EP3390712A1 - Procédé de régulation de la viscosité dans des pâtes pour dissolution - Google Patents

Procédé de régulation de la viscosité dans des pâtes pour dissolution

Info

Publication number
EP3390712A1
EP3390712A1 EP16876147.6A EP16876147A EP3390712A1 EP 3390712 A1 EP3390712 A1 EP 3390712A1 EP 16876147 A EP16876147 A EP 16876147A EP 3390712 A1 EP3390712 A1 EP 3390712A1
Authority
EP
European Patent Office
Prior art keywords
stage
pulp
peroxide
pacid
viscosity
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP16876147.6A
Other languages
German (de)
English (en)
Other versions
EP3390712A4 (fr
Inventor
Maria WENNERSTRÖM
Sofia BYLUND
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Valmet Technologies Oy
Valmet AB
Original Assignee
Valmet Oy
Valmet AB
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Valmet Oy, Valmet AB filed Critical Valmet Oy
Publication of EP3390712A1 publication Critical patent/EP3390712A1/fr
Publication of EP3390712A4 publication Critical patent/EP3390712A4/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/16—Bleaching ; Apparatus therefor with per compounds
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/16—Bleaching ; Apparatus therefor with per compounds
    • D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C3/00—Pulping cellulose-containing materials
    • D21C3/04—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides
    • D21C3/06—Pulping cellulose-containing materials with acids, acid salts or acid anhydrides sulfur dioxide; sulfurous acid; bisulfites sulfites
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/001—Modification of pulp properties
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/1026—Other features in bleaching processes
    • D21C9/1052—Controlling the process
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
    • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
    • D21C9/10—Bleaching ; Apparatus therefor
    • D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16

