Sooda-AQ-keitto alkali-esiuutetulle koivuhakkeelle

The prices of energy and raw materials are on the rise. In order to improve their competitive position, cellulosic pulp manufacturers try to expand their product portfolio beyond high quality pulp by utilizing different fractions of wood more efficiently. Conventionally dissolved hemicelluloses are burned with the black liquor despite their low heat value. Therefore the interest to utilize wood hemicelluloses as raw material for new valuable side products is increasing within the industry. High alkali pre-treatment is seen as a one method to extract hemicelluloses before pulping: however, this method places substantial limitations on the cooking conditions to be used. In conventional processing, approximately 50% of the hemicelluloses degrade during pulping, but the remaining hemicelluloses are important for the paper strength properties. Therefore the demands of the final product need to be considered, when the hemicelluloses are extracted. The primary objective of this work was to optimize cooking conditions for high alkaline pre-extracted birch wood in order to retain good pulp and paper quality despite removing a large proportion of the xylan prior to cooking stage. The selected pre-extraction conditions gave a reasonably good yield of hemicelluloses, with tolerably low lignin contamination levels, but the sodium hydroxide charge exceeds that of conventional Kraft cooking by almost four times. Therefore a special attention was paid to precise determination of the alkali consumption during the pre-extraction and cooking stages and an efficient method for alkali collection was established to make the process commercially interesting. Filtration treatment for increasing the xylan-to-caustic ratio of the pre-extract in order to reintroduce the xylan into the pulp during oxygen delignification was set up as a secondary objective of this thesis. As a result of this study, an operational two-step process for birch wood consisting of alkaline pre-extraction and soda-anthraquinone (AQ) cooking was established, allowing the concurrent production of polymeric xylan and pulp. The pulp yield of the two-step process remained (4.5% on raw wood) lower than that of the one-step reference process, but the extracted xylan yield (5.2 % on raw wood) more than compensated for this difference. The chemical consumption in the two-step process was also brought below commercially acceptable values (20% on raw wood). Xylan was successfully reintroduced into the pulp in the oxygen de lignification step, but under the selected conditions, xylan precipitation on the pulp was ineffective.Nykypäivänä energian sekä raaka-aineiden hinta nousee jatkuvasti. Selluloosatehtaat pyrkivät vastaamaan kiristyvään kilpailuun hyödyntämällä puun eri komponentteja entistä tehokkaammin ja monipuolistamalla tuotevalikoimaansa. Puun komponenteista hemiselluloosa on perinteisesti poltettu mustalipeän mukana, huolimatta hemiselluloosan matalasta lämpöarvosta. Tämän takia kiinnostus käyttää hemiselluloosaa uusien sivutuotteiden raaka-aineena kasvaa jatkuvasti selluloosateollisuudessa. Korkea-alkalinen esikäsittely on yksi keino, jolla hemiselluloosaa voidaan uuttaa hakkeesta ennen keittovaihetta, mutta kyseinen esikäsittelymenetelmä vaikuttaa paljon keitto-olosuhteisiin. Perinteisessä prosessissa noin 50 % hemiselluloosasta liukenee keiton aikana. Massaan jäävä hemiselluloosa vaikuttaa paperin lujuusominaisuuksiin, joten hemiselluloosaa eristettäessä on huomioitava lopputuotteen vaatimukset. Tämän työn päätavoitteena oli optimoida koivuhakkeelle keitto-olosuhteet, joilla voidaan säilyttää massan saanto ja paperin hyvä laatu, vaikka suuri osa koivun xylaanista eristetään ennen keittoa. Työssä todettiin, että korkea-alkaliset esikäsittelyolosuhteet antavat suhteellisen hyvän xylaanisaannon, siedettävän ja alhaisen ligniinikontaminaation, mutta esikäsittelyn natriumhydroksidiannostus ylittää perinteisen sulfaatti-prosessin annostuksen lähes nelinkertaisesti. Tästä johtuen kulumattoman alkalin talteenotto oli tarpeen kehittää, jotta menetelmä olisi teollisesti sovellettavissa. Työn toinen tavoite oli prosessoida esikäsittelyn alkalinen xylaaniliuos nano- sekä diasuodatuksella, sellaiseksi että sitä voitiin käyttää happidelignifioinnissa alkali- ja hemiselluloosalähteenä. Työn tuloksena kehitettiin toimiva kahden vaiheen prosessi, joka sisältää alkalisen esikäsittelyn hemiselluloosan eristämiseksi sekä sooda-antrakinonikeiton (AQ-keitto), joka tuottaa koivuhakkeesta polymeeristä xylaania sekä selluloosamassaa. Kehitetyn prosessin saanto jäi (4,5 massa % raakapuusta) referenssiprosessia alhaisemmaksi, mutta eristetyn xylaanin saanto (5,2 massa % raaka puusta) kompensoi erotuksen. Kemikaalikulutus onnistuttiin saamaan alle teollisuusarvojen, (20 massa % raakapuusta). Lisäksi eristetty xylaani kyettiin viemään takaisin massaan happidelignifioinnin aikana. mutta sen sitoutuminen massaan ei ollut tehokasta valituissa olosuhteissa

