JPH05287690A - Scale sticking prevention in digester in kraft pulp production process - Google Patents

Abstract

PURPOSE:To prevent scale sticking to a digester for kraft pulp production in an industrially advantageous way, using inexpensive compounds by adding a water-soluble polymer having side chain containing amino, hydroxyl and ether groups to the digester. CONSTITUTION:Firstly, a monomer having substituted imino structure of formula I is prepared by charging a reaction vessel with ion-exchanged water, sodium hydroxide and iminodiacetic acid followed by dripping allyl glycidyl ether into the system under agitation at 65 deg.C to carry out reaction. Second, acrylic acid and sodium persulfate are added to the aqueous solution of this monomer followed by polymerization at 95 deg.C for 60min to produce a water-soluble polymer made up of a structural unit of formula II [R<1> and R<2> are each H, CH2COOX<1> (X<1> is H, monovalent metal, divalent metal, or inorganic or organic ammonium), etc.]. Then, this polymer is added to a digester for kraft pulp production, thus efficiently preventing scale sticking to the digester at low cost during kraft pulp production process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing scale from adhering to the inside of a digester in a kraft pulp manufacturing process.

[0002]

2. Description of the Related Art Kraft pulp is made of sodium hydroxide,
Manufactured by steaming wood chips under high temperature and pressure with an alkaline solution (white liquor) containing sodium carbonate and sodium sulfide to efficiently elute and remove lignin, which is a coloring component contained in wood. ..

Cooking is usually carried out in a reaction kettle called a digester, and there are two types, a fixed type digester and a continuous digester. When these digesters are continuously used for a long time, the calcium content present in the wood chips and the water, and the (heavy) carbonic acid present in the water and the alkaline cooking solution or carbon dioxide in the air are combined, Scale mainly composed of calcium carbonate adheres to the wall of the kettle.

When a large amount of the above scale is attached, the thermal efficiency of the digester is remarkably reduced, leading to energy waste.
Workability also deteriorates.

In order to solve this scale trouble, polymaleic acid (salt), maleic acid / acrylic acid copolymer (see JP-A-60-134092, JP-A-61-75892, JP-A-3-167382, etc. The use of polycarboxylic acids (salts) such as (salts) and poly (meth) acrylic acid (salts) has been proposed and has been relatively well evaluated.

[0006]

However, since the above-mentioned polycarboxylic acid (salt) does not have sufficient salt resistance, the concentration of polyvalent metal ions such as calcium ion, magnesium ion, iron ion and copper ion in the cooking liquor is high. When the ratio is high, there is a problem that the scale preventing effect is lowered because the polyvalent metal ions are bound and insolubilized.

The present invention provides a method capable of preventing scale from adhering to the inside of a digester without reducing its effect even in a cooking operation with a cooking liquor having a high concentration of various polyvalent metal ions. The purpose is to

[0008]

The scale prevention method of the present invention comprises the following formula in a digester in a kraft pulp manufacturing process.

[0009]

[Chemical 3]

(In the formula, R ¹ and R ² represent hydrogen or a substituent containing carbon, and at least one of R ¹ and R ² is --CH ₂ COOX ¹ , --CH ₂ CH ₂ COOX ² , X ^{1 to} X ⁹ each independently or together add a water-soluble polymer containing a structural unit (I) represented by hydrogen, a monovalent metal, a divalent metal, an inorganic or organic ammonium group). It is characterized by doing.

It is necessary that at least one of R ¹ and R ^{2 in} the above structural unit (I) is selected from the above functional group group (A), and among them, at least one of R ¹ and R ² is _{^{, -CH 2 COOX 1, -CH 2}} CH 2 COO
X ² , It is preferable that the resulting water-soluble polymer has a high scale adhesion preventing effect.

Particularly preferably, at least one of R ¹ and R ² is Is Rukoto. Then, if one of R ¹ and R ² is selected from the functional groups (B) or functional groups (C), leaving the other functional group (R ¹ or R ²⁾ as the functional groups (B)
It is preferably selected from the following.

Examples of the water-soluble polymer include homopolymers and copolymers of the structural unit (I), and among them, a copolymer containing the structural unit (I) in an amount of 2 to 80 mol% is particularly preferable.