Definitions

  • the present disclosure relates in general to a method for producing dissolving pulp of low viscosity from lignocellulosic material.
  • the dissolving pulp process for producing low viscosity pulp conventionally contains a sulfite cooking stage and thereafter bleaching for reduction and brightness increase. In commercial systems is often only used a first sulfite cooking stage and a subsequent alkaline extraction stage followed by peroxide bleaching.
  • sulfite pulping has a higher cellulose yield for softwood pulp compared with kraft pulping.
  • kraft pulping could have a higher yield.
  • the lignin content in cooked sulfite pulp is low which makes the subsequent treatment downwards easier, i.e. easier to bleach. Since the sulfite pulp is easier to bleach TCF-sequences are often used, mostly with hydrogen peroxide. Oxygen stages are not frequently used for sulfite pulping due to several reasons, one of them is the environmental aspect.
  • very competitive low cost systems for dissolving pulp may be obtained from a sulfite cook as the cooked pulp has a relative low metal content due to the acidic cooking conditions, and the subsequent bleaching may be obtained using only an alkaline extraction stage followed by peroxide bleaching, i.e. using a Cook- (w)-E-(w)-P sequence, where (w) stands for a washing stage.
  • peroxide bleaching i.e. using a Cook- (w)-E-(w)-P sequence, where (w) stands for a washing stage.
  • Dissolving pulp has emerged as a reborn alternative growing market for pulp mills and much attention has been given to modify the pulping processes to be able to produce different grades of dissolving pulp which is used to produce a multitude of products like Rayon-grade pulp or specialty pulps.
  • the interest to find alternative textile materials to cotton has increased due to short term shortage and increase in costs for cotton and an increased competition in long term for land to grow an increasing demand of cotton on.
  • Dissolving pulp can consist of cotton linters, pulp originating from wood or annual plants made by the sulfite process or the prehydrolysis kraft process.
  • dissolving pulp is generally referred to as a bleached pulp produced from wood that has a high alpha cellulose content, typically over 92%, and only small content of hemicelluloses, typically below 10%. Hence, the wood yield of dissolving pulp from the process is typically low, at about 35-40%.
  • Dissolving pulp is used to manufacture various cellulose- derived products such as rayon yarn for use in e.g. textile industry and specialty chemicals and materials such as cellulose acetate and carboxy methyl cellulose. When making rayon yarns the dissolving pulp is converted to cellulose xanthate which dissolves in caustic soda and the resulting viscous liquid is extruded in acidic baths to yield fibers.
  • the dissolving pulp can be dissolved in ionic solvents to make extruding to fibers possible.
  • the viscosity of the dissolving pulp is both low and within a specific narrow range suitable for the process, in order to run derivatisation/dissolution process smoothly.
  • the required intrinsic viscosity in the final bleached dissolving pulp must be as low as 350 ml/g and within a narrow acceptance range of only ⁇ 20 ml/g. This requires a low viscosity already after cooking or possibilities to lower the viscosity in a controlled manner and to a greater extent in subsequent delignification and/or bleaching stages.
  • viscosity is used as the dominant pulp property for dissolving pulp.
  • the viscosity number is expressed as intrinsic viscosity and measured in ml/g.
  • a standard test method for intrinsic viscosity of cellulose could be found in ISO-standard ISO 5351 .
  • viscosity measurements is indicative for the average molecular weight of the cellulose polymers, i.e. the length of the cellulose chains.
  • the length of the cellulose chains impact the derivatisation and solubilisation process as well as the characteristics of the final product.
  • the viscosity is often about or below 1 100 ml/g after cook and below 600 ml/g after final bleaching. Most often the viscosity target for the final dissolving pulp is kept within 400-600 ml/g and within a narrow acceptance range of only ⁇ 20 ml/g for the specific grade. Examples of specification of higher grade dissolving pulps are Ethers (viscosity 470-600 ml/g), Nitrates (viscosity 550-650 ml/g), Acetates (viscosity 600-700 ml/g) and Viscose (viscosity 300-500 ml/g).
  • the problem with production of dissolving pulp is to reach the low viscosity of the final pulp requested and most often is extended and intensified cooking, i.e. both longer cooking time and tougher cooking conditions as of alkali charge or other cooking chemicals and temperature, needed in order to obtain a low enough viscosity after the cook.
  • extended cooking occurs if it is desired to increase the production in existing pulp mills as increased production results in decreased cooking time if the equipment is the same. This results in higher viscosity when the throughput of the lignocellulosic material increases.
  • the viscosity reduction may be increased marginally in the order of 50 ml/g in final bleaching, by implementing tougher bleaching conditions in the final bleaching stages as of temperature and additional bleaching agents or increased charge of the standard bleaching agents used.
  • Ozone stages are also capable of reducing viscosity to a larger extent, but this at expense of increased costs, especially in an existing bleaching plant, as the ozone stages are at the higher range of investment costs for a bleaching stage.
  • transition metal ions Fe, Mn, Ca, Co etc.
  • the amounts of catalytically active transition metal ions as Mn and Fe are also important to keep at a low level when hydrogen peroxide is used to avoid uncontrolled peroxide decomposition.
  • the main objective problem with the present invention is to enable increased production of dissolving pulp in existing sulfite pulp mills using TCF bleaching using mainly alkali and peroxide in bleaching while still being able to reach the lower viscosity requested in finally bleached dissolving pulp, and being able to control this low viscosity within a narrow range suitable for the final dissolving pulp grade.
  • the inventive method is thus optimized for producing low viscosity dissolving pulp from lignocellulosic material, said method comprising a sulfite cooking process producing cooked pulp which cooked pulp thereafter is washed producing cooked and washed pulp, said cooked and washed pulp subsequently further bleached with a TCF-sequence in at least 2 stages using alkaline extraction (E) and alkaline peroxide bleaching (P) and optionally ozone or oxygen, and wherein the final target viscosity of the bleached dissolving pulp is primarily controlled by
