RU2746828C2 - Application of comb-like polymers as sediment inhibitors in production of cellulose by sulfate method (kraft process) - Google Patents

Abstract

FIELD: polymers.SUBSTANCE: invention relates to the use of comb-like polymers, which can be obtained by radical polymerization of monoethylene-unsaturated monomers from Group A1) monoethylene-unsaturated acids and their salts and Group A2) monoethylene-unsaturated polyesters, as a sediment inhibitor in the production of cellulose by the sulfate method (kraft process).EFFECT: use of comb-like polymers as a sediment inhibitor in the production of cellulose by the sulfate method (kraft process) is proposed.7 cl, 2 tbl, 2 ex

Description

The present invention relates to the use of comb polymers as scale inhibitors in kraft pulp production.

The most important and most commonly used method of making pulp is the kraft process. In 1884, C.F. Dahl patented a method using sodium sulfide or sodium sulfate. The resulting sulphate pulp, due to its high strength, in particular in the case of paper subjected to high mechanical stress, is called kraft paper, and accordingly also kraft pulp.

The method is based on the partial solubility of lignin in hot solutions. The alkaline process uses cooking liquors that contain sodium hydroxide, sodium sulfide, sodium sulfate and sodium carbonate. The chips are processed in an autoclave for three to six hours at an elevated pressure (7-10 bar) and a temperature of 140-170 ° C.

On the one hand, sodium sulfide enhances delignification, while lignin is cleaved due to the nucleophilic attack of sulfide anions and turns into the so-called black liquor (soluble alkaline lignin), and on the other hand, the length of the fibers increases. Along with lignin, carbohydrates are also decomposed in the more alkaline range. Polysulfide-containing liquors stabilize polysaccharides. Kraft pulp paper is tear resistant, break resistant and tensile strength. The advantages of the sulphate method are good impregnation of chips in an alkaline solution and, therefore, a shorter cooking time, it can be used for almost any wood. Sulphate cellulose contains even more polysaccharides and is darker than sulphite cellulose. It does not have a high enough α-cellulose content to produce cellulose derivatives. The lignin-containing waste liquor accumulated in the sulphate process is thickened and burned, which can satisfy the energy demand of the entire process. Turpentine and about 30-35 kg of tall oil per 1000 kg of cellulose are obtained as valuable by-products.

During the cooking process, calcium ions are released from the wood into the solution. They react with sodium carbonate present in the cooking liquor to form poorly soluble calcium carbonate. The resulting calcium carbonate is deposited inside the cooker on pipelines, heat exchangers, etc. This reduces the flow through the digester, the effective amount of liquor, and also the heat transfer. Finally, the installation must be stopped after a short time for cleaning. Calcium carbonate scale inhibitors are added to the cooking process to extend the cleaning intervals.

These scale inhibitors are described in various patents and publications. A good overview of phosphonic acid based calcium carbonate scale inhibitors is found in patent applications WO 02/098802 A1 and WO 02/98803 A1 from Solutia Inc.

In addition, a large number of patents have also been published relating to acrylate-based polymers. Thus, JPH 1025684 (A) describes a terpolymer based on maleic acid, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) with a molecular weight of 500 to 20,000 g / mol.

US Pat. No. 5,409,571 A describes a maleic acid-acrylic acid copolymer that has been polymerized with the addition of hypophosphite. The molecular weight ranges from 500 to 10,000 g / mol.

The use of polyitaconic acid in a mixture with phosphonic acids is known from JP 2011-052358 (A). In the case of "scale inhibitor-1", polyitaconic acid and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) are mixed.

A mixture of two polyitaconic acid polymers with different molecular weights is known from JP 2014-147911 (A). Polymer A has a molecular weight of 500 to 15,000 g / mol and polymer B has a molecular weight of 15,000 to 40,000 g / mol.

WO 00/12436 A patents a copolymer of 1,2-dihydroxy-3-butene and another monomer from the group of maleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, N-tert-butyl acrylamide, butoxymethyl acrylamide, N, N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid and their salts.

The publications listed relate exclusively to the inhibition of inorganic calcium carbonate deposits.

If a highly resinous hardwood such as birch is used in the sulphate pulp process, an additional problem arises. The contained resin leads to sticky deposits, so-called "varu" or "sticky", which during production can lead to an increase in the amount of bleaching chemicals or problems on the paper machine. To remove these sticky substances from the process, resin dispersants are added during the cooking process.

WO 2010/019425 A1 describes the prior art with a good overview of what substances can be used as a resin dispersant.

