Browsing by Author "Pius, Moses Tuutaleni"
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- ItemAlkaline polyol fractionation of sugarcane bagasse and eucalyptus grandis into feedstock for value added chemicals and materials(Stellenbosch : Stellenbosch University, 2017-03) Pius, Moses Tuutaleni; Gorgens, Johann F.; Chimphango, Annie F. A.; Tyhoda, Luvuyo; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.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.