Steam pretreatment of acid-sprayed and acid-soaked barley straw for production of ethanol
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- Linde, M., Galb, M. & Zacchi, G. Appl Biochem Biotechnol (2006) 130: 546. doi:10.1385/ABAB:130:1:546
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Barley is an abundant crop in Europe, which makes its straw residues an interesting cellulose source for ethanol production. Steam pretreatment of the straw followed by enzymatic hydrolysis converts the cellulose to fermentable sugars. Prior to pretreatment the material is impregnated with a catalyst, for example, H2SO4, to enhance enzymatic digestibility of the pretreated straw. Different impregnation techniques can be applied. In this study, soaking and spraying were investigated and compared at the same pretreatment condition in terms of overall yield of glucose and xylose. The overall yield includes the soluble sugars in the liquid from pretreatment, including soluble oligomers, and monomer sugars obtained in the enzymatic hydrolysis. The yields obtained differed for the impregnation techniques. Acid-soaked barley straw gave the highest overall yield of glucose, regardless of impregnation time (10 or 30 min) or acid concentration (0.2 or 1.0 wt%). For xylose, soaking gave the highest overall yield at 0.2 wt% H2SO4. An increase in acid concentration resulted in a decrease in xylose yield for both acid-soaked and acid-sprayed barley straw. Optimization of the pretreatment conditions for acid-sprayed barley straw was performed to obtain yields using spraying that were as high as those with soaking. For acid-sprayed barley straw the optimum pretreatment condition for glucose, 1.0 wt% H2SO4 and 220°C for 5 min, gave an overall glucose yield of 92% of theoretical based on the composition of the raw material. Pretreatment with 0.2wt% H2SO4 at 190°C for 5 min resulted in the highest overall xylose yield, 67% of theoretical based on the composition of the raw material.