FI121385B - Process for Reducing Extract Substance in High Yield Masses and Process for Preparing Bleached High Yield Masses - Google Patents

Abstract

The invention relates to a method for reducing the content of extractives of a high-yield pulp in a peroxide bleaching stage, said stage including peroxide bleaching and a subsequent dewatering or washing, said method comprising contacting the pulp in the peroxide bleaching with an organic stabilizer and in or after the peroxide bleaching with a surfactant, and thereafter subjecting the bleached pulp to said dewatering or washing for removing extractives along with the aqueous phase. The invention also relates to a method for producing bleached high-yield pulp.

Description

Method for reducing the extractable content of high-yield pulps and for the production of bleached high-yield pulps - Förfarande för re-ducering av extraktämneshalten i högutbytcsmassor och förfarande för fram-ställning av blekta högutbytesmassor 5

Field of the Invention

The present invention relates to a process for reducing the extract content of high mechanical mechanical pulps. The invention also relates to a process for preparing bleached high yield pulps with reduced extractant content.

Description of the Related Art

Extractives are known constituents of wood and pulp grades that can be extracted with organic solvents. Of the chemical groups present in the extractives, the most prominent are fatty and resin acids, terpenes, phytosterols and phenolic compounds. Extract-15 agents exist in esterified, glycosylated and non-derivatized. The most problematic extractants in wood are mainly oleophilic compounds. They are fatty acids, resin acids, tetracenes, and sterols and serve to protect wood by preventing attacks by germs, fungi, etc. Scandinavian softwoods contain approximately 1.5% by weight of extractives, whereas deciduous hardwoods usually contain 2% to 2.5% by weight. Generally, problematic extractives are commonly referred to as whiskers. Problems usually occur in areas of high shear forces and when temperature, pH or pitch content changes.

The common side effects caused by small in different areas are as follows. Bleaching plants form precipitates and may also increase the consumption of chemicals. Stains and high levels of extractants are found in the final product.

The modern mechanical pulp bleaching process often involves high consistency peroxide bleaching (PHC). After peroxide bleaching, the pulp is often diluted with recycled water from the papermaking machine, and then the pulp slurry is dewatered. This washing step reduces the transfer of anionic waste to the papermaking machine and also allows the recycling of residual peroxide. The alkaline peroxide oxidizes and removes the extractants quite effectively. However, if the pulp at the bottom of the PHC bleaching tower or after PCH bleaching is diluted with circulating water, the extracts may be re-precipitated on the surface of the pulp or process equipment due to lower water pH, high hardness or electrolyte (salt) content. The precipitated extracts are transferred to the paper machine on the fiber surface, resulting in problems at the wet end and in paper quality. When the PHC washing filtrate is recycled back to the earlier stages of the process, any extracts that may be present in the washing filtrate may be precipitated in the process equipment or fibers in an acidic or neutral environment.

US 4,363,699 describes a process for stabilizing basic solutions of peroxy di compounds used in bleaching, which comprises adding to the solution a basic salt of poly-alpha-hydroxyacrylic acid. 10 Stabilized solutions can be used for bleaching paper pulp and textiles. When bleaching textiles, the bleaching solution may contain a wetting agent, which is a surfactant.

US 4,963,157 discloses a process for bleaching cellulosic fibrous material, particularly cotton, with hydrogen peroxide. The method comprises impregnating the fiber-15 material with a bleaching solution containing hydrogen peroxide and a stabilizer. The stabilizer contains poly-alpha-hydroxyacrylic acid or a salt thereof or a corresponding polylactone and an organic phosphonic acid or a salt thereof.

DE 34 23 452 discloses a solution to avoid the use of water glass comprising a homopolymer of a poly-alpha-hydroxy acrylic acid (PHAA) and a water-soluble acrylic or methacrylic acid homopolymer or a copolymer of acrylic acid and / or maleic acid. The salts, in particular the sodium salt of PHAA and the sodium salt of the polycarboxylate polymer, are mixed together. Clotting agents may be added to the blend to provide an improved stabilizer blend for bleaching processes. According to DE 34 23 452, the bleaching process is carried out using 25 basic peroxide bleaching solution containing said stabilizing mixture.

Summary of the Invention

The invention is based on the fact that the extractants are more soluble under basic conditions and when the pulp is diluted with dilution water, for example post-bleaching recirculated water, the extractants may re-precipitate on the fiber surfaces, particularly when the diluted water has a pH lower than pulp from the bleaching tower. In accordance with the present invention, it has been found that certain surfactants can inhibit the precipitation of extractives and thus retain them in the aqueous phase. The extracts can then be removed from the pulp by washing in a subsequent dewatering press, which in turn contributes to reducing the pulp extract content. Because the extractants 3 are dispersed and the particles are stabilized, the extractants do not re-precipitate when the filtrate is recycled to previous process steps.