When the water-soluble polymer is a copolymer, the comonomer component is not particularly limited and a wide range of monomers can be used. For example, amide-based monomers such as (meth) acrylamide and t-butyl (meth) acrylamide; hydrophobic monomers such as (meth) acrylic acid ester, styrene, 2-methylstyrene and vinyl acetate; vinyl sulfonic acid, Allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-acrylamide-
2-Methylpropanesulfonic acid, 3-allyloxy-2-
Hydroxypropanesulfonic acid, sulfoethyl (meth)
Acrylate, sulfopropyl (meth) acrylate,
2-hydroxysulfopropyl (meth) acrylate,
Sulfoethylmaleimide or monovalent metal thereof, 2
Unsaturated sulfonic acid type monomers such as partially neutralized products and fully neutralized products with valent metals, ammonia and organic amines; 3-methyl-3-buten-1-ol (isoprenol), 3-methyl-2-butene -1-ol (prenol), 2-methyl-3-buten-2-ol (isoprene alcohol), 2-hydroxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene Glycol monoisoprenol ether, polypropylene glycol monoisoprenol ether, polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, glycerol monoallyl ether, α-hydroxyacrylic acid, N-methylol (meth) acrole Hydroxyl group-containing unsaturated monomers such as lamide, glycerol mono (meth) acrylate and vinyl alcohol; cationic monomers such as dimethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylamide; such as (meth) acrylonitrile Nitrile type monomer; ethylene, propylene, 1-butene, isobutylene, α-amylene, 2-methyl-1-
Examples thereof include α-olefin monomers such as butene, 3-methyl-1-butene (α-isoamylene), 1-hexene and 1-heptene.

Above all, it is preferable to use an unsaturated carboxylic acid monomer represented by the following formula (II).

[0016] (Wherein, A ¹ and A ² are each independently hydrogen, methyl or -COOX ^11, and A ¹ and A ² does not become a -COOX ¹¹ simultaneously, A ³ is hydrogen, methyl or - CH ₂ COOX ¹² and A ³ is —CH ₂ C
In the case of OOX ¹² , A ¹ and A ² each independently represent hydrogen or a methyl group, and X ^{10 to} X ¹² are each independently or together hydrogen, a monovalent metal, a divalent metal, an ammonium group or an organic amine group. Examples of such unsaturated carboxylic acid type monomer (II) include acrylic acid, methacrylic acid,
Crotonic acid or its monovalent or divalent metals, ammonia, partially neutralized products or fully neutralized products with organic amines,
(Anhydrous) maleic acid, itaconic acid, fumaric acid, citraconic acid or their partially neutralized or completely neutralized products with monovalent metals, divalent metals, ammonia and organic amines can be mentioned. Examples of the monovalent metal include sodium and potassium, and examples of the divalent metal include calcium and magnesium. The organic amines include alkylamines such as monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine and triethylamine, alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine and dimethylethanolamine, pyridine. Etc. can be given.
Of these, sodium is most preferable because it is inexpensive and industrially available.

The water-soluble polymer used in the present invention may be either an acid type or a salt type. Examples of the salt type include monovalent metal salts, divalent metal salts, and inorganic or organic ammonium salts.

As the monovalent metal salt, for example, sodium salt,
Examples thereof include potassium salt and lithium salt. Examples of the divalent metal salt include calcium salt and magnesium salt. Examples of the inorganic or organic ammonium salt include alkylamine salts such as ammonium salt, monomethylamine salt, dimethylamine salt, trimethylamine salt, monoethylamine salt, diethylamine salt and triethylamine salt, monoethanolamine salt, diethanolamine salt, triethanolamine salt. Examples thereof include alkanolamine salts such as monoisopropanolamine salt and dimethylethanolamine salt, and pyridine salt. Of these, sodium salt is most preferable because it is inexpensive and industrially available.

Further, in order to make the polymer water-soluble, the content of the divalent metal salt is preferably 10 mol% or less based on the total carboxylic acid groups.

The water-soluble polymer of the present invention can be produced by various methods. For example, the epoxy group in the homopolymer or copolymer of allyl glycidyl ether can be converted into iminodiacetic acid (salt), iminodipropionic acid (salt), iminodisuccinic acid. (Salt), carboxymethyliminosuccinic acid (salt), hydroxyiminodisuccinic acid (salt), dithiocarbamic acid (salt), thiourea, methylamine and other primary or secondary amines Or by subjecting the ring-opened adduct thereof to phosphorylation modification using formalin and phosphorous acid as raw materials.

