JP3100589B1 - Calcium oxalate scale inhibitor in paper pulp manufacturing process and its control method - Google Patents

Abstract

The present invention provides a calcium oxalate scale inhibitor capable of efficiently suppressing calcium oxalate scale in a wide pH range in a paper pulp manufacturing process and a method thereof. SOLUTION: A calcium oxalate scale inhibitor in a paper pulp manufacturing process comprising, as an active ingredient, one or more of poly-α-hydroxyacrylic acid and its alkali metal salt, ammonium salt, and amine salt; The calcium oxalate scale inhibitor is added to the bleaching tower in the kraft pulp manufacturing process, any one of pulp slurry supplied to the bleaching tower, pulp washing water added to the bleaching tower, circulating white water in the papermaking process, and pulp slurry A method for suppressing calcium oxalate scale in a paper pulp manufacturing process, which is added as described above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oxalic acid capable of effectively suppressing calcium oxalate scale generated in a hypochlorous acid bleaching stage, a chlorine dioxide bleaching stage and a neutral papermaking process in a paper pulp manufacturing process. The present invention relates to a calcium scale inhibitor and a method for inhibiting the same.

[0002]

BACKGROUND ART Raw materials for paper pulp contain oxalic acid and calcium components which are eluted into process water, and oxidize organic substances in the bleaching process to form oxalic acid, which is also contained in process water. Due to the presence of a calcium component, it is accumulated as calcium oxalate in the process water, and is deposited as scale.

[0003] The calcium oxalate scale is particularly
Is easily generated at a pH of 4 or more. Therefore, in a hypochlorous acid bleaching stage (hereinafter, abbreviated as “H stage”) in a bleaching step having a pH of 7 to 10 or in piping and facilities around the same, the pH is 4 to 10. The formation is remarkable in the chlorine dioxide bleaching stage (hereinafter, abbreviated as “D stage”) 7 and the piping and facilities around the stage. It is also considerably generated in the paper machine in the neutral paper making process and its peripheral equipment. For example, in the bleaching process, it is generated in a filter wire, a shower nozzle, various pipes, a filtration tank, a bleaching tower, and the like, and in the paper making process, it is generated in a stuff box, a stock inlet, or the like, which poses a problem. When scale is generated in such a place, not only deteriorates the operability, but also due to clogging of the filter, lowering of drainage, lowering of washing performance,
Insufficient washing of the pulp causes instability of the pulp quality, requires a large amount of bleaching chemicals, and causes the adhesion of scale to fall off, resulting in paper cuts and spots and perforations in the final product. In some cases, the operation will be impaired, and operations may be urgently stopped.

[0004] Once formed, calcium oxalate scale is difficult to remove by acid washing such as calcium carbonate scale, and is currently mechanically removed.
Therefore, in order to suppress the formation of scale, a method of controlling the scale by using a water-soluble phosphate, a water-soluble phosphonate, a water-soluble phosphinate and an anionic water-soluble polymer electrolyte in combination (JP-A-61-153199), a water-soluble phosphorus A method in which an acid salt and a water-soluble acrylic acid polymer are used in combination (JP-A-1-143700), a method in which a copolymer of maleic acid, lower alkyl acrylate and vinyl acetate is used (JP-A-4-18184), A method using a copolymer of an acid and another ethylenically unsaturated compound [US Pat. No. 5,320,957 (1994)], a method using polyaminohexamethylene phosphonate [US Pat. No. 5,490,942 (1996)], and the like are proposed. Have been.

[0005] However, even with the conventional improvement method, the scale suppression of calcium oxalate is not sufficient, and particularly when the pH is in the range of 5 to 8, only a small scale suppression effect is exhibited. .

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the calcium oxalate scale produced in the hypochlorite bleaching stage, chlorine dioxide bleaching stage and neutral papermaking process in paper pulp production over a wide pH range, especially in a wide pH range. An object of the present invention is to provide a calcium oxalate scale inhibitor and a method thereof that can efficiently suppress pH even in the range of 5 to 8.

[0007]

The present inventors have conducted intensive studies on the calcium oxalate scale inhibitor in the above-mentioned paper pulp manufacturing process, and as a result, poly-α-hydroxyacrylic acid and / or salts thereof have been used for this purpose. It has been found that it is suitable and suppresses calcium oxalate scale very effectively, and has completed the present invention.

That is, the invention according to claim 1 is characterized in that poly-α-hydroxyacrylic acid and one or more of alkali metal salts, ammonium salts and amine salts thereof are contained as active ingredients. The calcium oxalate scale inhibitor in the hypochlorous acid bleaching stage, the chlorine dioxide bleaching stage and the neutral papermaking process in paper pulp production, and the invention according to claim 2 is the calcium oxalate scale according to claim 1 The inhibitor, in the hypochlorous acid bleaching stage in kraft pulp production, chlorine dioxide bleaching stage and neutral paper making process, pulp slurry in the bleaching stage, pulp slurry to be supplied, pulp washing water to be added, in the papermaking process In a paper pulp manufacturing process characterized by being added to one or more of circulating white water and pulp slurry This is a method for suppressing calcium oxalate scale.