The invention is particularly advantageous when the pulp is bleached without the use of silicate as a stabilizer, since it has been found that the silica has some dispersing power on the extractants. However, the invention also works well in the presence of silicate.

Detailed Description of the Invention

According to the present invention there is provided a process for reducing the high yield pulp extractant in a peroxide bleaching step, comprising the step of peroxide bleaching and subsequent dewatering or washing, comprising contacting the pulp in peroxide bleaching with an organic stabilizer and after or after surfactant bleaching. the pulp is subjected to said dewatering or washing to remove the extracts together with the aqueous phase.

In this context, the peroxide bleaching step includes pulp peroxide bleaching, optionally pulp dilution, and dewatering or washing of the pulp.

The present invention also provides a process for producing bleached high yield pulp with reduced pulp extract content, comprising bleaching the high yield pulp with peroxide, contacting the pulp in the peroxide bleaching with organic stabilizer, and after or after bleaching the surfactant in the surfactant bleach, or washing to remove extracts together with the aqueous phase and to produce bleached high yield pulp with reduced extractant content.

According to the present invention, the pulp extractants are derived from 25 wood pitches. The extraction agents include fatty acids, resin acids, terpenes, phytosterols and phenolic compounds in esterified, glycosylated and / or non-derivatized form. The most problematic extractants are fatty acids, resin acids, triglycerides, steryl esters, sterols and lignans.

The organic stabilizer and the surfactant may be added separately or these chemicals may be premixed with the bleaching solution. In addition, the organic stabilizer and the surfactant may be added simultaneously or separately as a single chemical mixture, i.e. as a product.

* 4

The organic stabilizer and surfactant may be added to the pulp during peroxide bleaching or prior to peroxide bleaching.

The surfactant can also be added to the pulp after the peroxide bleaching. The surfactant can then be added to the dilution water, which is added to the pulp between pe-oxide bleaching and dewatering or washing. The dilution water may be recycled water from a paper machine.

The organic peroxide stabilizer used in the methods of the invention is preferably a polymeric stabilizer such as poly-alpha-hydroxyacrylic acid or a salt thereof or a corresponding polylactone, homopolymer of acrylic acid, methacrylic acid or maleic acid, or copolymer of acrylic acid and / or methacrylic acid. The polymeric stabilizer may also be a mixture of poly-alpha-hydroxyacrylic acid and a homopolymer and / or copolymer. The unsaturated dicarboxylic acid is preferably maleic acid. The salt of poly-alpha-hydroxy-acrylic acid is preferably sodium, potassium or ammonium salt. The polyalpha-hydroxyacrylic acid may have a molecular weight of at least 5,000, preferably at least 10,000, and more preferably at least 15,000 (calculated as P1-IAA sodium salt). The homopolymer and copolymer may have a molecular weight of at least 4,000, preferably at least 10,000, and more preferably at least 20,000.

The organic stabilizer may also be phosphonic acid or a salt thereof. The salt is preferably sodium, potassium or ammonium salts. Suitable phosphonic acids include, for example, (poly) aminophosphonic acids such as aminotri (methylene phosphonic acid), ethylenediaminetetra (methylene phosphonic acid), i.e. EDTMPA, or diethylenetriaminepen (methylene phosphonic acid), i.e. DTPM.

In addition to said organic stabilizer, another stabilizer may be added. This second stabilizer may be an alkaline earth metal compound such as a magnesium and / or calcium compound. The alkaline earth metal compound may be in the form of a salt such as sulfate, chloride or other water-soluble salt or of a polymer or chelating agent complex. A preferred alkaline earth metal salt is magnesium sulfate.

Preferably, the amount of organic stabilizer is from 0.1 kg to 5 kg per ton of dry matter, more preferably from 0.25 kg to 3 kg of dry matter, and even more preferably from 0.5 kg to 3 kg of dry matter.

The surfactant used in the methods of the invention may be an anionic surfactant such as naphthalene sulfonate or lignosulfonate, or a nonionic surfactant such as an oil-in-water emulsifier such as fatty alcohol ethoxylate or alkyl phenol ethoxylate. A mixture of anionic and nonionic surfactants may also be used. Antifoaming agents may be used in combination with the surfactant (s).

