EP3568519B1 - Deposit prevention in pulp production according to the sulphate process (kraft process) - Google Patents

Description

The present invention relates to the use of comb polymers as deposit inhibitors in pulp production using the sulfate process (Kraft digestion).

The most important and most frequently used process for the production of pulp is the sulphate or Kraft process. In 1884 C. F. Dahl applied for a patent for a process using sodium sulfide or sodium sulfate. Because of its high strength, the resulting sulphate pulp is particularly preferred for "Kraft papers" which are subject to high mechanical loads and is therefore also referred to as Kraft pulp.

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

On the one hand, sodium sulphide increases delignification, in this case the lignin is split by a nucleophilic attack by the sulphide anion and changes into the so-called black liquor (soluble alkali lignin), and on the other hand, the fiber lengths are increased. In addition to lignin, carbohydrates are broken down in the more alkaline range. Polysulphide containing Alkalis stabilize the polyoses. Kraft pulp paper is tear-proof, break-proof and tensile strength. Advantages of the sulphate process are that the wood chips are soaked in an alkaline solution and thus shorter cooking times; practically all types of wood can be used. Sulphate pulps contain even larger amounts of polyoses and are darker than sulphite pulps. They do not have a sufficiently high content of α-cellulose for the production of cellulose derivatives. The lignin-containing waste liquors resulting from the sulphate process are concentrated and incinerated so that the energy requirements of the entire process can be covered. Turpentine oil and approx. 30 to 35 kg tall oil per 1,000 kg pulp are produced as valuable by-products.

Calcium ions are released from the wood during the cooking process. These react with the sodium carbonate present in the cooking liquor to form poorly soluble calcium carbonate. The calcium carbonate that forms is deposited inside the cooker in pipes, heat exchangers, etc. This reduces the flow through the cooker, the effective amount of lye and the heat transfer. Ultimately, the system has to be shut down and cleaned after a short time. To extend these cleaning intervals, deposit inhibitors against calcium carbonate are added to the cooking process.

These scale inhibitors are described in a variety of patents and publications. The patent applications give a good overview of phosphonic acid-based deposit inhibitors for calcium carbonate WO 02/098802 A1 and WO 02/98803 A1 from Solutia Inc.

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

U.S. 5,409,571 A discloses a copolymer based on maleic acid and acrylic acid which was polymerized with the addition of hypophosphite. The molecular weight is 500 to 10,000 g / mol.

The use of polyitaconic acid in a mixture with phosphonic acids is off JP 2011-052358 (A. ) known. With "Scale inhibitor-1", polyitaconic acid and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) are mixed.

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

WO 00/12436 A claims a copolymer of 1,2-dihydroxy-3-butene, and another monomer from the group maleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid, vinylsulphonic acid, styrenesulphonic acid, N-tert.-butylacrylamide, butoxymethylacrylamide, N, N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid and salts thereof.

The publications listed deal exclusively with the inhibition of deposits from inorganic calcium carbonate.

Are hardwoods rich in resin, such as e.g. When using birch, there is another problem. The contained resin leads to sticky deposits, so-called "pitch" or "sticky", which during the manufacturing process can lead to an increase in bleaching chemicals or to problems on the paper machine. In order to remove these sticky substances from the process, resin dispersants are already used during the manufacturing process added during the cooking process.

WO 2010/019425 A1 gives a good overview of the substances that can be used as resin dispersants in the prior art listed.

The application itself claims a mixture of triglyceride oil or triglyceride alkyl ester with polyalkylene glycol-based surfactants and / or resin, resin soaps, tall oil, tall oil soaps and derivatives thereof.

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

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

The publications listed deal exclusively with the inhibition of organic resin deposits.

It is known from practice that by using, e.g. Tall oil, although the resin problem is significantly improved in the cooking process, this significantly increases the tendency for inorganic deposits. The tendency increases with the calcium concentration present in the cooking liquor. The higher the concentration of calcium, the higher the tendency for calcium carbonate deposits to occur.

