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Extended impregnation kraft cooking of softwood: Effects on reject, yield, pulping uniformity, and physical properties
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. (Träkemi och Massateknologi)
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Converting wood into paper is a complex process involving many different stages, one of which is pulping. Pulping involves liberating the wood fibres from each other, which can be done either chemically or mechanically. This thesis focuses on the most common chemical pulping method, the kraft cooking process, and especially on a recently developed improvement of the impregnation phase, which is the first part of a kraft cook.

Extended impregnation kraft cooking (EIC) technique is demonstrated to be an improvement of the kraft pulping process and provides a way to utilize softwood to a higher degree, at higher pulp yield. We demonstrate that it is possible to produce softwood (Picea abies) kraft pulp using a new cooking technique, resulting in a pulp that can be defibrated without inline refining at as high lignin content as 8% on wood, measured as kappa numbers above 90. Lignin is the wood constituent that holds the wood fibres together in the wood matrix. The new cooking technique uses the differences in reaction rate between the diffusion and consumption of hydroxide ions; it is used to ensure a homogenous impregnation of wood chips at lower impregnation temperatures and longer impregnation times than are generally used in the industry. The applied cooking temperatures are also substantially lower than those used in conventional kraft pulping systems, promoting uniform delignification. This results in a narrower kappa number distribution than in lab-cooked conventional kraft pulp.

High-kappa-number pulps were investigated for pulp sheet properties such as tensile strength, tensile stiffness, and compression strength. It was demonstrated that an EIC pulp of kappa number 95 has strength properties comparable to those of a conventional pulp of kappa number 82. Comparing the effects of starch multilayers on conventional and EIC pulps reveals similar effects. The use of the starch multilayer treatment increased the tensile index and decreased the tensile stiffness and short-span compression test (SCT) indices.

The EIC technique has also been used to produce a series of bleachable-grade pulps. The results indicate the possibility of increasing the lignin content of the pulp entering the oxygen delignification stage, since the reject content of gently defibered pulp is lower than 0.1% at kappa number 49.

In this thesis, we recommend that wood chips be impregnated for 2 h at 110 °C to neutralize acidic compounds in the wood and impregnate the chips with cooking chemicals, and that the ensuing cook be performed at 135–140 °C, depending on the target kappa number. We also recommend increasing the available amounts of cooking chemicals in the impregnation stage by using a higher liquor-to-wood ratio and keeping the alkali profile fairly high in the ensuing cook. This concept will reduce the amount of reject material, increase the pulping uniformity, and increase the selectivity towards lignin degradation in the kraft cook.

Abstract [sv]

Omvandling av ved till papper är en komplicerad process som består av många olika steg där ett är massaframställningen (eng. pulping). Massaframställning medför att vedfibrerna frigörs från varandra på kemisk eller mekanisk väg. Denna avhandling fokuserar på den vanligaste kemiska metoden, sulfatkokning och speciellt den nyligen utvecklade förbättringen av impregnerings fasen, som är den första delen av ett sulfatkok.

Här visas att Extended Impregnation kraft Cooking (EIC) innebär en förbättring av sulfatkokningen och ett sätt att uppnå högre vedutnyttjande vid högre utbyte för barrved. Vi visar att det är möjligt att producera barrvedsmassa med en ny kokningsprincip som resulterar i en massa som är defibrerbar utan inline-raffinering vid så högt lignin innehåll som 8% (på ved), mätt som kappatal över 90. Lignin är den vedkomponent som håller ihop vedfibrerna i vedmatrisen. Kokningsprincipen utnyttjar skillnaderna i reaktionshastighet mellan diffusion och konsumtion av hydroxidjoner och nyttjas till att skapa en homogen impregnering av vedflisen vid lägre impregneringstemperatur och under längre tid än vad som vanligen används i industrin. De använda koktemperaturerna är också betydligt lägre än vid konventionell sulfatkokning vilket gynnar jämn delignifiering. Detta resulterar i en smalare kappatalsfördelning jämfört med laboratoriekokade konventionella massor.

Massor med höga kappatal undersöktes med avseende på egenskaper hos handark, såsom dragstyrka, dragstyvhet och kompressionsstyrka Det visades att handark från EIC massa vid kappatal 95 hade jämförbara styrkeegenskaper med konventionell massa vid kappatal 82. Vid jämförelse av effekten av stärkelse multilager på konventionella och EIC massor avslöjar liknande effekter. Användningen av stärkelsemultilager ökade dragindex och minskade dragstyvhets- och kompressions index (SCT, short-compression test).

Kokprincipen har även använts för att ta fram en serie blekbara massor. Resultaten visar på möjligheten att öka lignininnehållet i massan in till i syrgasdelignifierings-steget eftersom spetinnehållet för milt defibrerad massa var lägre än 0,1% vid kappatal 49.

