Alkaline polyol fractionation of sugarcane bagasse and eucalyptus grandis into feedstock for value added chemicals and materials

Pius, Moses Tuutaleni (2017-03)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

ENGLISH SUMMARY: The main components of lignocellulosic biomass cellulose, hemicellulose and lignin are feedstock for chemical and material manufacturing processes. Integrated biorefinery processes incorporate the production of these valuable components from lignocellulose feedstock in good yield and quality. The nature and complexity of lignocellulose materials and its components require a well-designed process to fractionate these components into individual streams, while special attention is paid to the easily hydrolysed component, hemicelluloses. In the present study, a novel process for the fractionating sugarcane (Saccharum officinarum) bagasse (SCB) and Eucalytpusgrandis (EC) biomass into their main constituents (cellulose pulp, aqueous hemicellulose and lignin) is designed. Research focused on obtaining hemicelluloses in polymeric form or as biopolymers, while maintaining high yields and quality of cellulose and lignin polymers. This was achieved by following organosolv technique using high boiling point alcohols, xylitol and ethylene glycol as the fractionating solvents at concentrations between 20-30% (w/w) and 50-70% (v/v) respectively. The fractionation process’ central composite design incorporated mild conditions, i.e. fractionation time between 2-4 hours, temperatures at 140-180 ºC catalysed by sodium hydroxide between 1-2 wt.% and also subsequently investigated the option of pre-extracting hemicelluloses from the feedstock at previously established conditions prior to further fractionation with ethylene glycol given its hemicellulose destructing nature from literature studies. Results show hemicellulose alkaline pre-extraction to provide higher dissolutions and recoveries of hemicelluloses as compared to those extracted by direct fractionation with the two solvents. At optimum conditions xylitol fractionations achieved higher component recoveries as compared to ethylene glycol. However, ethylene glycol fractionations are more severe in dissolving not only hemicellulose and lignin from both materials but also cellulose. Ethylene glycol fractionations were also accompanied by a high degree of cellulose dissolutions, in some runs up to 39% of the initial, mostly at extreme conditions. Hemicelluloses from all processes were recovered as biopolymers with weight-average molecular weight (Mw) evaluation revealing that alkaline pre-extracted hemicelluloses had highest weight-average molecular weights, 33 638 and 61 644 gmol-1 for sugarcane bagasse and Eucalytpus grandis respectively, as compared to direct raw material fractionation processes which all gave below 23 000 gmol-1 with xylitol processes giving higher molecular weights than ethylene glycol processes. Enzymatic hydrolysis of cellulose revealed ethylene glycol residues to be more digestible (≥60%) than xylitol derived residues (≤60%). Digestibility is further improved with fractionation of hemicellulose pre-extraction solids (≥80%). In terms of cellulose crystallinity, a general increase after fractionation was observed. Residual solids from ethylene glycol treatments displayed higher crystallinity (50.08% EC, 48.44% SCB) as compared to xylitol processes (32.44% EC, 43.98% SCB). Residual solids from the NaOH hemicellulose pre-extraction step also had high crystallinities (43.58% EC and 47.81% SCB) than the xylitol process but just lower than EG derived residual solids (≥48%). There is a major decline in the amount of syringyl and guaiacyl groups in the lignin residues after treatment for all processes supported by low intensity bands in Fourier Transform Infrared Resonance (FTIR). Minimal degradation of lignin fraction by both processes was observed with low fixed carbon content of lignin rich solids, below 20%. In conclusion, xylitol fractionations overweighed ethylene glycol in hemicellulose, lignin and cellulose recoveries, and lignin and hemicellulose quality while ethylene glycol produced good quality cellulose. When compared to conventional organosolv fractionations (i.e. ethanol), these two polyols overweigh organosolv in aspects such as quality of cellulose, hemicellulose and lignin but comes short in terms of component recoveries particularly with ethylene glycol fractionations.

