AU2018207866A1

AU2018207866A1 - Deposit prevention in pulp production according to the sulphate process (kraft process)

Info

Publication number: AU2018207866A1
Application number: AU2018207866A
Authority: AU
Inventors: Silvia Held-Beller; Bernd Horrer
Original assignee: CHT Germany GmbH
Current assignee: CHT Germany GmbH
Priority date: 2017-01-12
Filing date: 2018-01-09
Publication date: 2019-05-23
Anticipated expiration: 2038-01-09
Also published as: AU2018207866B2; ES2845552T3; EP3568519B1; RU2746828C2; CL2019001599A1; PL3568519T3; CA3043462A1; DE102017200430A1; WO2018130528A1; BR112019013116A2; EP3568519A1; RU2019121787A3; PT3568519T; RU2019121787A

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

Deposit Prevention in Pulp Production

According to the Sulphate Process (Kraft process)

The present invention relates to the use of comb polymers as deposition inhibitors in pulp production by the sulfate method (kraft pulping).

The most important and most frequently employed method for the production of pulp is the sulfate or kraft method. In 1884, C.F. Dahl filed a patent application for a method using sodium sulfide or sodium sulfate. Because of its high strength, the sulfate pulp produced thereby is preferred, in particular, for heavily mechanically stressed papers (kraft papers), and therefore, it is also referred to as kraft pulp.

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

Sodium sulfide on the one hand enhances delignification, whereby the lignin is cleaved by a nucleophilic attack of the sulfide anion to form 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 highly alkaline range. Liquors containing polysulfide stabilize the polyoses. Paper made from kraft pulp is tear-resistant, break-resista nt and tension-resistant. Advantages of the sulfate method include a high soaking efficiency of the chops in alkaline solution and thus shorter cooking times, and virtually all woods can be used. Sulfate pulps also contain major 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 obtained in the sulfate method are concentrated and incinerated, so that the energy demand of the overall process can be satisfied.

- 2 Turpentine oil and about 30 to 35 kg of tall oil are obtained as valuable by-products per 1000 kg of pulp.

During the cooking process, calcium ions are leached out of the wood. They react with the sodium carbonate present in the cooking liquor to form sparingly soluble calcium carbonate. The calcium carbonate formed will deposit within the digester in pipelines, heat exchangers etc. This reduces the flow rate through the digester, the effective amount of liquor, and the heat transition. Finally, the plant has to be shut down and cleaned already after a short period of time. In order to extend these cleaning intervals, deposition inhibitors against calcium carbonate are added to the cooking process.

Such deposition inhibitors are described in a large number of patents and publications. A good survey of deposition inhibitors for calcium carbonate based on phosphonic acids is found in the patent applications WO 02/098802 Al and WO 02/98803 Al of the company Solutia Inc.

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

US 5,409,571 A discloses a copolymer based on maleic acid and acrylic acid that has been polymerized with the addition of hypophosphite. The molecular weight is from 500 to 10,000 g/mol.

The use of polyitaconic acid in admixture with phosphonic acids is known from JP 2011-052358 (A). For scale inhibitor 1, polyitaconic acid and 1-hydroxyethylidene1,1-diphosphonic acid (HEDP) are mixed together.

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

- 3 WO 00/12436 A claims a copolymer of l,2-dihydroxy-3-butene and another monomer selected from the group consisting of maleic acid, acrylic acid, acrylamide, methacrylic acid, itaconic acid, vinylsulfonic acid, styrene sulfonic acid, N-tertbutylacrylamide, butoxymethylacrylamide, Ν,Ν-dimethylacrylamide, 2-acrylamido2-methylpropane sulfonic acid, and salts thereof.

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

If high-resin hard woods, such as birch, are used for pulp production by the sulfate process, another problem arises. The resin contained leads to sticky deposits, socalled pitch or sticky, which can require an increase of bleaching chemicals or lead to problems on the papermaking machine during the production process. In order to remove such sticky substances from the process, resin dispersants are added already during the cooking process.

Among the stated prior art, WO 2010/019425 Al provides a good survey of what substances can be employed as a resin dispersant.

