WO2018130528A1 - Deposit prevention in pulp production according to the sulphate process (kraft process) - Google Patents

Abstract

The invention relates to the use of comb polymers as deposit inhibitors in pulp production according to the sulphate process (Kraft process), which comb polymers can be obtained by radical polymerisation of monoethylenically unsaturated monomers from group A1) monoethylenically unsaturated acids and the salts thereof, and from group A2) monoethylenically unsaturated polyethers.

Description

 Deposition prevention in pulp production by the sulphate process (force breakdown)

The present invention relates to the use of comb polymers as scale inhibitors in pulp production by the sulfate process (Kraft pulping).

The most important and most frequently used process for the production of pulp is the sulphate or kraft process. In 1884, C.F. Dahl patented a process using sodium sulfide or sodium sulfate, respectively. The resulting sulphate pulp is preferred because of its high strength, especially for mechanically stressed paper "kraft papers" and therefore also kraft pulp.

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

On the one hand, sodium sulfide increases the delignification, in which the lignin is split by a nucleophilic attack of the sulfide anion and turns 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 also degraded in the more alkaline range. Polysulfide-containing lyes stabilize the polyoses. Paper made of Kraftpulp is tear-resistant, unbreakable and tensile. Advantages of the sulphate process are a good impregnation of the chips in alkaline solution and thus shorter cooking times, it can be used virtually all woods. Sulfate pulps contain even larger amounts of polyoses and are darker than sulfite pulps. They do not have a sufficiently high content of α-cellulose for the production of cellulose derivatives. The lignin-containing waste liquors arising from the sulphate process are concentrated and incinerated so that the energy requirement of the entire process can be met. As valuable by-products, turpentine oil and about 30 to 35 kg of tall oil per 1,000 kg of pulp are produced.

During the cooking process, calcium ions are released from the wood. These react with the sodium carbonate present in the cooking liquor to form sparingly soluble calcium carbonate. The forming calcium carbonate deposits inside the digester in piping, heat exchangers, etc. This reduces the flow through the stove, the effective amount of liquor and the heat transfer. Finally, the system must be shut down and cleaned after a short time. To prolong these cleaning intervals, calcium carbonate scale inhibitors are added to the cooking process.

These scale inhibitors are described in a variety of patents and publications. A good overview of phosphonic acid based deposit inhibitors for calcium carbonate gives the patent applications WO 02/098802 Al and WO 02/98803 Al of the Fa. Solutia Inc.

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

No. 5,409,571 A discloses a copolymer based on maleic acid and acrylic acid which has been 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 known from JP 2011-052358 (A). In "Scale inhibitor-1" polyitaconic acid and l-hydroxyethylidene-l, l-diphosphonic acid (HEDP) are mixed.

JP 2014-147911 (A) discloses a mixture of two polyitaconic acid polymers having different molecular weights. 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 claims a copolymer of l, 2-dihydroxy-3-butene, and another monomer from the group of maleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid, vinylsulfonic acid, styrenesulfonic acid, N-tert-butylacrylamide, butoxymethylacrylamide , N, N-dimethylacrylamide, 2-acrylamido-2-methylpropanesulfonic acid and salts thereof. The publications listed are exclusively concerned with the inhibition of deposits of inorganic calcium carbonate.

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

WO 2010/019425 AI gives in the cited prior art a good overview of which substances can be used as a resin dispersant.

The application itself claims a mixture of triglyceride oil or triglyceride alkyl esters with polyalkylene glycol based surfactants and / or resin, rosin 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. Also mentioned are enzymes which catalyze the hydrolysis of resin.

WO 2004/057101 A1 discloses a mixture of fatty acids and resin acids as an effective dispersant with respect to extractable substances. The publications listed are exclusively concerned with the inhibition of organic resin deposits.

From practice it is known that through the use of, for. As tall oil in the cooking process, although the resin problem is significantly improved, as ^¬ by the tendency of inorganic deposits is significantly increased sig- nificant. The tendency increases with the existing calcium concentration in the cooking liquor. The higher the concentration of calcium, the higher the tendency for calcium carbonate deposits to form.

In addition, there is a second negative effect from the addition of tall oil. The previously effective deposit inhibitors are reduced by the added tall oil in their effect. Even an increase in dosing quantities is no longer sufficient in these cases. It comes to massive deposits in the stove, pipes and heat exchangers.

The prior art does not work is known, t he has made the nega ^¬ tive impact of Harzdispergiermitteln on t he deposit tendency of calcium carbonate to the task.

