Critical conditions for improved fermentability during overliming of acid hydrolysates from spruce.
ABSTRACT Bioethanol can be produced from wood via acid hydrolysis, but detoxification is needed to achieve good fermentability. Overliming was investigated in a factorial designed experiment, in which pH and temperature were varied. Degradation of inhibitory furan aldehydes was more extensive compared to monosaccharides. Too harsh conditions led to massive degradation of sugars and formation of inhibiting acids and phenols. The ethanol productivity and yield after optimal overliming reached levels exceeding reference fermentations of pure glucose. A novel metric, the balanced ethanol yield, which takes both ethanol production and losses of fermentable sugars into account, was introduced and showed the optimal conditions within the investigated range. The findings allow process technical and economical considerations to govern the choice of conditions for overliming.
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ABSTRACT: In this study, switchgrass, which is a promising energy crop, was treated with two new pretreatment methods for the production of bioethanol. Acidic electrolyzed water (AEW) and alkaline electrolyzed water (ALEW) were first used as pretreatment catalysts at three temperatures (170, 185, and 200 o C) and 3 treatment times (5, 15, and 25 min). In the two-stage pretreatment, 1.0, 2.0 and 3.0% H 2 O 2 solutions were used to partially remove hemicellulose and lignin during the 1 st stage at 50 o C for 16, 24, or 32 h at a solid concentration of 5%. The supernatant of the 1 st stage was used for hemicellulose precipitation. The remaining solids were subjected to a 2 nd stage treatment with hot water at 121 o C for 30 min in an autoclave at a solid concentration of 12.5%. In the electrolyzed water pre-treatment, the highest glucose yield was achieved by pretreatment with ALEW at 200 o C and 25 min, which resulted in the release of 23.8 g glucose from 100 g dry switchgrass. The hydrolyzate obtained from switchgrass pretreated with 3% H 2 O 2 for 16 h followed by enzymatic hydrolysis was fermented using S. cerevisiae at 30 o C for 96 h without any concentration or detoxification steps. The final ethanol concentration was 11.8 g/L and the productive yield was 74% of the theoretical yield. A mass balance for the two-stage process showed that 12 g of ethanol was produced from 100 g dry switchgrass.Biotechnology and Bioprocess Engineering 01/2012; 17:624-633. · 1.28 Impact Factor
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ABSTRACT: Clostridium spp. produce n-butanol in the acetone/butanol/ethanol process. For sustainable industrial scale butanol production, a number of obstacles need to be addressed including choice of feedstock, the low product yield, toxicity to production strain, multiple-end products and downstream processing of alcohol mixtures. This review describes the use of lignocellulosic feedstocks, bioprocess and metabolic engineering, downstream processing and catalytic refining of n-butanol.Biotechnology Letters 04/2012; 34(8):1415-34. · 1.85 Impact Factor
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ABSTRACT: Bioconversion of lignocellulose by microbial fermentation is typically preceded by an acidic thermochemical pretreatment step designed to facilitate enzymatic hydrolysis of cellulose. Substances formed during the pretreatment of the lignocellulosic feedstock inhibit enzymatic hydrolysis as well as microbial fermentation steps. This review focuses on inhibitors from lignocellulosic feedstocks and how conditioning of slurries and hydrolysates can be used to alleviate inhibition problems. Novel developments in the area include chemical in-situ detoxification by using reducing agents, and methods that improve the performance of both enzymatic and microbial biocatalysts.Biotechnology for Biofuels 01/2013; 6(1):16. · 5.55 Impact Factor