Ionisiin nesteisiin perustuva hemiselluloosien eristys Kraft sellumassasta

This study introduces the IONCELL-P(ulp) process, which refines hemicellulose-rich bleached paper grade pulp to high purity dissolving pulp and polymeric hemicelluloses without yield losses or polymer degradation. Both fractions, the cellulose and dissolved hemicellulose, can be recovered quantitatively, providing a basis for a new stream of hemicellulose products and dissolving pulp production. In order to provide valuable information for the process up-scaling, the features that affect the extraction (solvent and substrate properties, reaction conditions) and equipment requirements were studied profoundly. The studies progressed by examining the usability of the separated polymer fractions, by investigating the purity, reactivity and integrity of the polymers. The results revealed that the solvation selectivity towards hemicelluloses was governed by the molecule size of the carbohydrate polymers. Short hemicelluloses dissolve more readily in aqueous ionic liquids, while the cellulose fraction remains intact. Thus, the molar mass distribution (MMD)of the pulp is a decisive feature regarding the suitability of this pulp for the IONCELL-P process. A distinct difference in the size of hemicelluloses and cellulose allows for a more accurate tuning of the solvent-water mixture for the selective and efficient extraction of hemicelluloses. A selection of different cellulose dissolving ionic liquids were tested in the process and a joint behaviour of the solvent mixtures was found, when the β-value, describing the anion's ability to accept hydrogen bonds, was divided with the water molar fraction of the solvent system. The resulting β/χ(H2O)-value gives an approximation of the relative strength of the solvent, which is needed for maximal hemicellulose solvation, but it does not describe the limit, where a certain solvent mixture loses its selectivity towards hemicelluloses and begins to dissolve increasing amounts of cellulose. The selectivity of the solvent system was also investigated in the terms of pH. Low pH ionic liquids demanded less water to render them to hemicellulose solvents and they were less inclined to swell and dissolve cellulose. Combining these findings, the IONCELL-P process is most efficient when using a pulp with a distinct difference in the MMD between the cellulose and hemicellulose fractions and an ionic liquid with low pH and relatively high β-value. The IONCELLP purified pulp is highly reactive and suitable for various applications such as cellulose acetate production. The process preserves the cellulose I crystalline structure and neither of the fractions, cellulose or hemicellulose, undergoes degradation reactions.Tämä väitöskirja käsittelee IONCELL-P(ulp)-prosessia, jonka avulla jalostetaan hemiselluloosapitoisesta paperisellusta puhdasta liukosellua ja polymeeristä hemiselluloosaa. Erotetut fraktiot (selluloosa ja hemiselluloosa) voidaan kerätä ilman saantohävikkiä tai polymeerien hajoamista, jalisäksi prosessi säilyttää selluloosan luontaisen kiderakenteen. Täten prosessi tarjoaa korkeasaantoisen liukosellun tuotannon rinnalle perustan hemiselluloosa pohjaisille tuotteille. Työssä on tutkittu eristyksen tehokkuuteen vaikuttavia tekijöitä (liuottimen ja