liquor, which is concentrated to 60 to 75% in a concentration can and then incinerated in a recovery boiler. The black liquor contains inorganic salts such as sodium hydroxide, sodium sulfide, sodium carbonate, sodium polysulfide, sodium sulfate, sodium thiosulfate, sodium sulfite, and sodium chloride. Sodium sulfide, sodium polysulfide, and sodium thiosulfate cause severe corrosion of carbon steel, which is the main material of black liquor concentrators at high temperatures (about 120 ° C.). In particular, sodium thiosulfate is considered to be a major cause for corrosion (WA Murller, 1st International Seminar on Corrosion in the Pulp and Paper Industry, May 1974, Chicago, USA).

[0003] Therefore, as a means for suppressing the corrosion, methods such as stainless steel lining and passivation of carbon steel by adding polysulfide have been adopted.

[0004]

However, even with the conventional improvement methods, the corrosion of the black liquor can has not been sufficiently suppressed, and a more effective corrosion control measure is desired. An object of the present invention is to provide a corrosion inhibitor for a black liquor concentrated can in a kraft pulp manufacturing process and a method for suppressing the corrosion, which are effective in solving such an unsolved problem.

[0005]

SUMMARY OF THE INVENTION The present inventor intends to establish a method for suppressing corrosion in a black liquor concentrating can in a kraft pulp manufacturing process. As a result of intensive studies on the method of inhibiting corrosion of black liquor canisters using the same, a specific ternary system comprising two types of unsaturated carboxylic acid components, maleic acid component and acrylic acid component, and hypophosphorous acid component The inventors have found that the copolymer exhibits a high inhibitory effect on the corrosion of the black liquor can caused by the black liquor, and have completed the present invention.

That is, the invention of claim 1 comprises a maleic acid component, an acrylic acid component and a hypophosphorous acid component,
The molar ratio of the maleic acid component and the acrylic acid component is 1: 3 to
3: 1, the hypophosphorous acid component is 1 to 20 mol% of all monomers, and the weight average molecular weight is 500 to 10,000.
A ternary copolymer that is a ternary copolymer which is a corrosion inhibitor for a black liquor canister in a kraft pulp manufacturing process, characterized in that the black liquor in the kraft pulp manufacturing process is A method for inhibiting corrosion of black liquor cans in a kraft pulp manufacturing process, wherein 1 to 100 ppm of the corrosion inhibitor for black liquor cans according to claim 1 is added.

[0007]

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

The copolymer used as a corrosion inhibitor for the black liquor canister of the present invention is a terpolymer composed of a maleic acid component, an acrylic acid component and a hypophosphorous acid component. The constituent molar ratio of the acrylic acid component is 1: 3 to
The ratio is 3: 1, preferably 1: 2 to 2: 1, and more preferably 1: 1.5 to 1.5: 1. This constituent molar ratio is 1:
Outside the range of 3 to 3: 1, the effect of inhibiting corrosion, which is the object of the present invention, is small and not practical. Further, the hypophosphorous acid component accounts for 1 to 20 mol%, preferably 5 to 15 mol% of all monomers,
More preferably, it is 7 to 12 mol%. If the amount is out of the range of 1 to 20 mol%, the effect of inhibiting corrosion, which is the object of the present invention, is small and not practical.

The weight average molecular weight of the copolymer is from 500 to 1
000, preferably 700 to 7,000, and more preferably 1,000 to 5,000.

If the weight average molecular weight is out of the range of 100 to 5,000, the effect of inhibiting corrosion, which is the object of the present invention, is small and not practical.

According to the study of the present inventors, the polymer composition,
The degree of polymerization has a great influence on the corrosion inhibiting effect aimed at by the present invention. When performing polymerization, maleic acid component,
The acrylic acid component and the hypophosphorous acid component may be used in a free state, respectively, or may be used as an alkali metal salt such as a sodium salt and a potassium salt or an ammonium salt.

Further, maleic acid can be added to the polymerization system as an anhydride.

The method for producing the polymer of the present invention is not particularly limited. For example, maleic anhydride is added to water, an alkali metal hydroxide is added and dissolved, and hypophosphite is further added thereto. In addition, it can be achieved by dropping acrylic acid (salt) and polymerization initiator under the condition of 80 to 110 ° C.

The polymerization initiator to be used is not limited to the present invention because it varies depending on the polymerization conditions. However, it is sufficient that the polymerization initiator decomposes under the polymerization conditions to generate free radicals.
For example, peroxides such as sodium persulfate, hydrogen peroxide, chlorine peroxide, and butyl hydroperoxide, and azo compounds such as azobisisobutyronitrile are included. Preferred polymerization initiators are hydrogen peroxide and persulfate. 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.

Water is most preferred as the solvent used in the polymerization. However, organic solvents such as alcohols and dioxane can be used alone or in a mixed water-organic solvent system.