Preferably, the amount of surfactant is 0.005 kg to 2 kg per tonne of dry matter, more preferably 0.05 kg to 1 kg of dry matter.

The methods of the invention are used to bleach high-yield mechanical pulps, such as ground, stone, pressure (CW, SGW, PGW), pulp (RMP), hot pulp (TMP) and chemical pulp (CTMP, APMP).

Hydrogen peroxide is preferably used as a bleaching agent in peroxide bleaching. Other chemicals such as bleach stabilizers, coiling agents and / or magnesium sulfate may be used in bleaching. It is particularly advantageous to add the chemicals before or at the same time as the bleaching chemicals. If there are several bleaching steps, the chemicals can be added at any one of them or in several steps.

The residence time in bleaching can vary widely, ranging from 30 to 240 minutes, preferably from 45 to 180 minutes, and most preferably from 60 to 120 minutes. The residence time also depends on the temperature used in bleaching.

The bleaching of the high yield pulps can be carried out at a temperature of 30-90 ° C, preferably at a temperature of 50-90 ° C. Bleaching can be performed at any consistency, but it is most preferred to perform bleaching at high consistency, i.e., about 30% or greater. Bleaching can also be carried out in two steps, with a dewatering step between them.

The alkaline bleaching according to the invention may have a pH of 7-14, preferably 8-11. The ratio of base, typically sodium hydroxide, to hydrogen peroxide can vary widely depending on the raw materials and the degree of bleaching. Alternative base sources such as sodium carbonate may also be used.

The present invention is illustrated by the following examples. Percentages are by weight unless otherwise indicated. "Kg / t" refers to kilograms per tonne dry matter. “Cs” stands for consistency. “P” stands for perok-30 dressing step.

6

eXAMPLES

Comparative Example The purpose of this comparative example is to illustrate the problem solved by the invention. The TMP pulp (six) was bleached at high consistency using water glass or poly-α-hydroxy acrylate (PHAA) as a stabilizer on the peroxide. The pulp was then diluted with deionized water and then dewatered to a consistency of 30%. Detailed test results are shown in the table below.

P_P

T, ° C 70 70 h, min 120 120

Cs,% 27 30 pH initially 10.4 10.4 pH finally 9.5 9.5 H 2 O 2, kg / t 30 30

NaOH, kg / t 30 30

Water glass, kg / t 24 0

Stabilizer 0 PHAA

Doses, kg / t _0_2

Dilution to 5 ^ T, ° C 50 50 h, min 15 15

Cs,% 5 5 pH 9.3 9.2 TOC, kg / t 21.0 19.3 COD, kg / t 58.9 51.1

Turbidity, NTU 301 233 Residual H 2 O 2, kg 6.2_5.9

T T

7

Dewatering to a consistency of 30%

Brightness,% ISO 77.6 77.5

Water extract (SCAN-CM 44:97)

Turbidity, NTU 24.8 32.1 Bleach COD, mg / 1 310 360 mat mass

Pulp extracts

Fatty acids, mg / kg 150 220 390

Resin acids, mg / kg 110 120 550

Lignans, mg / kg 10 13 130

Sitosterol, mg / kg 37 54 110

Sterile Sterilizers, mg / kg 230,430,720

Triglycerides, mg / kg 210 710 1300

Total 747 1,547__3,200

The high turbidity of the filtrates after dilution may be due to the extraction agents. Analysis of the extractants shows that most of the extractants were removed in bleaching. The results also show that the silicate (water glass) has some dispersing ability of the extractants, since the extractant content is much higher when using an acrylate-based stabilizer. This means that especially when silicates are not used in bleaching, picid dispersants are preferred.

Example 1

A CTMP pulp sample (aspen) was taken from the factory and bleached with peroxide to 10 to 83-84% ISO. Bleaching conditions were as follows: t = 120 min, 70 ° C, 30% consistency, H 2 O 2 38 kg / h, NaOH 21 kg / h, Na 2 CO 3 8 kg / h. The pulp was already factory chelated and had a manganese content of 1.5 ppm, Fe 5 ppm. The additives were dosed in the peroxide bleaching step, and after bleaching, the pulp was diluted to 10% consistency at various pH values, followed by dewatering. Table 15 below shows the turbidity of the filtrate after dewatering. The experiment of this invention was carried out using 2 kg of polymer (poly-α-hydroxyacrylate) as a stabilizer and 0.1 kg of naphthalene sulfonate + 0.1 kg of nonionic surfactant (fatty alcohol ethoxylate 7 mol EO, C C14, HLB 12.3). In the comparative tests, water glass and poly-a-hydroxyacrylate were used as stabilizers. Bleaching results and chemical consumption were approximately the same in each case.