raaka-aineen ominaisuudet sekä reaktio-olosuhteet) ja laitteistolle välttämättömiä ominaisuuksia prosessin kapasiteetin nostoa varten. Eristettyjen fraktioiden käytettävyyttä arvioitiin analysoimalla niiden puhtautta, reaktiivisuutta ja muuttumattomuutta. Tulokset osoittivat, että liuotuksen selektiivisyys hemiselluloosia kohtaan perustuu hemiselluloosien pienempään molekyylikokoon. Lyhyet hemiselluloosamolekyylit liukenevat suotuisammin ionisen nesteen vesiliuokseen selluloosan jäädessä kiinteään muotoon. Tämän takia sellumassan polymeerien moolimassajakauma on tärkeä ominaisuus arvioitaessa massan soveltuvuutta IONCELL-P-prosessiin. Mitä selkeämpi ero selluloosan ja hemiselluloosan molekyylikoissa on, sen paremmin on mahdollista optimoida veden määrä ionisessa nesteessä, vaikuttamaan vain hemiselluloosiin. Valikoima selluloosaa liuottavia ionisia nesteitä testattiin prosessissa ja niistä löytyi yhteinen käyttäytymismalli. β/χ(H2O)-arvo muodostuu, kun liuotinseoksen β-arvo, joka kuvaa anionin kykyä vastaanottaa vetysidoksia, jaetaan veden moolifraktiolla. Tämä arvo antaa arvion seoksen liuotinvahvuudesta, joka tarvitaan hemiselluloosien eristämiseen, mutta ei kuvaa sitä rajaa, missä liuotinseos menettää selektiivisyytensä ja alkaa liuottaa myös selluloosaa. Tämän vuoksi systeemin selektiivisyyttä tutkittiin myös pH:n funktiona. Tuloksista ilmeni, että matalan pH:n ioniset nesteet vaativat vähemmän vettä selektiiviseen hemiselluloosien liuotukseen. Tämän lisäksi matalan pH:n ioniset nesteet olivat vähemmän taipuvaisia turvottamaan ja liuottamaan selluloosaa. Nämä löydökset yhdistämällä voidaan päätellä, että IONCELL-P-prosessiin soveltuu parhaiten massa, jonka selluloosa- ja hemiselluloosafraktioilla on selkeä kokoero, sekä ioninen neste, jolla on matala pH ja suhteellisen korkea β-arvo

Single fiber swelling behavior for natural and man-made cellulose fibers under alkaline treatment

The financial support from Jenny and Antti Wihuri Foundation (Grant No. 131219) is gratefully acknowledged. The authors wish to thank Maija Nenonen and Sari Larmu for simulating the industrial viscose process. We thank Dr. Daisuke Sawada (Aalto University) for the crystallinity calculation. Additionally, the authors acknowledge the provision of the facility and technical support by Aalto University at OtaNano-Nanomicroscopy Center (Aalto NMC).Swelling behavior of cotton, dissolving wood pulp (DWP), viscose staple fiber, and Tencel staple fiber in varying sodium hydroxide (NaOH) concentration were investigated by means of optical microscopy and were characterized by molecular mass distribution, X-ray diffractometer, and dynamic vapor sorption. The effect of temperature (20–45 °C) and duration (0–120 min) was studied. The results reveal that the swelling ratio of fiber in alkali solution depends on fiber accessibility and NaOH concentration. Viscose staple fiber exhibited the highest swelling ratio and lowest swelling ratio observed for dissolving wood pulp fiber among all the materials. The cotton or DWP fibers provide maximum swelling during alkaline steeping (18wt % lye) at higher temperatures, i.e., 45 °C. As for viscose staple fiber and Tencel staple fiber, using 12 wt% lye concentration and steeping at lower temperatures, i.e., 20 °C maximum swelling behavior.Peer reviewe