In addition, there is a second negative effect due to the addition of tall oil. The previously effective deposit inhibitors are reduced in their effect by the added tall oil. Even increasing the dosage is no longer sufficient in these cases. There are massive deposits in the cooker, pipes and heat exchangers.

No work is known from the prior art which addresses the negative effects of resin dispersants on the deposition tendency of calcium carbonate.

EP 2 020 422 A1 discloses emulsifying polymers and the use of these polymers for the stable emulsification of hydrophobic additives in aqueous concrete plasticizers. The polymers are obtainable by copolymerizing at least one ethylenically unsaturated monomer which comprises ionic groups with at least one ethylenically unsaturated monomer which has hydrophilic oxyalkylene groups and at least one ethylenically unsaturated monomer which has vinyl aromatics and at least one hydrophobic ethylenically unsaturated monomer.

Out DE 10 2013 207778 A1 the use of comb polymers in detergents and cleaning agents is known, especially in textile finishing, and corresponding agents. The comb polymers used are obtainable by A) a radical polymerization of monoethylenically unsaturated monomers of a group A1) monoethylenically unsaturated acids and their salts and a group A2) monoethylenically unsaturated polyethers and / or a group A3) monoethylenically unsaturated acids, which were previously terminally hydrophobic with one side blocked polyalkylene oxides, or by B) a polymer-analogous reaction by esterification and / or amidation of a group B1) polycarboxylic acids and their salts with a group B2) monohydroxy polyethers and / or a group B3) monoamine compounds.

The object of the present invention is therefore to effectively prevent the negative influence of resin dispersants on the CaCO ₃ deposition inhibitors during the Kraft cooking process. According to the invention, polymers are to be provided which effectively inhibit the deposits of CaCO ₃ during the cooking process when the process is carried out with the addition of resin dispersants based on organic carboxylic acids.

Surprisingly, it has been found that comb polymers with polyether side chains significantly reduce the tendency for calcium carbonate to deposit during the cooking of pulp using the sulfate process. Used a cooking process performed with resin dispersant and a standard CaCO ₃ deposition inhibitor Comb polymer added, there is a significant reduction in CaCO ₃ deposits.

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

• der Gruppe A1) monoethylenisch ungesättigte Säuren oder deren Salze
• und der Gruppe A2) monoethylenisch ungesättigte Polyether

als Ablagerungsinhibitoren in der Zellstoffherstellung nach dem Sulfatverfahren (Kraft-Aufschluss).The invention therefore relates to the use of comb polymers, obtainable by free radical polymerization of monoethylenically unsaturated monomers

• of group A1) monoethylenically unsaturated acids or their salts
• and group A2) monoethylenically unsaturated polyethers

as deposit inhibitors in pulp production using the sulphate process (Kraft pulping).

The effect or the influence on the deposit inhibition with respect to calcium carbonate is not mentioned in the prior art. The effect or the influencing of the deposit-inhibiting effect through the addition of resin dispersants based on tall oil is likewise not addressed in the prior art.

The preparation of the comb polymers used according to the invention via free radical polymerization is known to the person skilled in the art and can be based on the European patent application EP 0 537 870 A carried out will. In this respect, reference is made in full to this publication.

Examples of the monomers of group A1, the monoethylenically unsaturated acids and their salts are acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, 2-acrylamido-2-methyl-propanesulfonic acid, styrenesulfonic acid, vinylphosphonic acid. The monomers of group A1 can be used individually or as a mixture of different monomers. Acrylic acid, methacrylic acid or maleic acid are preferably used in an amount of 5 to 95% by weight, based on the polymer, and acrylic acid or maleic acid is particularly preferably used in an amount of 10 to 90% by weight, based on the polymer.