The object of the present invention is the ne gative ^¬ influencing the CaC0 ₃ -Ablagerungsinhibitoren by resin dispersant during the kraft cooking process effectively unterbin ^¬. According to the invention, polymers are to be provided which effectively inhibit the deposits of CaCO ₃ during the cooking process. when working 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 of calcium carbonate to deposit during pulp cooking after the sulphate process. When a comb polymer is added to a cooking process performed with resin dispersant and a standard CaC0 ₃ deposition inhibitor, there is a significant reduction in CaCO ₃ deposits.

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

The invention therefore provides the use of comb polymers obtainable by a free-radical polymerization of monoethylenically unsaturated monomers

the group AI) monoethylenically unsaturated acids or their salts and the group A2) monoethylenically unsaturated polyethers as scale inhibitors in pulp production by the sulfate process (Kraft pulping). The effect on deposit inhibition over calcium carbonate is not mentioned in the prior art. The effect or the influence of the deposit-inhibiting effect by the addition of tall oil-based resin dispersants is likewise not addressed in the prior art.

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

Examples of the monomers of group AI, 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-methylpropanesulfonic acid, styrenesulfonic acid, vinylphosphonic. The monomers of group AI can be used individually or as a mixture of different monomers. Preference is given to acrylic acid, methacrylic acid or maleic acid in an amount of from 5 to 95% by weight, based on the polymer, acrylic acid or maleic acid being particularly preferably used in an amount of from 10 to 90% by weight, based on the polymer.

Examples of the monomers of group A2, the monoethylenically unsaturated polyethers are polyethylene glycol monoallyl ether, polypropyleneglycol monoallyl ether and polyethylene-polypropylene monoallyl ether; these are, for example, by the company. Clariant under the product number polyglycol ^® A, from Fa. BASF ^® under the product number Pluriol A ... R or by the company. NOF Corporation under the product rows Uniox ^® 'Unisafe ^® and Unilube ^® commercially available. Further examples are Polyethylenglycolmonovinylether (range from Clariant. Polyglycol ^® R) Isoprenylethoxilate (product series from BASF. Pluriol ^® A ... I) and Vinyloxybutylethoxilate (product series from BASF. Pluriol ^® A ... V).

The monomers of group A2 can be OH-terminated or have an end-group bond. The monomers may be used singly or as mixtures of different monomers. Preference is given to using polyalkyl glycol monoallyl ethers in an amount of from 2 to 25% by weight, based on the polymer, more preferably using polyethylene glycol monoallyl ether and polyethylene-polypropylene monoallyl ether with an amount of from 5 to 20% by weight, based on the polymer.

The use according to the invention can be carried out as part of pulp production by the sulphate process in a continuous or discontinuous process such that the comb polymer is added separately to a cooking liquor, or the comb polymer is introduced into the cooking liquor as a constituent of the CaC0 ₃ deposition inhibitor or the resin dispersant. Another object of the invention is therefore a CaC0 ₃ deposition inhibitor containing a comb polymer according to the invention.

CaC0 ₃ deposition inhibitors and resin dispersants containing the comb polymer to be used in the present invention may contain any of the usual ingredients of such agents which do not undesirably interact therewith. In a preferred embodiment, such a CaC0 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-butylacrylamide, butoxymethylacrylamide and N, N-dimethylacrylamide.

The following examples illustrate the advantages of the comb polymers used

EXEMPLARY EMBODIMENTS:

1. Preparation of comb polymers

Synthesis Example (Radical Polymerization):

In a 2-liter four-necked flask equipped with thermometer, reflux condenser and feed and inert gas purge connections were added 328 g of water, 61 g (0.06 mol) of polyalkylene glycol 100OO-monoallyl ether (Polyglycol A 31/1000, Clariant) and 5 g of butyl diglycol , as a solubilizer, submitted. Separately, the following mixtures were prepared: Monomer solution: 365 g (5.07 mol) of acrylic acid in 65 g of water. Solution 1: 10 g of sodium persulfate in 80 g of water. Solution 2: 26 g of sodium hypophosphite x 1 Η ₂ 0 in 60 g of water. The original was heated to 90 ° C. At this temperature, the solutions listed above via separate feeds with a constant mass flow over 3 hours (monomer and solution 2) and over 3.5 h (solution 1) were added. To Addition end was post-reacted at 90 ° C for 1 hour. A clear, colorless, aqueous polymer solution having a solids content of 46% by weight was obtained.

In an analogous manner, the comb polymers listed in Table 1 were prepared.