The application itself claims a mixture of triglyceride oil or triglyceride alkyl ester with surfactants based on polyalkylene glycol 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 as well as hydrophobically modified hydroxyethylcellulose as detackifiers. In addition, enzymes catalyzing the hydrolysis of resin are mentioned.

WO 2004/057101 Al discloses a mixture of fatty acids and resin acids as an effective dispersant for extractable substances.

The stated publications deal exclusively with the inhibition of organic resin depositions.

From practice, it is known that although the use of, for example, tall oil in the cooking process clearly improves the resin problems, the tendency to inorganic deposits is significantly increased. The tendency increases with the calcium concentration

- 4 present in the cooking liquor. The higher the concentration of calcium, the higher the tendency for calcium carbonate deposits to occur.

In addition, a second negative effect results from the addition of tall oil. The deposition inhibitors, which were heretofore effective, are reduced in effect by the added tall oil. Even an increase of the dosing amounts is no longer sufficient in such cases. Massive deposits in the digester, lines and heat exchanger occur.

No work is known from the prior art that addresses the negative effects of resin dispersants on the tendency to deposit of calcium carbonate.

Therefore, the object of the present invention is to efficiently prevent the negative influence on the CaCCE deposition inhibitors by resin dispersants during the kraft cooking process. According to the invention, polymers that efficiently inhibit the deposition of CaCCE during the cooking process when working with the addition of resin dispersant based on organic carboxylic acids are to be provided.

Surprisingly, it has been found that comb polymers with polyether side chains significantly reduce the deposition tendency of calcium carbonate during pulp cooking according to the sulfate method. If a comb polymer is added to a cooking process performed with a resin dispersant and a standard CaCCE deposition inhibitor, there is a significant reduction of CaCCE deposits.

The comb polymers employed according to the invention can be obtained by freeradical polymerization of monoethylenically unsaturated monomers from group Al) monoethylenically unsaturated acids and salts thereof, and from group A2) monoethylenically unsaturated polyethers.

Therefore, the invention relates to the use of comb polymers obtainable by freeradical polymerization of monoethylenically unsaturated monomers from group Al) monoethylenically unsaturated acids or salts thereof, and from group A2) monoethylenically unsaturated polyethers,

- 5 as deposition inhibitors in the pulp production according to the sulfate method (kraft pulping).

The effect or influence on the inhibition of the deposition of calcium carbonate is not mentioned in the prior art. The effect or influence on the deposition-inhibiting effect by the addition of resin dispersants based on tall oil is not mentioned in the prior art, either.

The production of the comb polymers employed according to the invention by freeradical polymerization is known to the skilled person and can be performed by analogy with European Patent Application EP 0 537 870 A. In this respect, this publication in its entirety is included herein by reference.

Examples of the monomers from group Al, the monoethylenically unsaturated acids and salts thereof, include 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. The monomers from group Al can be employed singly or as a mixture of different monomers. Acrylic acid, methacrylic acid or maleic acid in an amount of from 5 to 95% by weight, based on the polymer, are preferred, and more preferably, acrylic acid or maleic acid in an amount of from 10 to 90% by weight, based on the polymer, are employed.

Examples of the monomers from group A2, the monoethylenically unsaturated polyethers, include polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, and polyethylene-polypropylene monoallyl ether; these are commercially available, for example, from the company Clariant under the product series Polyglykol® A, from the company BASF under the product series Pluriol® A to R, or from the company NOF Corporation under the product series Uniox®, Unisafe® and Unilube®. Further examples include polyethylene glycol monovinyl ether (product series of the company Clariant: Polyglycol® R), isoprenyl ethoxylate (product series of the company BASF: Pluriol® A to I), and vinyloxybutyl ethoxylate (product series of the company BASF: Pluriol® A to V).

The monomers from group A2 may be OH-terminated, or have an end group cap. The monomers can be employed singly or as a mixture of different monomers.

- 6 Polyalkylglycol monoallyl ethers in an amount of from 2 to 25% by weight, based on the polymer, are preferred, and more preferably, polyethylene glycol monoallyl ether and polyethylene-polypropylene monoallyl ether in an amount of from 5 to 20% by weight, based on the polymer, are employed.