This application itself discloses a mixture of triglyceride oil or triglyceride alkyl ether with polyalkylene glycol surfactants and / or resin, rosin soap, tall oil, tall oil and derivatives thereof.

WO 2008/057492 A2 describes a vinyl alcohol / vinyl acetate copolymer and hydrophobically modified hydroxyethyl cellulose as a tackifier. In addition, enzymes are mentioned which catalyze the hydrolysis of the resin.

WO 2004/057101 A1 describes a mixture of fatty acids and resin acids as an effective dispersant of extractables.

The publications listed relate exclusively to the inhibition of organic resin deposits.

It is known from practice that although the use of, for example, tall oil in the cooking process reduces resin problems noticeably, this significantly increases the tendency to form inorganic deposits. This trend increases with the concentration of calcium present in the cooking liquor. The higher the calcium concentration, the higher the tendency to form calcium carbonate deposits.

In addition, there is a second negative effect of adding tall oil. Previously effective scale inhibitors are reduced by the addition of tall oil. Even increasing the dosage in these cases is no longer enough. Intensive deposition occurs in boilers, pipes and heat exchangers.

There is no prior art known to address the adverse effect of resin dispersants on the tendency to calcium carbonate deposition.

Thus, it is an object of the present invention to effectively prevent the resin dispersant from negatively affecting the CaCO ₃ precipitation inhibitors in the kraft process. According to the invention, it is necessary to provide polymers which effectively inhibit CaCO ₃ deposition during cooking in the case of adding resin dispersants based on organic carboxylic acids.

Surprisingly, it has been found that comb polymers with polyether side chains significantly reduce the tendency to form calcium carbonate deposits during sulfate pulping. When a comb polymer is added to the cooking process with a resin disperser and a standard CaCO ₃ deposition inhibitor, there is a significant reduction in CaCO ₃ deposition.

The comb polymers used in accordance with the invention can be obtained by radical polymerization of monoethylenically unsaturated monomers from group A1) monoethylenically unsaturated acids and their salts and from group A2) monoethylenically unsaturated polyethers.

Therefore, the object of the invention is the use of comb-like polymers obtained by radical polymerization of monoethylenically unsaturated monomers

from group A1) monoethylenically unsaturated acids and their salts and

from group A2) monoethylenically unsaturated polyethers,

as inhibitors of deposits in the process of obtaining cellulose by the sulfate method (kraft process).

The effect or influence on the inhibition of calcium carbonate deposits has not been mentioned in the prior art. The effect or effect of adding tall oil resin dispersants on the scale inhibiting effect has also not been discussed in the prior art.

The preparation of the comb-like polymers used according to the invention by radical polymerization is known to the person skilled in the art and can be carried out in accordance with European patent application EP 0537870 A. In this connection, the entire content of this publication is introduced by reference.

Examples of monomers of group A1, i.e. monoethylenically unsaturated acids and their salts are acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, vinyl sulfonic acid, allyl sulfonic acid, metal sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, styrene ... Group A1 monomers can be used individually or as a mixture of different monomers. Preferably, acrylic acid, methacrylic acid or maleic acid is used in an amount of 5 to 95% by weight based on polymer, particularly preferably acrylic acid or maleic acid is used in an amount of 10 to 90% by weight based on polymer.

Examples of monomers of the A2 group, i.e. monoethylenically unsaturated polyethers are polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether and polyethylene-polypropylene monoallyl ether; they are available for purchase, for example, from Clariant under the Polyglykol® A product line, from BASF under the Pluriol® A ... R product line, or from NOF Corporation under the Uniox®, Unisafe® and Unilube® product lines. Other examples are polyethylene glycol monovinyl ether (Clariant's Polyglycol® R product line), isoprenylethoxylates (BASF's Pluriol® A ... I product line) and vinyloxybutylethoxylates (BASF's Pluriol® A ... V product line).

Group A2 monomers can be terminally OH or terminated. Monomers can be used singly or as a mixture of different monomers. It is preferable to use polyalkyl glycol monoallyl ethers in an amount of 2 to 25% by weight based on polymer, particularly preferably polyethylene glycol monoallyl ether and polyethylene-polypropylene monoallyl ether in an amount of 5 to 20% by weight based on polymer.

According to the invention, the sulfate pulping application can be carried out continuously or batchwise by adding the comb polymer to the cooking liquor separately, or by introducing the comb polymer into the cooking liquor as a component of a CaCO ₃ scale inhibitor or resin dispersant. Therefore, a further object of the invention is a CaCO ₃ scale inhibitor which comprises a comb-like polymer according to the invention.