Examples of the monomers of group A2, the monoethylenically unsaturated polyether, are polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether and polyethylene-polypropylene monoallyl ether; these are e.g. Commercially available from Clariant under the Polyglykol® A product series, from BASF under the Pluriol® A ... R product series or from NOF Corporation under the Uniox®, Unisafe® and Unilube® product series. Further examples are polyethylene glycol monovinyl ether (product range from Clariant: Polyglycol® R), isoprenyl ethoxylates (product range from BASF: Pluriol® A ... I) and vinyloxybutyl ethoxylates (product range from BASF: Pluriol® A ... V).

The monomers of group A2 can be OH-terminated or have an end group cap. The monomers can be used individually or as a mixture of different monomers. Polyalkyl glycol monoallyl ethers are preferably obtained in an amount of from 2 to 25% by weight based on the polymer, particularly preferably polyethylene glycol monoallyl ether and polyethylene-polypropylene monoallyl ether are used in an amount of from 5 to 20% by weight, based on the polymer.

The use according to the invention can be carried out in the context of a pulp production according to the sulfate process in a continuous or discontinuous process in such a way that the comb polymer is added separately to a cooking liquor, or the comb polymer is introduced into the cooking liquor as a component of the CaCO ₃ deposition inhibitor or the resin dispersant. The disclosure therefore also relates to a CaCO ₃ deposition inhibitor which contains a comb polymer according to the invention. In a preferred embodiment of the invention, a comb polymer according to the invention is used in a deposit inhibitor, the deposit inhibitor for pulp production by the sulfate process (Kraft digestion) 0.1 to 30% by weight, in particular 0.5 to 25% by weight of comb polymer , obtainable by a radical polymerization of monoethylenically unsaturated monomers
a group A1) monoethylenically unsaturated acids and their salts and
from group A2) monoethylenically unsaturated polyethers,
includes.

CaCO ₃ deposition inhibitors and resin dispersants which contain the comb polymer to be used according to the invention can all be customary contain other ingredients of such agents which do not interact with them in an undesired manner.

In a preferred embodiment, such a CaCO ₃ deposition inhibitor contains polymers as mono-, co- and terpolymers based on monoethylenically unsaturated acids and their salts, such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, 2- Acrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylphosphonic acid, acrylamide, N-tert-butyl acrylamide, butoxymethylacrylamide and N, N-dimethylacrylamide.

Another object of the invention is the use of comb polymers, obtainable by a radical polymerization of monoethylenically unsaturated monomers of a group A1) monoethylenically unsaturated acids and their salts and group A2) monoethylenically unsaturated polyethers, in the pulp washing after the sulfate cooking process.

The following examples illustrate the advantages of the comb polymers used

Embodiments: 1. Manufacture of comb polymers Synthesis example (radical polymerization):

328 g of water, 61 g (0.06 mol) of polyalkylene glycol 1000 monoallyl ether (Polyglycol A 31/1000, Clariant) and 5 g of butyl diglycol were placed in a 2 liter four-necked flask equipped with a thermometer, reflux condenser and connections for feeds and inert gas flushing , presented as a solubilizer. The following mixtures were prepared separately: Monomer solution: 365 g (5.07 mol) of acrylic acid in 65 g of water. Solution 1: 10 g sodium persulfate in 80 g water. Solution 2: 26 g sodium hypophosphite x 1 H ₂ O in 60 g water. The template was heated to 90 ° C. At At this temperature, the solutions listed above were metered in via separate feeds with a constant mass flow over 3 hours (monomer and solution 2) and over 3.5 hours (solution 1). After the addition was complete, the mixture was reacted at 90 ° C. for 1 hour. A clear, colorless, aqueous polymer solution with a solids content of 46% by weight was obtained.