I den här avhandlingen rekommenderar vi att vedflis impregneras i 2 timmar vid 110 °C för att neutralisera sura komponenter i veden och impregnera flisen med kokkemikalier, samt att utföra det efterföljande koket vid 135–140 °C beroende på önskat kappatal. Vi rekommenderar även att öka den tillgängliga mängden kokkemikalier i impregneringssteget genom att använda högre vätske-ved förhållande och att hålla alkali profilen relativt hög i det efterföljande koket. Detta koncept reducerar spetmängden, ger jämnare kokning och ökar selektiviteten för nedbrytning av lignin i sulfatkoket.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2009. , 40 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:59
Keyword [en]
high kappa number pulp, extended impregnation, softwood, spruce, picea abies, pine, pinus sylvestris, uniform delignification, kappa number distribution, reject, yield, tensile index, tensile stiffness index, SCT, starch multilayers, mechano-sorptive creep, hygroexpansion, dimensional stability, eucalypt, birch, acacia
National Category
Paper, Pulp and Fiber Technology
Identifiers
URN: urn:nbn:se:kth:diva-11721ISBN: 978-91-7415-496-2 (print)OAI: oai:DiVA.org:kth-11721DiVA: diva2:280057
Presentation
2009-12-18, STFI-salen, Innventia AB, Drottning Kristinas väg 61, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Note
QC 20120216Available from: 2009-12-09 Created: 2009-12-08 Last updated: 2012-02-16Bibliographically approved
List of papers
1. Extended Impregnation Cooking of Norway Spruce: Effects on Pulping Uniformity and Pulp Strength Properties
Open this publication in new window or tab >>Extended Impregnation Cooking of Norway Spruce: Effects on Pulping Uniformity and Pulp Strength Properties
2009 (English)Manuscript (preprint) (Other academic)
Abstract [en]

Extended impregnation kraft cooking is a demonstrated improvement of the kraft pulping process and offers a way to use softwood more efficiently. We demonstrate the possibility of producing Norway spruce (Picea abies) kraft pulp using a new cooking concept, producing a pulp that can be defibrated without inline refining at kappa numbers of approximately 90. The cooking concept uses the differences in reaction rate between the diffusion and consumption of hydroxide ions in the prolonged impregnation step. Lowering the impregnation temperature will favour the diffusion of cooking chemicals over neutralization reactions, thereby improving chemical distribution throughout the chips. Impregnation conditions in combination with cooking temperatures lower than those of conventional kraft pulping are demonstrated to produce pulp with a narrower kappa number distribution and comparable strength properties at a considerably higher yield.

Publisher
40 p.
Keyword
Uniform delignification, kappa number distribution, high-kappa-number pulp, reject, yield, tensile index, tensile stiffness index, SCT, starch multilayers
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-11714 (URN)978-91-7415-496-2 (ISBN)
Note
QC 20101014Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2013-06-12Bibliographically approved
2. Applying a novel cooking technique to produce high kappa number pulps: the effects on physical properties
Open this publication in new window or tab >>Applying a novel cooking technique to produce high kappa number pulps: the effects on physical properties
2009 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 24, no 4, 415-420 p.Article in journal (Refereed) Published
Abstract [en]

A recently developed kraft cooking technique, with a longer impregnation time at lower temperatures to facilitate diffusion over consumption of active cooking chemicals, makes it possible to produce kraftliner pulp without inline refining. This technique was applied to prepare two pulps with different lignin contents, which were compared with two industrial pulps from conventional kraft cooks in order to evaluate the physical properties of the pulps.

It was demonstrated that pulps with lower lignin content can increase tensile stiffness, decrease hygroexpansion, and decrease the mechano-sorptive creep of handsheets. However, no difference in SCT and tensile energy absorption values due to different lignin contents was observed. It was further demonstrated that pulps made with Extended Impregnation Cooking (EIC) results in straighter pulp fibres with higher cellulose content. These pulps tended to have lower mechano-sorptive creep than conventional pulps. A higher brightness of the pulp sheets can also be obtained by choosing a higher alkali profile.

Keyword
High kappa number pulp, Extended impregnation, Softwood, Mechano-sorptive creep, Hygroexpansion, Tensile properties
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-11718 (URN)000273724200007 ()2-s2.0-76349088958 (Scopus ID)
Note
QC 20100629Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2017-12-12Bibliographically approved
3. The relationship between hygroexpansion, tensile stiffness, and mechano–sorptive creep in bleached hardwood kraft pulps
Open this publication in new window or tab >>The relationship between hygroexpansion, tensile stiffness, and mechano–sorptive creep in bleached hardwood kraft pulps
Show others...
2010 (English)In: Appita journal, ISSN 1038-6807, Vol. 63, no 1, 231- p.Article in journal (Refereed) Published
Abstract [en]

Hygroexpansion coefficient and tensile stiffness are important parameters in many paper applications. This study compares several bleached industrial hardwood kraft pulps, comprising five eucalypt pulps from South America, Europe, and Africa as well as an acacia pulp from Asia and a birch pulp from Scandinavia. Refined and unrefined pulps are compared. The results indicate significant differences in hygroexpansion but smaller differences in tensile stiffness index at comparable densities. No single factor offering a reasonable explanation of these differences in hygroexpansion coefficient, such as carbohydrate composition, fibre dimensions, or fibre form, was found. However, correlation between hygroexpansion coefficient and the mechano-sorptive creep stiffness was observed. We suggest that the hygroexpansion coefficient at a given tensile stiffness level can be used to rank pulps in terms of their mechano-sorptive creep properties.

Keyword
Mechano–sorptive creep, hygroexpansion, dimensional stability, eucalypt, birch, acacia
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-11719 (URN)000279222500012 ()2-s2.0-77956655760 (Scopus ID)
Note

QC 20100629

Available from: 2009-12-08 Created: 2009-12-08 Last updated: 2017-12-12Bibliographically approved

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