The CaCO ₃ scale inhibitors and resin dispersants which contain the comb-like polymer used according to the invention may contain any of the usual ingredients of such agents which do not interact with the polymer in an undesirable manner.

In one preferred embodiment, such a CaCO ₃ scale inhibitor comprises polymers such as homopolymers, copolymers and terpolymers based on monoethylenically unsaturated acids and their salts such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, vinyl sulfonic acid, allyl sulfonic acid, metal sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, styrene sulfonic acid, vinyl phosphonic acid, acrylamide, N-tert-butyl acrylamide, butoxymethyl acrylamide and Ν, Ν-dimethyl.

The following examples illustrate the advantages of the comb polymers used.

Examples of implementation

1. Obtaining comb-shaped polymers

Synthesis example (radical polymerization):

In a 2-liter four-necked flask with a thermometer, a reflux condenser and connections for feeding the raw material and purging with an inert gas was added 328 g of water, 61 g (0.06 mol) of polyalkylene glycol-1000 monoallyl ether (polyglycol A 31/1000, Clariant), and 5 g of butyldiglycol as dissolving agent. Separately, the following mixtures were prepared: monomer solution: 365 g (5.07 mol) acrylic acid in 65 g water; solution 1: 10 g sodium persulfate in 80 g water; solution 2: 26 g of sodium hypophosphite x 1 Η ₂ O in 60 g of water. The batch was heated to 90 ° C. At this temperature, the above solutions were added through separate inlets at constant mass flow over 3 hours (monomer and solution 2) and over 3.5 hours (solution 1). After the addition was complete, the reaction was continued at 90 ° C for 1 hour. A clear, colorless aqueous polymer solution with a solids content of 46 wt.% Was obtained.

The comb polymers shown in Table 1 were prepared in a similar manner.

Table 1

Comb polymer Monoethylene unsaturated polyester Qty (g) Monoethylenically unsaturated acid Qty (g) KP-1 polyglycol A 31/1000 61 acrylic acid 365 KP-2 polyglycol A 11/1800 61 acrylic acid 365 KP-3 Pluriol A10R 61 acrylic acid 365 KP-4 polyglycol A 1100 61 acrylic acid 365

2. Application of comb polymers

An example of implementation: (cooking cellulose by the sulfate method)

The conditions for cooking cellulose by the sulfate method were simulated by the following laboratory method. Into a 200 ml Labomat beaker from Mathis AG equipped with an addition block (septum seal) was placed 100 ml of synthetic white liquor of the following composition:

30.0 g / l sodium hydroxide 100%

11.0 g / l sodium sulfide

7.5 g / l sodium carbonate

2.0 g / l sodium sulfate

The solution was prepared with demineralized water.

Various amounts of scale inhibitor and 100 mg tall oil (from a pulp mill) were added to 100 ml of white liquor and the beaker was closed.

The contents of a Labomat beaker from Mathis AG were heated to 140 ° C and held at this temperature for 60 minutes. After 60 minutes, 8 ml of 0.25 mol / L CaC solution was added with a suitable syringe through the septum. In the first approximation, this corresponds to a concentration of 800 mg / l of Ca ^{2+ ions} in solution.

The temperature was maintained at 140 ° C for an additional 30 minutes. Then the contents of the beaker were cooled to 80 ° C, the beaker was opened and the hot solution was filtered through a black filter.

The filterability, the appearance of the filtrate and the appearance of the filter deposits were evaluated.

Criteria for evaluation:

a) filtration rate

- high <20 sec - - low 20-30 sec + - very low > 30 sec ++

b) appearance of the filtrate

- transparent

- cloudy

- very cloudy

c) appearance of filter deposits

1 = black filter without deposits

2 = black filter with little deposits

3 = crystalline deposits comparable to blank

4 = crystalline deposits, less than blank

5 = amorphous and crystalline deposits

6 = amorphous deposits

A slow filtration rate (> 30 sec), cloudy filtrate, and amorphous filter deposits were considered good sludge inhibition effects.

