JP3194867B2 - Scale adhesion inhibitor and method for suppressing scale adhesion in pulp digester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe in and around a digester in a kraft pulp manufacturing process of the paper and pulp industry.
The present invention relates to an inhibitor and a method for continuously suppressing scale adhering to equipment and the like.

[0002]

2. Description of the Related Art Kraft pulp is made by pulping wood chips, which are raw materials, in a cooking liquor containing caustic soda and sodium sulfide as a main component at a high temperature and a high pressure to elute ligulin contained in the wood. 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. White liquor is approximately 55 to 100 g / l of caustic soda, sodium sulfide 1
It is an aqueous solution containing 8 to 45 g / l and 10 to 30 g / l of sodium carbonate (all in terms of Na ₂ O). However,
During this digestion process, calcium ions are eluted from the wood chips, react with carbonate ions in the cooking liquor, and calcium carbonate is generated and precipitated in the system and adheres to the digester and subsequent tank piping to form scale. There is. If the scale adheres to the heating section, the strainer section, etc. of the digester, it causes obstacles such as a decrease in heat exchange rate, an obstruction of liquid and chip flow, a decrease in productivity, and a nonuniform pulp quality, which is a major obstacle in operation.

Therefore, the operation is periodically stopped to remove the adhered scale by acid washing or the like. However, descaling is a labor intensive task in itself,
Further, it is extremely unfavorable in terms of production efficiency such as production loss and energy loss due to a temporary stop of operation.

[0004] Therefore, there is an urgent need for a method of minimizing the scale removing operation by continuously suppressing the adhesion of scale. For example, a method of using a maleic acid polymer as a scale adhesion inhibitor (Japanese Patent Publication No. 2-53551), a method of using a polyaminopoly (methylene phosphate) and an alkylphenol alkylene oxide adduct as a scale adhesion inhibitor (U.S. Pat. 799,995) have already been reported.

[0005]

However, even with the conventional improvement method, it has not been possible to completely suppress the scale, and there is a demand for a more effective one.

An object of the present invention is to solve such an unsolved problem, and to provide a scale adhesion inhibitor and a method for suppressing the adhesion of the scale which are excellent in a digester in a kraft pulp manufacturing process and piping and equipment around the digester. It is in.

[0007]

Means for Solving the Problems The inventors of the present invention intend to establish a method for continuously suppressing the adhesion of scale in a digester in a kraft pulp manufacturing process, and to suppress the scale formation in a cooking liquor. As a result of a thorough study, a ternary copolymer having a specific composition comprising two types of unsaturated carboxylic acid components, a maleic acid component and an acrylic acid component, and a 2-acrylamido-2-methylpropanesulfonic acid component (hereinafter referred to as “AMPS”) It has been found that the polymer exerts an extremely high effect on suppression of scale formation in the cooking liquor than maleic acid homopolymer, acrylic acid homopolymer or maleic acid-acrylic acid copolymer, and completes the present invention. Reached.

That is, the present invention comprises a maleic acid component, an acrylic acid component and an AMPS component, wherein the maleic acid component and the acrylic acid component have a molar ratio of 10: 2 to 10:15, and the AMPS component is composed of all monomers. 3 to 20 mol%,
Further, it is a scale adhesion inhibitor for a digester in a kraft pulp manufacturing process containing a terpolymer having a weight average molecular weight of 500 to 20,000 as an active ingredient. The present invention further relates to a digester and peripheral equipment for a kraft pulp production process, wherein the scale adhesion inhibitor is added in an amount of 0.01 to 10 ppm based on 1 ppm of calcium ions present in the digester in the digester in the kraft pulp production process. This is a method for preventing scale adhesion.

[0009]

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

The copolymer used for the scale adhesion inhibitor of the present invention comprises a maleic acid component, an acrylic acid component and AMPS.
The component molar ratio of the maleic acid component to the acrylic acid component is 10: 2 to 10:15, preferably 10: 3 to 10:10. 10: 2 to 10:15
Outside the range, the scale suppressing effect is not so large and may not be practical. The AMPS component accounts for 3 to 20 mol%, preferably 4 to 10 mol% of the total monomers. Outside the range of 3 to 20 mol%, the effect of suppressing scale is not so large, and may not be practical.