Table 1 :

2. Application comb polymers

Example of use: (pulp boiling after the sulphate process)

The conditions during the pulping by the sulfate method were simulated by the following laboratory method. 100 mL of a synthetic white liquor of the following composition were placed in 200 mL Labomat beakers from Mathis AG, which were provided with an addition unit (closure with septum):

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 of tall oil (from a pulp mill) are added to the 100 ml of white liquor and the cups are closed.

In Labomat from Mathis AG, the contents of the beaker were heated to 140 ° C. and this temperature was maintained for 60 minutes. After 60 minutes, 8 mL of a 0.25 mol / L CaC solution was metered in via the septum using a suitable syringe. This corresponded to a first approximation of 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 cup were then cooled to 80 ° C, the cups were opened and the hot solution filtered through black filter.

The assessment was made on the filterability, the appearance of the filter plate and the appearance of the deposits on the filter.

Assessment criteria:

a) Filtration speed

^■ fast <20 sec

^■ slowly for 20 - 30 sec +

^■ very slowly> 30 sec + + b) Appearance of the filtrate

^■ clear

^■ cloudy

^■ heavily 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 blank value

^■ 4 = Crystalline deposits, less compared to the blank value

^■ 5 = amorphous and crystalline deposits

^■ 6 = amorphous deposits

As a good deposit-inhibiting effect, a slow filtration rate (> 30 sec), a turbid filtrate and amorphous deposits on the filter were considered.

3. Results of the application test

 10 mg KP-4 lil

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

Discussion of the results:

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

Experiment No. 1 clearly shows what massive crystalline deposits can be formed under pulp cooking conditions when no scale inhibitor is used. The coarse-crystalline structure leads to a complete and rapid filtration of the deposits, the filtrate is clear. In Runs # 2 through # 4, different levels of scale inhibitors were added. For the amounts used of 20 and 30 mg (experiments Nos. 2 and 3), the test parameters are only insignificantly influenced. Mainly coarse-crystalline structures are formed, which lead to rapid and complete filtration. From a concentration of 40 mg, the results change abruptly. The crystal structure changes from coarse-crystalline to fine-amorphous. The pores of the filter material are added quickly and there is a significant reduction in the filtration rate. From experience, the mechanism of crystal modification is necessary to practice effective to prevent CaC0 ₃ deposits during pulp cooking.

Experiment No. 5 shows the effect of tall oil on the resulting deposits. Compared to experiment # 1, the deposits on the filter have obviously increased. Experiment No. 6 now discloses the whole problem known from practice that the standard polymers fail by the use of tall oil and are no longer sufficiently effective. If the standard polymer in Experiment No. 4 could still effectively modify the resulting deposits, it completely fails in Experiment No. 6. An increase in the amount used (experiments Nos. 7 and 8) does improve the situation, but it is far from having sufficient effect.

Experiments Nos. 9 to 12 show the excellent effect of the comb polymers used according to the invention. All tests show fine amorphous, no crystalline, deposits on the filter paper. The filtration rate has increased significantly and the deposits could even be finely dispersed so that turbidity of the filtrate occurs. Another positive effect is the amount of polymer used. By using the comb polymers, the amount of standard polymer used could even be reduced.

Claims

claims 1. Use of comb polymers obtainable by a radical polymerization of monoethylenically unsaturated monomers of a group AI) monoethylenically unsaturated acids and their salts and the group A2) monoethylenically unsaturated polyethers as scale inhibitors in pulp production by the sulfate process (Kraft pulping). 2. Use of the comb polymers according to claim 1 in a continuous or discontinuous process of pulp cooking by the sulfate process. 3. Use of the comb polymers according to claim 1 as a separate additive or as part of a conventional CaCO 3 deposition inhibitor or a resin dispersant in the cooking liquor. 4. Deposition inhibitor for pulp production by the sulphate process (Kraft pulping) comprising 0.1 to 30% by weight, in particular 0.5 to 25% by weight, of comb polymers obtainable by free-radical polymerization of monoethylenically unsaturated monomers of a group AI) monoethylenically unsaturated acids and their salts and the group A2) monoethylenically unsaturated polyethers. 5. Deposition inhibitor according to claim 4, characterized in that the constituents of 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-butylacrylamide, butoxymethylac- rylamid and Ν, Ν-dimethylacrylamide are selected. 6. Deposition inhibitor according to claim 4 or 5, 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. Deposition inhibitor according to any one of claims 4 to 6, characterized in that the constituents of the resin dispersant 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. 8. Use of comb polymers, obtainable by a radical polymerization of monoethylenically unsaturated monomers of a group AI) monoethylenically unsaturated acids and their salts and the group A2) monoethylenically unsaturated polyethers in pulp washing after the sulfate cooking process.