Water glass, Acrylate polymer 25 kg / t__2 kg / t__ according to the invention pH Turbidity, pH Turbidity, pH Turbidity,

_NTU__NTU__NTU

6.6 1,510 6.3 1,353 6.5 1464 7.5 1430 7.3 1,317 7.2 1440 7.8 1465 7.7 1389 7.5 1481 5 As can be seen from the results, a glass of water (sodium silicate) originating from herring increases turbidity. This may be due to the higher extractant content of the filtrate. When the silicate is replaced by a polymer-based stabilizer, the turbidity is lower and thus the extractant content of the pulp is higher. The chemical composition of the present invention achieves greater turbidity, indicating that the extracts dissolved in the basic peroxide do not precipitate after dilution.

Example 2

A CTMP pulp sample (aspen) was taken from the mill and bleached with high peroxide. Bleaching conditions and results are shown in Table 15 below. The surfactants were added in the bleaching step, and after bleaching the pulp was diluted with deionized water. Here, the composition of the surfactants contained a condensation product (Na salt) of naphthalenesulfonic acid and a fatty alcohol ethoxylate (same as in the previous example) in a weight ratio of 2: 1 (dosage i in 20% aqueous solution). The polymer-based stabilizer was a mixture of poly-alpha-20 hydroxy acrylate and maleate-acrylate copolymer (1: 4 w / w) with 25% active ingredient content.

9

P P P P

According to the invention No No Yes Yes t, min 120 120 120 120 T, ° C 70 70 70 70

Cs,% 30 30 30 30 pH initially 8.7 8.6 8.8 8.8 pH 8.4 8 8.4 8.3

Stabilizer, kg / t 2 2 2 2

Na 2 CO 3, kg / t 8 8 8 8

NaOH, kg / t 21 21 21 21 H 2 O 2, kg / t 38 38 38 38

Surfactant, kg / t 0 0 11

Polyvinyl alcohol, kg / t 0 10 1

Polyethylene glycol, kg / t 0 1 10, Residual H 2 O 2, kg / t 27.4 27.3 28.3 27.7 _Lightness,% ISO 73.4 81.0 80.9 81.2 81.2

Dilution with ion-exchanged water __ T T ▼ ▼ t, min 10 10 10 10 T, ° C 70 70 70 70

Cs,% 5 5 5 5 pH 8.2 8.1 8.2 8.3

Turbidity, NTU 608 607 627 651 _PCM Extract *,% 0.38 0.35 0.27 0.25 *% DCM means dichloromethane.

The results show that the process of the invention reduces the pulp extracts but does not affect the bleaching result.

Example 3

A CTMP pulp sample (aspen) was taken from the factory and bleached to 83-84% ISO with peroxide. The surfactant additives were metered in the peroxide bleaching step, and after bleaching, the pulp was diluted to 10% consistency at various pH values, followed by dewatering. In one experiment, the surfactant additive was also administered after dilution. The results are shown in the table below. The surfactant additives used herein were naphthalene sulfonate condensation product (A) and fatty alcohol ethoxylate (B, 25 moles EO, C16-C18, HLB 16). The polymer-based stabilizer was a mixture of poly-alpha-hydroxy acrylate and maleate-acrylate copolymer (1: 4 w / w) with 25% active ingredient content.

P P P P

t, min 120 120 120 120 T, ° C 70 70 70 70

Cs,% 30 30 30 30 pH initially 9 8.9 9 9 pH finally 8.5 8.3 8.5__8.3

Stabilizer, kg / t 0 2 2__2

Water glass, kg / t 25 0 0__0

Na 2 CO 3, kg / t 8 8 8 8

NaOH, kg / t 19 21 21 21 H 2 O 2, kg / t 38 38 38 38

Additive - B A

Dosage kg / t - 1 1__ 5 4 4

In accordance with the invention No ___ No__K__ Yes Yes Yes No, min 60__60__60 60__60__60__60 T, ° C 70__70 70 70 70 70 70

Cs,% 10 10 10 10 10 10 10 pH Initially 5.5__6j5__K2__6.4 6.5__6j6__6.6 pH Finally 5.6__6 ^ 6__7 ^ 9__6A__6 ^ 6.8__6.6

Additive _-__-__-__ A - -

Dose in kg / h -__-__-__-__ 0.5 - Residual H2O2, kg / h 27.3 27.6 27.2 27.4 27.9 27.5 27.1

