UBC Theses and Dissertations
Study of fermentability of pretreated Acid Catalyzed Organosolv Saccharification (ACOS) hydrolysate by Saccharomyces diastaticus highly flocculating yeast Jeong, Cheol
Sugar production from spruce wood chips, the presence of fermentation inhibitors (carbohydrate degradation products, extractives and phenolic compounds), their removal and the fermentability of ACOS (&cid catalyzed Qrganosolv Saccharification) hydrolysates were extensively studied. In percolation type runs 92.75% of the theoretical sugars were recovered in 30 to 40 mm runs at 180° C with 80:20 acetone:water solutions containing 0.04 N sulfuric acid as the hydrolysis catalyst. This hydrolysis process was not optimized. 96% of the wood charge was dissolved. 4.0 % of the total dissolved sugars were in the form oligomers, mainly cellobiose and cellotetraose, in crude ACOS hydrolysate. Furfural was not found but trace amount of hydroxylmethylfurfural (HF) was detected in the hydrolysate. Recovery of the solvent precipitated the bulk of the waterinsoluble lignin. The lignin precipitate removed the dissolved extractives (resin- and fatty acids) almost completely making the hydrolysate free of extractives. Although the untreated ACOS hydrolysates contained 1.269 mg/rnL phenolic materials, the sugars were fermentable to ethanol without hydrolysate pretreatment in 24 h by Saccharomyces diastaticus, a flocculating yeast, when 25 g dry-weight cell mass/L was employed. This demonstrated that with high cell mass the inhibition could be alleviated or removed. The ACOS hydrolysate can be considered free of inhibitors since extractives and furans were absent and those of lignin origin could be easily overcome. Secondary hydrolysis for lh at 1200 C at 4% sulfuric acid catalyst concentration improved the monomeric sugar yield by as much as 57% mainly by conversion of suspected isopropylidenes and some oligomers to their monomeric sugars. Among the various hydrolysate clarification treatments extraction with diethyl ether, treatment with charcoal, IRN 150 mixed ion exchange resin, XAD-16 adsorption resin were tried. All these treatments improved the fermentation rate and ethanol yield from the sugars by the removal of phenolic materials. In the alcoholic fermentation only glucose and mannose were utilized. Residual color of the hydrolysate after treatment seemed to have little effect on the fermentation rate since in all treated hydrolysates (6% sugar solids) 88% of the fermentable glucose and mannose was consumed in 1 to 2 h and maximum ethanol yield (about 0.4228 - 0.4729 g/g sugar consumed) was achieved in 3 to 6 h. The XAD-l6 plus charcoal polishing treatment removed watersoluble phenolic materials in the hydrolysate up to 79%. Combined treatment of the hydrolysate with XAD-l6 resin and charcoal (polishing) resulted in a water-clear hydrolysate and produced up to 0.4729 g ethanol/g sugar consumed at 6% sugar solid fermentation in 3 h and 0.4416 g ethanol/g sugar consumed at 15% sugar solid in 24 h reaching 6.12 % ethanol concentration in the beer. Arabinose, galactose and xylose did not ferment to ethanol but some xylitol was detected by HPLC (High Performance Liquid Chromatography). Combination of proper pretreatment and high cell density seemed to be the most desirable way of removing inhibition in fermentation of the ACOS wood hydrolysate. Based on these results the ACOS process can be projected to produce 354.98 L of ethanol per ton of unextracted spruce wood analyzed at 57.46% hexoses (glucose and mannose only) Additional ethanol can be expected on second fermentation of xylose to xylitol and conversion of residual sugars left in the still bottoms.
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