The use according to the invention can be realized within the scope of a pulp production by the sulfate method in a continuous or batch process in a way involving steps in which the comb polymer is separately added to a cooking liquor, or the comb polymer is introduced into the cooking liquor as a component of the CaCCL deposition inhibitor or of the resin dispersant. Therefore, the invention further relates to a CaCCE deposition inhibitor containing a comb polymer according to the invention.

CaCO3 deposition inhibitors and resin dispersants that contain the comb polymer to be used according to the invention may also contain all the other usual components of such agents unless they undesirably interact with them.

In a preferred embodiment, such a CaCCE deposition inhibitor contains 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, 2acrylamido-2-methylpropane sulfonic acid, styrene sulfonic acid, vinylphosphonic acid, acrylamide, N-tert-butylacrylamide, butoxymethylacrylamide, and N,Ndimethylacrylamide.

The following Examples illustrate the advantages of the comb polymers employed.

Examples

1. Production of comb polymers

Synthetic Example (free-radical polymerization):

In a 2-liter four-necked flask with a thermometer, reflux condenser and ports for feeds and inert gas purge, 328 g of water, 61 g (0.06 mol) of polyalkylene glycol1000 monoallyl ether (Polyglycol® A 31/1000, Clariant) and 5 g of butyldiglycol as a solubilizer were charged. Separately, the following mixtures were prepared:

- 7 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 H2O in 60 g of water. The charge was heated at 90 °C. At this temperature, the above described solutions were metered thereto through separate feeds with a constant mass flow over 3 hours (monomer solution and solution 2) and over 3.5 hours (solution 1). After the end of the metering, the mixture was allowed to react further 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 shown in Table 1 were prepared in an analogous manner.

Table 1:

Comb polymer	Monoethylenically unsaturated polyethers	Amount [g]	Monoethylenically unsaturated acid	Amount [g]
CP-1	Polyglycol® A 31/1000	61	Acrylic acid	365
CP-2	Polyglycol® A 11/1800	61	Acrylic acid	365
CP-3	Pluriol® A 10 R	61	Acrylic acid	365
CP-4	Polyglycol® A 1100	61	Acrylic acid	365

2. Application of comb polymers

Application Example (pulp cooking according to the sulfate method):

The conditions during pulp cooking according to the sulfate method were simulated with the following laboratory method. In 200 ml Labomat cups from the company Mathis AG, which are provided with an adding unit (closure with septum), 100 ml each of a synthetic white liquor with the following composition was charged:

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.

- 8 Variable amounts of deposition inhibitor and 100 mg of tall oil (from a pulp plant) are added to said 100 ml of white liquor, and the cups were closed.

In a Labomat from the company Mathis AG, the contents of the cups were heated at 140 °C, and this temperature was maintained for 60 minutes. After 60 minutes, 8 ml of a 0.25 mol/l CaCU solution was metered through the septum using a suitable syringe. In a first approximation, this corresponded to a concentration of 800 mg/l Ca²⁺ ions in the solution.

The 140 °C was maintained for another 30 minutes. Subsequently, the contents of the cups were cooled down to 80 °C, the cups were opened, and the hot solution was filtered off through black filters.

The evaluation was effected by means of the filterability, the appearance of the filtrate, and the appearance of the deposits on the filter.

Evaluation criteria:

a) Filtering speed

fast	< 20 sec -
slow	20 to 30 sec +
very slow	> 30 sec ++

b) Appearance of the filtrate clear turbid highly turbid

c) Appearance of the deposits on the filter

- black filter with no deposits = black filter with few deposits

- crystalline deposits, comparable to blank = crystalline deposits, less than blank

- amorphous and crystalline deposits = amorphous deposits

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

3. Results of the application-technical test

Experiment No.:	Designation	Filter	Filtering speed [sec]	Appearan ce of filtrate	Appearan ce of deposits
1	800 ppm calcium with no tall oil with no polymer	0	-	clear	crystalline deposits
2	800 ppm calcium with no tall oil 20 mg of standard polymer	o	-	clear	crystalline deposits
3	800 ppm calcium with no tall oil 30 mg of standard polymer	0 -_____	-	clear	crystalline deposits
4	800 ppm calcium with no tall oil 40 mg of standard polymer	o	+ +	clear	amorphous deposits
5	800 ppm calcium 100 mg of tall oil with no polymer	o	-	clear	amorphous and crystalline deposits
6	800 ppm calcium 100 mg of tall oil 40 mg of standard polymer	o	-	clear	crystalline deposits