Brightness,% ISO 82.7 83.5 83.2 83.2 83.2 82.6 82.7

Extraction substance, mg / kg ________

Fatty Acids 550__ 470 530__410__420__430__490

Resin acids 170 140 130 120 120 130 130

On lignan 71__56__55__41__42__67__55

Sitosterol it 8__6__7 3 3 8 7

Sterile Esters 420 280 250 240 230 280 310

Triglycerides 1300 1010 940 810 800 980 1020

Total 2,519,1962 1,912 1,1624 1615 1,1,895 2,012 π

The results show that a combination of a polymer-based stabilizer and an anionic and / or nonionic surfactant results in lower extractant concentrations than water glass.

Claims (19)

A method for reducing the high yield mass extractor content of a peroxide bleaching step, comprising the step of peroxide bleaching and subsequent dewatering or washing, comprising contacting the pulp in the peroxide bleaching with an organic stabilizer and then during or after bleaching with the surfactant. said dewatering or washing to remove the extraction agents together with the aqueous phase. The method of claim 1, wherein the organic stabilizer 10 and the surfactant are added to the pulp in the peroxide bleaching process. The process of claim 1, wherein the organic stabilizer and the surfactant are added to the pulp prior to peroxide bleaching. The method of claim 1, wherein the surfactant is added to the pulp after the peroxide bleaching. The process according to any one of claims 1 to 4, wherein the dilution water is added to the pulp between the peroxide bleaching and dewatering or washing. The method of claim 5, wherein the surfactant is added to the dilution water. The process according to any one of claims 1 to 6, wherein the organic stabilizer is a polymeric stabilizer such as poly-alpha-hydroxyacrylic acid or a salt thereof or a corresponding polylactone, homopolymer of acrylic acid, methacrylic acid or maleic acid, or acrylic acid and / or methacrylic acid. a copolymer of dicarboxylic acid or a mixture of these polymers. The process according to any one of claims 1 to 7, wherein the amount of organic stabilizer is from 0.1 kg to 5 kg per ton of dry matter, preferably from 0.25 kg to 3 kg of dry matter. The method of any one of claims 1 to 8, wherein the surfactant is an anionic surfactant such as naphthalene sulfonate or lignosulfonate, or a nonionic surfactant such as an oil-in-water emulsifier, e.g. 30 fatty alcohol ethoxylate or alkylphenol ethoxylate. . The process according to any one of claims 1 to 9, wherein the surfactant is present in an amount of 0.005 kg to 2 kg per ton of dry matter, preferably 0.05 kg to 1 kg of dry matter. A process for making a bleached high yield pulp with reduced extract content of pulp, comprising bleaching the high yield pulp with petroxide, contacting the pulp in the peroxide bleaching with the organic stabilizer, and after or after bleaching the surface bleaching agent in the bleached pulp or water. together with the aqueous phase and for the preparation of a bleached high yield pulp with a reduced extractant content of 10. The method of claim 11, wherein the organic stabilizer and the surfactant are added to the pulp during peroxide bleaching. The method of claim 11, wherein the organic stabilizer and surfactant are added to the pulp prior to peroxide bleaching. The method of claim 11, wherein the surfactant is added to the pulp after the peroxide bleaching. The method of any one of claims 11 to 14, wherein the dilution water is added to the pulp between peroxide bleaching and dewatering or washing. The method of claim 15, wherein the surfactant is added in dilution with water. The process according to any one of claims 11 to 16, wherein the organic stabilizer is a polymeric stabilizer such as poly-alpha-hydroxyacrylic acid or a salt thereof or a corresponding polylactone, homopolymer of acrylic acid, methacrylic acid or maleic acid or acrylic acid and / or methacrylic acid and / or methacrylic acid copolymer or a mixture of these polymers. The method according to any one of claims 11 to 17, wherein the amount of organic stabilizer is 0.1 kg to 5 kg per ton of dry matter, preferably 0.25 kg to 3 kg of dry matter. The method of any one of claims 11 to 18, wherein the surfactant is an anionic surfactant such as naphthalene sulfonate or lignosulfonate, or a nonionic surfactant such as an oil-in-water emulsifier, e.g. alcohol ethoxylate or alkyl phenol ethoxylate. The method according to any one of claims 11 to 19, wherein the amount of surfactant is 0.005 kg to 2 kg per ton of dry matter, preferably 0.05 kg to 1 kg of dry matter per ton of dry matter. j