3. Results of technical tests

Experience no. Designation Filter Filtration speed [sec] Filtrate appearance Deposits appearance one 800 ppm calcium
without tall oil,
without polymer

- transparent crystalline deposits 2 800 ppm calcium
without tall oil,
20mg standard polymer

- transparent crystalline deposits 3 800 ppm calcium
without tall oil,
30mg standard polymer

- transparent crystalline deposits four 800 ppm calcium
without tall oil,
40mg standard polymer

++ transparent amorphous deposits five 800 ppm calcium
100mg tall oil
without polymer

- transparent amorphous and crystalline deposits 6 800 ppm calcium
100mg tall oil
40mg standard polymer

- transparent crystalline deposits 7 800 ppm calcium
100mg tall oil
50mg standard polymer

- transparent crystalline deposits eight 800 ppm calcium
100mg tall oil
60mg standard polymer

+ transparent amorphous and crystalline deposits nine 800 ppm calcium
100mg tall oil
30mg standard polymer
10 mg KP-1

++ slightly cloudy amorphous deposits 10 800 ppm calcium
100mg tall oil
30mg standard polymer
10 mg KP-2

++ turbid amorphous deposits eleven 800 ppm calcium
100mg tall oil
30mg standard polymer
10 mg KP-3

++ turbid amorphous deposits 12 800 ppm calcium
100mg tall oil
30mg standard polymer
10 mg KP-4

++ turbid amorphous deposits

Standard polymer = copolymer of acrylic acid and maleic acid, which is used in practice as a scale inhibitor in kraft pulping.

The discussion of the results

Runs 1-4 show results without adding tall oil.

Test 1 clearly shows how significant crystalline deposits can occur under pulping conditions if a scale inhibitor is not used. The coarse crystalline structure leads to complete and rapid filtration of sediments, the filtrate is transparent. In Runs 2-4, different concentrations of scale inhibitors were added. The used amounts of 20 and 30 mg (tests 2 and 3) only slightly affect the performance of the test. In addition, mainly coarse crystalline structures are formed, which lead to rapid and complete filtration. Starting at 40 mg, the results change dramatically. The crystal structure changes from coarse crystalline to fine amorphous. The pores of the filter media quickly fill up and the filtration rate is greatly reduced. Experimental experience shows that a crystal modification mechanism is needed to effectively prevent the formation of CaCO ₃ deposits during pulping in practice.

Test 5 shows the effect of tall oil on the deposited deposits. Compared to test 1, the deposits on the filter clearly increased. Further, test 6 demonstrates the whole known problem from practice, which is that, due to the use of tall oil, standard polymers do not cope and are no longer effective enough. While the standard polymer in Run 4 could still effectively modify the deposited deposits, Run 6 failed at all. Although an increase in the amount used (experiments 7 and 8) somewhat improves the situation, this is far from giving a sufficient effect.

Tests 9-12 demonstrate the exceptional action of the comb-shaped polymers used according to the invention. All experiments show fine amorphous, non-crystalline, deposits on filter paper. The filtration rate has increased significantly and the deposits can even be so finely dispersed that the filtrate becomes cloudy. Another positive effect is the amount of polymer used. By using comb-like polymers, it is even possible to reduce the amount of standard polymer used.

Claims (12)

1. The use of comb-shaped polymers obtained by radical polymerization of monoethylenically unsaturated monomers from group A1) monoethylenically unsaturated acids and their salts, and from group A2) monoethylenically unsaturated polyethers, as inhibitors of deposits in the production of cellulose by the sulfate method (kraft process). 2. The use of comb-like polymers according to claim 1 in a continuous or batch process of pulping using the sulfate method. 3. The use of comb polymers according to claim 1 in cooking liquor as a separate additive or as a component of a conventional CaCO ₃ scale inhibitor or resin dispersant. 4. The use according to any one of paragraphs. 1-3, in which said scale inhibitor for the production of cellulose by the kraft process (kraft process) contains from 0.1 to 30 wt.%, In particular from 0.5 to 25 wt.%, Comb polymers obtained by radical polymerization of monoethylene- unsaturated monomers from group A1) monoethylenically unsaturated acids and their salts, and from group A2) monoethylenically unsaturated polyethers. 5. Use according to claim 4, wherein said scale inhibitor is characterized in that said components are selected from polymers such as homopolymers, copolymers and terpolymers based on monoethylenically unsaturated acids and their salts such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, vinyl sulfonic acid, allyl sulfonic acid, metal sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid, vinyl phosphonic acid, acrylamide, N-tert-butyl-butyl-acrylamide ... 6. Use according to claim 4 or 5, wherein said scale inhibitor is characterized in that it further comprises phosphonic acids, in particular HEDP, ATMP and / or DTPMP, phosphonopolycarboxylic acids, in particular PBTC, aminopolycarboxylic acids, in particular MGDA, GLDA , IDS and / or EDDS, and / or hydroxycarboxylic acids, in particular gluconic acid and / or citric acid. 7. The use according to any one of paragraphs. 3-6, wherein said scale inhibitor is characterized in that the resin dispersant components are selected from nonionic or anionic surfactants, tall oil, tall oil soaps, fatty acids and their soaps, resin acids and their soaps, triglyceride oils and triglyceride alkyl esters.