The comb polymers listed in Table 1 were prepared in an analogous manner. Table 1: Comb polymer Monoethylenically unsaturated polyethers Amount [g] Monoethylenically unsaturated acid Amount [g] KP-1 Polyglycol® A 31/1000 61 Acrylic acid 365 KP-2 Polyglycol® A 11/1800 61 Acrylic acid 365 KP-3 Pluriol® A 10 R 61 Acrylic acid 365 KP-4 Polyglycol® A 1100 61 Acrylic acid 365

2. Application of comb polymers Application example: (pulp boiling according to the sulphate process)

• 30,0 g/L Natriumhydroxid 100%
• 11,0 g/L Natriumsulfid
  • 7,5 g/L Natriumcarbonat
  • 2,0 g/L Natriumsulfat

The conditions during the pulp cooking according to the sulfate process were simulated using the following laboratory method. In 200 mL Labomat beakers from Mathis AG, which are equipped with an addition unit (Closure with septum), 100 mL of a synthetic white liquor with the following composition were placed in each case:

• 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 made with demineralized water.

Variable amounts of scale inhibitor and 100 mg tall oil (from a pulp mill) are added to the 100 mL white liquor and the beakers are sealed.

The contents of the beaker were heated to 140 ° C. in the Labomat from Mathis AG and this temperature was maintained for 60 minutes. After 60 minutes, 8 mL of a 0.25 mol / L CaCl ₂ solution were metered in with a suitable syringe via the septum. As a first approximation, this corresponded to a concentration of 800 mg / L Ca ²⁺ ions in the solution.

The 140 ° C was maintained for a further 30 minutes. The contents of the beaker were then cooled to 80 ° C., the beakers were opened and the hot solution was filtered off through black filters.

The assessment was based on the filterability, the appearance of the filtrate and the appearance of the deposits on the filter.

Assessment criteria: a) Filtration rate

▪ quickly <20 sec - ▪ slowly 20 - 30 sec + ▪ very slowly > 30 sec ++

b) Appearance of the filtrate

• ▪ clear
• ▪ cloudy
• ▪ very cloudy

c) Appearance of the deposit on the filter

▪ 1 = Black filter without deposits ▪ 2 = Black filter with few deposits ▪ 3 = Crystalline deposits, comparable to the blank value ▪ 4 = Crystalline deposits, less compared to the blank value ▪ 5 = Amorphous and crystalline deposits ▪ 6 = Amorphous deposits

A slow filtration speed (> 30 sec), a cloudy filtrate and amorphous deposits on the filter were considered to have a good deposit-inhibiting effect.

3. Results of the application test

Experiment no .: designation filter Filtration speed [sec] Appearance of the filtrate Appearance of the deposits 1 800 ppm calcium

- clear Crystalline deposits Without tall oil Without polymer 2 800 ppm calcium

- clear Crystalline deposits Without tall oil 20 mg standard polymer 3 800 ppm calcium

- clear Crystalline deposits Without tall oil 30 mg standard polymer 4th 800 ppm calcium

++ clear Amorphous deposits Without tall oil 40 mg standard polymer 5 800 ppm calcium

- clear Amorphous and crystalline deposits 100 mg tall oil Without polymer 6 800 ppm calcium

- clear Crystalline deposits 100 mg tall oil 40 mg standard polymer 7th 800 ppm calcium

- clear Crystalline deposits 100 mg tall oil 50 mg standard polymer 8th 800 ppm calcium

+ clear Amorphous and crystalline deposits 100 mg tall oil 60 mg standard polymer 9 800 ppm calcium

++ Slightly cloudy Amorphous deposits 100 mg tall oil 30 mg standard polymer 10 mg KP-1 10 800 ppm calcium

++ cloudy Amorphous deposits 100 mg tall oil 30 mg standard polymer 10 mg KP-2 11 800 ppm calcium

++ cloudy Amorphous deposits 100 mg tall oil 30 mg standard polymer 10 mg KP-3 12 800 ppm calcium

++ cloudy Amorphous deposits 100 mg tall oil 30 mg standard polymer 10 mg KP-4

Standard polymer = acrylic acid / maleic acid copolymer, which is used in practice as a deposit inhibitor in pulp boiling according to the sulfate process.

Discussion of the results:

The tests of numbers 1 to 4 show results without the addition of tall oil.