7	800 ppm calcium 100 mg of tall oil 50 mg of standard polymer	o	-	clear	crystalline deposits
8	800 ppm calcium 100 mg of tall oil 60 mg of standard polymer	0	+	clear	amorphous and crystalline deposits
9	800 ppm calcium 100 mg of tall oil 30 mg of standard polymer 10 mg KP-1	o	+ +	slightly turbid	amorphous deposits
10	800 ppm calcium 100 mg of tall oil 30 mg of standard polymer 10 mg KP-2	o	+ +	turbid	amorphous deposits
11	800 ppm calcium 100 mg of tall oil 30 mg of standard polymer 10 mg KP-3		+ +	turbid	amorphous deposits
12	800 ppm calcium 100 mg of tall oil 30 mg of standard polymer 10 mg KP-4	)	+ +	turbid	amorphous deposits

Standard polymer = acrylic acid/maleic acid copolymer, which is employed as a deposition inhibitor in pulp cooking by the sulfate method in practice.

Discussion of the results:

The experiments of Nos. 1 to 4 show results without the addition of tall oil.

- 11 Experiment No. 1 clearly shows what massive crystalline deposits may form under the conditions of pulp cooking if no deposition inhibitor is employed. The coarsecrystalline structure results in the deposits being completely and quickly filtered off, and the filtrate is clear. In experiments No. 2 to No. 4, different concentrations of deposition inhibitors were added. For amounts employed of 20 and 30 mg (experiments No. 2 and 3), the test parameters are hardly influenced. Mainly coarsecrystalline structures continue to be formed, leading to a quick and complete filtering. From a concentration of 40 mg, the results change abruptly. The crystal structure changes from coarse-crystalline to finely amorphous. The pores of the filter material are quickly clogged, and a significant reduction of the filtration speed occurs. From experience, the mechanism of crystal modification is necessary in practice to effectively prevent CaCCL depositions during pulp cooking.

Experiment No. 5 shows the effect of tall oil on the deposits formed. As compared to experiment No. 1, the deposits on the filter obviously have increased. Experiment No. 6 now discloses the whole problematic situation, that the standard polymers fail because of the use of tall oil and are no longer sufficiently efficient. While the standard polymer still could efficiently modify the forming deposits in experiment No. 4, this is completely unsuccessful in experiment No. 6. Although an increase of the amount employed (experiments Nos. 7 and 8), improves the situation to some extent, this is far from a sufficient effect.

Experiments Nos. 9 to 12 show the excellent effect of the comb polymers employed according to the invention. In all experiments, fine amorphous rather than crystalline deposits can be found on the filter paper. The filtration speed has significantly increased, and the deposits could be dispersed in an even so finely divided state that there is turbidity of the filtrate. Another positive effect is the amount of polymer employed. The amount of standard polymer employed could be even reduced by using comb polymers.

Claims

CLAIMS:

1. Use of comb polymers obtainable by free-radical polymerization of monoethylenically unsaturated monomers from group Al) monoethylenically unsaturated acids and salts thereof, and from group A2) 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 CaCCL deposition inhibitor, or of a resin dispersant into the cooking liquor.
4. A deposition inhibitor for pulp production according to the sulfate method (kraft pulping), comprising 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 Al) monoethylenically unsaturated acids and salts thereof, and from group A2) monoethylenically unsaturated polyethers.
5. The deposition inhibitor according to claim 4, 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-2methylpropane sulfonic acid, styrene sulfonic acid, vinylphosphonic acid, acrylamide, N-tert-butylacrylamide, butoxymethylacrylamide, and N,Ndimethylacrylamide.
6. The deposition inhibitor according to claim 4 or 5, 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 deposition inhibitor according to any of claims 4 to 6, 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 Al) monoethylenically unsaturated acids and salts thereof, and from group A2) monoethylenically unsaturated polyethers, in pulp washing after the sulfate cooking process.