Alternatively, allyl glycidyl ether may be used as iminodiacetic acid (salt), iminodipropionic acid (salt), iminodisuccinic acid (salt), carboxymethyliminosuccinic acid (salt), hydroxyiminodisuccinic acid (salt), dithiocarbamic acid (salt). (Salt), thiourea, methylamine, etc. ring-opening addition with primary or secondary amines, or homopolymerization or copolymerization of monomers obtained by phosphorylation modification of the ring-opening adduct. It is obtained by

Among the primary or secondary amines, the use of iminodisuccinic acid (salt), carboxymethyliminosuccinic acid (salt) and hydroxyiminodisuccinic acid (salt) (both are secondary amines) is preferred. It is preferable because the resulting water-soluble polymer is particularly excellent in the scale adhesion preventing effect.

The molecular weight of the water-soluble polymer is not particularly limited, but the weight average molecular weight is 500 to 100,000.
0 is preferred.

The amount of the water-soluble polymer used is not particularly limited, but it is 1 to 100 ppm with respect to the cooking liquor in the digester.
It is preferably added. If the amount used is less than 1 ppm, the effect of preventing scale adhesion tends to decrease. Further, even if it is used in excess of 100 ppm, the effect commensurate with the increase in amount cannot be obtained.

The method of supplying the water-soluble polymer to the digester is not particularly limited and various methods are possible. For example, it may be added to either or both of white liquor and black liquor and introduced into the digester, or in the case of a continuous digester, it is continuously added to a liquid circulation line for extracting the liquid through a strainer. It is also possible to introduce it. Furthermore, it is also possible to sprinkle it on the wood chips and introduce it. Using any of these methods results in 1-100 for the cooking liquor.
It is preferable to add it so as to be ppm.

The ease of scale attachment is closely related to the total carbonic acid concentration of the cooking liquor, and the water-soluble weight ratio is 0.001 to 1 part by weight based on 100 parts by weight of total carbonic acid. It is preferable to use a coalesce in order to effectively prevent scale from adhering.

When the water-soluble polymer is used, the reason why the scale adherence in the digester disappears or becomes extremely small is not clear, but it is presumed as follows. That is, it is considered that the water-soluble polymer has a specific nitrogen-containing functional group structure, which strongly inhibits the formation of scale, and has a significantly high dispersive power with respect to the scale, which prevents adhesion to the digester wall. Be done. It is also considered that this is because the stability against polyvalent metal ions such as calcium ions, magnesium ions, iron ions, and copper ions is extremely high, so that it may effectively act to prevent scale adhesion.

The cooking is usually carried out at a temperature of around 165 ° C. and a pressure of 8 to.
It is performed under severe conditions of 9 kg / cm ² and pH 11-12. Further, calcium carbonate (scale) has a low solubility under high temperature and high alkali, so that it is in a condition in which formation and adhesion thereof are extremely likely to occur. Furthermore, since the temperature is as high as around 165 ° C., considerable heat resistance is required as a scale adhesion preventing agent.

As described above, the polymer of the present invention exhibits an excellent scale preventing effect under the extremely severe conditions of the digester.

[0030]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In addition, part and% in an example show a weight part and weight%, respectively.

Method for producing water-soluble polymer 1 In a glass reactor having a capacity of 2 liters equipped with a stirrer and a condenser, 433.8 parts of ion-exchanged water, 429.6 parts of 48% sodium hydroxide and 342.9 parts of iminodiacetic acid. Was charged. 293.7 parts of allyl glycidyl ether was dropped from the dropping nozzle in 60 minutes while maintaining the temperature at 65 ° C. under stirring.
After completion of dropping, the reaction was completed by keeping the same temperature for 30 minutes.

Chemical formula with a concentration of 50% A monomer (a) having an iminodi structure represented by

In a 2 liter capacity glass reactor equipped with a stirrer and a condenser, the above monomer (a) 50 was added.
% Aqueous solution 573 parts and ion exchange water 449.5 parts were charged and the temperature was raised to 95 ° C. 80% acrylic acid aqueous solution 3 with stirring
Polymerization was completed by adding 54.4 parts and 123.1 parts of a 20% aqueous sodium persulfate solution through separate dropping nozzles over 60 minutes and maintaining the same temperature for 10 minutes.

