Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The extraction of hemicelluloses prior to pulping that would have been dissolved in black
liquor during pulping process, is an attractive alternative for pulp and paper mills as they, in
addition to their core products, can increase their revenue by producing biofuels, biopolymers,
paper additives and other chemicals. However, the amount of hemicelluloses extracted will be
limited by the requirement to maintain pulp yield and pulp quality in comparison to existing
pulping processes.
In the present study, mild alkaline (NaOH) and dilute sulphuric acid conditions were used to
extract hemicelluloses from Eucalyptus grandis, giant bamboo (Bambusa balcooa) and
sugarcane (Saccharum officinarum) bagasse (SCB) prior to kraft or sodaAQ pulping
processes. The effects of catalyst concentration, temperature and reaction time on
hemicelluloses pre-extraction were studied, using a statistical experimental design to
investigate conditions under which hemicelluloses could be extracted prior to alkaline pulping
with minimal interference on cellulose (glucan) content. Subsequently, selected pre-extracted
materials were subjected to kraft or sodaAQ pulping to evaluate the effect of the
hemicelluloses pre-extraction on cooking chemicals, pulp yield and properties. This study
also included evaluation of hot water hemicelluloses pre-extraction of SCB as it was part of a dilute sulphuric acid experimental design. The pulp yield, cooking chemicals and handsheet
strength properties were compared with those obtained from kraft or sodaAQ pulping of non
extracted raw materials.
The results showed that alkaline pre-extraction options investigated preserves the pulp yield
with minimal effect on handsheet strength properties depending on the choice of the
subsequent pulping method while a fraction of xylan was extracted in polymeric form. In
addition, less active alkali was required to delignify the xylan extracted materials.
The integration of hemicelluloses pre-extraction by alkaline methods into a kraft pulping
process was preferred for giant bamboo and E. grandis since it maintained pulp yields at
desired industrial levels of 50%, and pulps within a bleachable kappa number range. Another advantage observed was the reduction in total cooking active alkali required to
delignify alkaline extracted giant bamboo or E. grandis by 8or 3 percentage points
respectively. However, the compromise to maintain the pulp yield was obtained when only
13.6% or 12.4% polymeric xylan was solubilised from giant bamboo or E. grandis
respectively. Slight improvement in burst index of the handsheet was observed for extracted
giant bamboo. On the other hand, pulp viscosity was increased by 13% due to the removal of
low molecular weight hemicelluloses, while the breaking strength of the handsheet was also
increased by 8.9% for pulps produced from extracted E. grandis.
In the case of sugarcane bagasse, hemicelluloses pre-extraction by alkaline methods
integrated well with the sodaAQ pulping process. It enabled a xylan recovery of 69.1%, while
providing pulp with higher screened pulp yield (45.0%), with an advantageous decrease in
kappa number (15.5). The handsheet tear index was superior without reduction in viscosity
compared to pulp produced from non extracted SCB. On the contrary, results obtained from optimised dilute sulphuric acid pre-extraction of all the
tested feedstocks were found to negatively impact subsequent kraft or sodaAQ pulping
processes resulting in lower pulp yields and poorer strengths properties. Nonetheless, the
differences were better when sodaAQ pulping was used compared to kraft pulping. SodaAQ
protects the carbohydrates against the peeling reaction under alkaline medium.
Conversely, pre-extraction of SCB with hot water resulted in low concentration of xylooligomers
(5.7%), while the subsequent sodaAQ pulping resulted in no pulp yield reduction.
The tear index and optical brightness of the handsheet papers produced from hot water
extracted SCB were slightly improved while the breaking length, tensile and burst indexes
were similar to those of pulps produced from non extracted SCB fibres.
Of equal importance were the observed higher tear and burst indexes of handsheets produced
from giant bamboo compared to E. grandis for both extracted and non extracted materials
prepared under similar pulping processes. The advantage of bamboo was due to the larger
fibre length and different morphological properties to those of hardwoods. However, the pulps produced from giant bamboo showed higher kappa numbers than those
pulps produced from E. grandis due to the high condensation behaviour of bamboo lignins
under alkaline conditions. Higher kappa numbers explained the higher demand for subsequent
bleaching chemicals.