[0009]

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

The calcium oxalate scale inhibitor of the present invention contains, as an active ingredient, poly-α-hydroxyacrylic acid and one or more of alkali metal salts, ammonium salts and amine salts thereof. Examples of the alkali metal salt include a lithium salt, a sodium salt, and a potassium salt. As the amine compound constituting the amine salt, a general amine compound can be used. For example, methylamine, ethylamine, diethylamine, triethylamine, butylamine, ethanolamine, ethylenediamine and the like can be mentioned. Especially poly-α
-Hydroxyacrylic acid sodium salt is industrially easily available and practically advantageous.

The weight average molecular weight of the poly-α-hydroxyacrylic acid component is preferably from 1,000 to 60,000.
0, more preferably 3,000 to 40,000. This preferred molecular weight range is selected from the effect of suppressing the scale, and the effect may be reduced outside this range.

The calcium oxalate scale inhibitor of the present invention comprises one of the above-mentioned poly-α-hydroxyacrylic acid and its alkali metal salt, ammonium salt and amine salt.
The seed or two or more are dissolved in water or a suitable organic solvent and added during the process.

In the bleaching step, the bleaching step includes chlorite bleaching step, pulp slurry in the chlorine dioxide bleaching step, pulp slurry or pulp washing water supplied to the bleaching step, circulating white water, pulp slurry in the neutral papermaking step. Etc., and is added to a portion where calcium oxalate scale adheres or an upstream portion thereof. For example, in the pulp bleaching process, H
It is added to the pulp slurry before entering the stage or the stage D, or to the washing water added to the stage H or the stage D for washing the pulp. In the paper making process, the pulp slurry is continuously added to the pulp slurry in the stuff box or the circulating white water which is removed by the paper making wire and mixed with the pulp slurry again.

[0014] The amount of addition varies depending on the desired process conditions and the degree of demand, and cannot be specified uniformly. However, the amount of addition is usually based on the concentration of calcium present in the pulp slurry or white water. 0.005 to 2 ppm, preferably 0.0 to 2 ppm of poly-α-hydroxyacrylic acid or a salt thereof with respect to 1 ppm of calcium ions.
2-1 ppm, more preferably 0.05-0.5 pp
m. If the concentration is lower than 0.005 ppm, the effect cannot often be sufficiently expected. On the other hand, when the concentration exceeds 2 ppm, the effect is sufficiently high, but the improvement of the effect is small for the added amount, and it is often not preferable from an economic viewpoint.

In applying the inhibitor of the present invention, a pitch control agent or another type of scale inhibitor may be used in combination as long as the effects of the present invention are not impaired, and the present invention imposes no restrictions on these combinations. It does not add.

[0016]

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

[Poly-α-hydroxyacrylic acid used in Examples] Compound-A; sodium poly-α-hydroxyacrylate (weight average molecular weight: 3,500) [Pale, manufactured by Nippon Peroxide Co., Ltd.] Plaque 2
50 "(product name)]. Compound-B; sodium poly-α-hydroxyacrylate (weight average molecular weight: 10,500) [Pale plaque 1 manufactured by Nippon Peroxide Co., Ltd.
200 "(product name)]. Compound-C; sodium poly-α-hydroxyacrylate (weight average molecular weight: 40,000) [Pale plaque 5 manufactured by Nippon Peroxide Co., Ltd.
000 "(product name)]. Compound-D: potassium poly-α-hydroxyacrylate (weight average molecular weight: 3,500) The polymer-A was passed through a column filled with a cation exchange resin to obtain acid-type poly-α-hydroxyacrylic acid. The pH was adjusted to 8 by adding a 50% aqueous potassium hydroxide solution to obtain potassium poly-α-hydroxyacrylate. Compound-E; poly-α-hydroxyammonium acrylate (weight average molecular weight: 3,500) An acid-type poly-α-hydroxyacrylic acid was passed through polymer-A through a column filled with a cation exchange resin. Aqueous ammonia was added to adjust the pH to 8, and poly-α
-Ammonium hydroxyacrylate.