Experiment no. 1 clearly shows the massive crystalline deposits that can arise under the conditions of a cellulose boil if no deposit inhibitor is used. Due to the coarse crystalline structure, the deposits are completely and quickly filtered off, the filtrate is clear. In experiments No. 2 to No. 4, different concentrations of scale inhibitors were added. The test parameters are only insignificantly influenced when using 20 and 30 mg (tests 2 and 3). Mainly coarse crystalline structures continue to arise, which lead to rapid and complete filtration. The results change suddenly from a concentration of 40 mg. The crystal structure changes from coarse crystalline to fine amorphous. The pores of the filter material are quickly clogged and there is a significant reduction in the rate of filtration. From experience the mechanism of crystal modification is necessary in order to work effective to prevent CaCO ₃ deposits during pulp boiling.

Experiment no. 5 shows the effect of tall oil on the resulting deposits. Compared to experiment no. 1, the deposits on the filter have obviously increased. Experiment no. 6 now reveals the entire problem known from practice that the standard polymers fail due to the use of tall oil and are no longer sufficiently effective. If the standard polymer in experiment no. 4 was still able to effectively modify the deposits formed, it failed completely in experiment no. 6. Increasing the amount used (experiment nos. 7 and 8) improves the situation somewhat, but it is far from having a sufficient effect.

Experiments No. 9 to 12 show the excellent effect of the comb polymers used according to the invention. In all tests, fine amorphous, not crystalline, deposits were found on the filter paper. The filtration speed has increased significantly and the deposits could even be dispersed so finely that the filtrate becomes cloudy. Another positive effect is the amount of polymer used. By using the comb polymers, it was even possible to reduce the amount of standard polymer used.

Claims (8)

1. Use of comb polymers obtainable by free-radical polymerization of monoethylenically unsaturated monomers

   from group A1) of monoethylenically unsaturated acids and salts thereof, and

   from group A2) of monoethylenically unsaturated polyethers,

   as deposition inhibitors in the pulp production according to the sulfate method (kraft pulping).
2. The use of the comb polymers according to claim 1 in a continuous or batch process of pulp cooking according to the sulfate method.
3. The use of the comb polymers according to claim 1 as a separate additive or as a component of a conventional CaCO₃ deposition inhibitor, or of a resin dispersant into the cooking liquor.
4. The use according to any of claims 1 to 3, wherein said deposition inhibitor for pulp production according to the sulfate method (kraft pulping) comprises from 0.1 to 30% by weight, especially from 0.5 to 25% by weight, comb polymers obtainable by free-radical polymerization of monoethylenically unsaturated monomers

   from group A1) of monoethylenically unsaturated acids and salts thereof, and

   from group A2) of monoethylenically unsaturated polyethers.
5. The use according to claim 4, wherein said deposition inhibitor is characterized in that the components are selected from polymers as mono-, co- and terpolymers based on monoethylenically unsaturated acids and salts thereof, such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid, vinylphosphonic acid, acrylamide, N-tert-butylacrylamide, butoxymethylacrylamide, and N,N-dimethylacrylamide.
6. The use according to claim 4 or 5, wherein said deposition inhibitor is characterized by further containing phosphonic acids, especially HEDP, ATMP and/or DTPMP, phosphonopolycarboxylic acids, especially PBTC, aminopolycarboxylic acids, especially MGDA, GLDA, IDS and/or EDDS, and/or hydroxycarboxylic acids, especially gluconic acid and/or citric acid.
7. The use according to any of claims 4 to 6, wherein said deposition inhibitor is characterized in that the components of the resin dispersant are selected from non-ionogenic or anionic surfactants, tall oil, tall oil soaps, fatty acids and soaps thereof, resin acids and soaps thereof, triglyceride oils and triglyceride alkyl esters.
8. Use of comb polymers obtainable by free-radical polymerization of monoethylenically unsaturated monomers

   from group A1) of monoethylenically unsaturated acids and salts thereof, and

   from group A2) of monoethylenically unsaturated polyethers,

   in pulp washing according to the sulfate cooking process.