In conclusion, the pulp mill biorefinery concept through hemicelluloses pre-extraction with
NaOH can be achieved with modified kraft pulping or the sodaAQ pulping processes, but it
depends on the type of raw material, extraction method and quality and performance
requirements of a particular paper. The low pulping chemicals demand, comparable pulp
yields and the improvement in some physico-chemical properties of the pulps from preextracted
materials were observed. Furthermore, owing to xylan pre-extraction a larger
amount of (extracted) material could be loaded into the digester as when non-extracted
materials were used. / AFRIKAANSE OPSOMMING: Ekstraksie van hemiselluloses wat tydens verpulping in die swartloog opgelos word, bied ‘n
aantreklike alternatief aan pulp- en papiermeulens om, addisioneel tot hul hoofprodukte, hul
inkomste deur die vervaardiging van biobrandstowwe, biopolimere, papierbymiddels en ander
chemikalië, daardeur te kan verhoog. Die hoeveelheid hemiselluloses wat ge-ekstraheer kan
word, sal egter beperk word deur die vereiste dat pulpopbrengs en –kwaliteit tydens bestaande
verpulpingsprosesse gehandhaaf moet word.
In hierdie ondersoek is matige alkaliese (NaOH) en verdunde swawelsuurtoestande gebruik
om hemiselluloses vóór kraft- of natriumantrakinoonverpulping uit Eucalyptus grandis, reuse
bamboes (Bambusa balcooa) en suikerriet (Saccharum officinarum) bagasse, mee te
ekstraheer.
Die invloed van katalisatorkonsentrasie, temperatuur en reaksietyd is mbv ‘n statistiese,
eksperimentele ontwerp ondersoek om die toestande te bepaal waaronder hemiselluloses, met
minimale effek op die sellulose (glukaan) –inhoud, vóór alkaliese verpulping ge-ekstraheer
kan word. Die pre-ge-ekstraheerde materiale, met hoë glukaan- en voldoende hemisellulosesinhoud,
is vervolgens aan kraft- en natriumantrakinoonverpulping onderwerp om die invloed
van pre-ekstraksie van hemiselluloses op die verpulpingsreagense, pulpopbrengs en -
eienskappe vas te stel. Hierdie studie het ook die evualering van warmwater hemisellulosespre-ekstraksie van suikerrietbagasse, wat deel is van ‘n verdunde swawelsuur
eksperimentele uitleg, ingesluit. Pulpopbrengs, die hoeveelheid verpulpingsreagense en
handveleienskappe van dieselfde materiale wat nie vooraf ge-ekstraheer is nie, is vergelyk.
Die resultate toon dat alkaliese pre-ekstraksie metodes wat ondersoek is die pulpopbrengs met
minimale effek op handvel sterkte-eienskappe afhangende van die keuse van daaropvolgende
pulpmetode kon handhaaf terwyl ‘n fraksie van xilaan in polimeriese vorm ge-ekstraheer is.
Addisioneel, is minder aktiewe alkali benodig om die xilaan ge-ekstraheerde materiale te
delignifiseer. Die integrasie van hemisellulosespre-ekstraksie dmv alkaliese metodes tydens ‘n kraft
verpulpingsproses is vir reuse bamboes en E. grandis verkies omdat pulpopbrengste op ideale
industriële vlakke van 50% gehandhaaf en is en pulp in ‘n bleikbare kappa nommergebied
interval kon lewer. ‘n Verdere voordeel wat waargeneem is was die vermindering in die totale
gekookte aktiewe alkali benodig vir reuse bamboes of E. grandis met 8 of 3 persentasiepunte
onderskeidelik. Die kompromie om die pulpopbrengs te handhaaf is verkry toe slegs 13.6% of
12.4% polimeriese xilaan opgelos is vanuit reuse bamboes of E. grandis onderskeidelik. ‘n
Effense verbetering in bars-indeks van die handvelle is waargeneem vir ge-ekstraheerde reuse
bamboes. Pulpviskositeit het met 13% gestyg agv die verwydering van die lae molekulêre
massa hemiselluloses, terwyl breeksterkte van handvelle ook met 8.9% toegeneem het vir
pulp verkry uit pre-gekstraheerde E. grandis.