[0016] The polymerization is usually carried out at 80 to 110 ° C. 8
Polymerization at a temperature lower than 0 ° C. is not preferable because unreacted monomers may remain.

The addition amount of the corrosion inhibitor of the present invention is in the range of 1 to 100 ppm, preferably 2 to 80 ppm, more preferably 5 to 50 ppm, based on the black liquor. 1
When the amount is less than ppm, the effect is not sufficient, and when the amount exceeds 100 ppm, the effect is sufficiently recognized, but the effect corresponding to the added amount is not improved, which is not preferable from an economic viewpoint.

The method of adding the corrosion inhibitor of the present invention to the black liquor concentrate can be, but not limited to, directly into the black liquor concentrate or from the pulp digester to the black liquor concentrate. It is convenient for the operation to add to the liquid. The corrosion inhibitor of the present invention is also effective in controlling the scale mainly of calcium carbonate. Therefore, when it is added to the circulating white liquor of the pulp digester, the corrosion control is achieved together with the scale control of the digester, and the black liquor after the digestion is achieved. In some cases, the black liquor concentration can enters the concentration can, which is advantageous in preventing corrosion. However, most of the corrosion inhibitors added to the white liquor circulating in the digester are attached to the pulp and sent to the papermaking process, and the concentration of the corrosion inhibitor remaining in the liquor entering the black liquor can becomes extremely low. It is not enough to satisfy the corrosion inhibition of the concentration can. It is necessary to additionally add the liquor directly to the black liquor concentrate or into the liquor from the pulp digester to the black liquor concentrate.

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.

[0020]

Next, several preferred embodiments of the present invention will be described in detail. However, it goes without saying that the present invention is not limited to only these examples. Representative examples of the production of the polymer are shown below.

[Production of polymer] Production of polymer-C: 22.1 g (0.225 mol) of maleic anhydride and 50 of water were placed in a 500 mL five-necked flask.
g was added thereto, and a 50% aqueous sodium hydroxide solution was gradually added thereto to dissolve maleic anhydride. Further, 5.3 g (0.050 mol) of sodium hypophosphite monohydrate was added. A nitrogen gas atmosphere was set in the flask, and the solution was heated to 80 ° C., and while stirring, a solution in which 4.0 g of sodium persulfate was dissolved in 20 g of water from a dropping funnel, and acrylic acid 1
6.2 g (0.225 mol) were each slowly added dropwise. After the dropwise addition, the mixture was further stirred at 80 ° C. for 3 hours, and then cooled to obtain a pale yellow aqueous copolymer solution. The copolymer was measured for residual monomer concentration by ion chromatography. As a result, no unreacted monomer was present, and the reaction rate was almost 100%.
Was confirmed. The molecular weight of the obtained copolymer was 1.300 as a result of gel permeation chromatography.

The effects of the present invention were evaluated using the copolymer solution obtained as a result of the reaction.

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.

In addition, the following compounds, which are known as a corrosion inhibitor for a cooling water system, were similarly used for comparison.

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

[0026]

[Table 1]

[Evaluation of Corrosion Inhibition Effect] A Corrosion Inhibition Test Using Diluted Black Liquor Supply to Liquid Film Flowing-Down Type Black Liquor Concentrator in Paper Mill A 100 mL of the diluted black liquor was placed in a glass beaker and stirred. A predetermined amount of a corrosion inhibitor was added and uniformly dissolved.
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 20 ° C. for 24 hours. Next, the autoclave was immersed in tap water and quenched, then the test piece was taken out, and the corrosion products on the surface were removed with a nylon scourer, 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.

[0029]

[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.

[0031]

[Table 3]

From the results shown in Tables 2 and 3, it can be seen that the corrosion inhibitor of the present invention is composed of a diluted black liquor (ie, a liquid entering a black liquor can) and a dark black liquor (ie, a liquid concentrated in a black liquor can). It can be seen that it has an extremely high inhibitory effect on the corrosion caused by ()).

[0033]

As described above, by applying the corrosion inhibitor and the method for inhibiting corrosion in the kraft pulp manufacturing process black liquor canister of the present invention to the process, it is possible to continuously inhibit corrosion. The life of the equipment can be greatly extended, and stable and stable operation can be performed over a long period of time.

Claims (2)

[Claims] The present invention comprises a maleic acid component, an acrylic acid component and a hypophosphorous acid component, wherein the maleic acid component and the acrylic acid component have a molar ratio of 1: 3 to 3: 1, and the hypophosphorous acid component is a single unit. Inhibitor for black liquor concentrate can in kraft pulp manufacturing process, characterized in that it contains a terpolymer having 1 to 20 mol% of a monomer and a weight average molecular weight of 500 to 10,000. . 2. The black liquor concentrating agent according to claim 1, which 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.