  • inventive method is further distinguished in that said dissolving pulp process comprising following steps in sequence;
  • step c) subjecting the pulp from step b) for an acidic peroxide stage (Pacid)-stage followed by a subsequent wash;
  • the viscosity of the final bleached dissolving pulp is kept within an acceptance range of ⁇ 20 ml/g.
  • the acidic peroxide stage (Pacid)-stage is established at the following conditions;
  • the sulfite cooking process may dissolve most of the metal content from the wood material into the spent cooking liquor, but for largest viscosity control span in the acidic peroxide stage is the pulp subjected to an additional metal extraction stage (Q) followed by washing before the acidic peroxide stage, Also, for improved bleaching could also the pulp be subjected to an additional second alkaline peroxide stage with subsequent washing after the first alkaline peroxide stage with subsequent washing and before obtaining the final dissolving pulp quality.
  • Q metal extraction stage
  • bleaching could also the pulp be subjected to an additional second alkaline peroxide stage with subsequent washing after the first alkaline peroxide stage with subsequent washing and before obtaining the final dissolving pulp quality.
  • the metal content dissolved in the sulfite cooking stage or the metal extraction stage should reach an order that the levels of Mn and Fe into the acidic peroxide stage (Pacid) should be; Mn ⁇ 5 mg/kg and Fe ⁇ 20 mg/kg. And most preferably the levels of Mn and Fe into the acidic peroxide stage (Pacid) is; Mn ⁇ 2 mg/kg and Fe ⁇ 5 mg/kg.
  • the invention is based upon the finding that a span with larger viscosity reductions may be obtained in an acidic peroxide stage if controlled charge of peroxide with strong chain cleavage abilities located close to or neighboring to cellulose are increased. Hence, the charge of peroxide should not be consumed or wasted in reactions with metal content in the filtrate. This can be achieved by e.g. an increase in hydroxyl radical formation formed close to the cellulose.
  • the radical has a higher reduction potential at lower pH.
  • the invention relates to a method for producing low viscosity dissolving pulp from lignocellulosic material, said dissolving pulp process comprising a sulfite cooking process. Said cooked and washed pulp subsequently further bleached with a TCF-sequence with less than 5 stages, and wherein the final target viscosity of the bleached dissolving pulp is primarily controlled by adjusting the conditions in the acidic peroxide stage, in following parts referred to as a Pacid-stage, by addition of hydrogen peroxide at low pH obtaining a reduction of viscosity in Q-E-Pacid-P in the range of 50-700 ml/g ⁇ 20 ml/g.
  • the viscosity reduction is decreased with approximately 50% if no hydrogen peroxide is used. It has been found that the Pacid-stage is possible to adjust whereby a large range of viscosity reduction could be obtained. Hence, the total production may be increased in any existing mills, leading to higher viscosity in the cooked pulp, which increased production is compensated by increased viscosity reduction in the Pacid-stage.
  • dissolving pulp process comprising following steps in sequence; a) subjecting comminuted cellulosic material to a sulfite cook
  • the cooking process according to the inventive method could equally well take place in a batch digester or a continuous digester. If the production is increased in an existing batch digester the cooking time needs to be reduced so that each batch digester may be emptied more frequently. If the production is increased in an existing continuous digester the retention time in the digester is normally reduced and thereby the viscosity reduction is decreased. The reduced retention time in batch or continuous digesters may in part be compensated by increasing the temperature, but this at high costs as this requires addition of steam capable of increasing the temperature at the normal cooking temperature at about 140- 170°C.
  • the Pacid-stage can take place in one or two successive treatment vessels where a single chemical mixing position could be located before said vessels, or with chemical mixers located before both vessels with split chemical charge and possibly with temperature profiling adding steam to second mixer.
  • TCF sequence according to the invention only includes alkalization, acidification and peroxide, besides optional usage of oxygen, ozone and chelating agents.
  • Figure 1 Show an example of a complete fiberline for manufacturing
  • Figure 2 show the viscosity in different bleaching stages of the fiberline in figure 1 ;
  • Figure 3 show the viscosity change with pH in the Pacid-stage
  • Figure 4 show the dependence of time, pH, temperature and hydrogen
  • Figure 5 show the viscosity dependence on hydrogen peroxide charge in the
  • the process will be further described with reference to the accompanying drawings. It should however be noted that the invention is not limited to the embodiments described below and shown in the drawings, but may be modified within the scope of the appended claims.
  • the invention is related to a method for producing low viscosity dissolving pulp from lignocellulosic material, said dissolving pulp process comprising a sulfite cooking process. Said cooked and washed pulp subsequently further bleached with a TCF-sequence with at least 2 but less than 5 bleaching stages.
  • the principle layout of such a dissolving pulp process is shown in Figure 1.
  • Lignocellulosic material preferably wood chips (CH) are fed to a sulfite cooking stage (Cook), and thereafter bleached for example in an optional first Q-stage, an extraction stage, (E), an acid hydrogen peroxide bleaching stage, (Pacid), and finally an alkali peroxide stage, (P) from which the dissolving pulp is fed out.
  • the first stage, Cook is more or less standard stage but the bleaching stages could have other configurations than the Q-E-Pacid-P sequence.
  • the viscosity reduction is increased with approximately 50% when using hydrogen peroxide compared with no charge of hydrogen peroxide.
  • a study was made to illustrate this. The study was made with a softwood (Picea abies) pulp which after a sulfite cook and bleaching QEP had an intrinsic viscosity of ⁇ 950 ml/g. The bleaching conditions and viscosity results are shown in Table 1.
  • Figure 2 shows the viscosity drop throughout the sequence Q-E-Pacid-P-P.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Wood Science & Technology (AREA)
  • Paper (AREA)