NaOH pre-ekstraksie van 69.1% xilaan (droë massa) uit suikerriet bagasse (SCB) het ‘n hoër
natriumantrakinoon, gesifte pulpopbrengs gelewer (45.0%) met ‘n verbeterde afname in
kappa-getal (15.5) en uitstekende skeursterkte sonder verlaging in viskositeit, soos vergelyk
met nie-ge-ekstraheerde suikkerrietbagasse. Daarteenoor het die resultate verkry met die geoptimeerde verdunde swawelsuur preekstraksie
van al die getoetste rumateriale getoon om‘n negatiewe effek te gehad het op die
daaropvolgende kraft- of natriumantrakinoonverpulping dws het laer pulpopbrengste en
swakker sterkte-eienskappe opgelewer. Die verskille was nietemin kleiner toe
natriumantrakinoonverpulping ipv kraftverpulping gebruik is. Antrakinoon beskerm die
koolhidrate teen die afskilreaksie in alkaliese medium. Daarteenoor het pre-ekstraksie van suikerrierbagasse met warm water tot 'n lae hoeveelheid
(5.7%) xilaanoligomere gelei, terwyl die daaropvolgende natriumantrakinoonverpulping geen
verlaging in pulpopbrengs veroorsaak het nie. Skeursterkte en optiese helderheid van
handvelle wat uit warm water ge-ekstraheerde suikerrietbagasse vervaardig is, het ietwat
verbeter terwyl breek-, trek- en barssterkte dieselfde was as van suikerrietbagasse pulp wat
nie ge-ekstraheer is nie. Net so belangrik was die waargenome hoër skeur- en barsindekse van
handvelle vervaardig van reuse bamboes in vergelyking met E. grandis van beide geekstraheerde
en nie ge-ekstraheerde materiale voorberei onder dieselfde verpulpings
toestande. Bamboes se sterker eienskappe was as gevolg van die hoër vesellengte en ander
morfologiese eienskappe as diévan loofhout. Pulp wat vervaardig is van reuse bamboes het ‘n
hoër kappanommer getoon as pulp van E. grandis as gevolg van die hoë kondensasiegedrag
van bamboeslignien onder alkaliese toestande. Hoër kappanommers kon die gepaardgaande
hoër aanvraag vir bleikchemikalieë verklaar. Ten slotte, die pulpmeul bio-raffinaderykonsep nl. deur hemisellulosesekstraksie met NaOH
gekombineer met óf ‘n gemodifiseerde kraft verpulping óf ‘n gemodifiseerde
natriumantrakinoon verpulping, is wel uitvoerbaar. Dit word egter sterk beïnvloed deur die
tipe ru-materiaal en die ekstraksie-metode gebruik, asook deur die kwaliteits- en
gebruiksvereistes van verskillende tipes papier. ‘n Lae aanvraag vir verpulpingschemikalieë,
vergelykbare pulpopbrengste en die verbetering in fisies-chemiese eienskappe van pulp vanaf
pre-ge-ekstraheerde materiale is waargeneem. Verder kon, as gevolg van xilaan ekstraksie,
meer ge-ekstraheerde materiaal in die verteerder gelaai word as wanneer nie-ge-ekstraheerde
materiaal gebruik is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80116 |
| Date | 03 1900 |
| Creators | Vena, Phumla Faith |
| Contributors | Gorgens, J. F., Rypstra, T., Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 251 p. : ill. |
| Rights | Stellenbosch University |
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