[Compounds used in Comparative Examples] Compound-F; sodium polyacrylate (weight average molecular weight: 2,000) [Alon A-, manufactured by Toagosei Co., Ltd.]
200U "(trade name)]. Compound-G; sodium polyacrylate (weight average molecular weight: 8,000) [Toa Gosei Co., Ltd., "Aron A-
20UN "(product name)]. Compound-H: sodium salt of acrylic acid / 2-acrylamide-2-methylpropanesulfonic acid (90:10 molar ratio) copolymer (weight average molecular weight: 10,000) [Toa Gosei Co., Ltd., "Aron" A-6016 "(product name)]
It was used. Compound-I; 1-hydroxyethylidene-1,1-diphosphonic acid [Sorcia Japan Co., Ltd. product, “Dequest 2010” (trade name)] was used. Compound-J: sodium diethylenetriaminepentamethylenephosphonate [manufactured by Sorcia Japan Co., Ltd.
“Dequest 2066” (trade name)] was used. Compound-K: 2-phosphonobutane-1,2,4-tricarboxylic acid [manufactured by Bayer K.K., “Baibit AM”
(Product name)]. Compound-L: Sodium hexametaphosphate [Kanto Chemical Co., Ltd., special grade reagent] was used. Compound-M: maleic acid / ethyl acrylate / vinyl acetate (80:10:10 molar ratio) terpolymer (weight average molecular weight: 1,000) [manufactured by FMC Co., Ltd., "Berklen 283" (product) Name)] was used. Compound-N: sodium salt of maleic acid / acrylic acid (50:50 molar ratio) copolymer (weight average molecular weight: 5,0
00) [Nippon Shokubai Co., Ltd., “Aqualic TL-3”
7 "(product name)].

[Evaluation of Effect of Preventing Precipitation of Calcium Oxalate] <Test 1> The pulp slurry supplied from the D-stage supplied from the pulp mill bleaching process was No. 1 6 Filtrate filtered through quantitative filter paper (calcium ion concentration: 53 ppm, oxalate ion concentration:
36 ppm, pH: 8.2), a predetermined amount of various scale inhibitors was added, and then sodium oxalate [Kanto Chemical Co., Ltd., special grade reagent] was added as 60 ppm oxalate ion, calcium chloride [Kanto Chemical Co., Ltd.] (Special grade reagent, manufactured by Co., Ltd.) as calcium ion at 27 ppm, and the pH was adjusted to a predetermined value with dilute hydrochloric acid and dilute sodium hydroxide. After this test solution was allowed to stand at 60 ° C. for 1 hour, the concentration of suspended substances (hereinafter abbreviated as “SS”) in the test solution was measured with a Poick integrating sphere SS densitometer manufactured by Nippon Seimitsu Kogaku Co., Ltd. The scale suppression rate was determined by the following equation. The precipitated suspended substance was confirmed to be calcium oxalate by an infrared spectrophotometer.

[0020]

(Equation 1)

The results are shown in Table 1.

[0022]

[Table 1]

Test 2 The D-stage filtrate collected from the pulp mill bleaching process 6 Filtrate filtered with quantitative filter paper [Calcium ion concentration: 30 ppm, oxalate ion concentration: 3
4 ppm, pH 5.7], a predetermined amount of various scale inhibitors, then 66 ppm of sodium oxalate [Kanto Chemical Co., Ltd., special grade reagent] as oxalate ions, and then diluted hydrochloric acid and diluted sodium hydroxide. To pH 5.7
Was adjusted. After leaving this test solution at 50 ° C. for 1 hour,
The concentration of suspended substances (hereinafter abbreviated as “SS”) in the test solution was measured with a Poick integrating sphere SS densitometer manufactured by Nippon Seimitsu Kogaku Co., Ltd., and the scale inhibition rate was determined by the following equation. The precipitated suspended substance was confirmed to be calcium oxalate by an infrared spectrophotometer.

[0024]

(Equation 2)

The results are shown in Table 2.

[0026]

[Table 2]

From the results shown in Tables 1 and 2, the poly-α of the present invention was
It can be seen that -hydroxyacrylic acid and its salt have an extremely high effect of suppressing calcium oxalate precipitation as compared with the scale inhibitor of the comparative example.

[0028]

By applying the scale inhibitor of the present invention,
Calcium oxalate scale can be effectively suppressed with a small amount of use even in a wide pH range, especially in a pH range of 5 to 8, and a hypochlorous acid bleaching stage, a chlorine dioxide bleaching stage and a neutral papermaking in paper pulp production. Problems such as deterioration of operability due to the adhesion of the scale in the process, increase in the cost of bleaching chemicals, instability of pulp quality, and increase in rejects of final products can be solved, and this is a great advantage for the paper pulp industry.

Claims (2)

(57) [Claims] 1. A hypochlorous acid for producing paper pulp, characterized by containing as active ingredient one or more of poly-α-hydroxyacrylic acid and its alkali metal salt, ammonium salt and amine salt. Calcium oxalate scale inhibitor in acid bleaching stage, chlorine dioxide bleaching stage and neutral papermaking process. 2. The pulp slurry in the bleaching stage in the hypochlorous acid bleaching stage, the chlorine dioxide bleaching stage and the neutral paper making process in the production of kraft pulp, wherein the calcium oxalate scale inhibitor according to claim 1 is used. A method for suppressing calcium oxalate scale, wherein the method is added to any one or more of pulp slurry to be supplied, pulp washing water to be added, circulating white water in a papermaking process, and pulp slurry.