Abstract

La présente invention concerne un procédé amélioré pour produire une pâte pour dissolution à partir d'un processus de cuisson au sulfite utilisant une séquence de blanchiment TCF contenant une extraction alcaline et un blanchiment au peroxyde alcalin dans le blanchiment de pâte. Le nouveau procédé ajoute un étage de peroxyde acide (Pacid) qui permet de contrôler une viscosité de pâte de manière efficace et de ne pas introduire de nouveaux produits chimiques de blanchiment dans le système de manipulation de filtrat.
EP16876147.6A 2015-12-14 2016-12-13 Procédé de régulation de la viscosité dans des pâtes pour dissolution Withdrawn EP3390712A4 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE1551638A SE1551638A1 (en) 2015-12-14 2015-12-14 Method for controlling viscosity in dissolving pulps
PCT/SE2016/051252 WO2017105322A1 (fr) 2015-12-14 2016-12-13 Procédé de régulation de la viscosité dans des pâtes pour dissolution

Publications (2)

Publication Number Publication Date
EP3390712A1 true EP3390712A1 (fr) 2018-10-24
EP3390712A4 EP3390712A4 (fr) 2019-05-22

Family

ID=58505023

Family Applications (1)

Application Number Title Priority Date Filing Date
EP16876147.6A Withdrawn EP3390712A4 (fr) 2015-12-14 2016-12-13 Procédé de régulation de la viscosité dans des pâtes pour dissolution

Country Status (3)

Country Link
EP (1) EP3390712A4 (fr)
SE (1) SE1551638A1 (fr)
WO (1) WO2017105322A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114808512B (zh) * 2022-04-26 2023-07-04 赣南师范大学 适用于碱尿素体系的竹溶解浆及其制备方法
FI20225592A1 (fi) * 2022-06-29 2023-12-30 Andritz Oy Menetelmä liukosellun viskositeetin alentamiseksi

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE420430B (sv) * 1978-02-17 1981-10-05 Mo Och Domsjoe Ab Forfarande for blekning och extraktion av lignocellulosahaltig material med peroxidhaltiga blekmedel
CN101457494B (zh) * 2008-12-24 2012-01-11 宜宾长毅浆粕有限责任公司 竹材化学溶解浆的制备方法
KR101739949B1 (ko) * 2009-05-28 2017-05-25 게페 첼루로제 게엠베하 화학적 크래프트 섬유로부터의 변형된 셀룰로즈 및 이들을 제조 및 사용하는 방법
PL2954115T3 (pl) * 2013-02-08 2022-05-02 Gp Cellulose Gmbh Włókno siarczanowe z drewna iglastego o polepszonej zawartości a-celulozy i jego zastosowanie w wytwarzaniu chemicznych produktów celulozowych
SE538064C2 (sv) * 2014-06-17 2016-02-23 Valmet Oy Metod för att producera dissolving massa från lignocellulosahaltiga material
FI127444B (en) * 2015-05-27 2018-06-15 Kemira Oyj A method for reducing the viscosity of a pulp in the manufacture of soluble cellulose

Also Published As

Publication number Publication date
EP3390712A4 (fr) 2019-05-22
WO2017105322A1 (fr) 2017-06-22
SE539147C2 (en) 2017-04-18
SE1551638A1 (en) 2017-04-18

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