AFRIKAANS OPSOMMING: Die hoof-komponente van lignosellulose biomassa (sellulose, hemisellulose en lignien) dien as voer vir chemiese en material-vervaardigingsprosesse. Geïntigreerde bio-raffinadery prosesse sluit die produksie (teen goeie opbrengste en kwaliteit) van hierdie waardevolle lignosellulose komponente in. Die aard en kompleksiteit van lignosellulose materiale beteken dat die fraksionering daarvan in individuale komponente ‘n goed-ontwerpte proses vereis, met spesiale aandag wat geskenk word aan die maklik gehidroliseerde komponent, hemisellulose. In hierdie studie word ‘n nuwe proses ontwerp vir die fraksionering van suikerriet (Saccharum officinarum) bagasse (SRB) en Eucalytpus grandis (EC) biomassa in hulle hoof-bestanddele (sellulose pulp, gehidreerde hemisellulose en lignien). Navorsing het gefokus op die verkryging van hemisellulose of in sy polimeriese vorm of as biopolimere, terwyl hoë opbrengste en kwaliteit van sellulose en lignien polimere gehandhaaf word. Dit is gedoen deur ‘n orgasolv tegniek te volg, wat behels dat kookpunt alkohole, xylitol en etileen-glikol as die fraksioneringsoplosmiddels gebruik is, by konsentrasies tussen 20-30% (w/w) en 50-70% (v/v), onderskeidelik. Die fraksioneringsproses se sentrale saamgestelde ontwerp het gematigde toestande geïnkorporeer; d.w.s ‘n fraksineringstyd tussen 2 en 4 ure, temperature tussen 140 en 180 ºC, en katalise deur natriumhidroksied tussen 1 en 2 massa%. Die opsie om die hemisellulose van die voer by voorheen vasgestelde toestande te ekstraheer, voor verdere fraksionering van etileenglikol, is ook ondersoek, as gevolg van die vernietigende aard daarvan (volgens literatuur). Die resultate wys dat alkaliese hemisellulose pre-ekstraksie beter oplossing en hoër opbrengste van hemisellulose gee as wat dit met direkte fraksionering (met die twee oplosmiddels) die geval is. By optimale toestande het xylitol fraksionerings hoër komponent opbrengste bereik as etileenglikol. Etileenglikol fraksionerings los egter meer aggressief op, sodat nie net hemisellulose en lignien nie, maar ook sellulose oplos. Etileenglikol fraksionerings is ook vergesel deur ‘n hoë mate van sellulose-verliese – in sommige lopies tot 39% van die aanvanklike hoeveelheid (meestal by ekstreme toestande). Hemisellulose was in al die prosesse herwin as biopolimere, met ‘n massa-gemiddelde molekulêre massa evaluering wat daarop dui dat alkaliese vooraf ge-ekstraheerde hemisellulose die hoogste molekulêre massas gehad het (onderskeidelik 33 638 en 61 644 gmol-1 vir suikerriet bagasse en E. grandis ). Hierteenoor het direkte roumateriaal fraksioneringsprosesse almal minder as 23 000 gmol-1 gelewer, met xylitol prosesse wat hoër molekulêre massas gelewer het as etileenglikol prosesse. Ensemiese hidroliese van sellulose het daarop gedui dat etileenglikol reste meer verteerbaar (≥60%) as xylitol afgeleide reste (≤60%) is. In terme van sellulose kristalliniteit was ‘n toename na fraksionering in die algemeen gevind. Vastestof reste, van etileenglikol behandelings, het hoër kristalliniteit (50.08% EC, 48.44% SCB) getoon as xylitol prosesse (32.44% EC, 43.98% SCB). Vastestof reste van die NaOH hemisellulose pre-ekstraksie stap het ook hoër kristalliniteite (43.58% EC en 47.81% SCB) tot gevolg gehad as die xylitol proses, maar net laer as EG afgeleide vastestof reste (≥48%). Daar is ‘n groot afname in die heoveelheid syringyl en guaiacyl groepe in die lignien-reste na behandeling vir alle prossesse, ondersteun deur lae-intensiteit bande in Fourier Transform Infrarooi Resonansie (FTIR). Minimale degradering van lignien is ge-observeer vir beide prosesse, met ‘n lae vaste-koolstof inhoud van die lignien-ryke vastestof (minder as 20%). Ten slotte het xylitol fraksionerings beter as etileenglikol in terme van die totale herwinning van hemisellulose, lignien en sellulose en die kwaliteit van hemisellulose. Hierteenoor het etileenglikol sellulose van ‘n goeie kwaliteit geproduseer. Wanneer hierdie twee poliole met konvensionele organosolv fraksionerings (d.w.s. etanol) vergelyk word, doen eersgenoemde beter in terme van sellulose, hemisellulose en lignien kwaliteit. Dit skiet egter tekort in terme van die komponent opbrengste – veral met etileenglikol fraksionerings.

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