Combined Production of Polymeric Birch Xylan and Paper Pulp by Alkaline Pre-extraction Followed by Alkaline Cooking

Alkaline pre-extraction of birch wood was performed to isolate polymeric xylan and subsequently produce a paper-grade pulp. At 95 °C and 2.5 mol/L NaOH, 7% of wood was transferred to the E-lye as polymeric xylan with an anhydroxylose-lignin ratio of 6.5. Xylan with a weight-average molar mass of 20 kDa was quantitatively precipitated from the solution previously concentrated from 7.4 to 37 g/L. The anhydroxylose-lignin ratio in the carbohydrate fraction increased to 29 g/g upon precipitation. Enzymatic hydrolysis of the commercial birch xylan with Pentopan Mono PG resulted in a uniform xylooligosaccharide product with low xylose content at a yield of 61%. The pre-extracted pulp had excellent papermaking properties but its yield was 4.9% units lower than that of the reference pulp. Commercial potential of the modified process was discussed

Separation of Hemicellulose and Cellulose from Wood Pulp by Means of Ionic Liquid/Cosolvent Systems

Pulp of high cellulose content, also known as dissolving pulp, is needed for many purposes, including the production of cellulosic fibers and films. Paper-grade pulp, which is rich in hemicellulose, could be a cheap source but must be refined. Hitherto, hemicellulose extraction procedures suffered from a loss of cellulose and the non-recoverability of unaltered hemicelluloses. Herein, an environmentally benign fractionation concept is presented, using mixtures of a cosolvent (water, ethanol, or acetone) and the cellulose dissolving ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIM OAc). This cosolvent addition was monitored using Kamlet–Taft parameters, and appropriate stirring conditions (3 h at 60 °C) were maintained. This allowed the fractionation of a paper-grade kraft pulp into a separated cellulose and a regenerated hemicellulose fraction. Both of these exhibited high levels of purity, without any yield losses or depolymerization. Thus, this process represents an ecologically and economically efficient alternative in producing dissolving pulp of highest purity

Comparison of pulp species in IONCELL-P: Selective hemicellulose extraction method with ionic liquids

Abstract In our recent studies, it was demonstrated that the IONCELL-P process selectively dissolves hemicelluloses from bleached birch kraft pulp in a mixture of 1-ethyl-3-methylimidazolium acetate ([emim][OAc]) and water as a solvent system. The IONCELL-P method refines paper-grade pulp to dissolving pulp with &lt;5% hemicelluloses and allows isolation of polymeric xylan without yield losses or polymer degradation. This paper is a comparative study where paper-grade pine, birch, and eucalyptus pulps are subjected to the IONCELL-P process with two [emim]-based ionic liquids (ILs), i.e. [emim]acetate and [emim]dimethylphosphate. Also, the effect of an endoglucanase pretreatment was investigated to check whether 1) the pulp viscosity could be adjusted for the following process steps before the hemicellulose extraction and 2) the decreasing pulp viscosity would open the fiber structure and thus enhance the extraction. Under optimum conditions, the birch xylan content could be reduced from 25.4% down to 1.3% and for eucalyptus from 16.6% to 2.4%. Pine pulp xylan and glucomannan were decreased from 8.1% and 7.1% to 0.9% and 2.2%, respectively. The residual hemicellulose contents of the pine pulp could be further decreased with a hemicellulase pretreatment. The selectivity of the dissolution towards hemicelluloses was better for hardwoods. Adjusting the pulp viscosity by endoglucanase prior to the IONCELL-P process reduced the selectivity as short-chain cellulose molecules were extracted along with the hemicelluloses.</jats:p