Mainly monomer (a) / acrylic acid = 2
A water-soluble polymer 1 composed of a / 8 (molar ratio) copolymer was obtained. The total polymerization rate of water-soluble polymer 1 was 99 mol%.
Further, the weight average molecular weight was measured by an aqueous GPC, and the results are shown in Table 1.

Water-soluble polymer 2-17 Water-soluble polymer 2-1 by the same method as water-soluble polymer 1
Got 7.

[0036]

[Table 1]

[0037]

[Table 2]

[Experimental Example 1] 400 parts of pulp chips and 12 parts of white liquor shown in Table 3 were placed in an autoclave having a volume of 2 liters.
00 parts and water-soluble polymer 1 obtained as described above
Was added in the amount shown in Table 4 (against white liquor) and then thoroughly mixed. Then add calcium chloride and iron (II) chloride to the above mixture.
I) and manganese sulphate against white liquor Ca ²⁺ 300ppm, Fe
^{3 +} 20 ppm and Mn ²⁺ 20 ppm were added.

Then, the mixture was heated at 170 ° C. for 5 hours to complete the cooking. After cooling, the contents were removed by decantation, and the state of the scale attached to the kettle wall was visually observed. The results are also shown in Table 4.

[0040]

[Table 3]

[Experimental Examples 2 to 17] Cooking was carried out in the same manner as in Experimental Example 1 except that the water-soluble polymers 2 to 17 were used instead of the water-soluble polymer 1. The state of the scale attached to the kettle wall was evaluated in the same manner as in Experimental Example 1. The results are shown in Table 4.

[0042]

[Table 4]

Comparative Examples 1 to 4 Cooking was carried out in the same manner as in Experimental Example 1 except that the scale adhesion preventive agent shown in Table 5 was used instead of the water-soluble polymer 1. The state of the scale attached to the kettle wall was evaluated in the same manner as in Experimental Example 1. The results are also shown in Table 5.

[0044]

[Table 5]

[0045]

As described above, by adding the water-soluble polymer of the present invention to the digester in the kraft pulp manufacturing process, it is possible to effectively prevent the scale from adhering to the digester, resulting in the digestion. The effect of enabling stable or continuous operation is provided.

Since the water-soluble polymer is inexpensive, it also has the effect of being industrially advantageous.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C08F 222/02 MLU 7242-4J 246/00 MPY 8416-4J

Claims (5)

[Claims] 1. The following formula in a digester: (In the formula, R ¹ and R ² represent hydrogen or a substituent containing carbon, and at least one of R ¹ and R ² is —CH ₂
COOX ¹ , -CH ₂ CH ₂ COOX ² , X ⁴ , X ⁵ , X ⁶ , X ⁷ , X ⁸ and X ⁹ each independently or together represent a hydrogen, a monovalent metal, a divalent metal, an inorganic or organic ammonium group). A method for preventing scale adhesion in a digester in a kraft pulp manufacturing process, which comprises adding a water-soluble polymer containing the polymer. 2. The water-soluble polymer has the following formula: (In the formula, A ¹ and A ² each independently represent hydrogen, a methyl group or —COOX ¹¹ , and A ¹ and A ² are simultaneously —
It does not become COOX ¹¹ , A ³ represents hydrogen, a methyl group or —CH ₂ COOX ¹² , and A ³ represents —CH ₂ COO.
In the case of X ¹² , A ¹ and A ² each independently represent hydrogen or a methyl group, and X ¹⁰ , X ¹¹ and X ¹² are independently or together hydrogen, a monovalent metal, a divalent metal, an inorganic or organic group. Of the formula (1) and R ¹ and R ² have the above-mentioned meanings, and n / m is 20/80 to 98/2). The method for preventing scale adhesion in the digester described in. 3. R ¹ and R in the formula of the water-soluble polymer
² independently or together, The scale adhesion preventing method in the digester according to claim 1 or 2, wherein the scale adhesion preventing method is selected. 4. R ¹ and R in the formula of the water-soluble polymer
^At least one of the two The method for preventing scale adhesion in the digester according to claim 3, wherein the method is selected from the group consisting of: 5. The amount of the water-soluble polymer added is 1 to 100 ppm with respect to the cooking liquor.
The method for preventing scale adhesion in the digester according to any one of 1.