The weight average molecular weight of the copolymer is 500 to 2
It is preferably from 10,000 to 10,000, more preferably from 3,000 to 8,000. If the molecular weight is less than 500 or more than 20,000,
The dispersing effect of the calcium scale and the effect of suppressing the scale become small, which is not preferable.

The composition ratios and molecular weights of these constituents have been found as the optimum ranges as a result of the study of the present inventors. Outside of these ranges, there is a certain effect, but not so large, and economical. However, it is not efficient.
According to the study of the present inventors, the polymer composition has a large effect on the effect, the maleic acid component and the acrylic acid component
AM acts to suppress calcium precipitation.
It is considered that the PS component has a function of dispersing the precipitated calcium particles and suppressing their growth as a scale.

The method for producing the terpolymer in the present invention is not particularly limited. For example, maleic acid,
This can be achieved by dropping a polymerization initiator dropwise at 80 to 110 ° C into an aqueous solution obtained by adding an alkali metal hydroxide to an aqueous solution of acrylic acid and AMPS.

In this case, maleic acid, acrylic acid, AM
Each component of PS may be polymerized in a free state, but may be subjected to a polymerization reaction as a sodium salt, a potassium salt, or an ammonium salt. Also, maleic acid can be added to the polymerization system as an anhydride.

Examples of the polymerization initiator include peroxides such as sodium persulfate, chlorine peroxide and butyl hydroperoxide, and azo compounds such as azobisisobutyronitrile. Preferred polymerization initiators are hydrogen peroxide and persulfate. The amount of the polymerization initiator used varies depending on the type of the polymerization initiator used. For example, in the case of hydrogen peroxide, 0.5 to 10 mol%, preferably 1 to 5 mol%, based on the total amount of the monomers.
It is.

Water is most preferred as the polymerization solvent, but organic solvents such as alcohols and dioxane can also be used.

The heating temperature during the polymerization is preferably from 80 to 110 ° C. If the polymerization is carried out at a low temperature, unreacted monomers remain, which is not preferable.

The scale adhesion inhibitor of the present invention is applied for the purpose of suppressing scale adhesion in a digester for digesting wood chips for pulp production and peripheral equipment. The place of addition is usually in the digestion, and the amount of addition is based on the amount of calcium ions present in the liquid. 0.01 to 10 ppm, preferably 0.05 to 5 p, per 1 ppm of calcium ion
pm, more preferably 0.1 to 3 ppm. If the content is less than 0.01 ppm, the effect is not sufficient, and if the content exceeds 10 ppm, the effect is sufficiently recognized, but no further improvement in the effect is recognized, which is not preferable from an economic viewpoint. For this purpose, it is preferable to sample the liquid in the digester from time to time, measure the calcium concentration in this liquid, and optimize the amount of the scale adhesion inhibitor added accordingly.

The method of adding the scale adhesion inhibitor of the present invention to the digester is not particularly limited, but it is added to either one or both of the white liquor supplied to the digester and the circulating digester. This is convenient for actual operation. Further, as long as the object of the present invention is achieved, there is no limitation on the use of additives of other optional components.

The calcium carbonate produced in the digester precipitates and becomes scale when the concentration becomes high. The scale adhesion inhibitor of the present invention has an effect of adsorbing the crystal growth nuclei and penetrating the crystal lattice at the stage of calcium carbonate crystal growth, inhibiting crystal growth, giving strain to the crystal, and making the crystal finer. Have. As a result, it is considered that calcium carbonate hardly precipitates, and the crystals become fine even when precipitated, so that it becomes difficult to form a scale.Moreover, it is thought that the precipitated calcium carbonate is dispersed in a liquid to suppress growth as a scale. Can be

[0021]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples.

[Production of Polymers] Various polymers as shown in Table 1 were produced.

Preparation of polymer-F: 35.1 g (0.358 mol) of maleic anhydride in a 500 ml five-necked flask
And 50 g of water, and a 50% aqueous sodium hydroxide solution was added thereto to adjust the pH to 6. The flask was set to a nitrogen gas atmosphere, the solution was heated to 90 ° C., and a solution prepared by dissolving 4.2 g of sodium persulfate in 50 g of water from a dropping funnel with stirring and 12.9 g (0.179 mol) of acrylic acid. , 4.7 g (0.023 mol) of AMPS and 50 g of water
Were slowly added dropwise. After dropping, stirring was further continued at 90 ° C. for 3 hours to obtain a copolymer aqueous solution. When the concentration of the residual monomer was measured by an ion chromatography method, no monomer was present, and the conversion was substantially 1
00% was confirmed. The obtained aqueous copolymer solution was used as it was for evaluating the calcium carbonate precipitation suppressing effect. The molecular weight of the copolymer was 4,500 as a result of gel permeation chromatography.

In the same manner, 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.

[0025]

[Table 1]

[Evaluation of Calcium Carbonate Precipitation Inhibiting Effect] A test of the scale adhesion inhibitor of the present invention was carried out for its ability to inhibit calcium carbonate precipitation in a highly alkaline white liquor.

Calcium carbonate precipitation inhibitory effect at 100 ° C. Simulated white liquor (NaOH 8.0% by weight, Na ₂ S 4.0% by weight, Na ₂ CO ₃ 3.5% by weight, KOH 0.5% by weight,
Aqueous solution consisting of 84.0% by weight of ion exchanged water
To each ml, calcium chloride was added so as to be 100 ppm as calcium ions, and various scale adhesion inhibitors were further added in predetermined amounts. Add 10 parts of this solution
After uniformly dissolving at 0 ° C. and leaving at 100 ° C. for 4 hours, filter paper No. 6. Filtered by suction. After drying the filter paper, weigh the calcium carbonate remaining on the filter paper,
This was defined as precipitated calcium carbonate, and was calculated as a precipitation inhibition rate by the following equation.

[0028]

(Equation 1)

The results are shown in Table 2.

[0030]

[Table 2]

Calcium carbonate precipitation inhibitory effect at 180 ° C. Simulated white liquor (NaOH 8.0% by weight, Na ₂ CO ₃ 3.5)
Wt%, KOH 0.5 wt%, ion exchange water 88.0
(Aqueous solution containing 100% by weight) was heated to 100 ° C., and calcium chloride was added thereto so that calcium ion became 150 ppm, and predetermined amounts of various scale adhesion inhibitors were added. This mixture was placed in an autoclave and left at 180 ° C. for 3 hours. After the autoclave was immersed in tap water and quenched, the sample water was filtered with a filter paper for quantitative determination.
o. The mixture was spontaneously filtered at 6, and the remaining calcium ions in the sample water were quantified by the atomic absorption method. The results are shown in Table 3.

[0032]

[Table 3]

From the results shown in Tables 2 and 3, it can be seen that the scale adhesion inhibitor comprising the polymer of the present invention is extremely effective.

[0034]

According to the present invention, when the scale adhesion inhibitor and the method for suppressing the scale adhesion in the digester of the kraft pulp production process of the present invention are applied to the corresponding process, the scale adhesion can be continuously suppressed, and the continuous operation period is extended, Improved productivity, uniform pulp quality, reduced energy loss,
Since the trouble due to scale adhesion is also drastically reduced, the effect of improving operability is great.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) D21C 7/12 D21C 3/22 C02F 5/10

Claims (2)

(57) [Claims] 1. A maleic acid component, an acrylic acid component and 2
-Acrylamide-2-methylpropanesulfonic acid component, the molar ratio of maleic acid component to acrylic acid component is 10: 2 to 10:15, and 2-acrylamide-2
The methylpropanesulfonic acid component is 3 to 20 of the total monomers;
Mol% and a weight average molecular weight of 500 to 20,
A scale adhesion inhibitor for a digester in a kraft pulp digestion step, comprising a terpolymer of 000. 2. With respect to 1 ppm of calcium ions present in a cooking liquor in a digester in a kraft pulp manufacturing process,
The scale adhesion inhibitor according to claim 1 is used in an amount of 0.01 to 10 p.
A method for suppressing scale adhesion in a digester and peripheral equipment in a kraft pulp production process, characterized by adding pm.