Abstract
BackgroundCocksfoot grass (Dactylis glomerata L.) with high biomass yield and rich cellulose can be used to produce bioethanol as fuel additive. In view of this, ultrasonic and hydrothermal pretreatments followed by successive alkali extractions were assembled into an integrated biorefinery process applied on cocksfoot grass to improve its enzymatic hydrolysis. In this work, the effects of ultrasonic and hydrothermal pretreatments followed by sequential alkali extractions on the enzymatic hydrolysis of cocksfoot grass were investigated. In addition, since large amount of hemicelluloses were released during the hydrothermal pretreatment and alkali extraction process, the yields, structural characteristics and differentials of water- and alkali-soluble hemicellulosic fractions isolated from different treatments were also comparatively explored.ResultsThe integrated treatment significantly removed amorphous hemicelluloses and lignin, resulting in increased crystallinity of the treated residues. A maximum saccharification rate of 95.1% was obtained from the cellulose-rich substrate after the integrated treatment. In addition, the considerable hemicelluloses (31.4% water-soluble hemicelluloses and 53.4% alkali-soluble hemicelluloses) were isolated during the integrated treatment. The released water-soluble hemicellulosic fractions were found to be more branched as compared with the alkali-soluble hemicellulosic fractions and all hemicellulosic fractions were mixed polysaccharides mainly composed of branched xylans and β-glucans.ConclusionThe combination of ultrasonic and hydrothermal pretreatments followed by successive alkali extractions can dramatically increase the enzymatic saccharification rate of the substrates and produce considerable amounts of hemicelluloses. Detailed information about the enzymatic hydrolysis rates of the treated substrates and the structural characteristics of the co-produced hemicelluloses will help the synergistic utilization of cellulose and hemicellulose in cocksfoot grass.
Highlights
Cocksfoot grass (Dactylis glomerata L.) with high biomass yield and rich cellulose can be used to produce bioethanol as fuel additive
As compared with RM, relatively higher glucan (39.6%) and lower xylan (14.4%) were obtained in R90, which suggested that partial hemicelluloses were dissolved from the raw material during the ultrasound and hot water extraction process
The hemicelluloses were further released, and the cellulose content of R 150 increased significantly from 39.6 to 45.6%. It seems that the pretreatments executed in this study had no obvious effect on delignification as compared with hemicelluloses, which may be due to the links between lignin monolignols are not very sensitive to this pretreated condition
Summary
Cocksfoot grass (Dactylis glomerata L.) with high biomass yield and rich cellulose can be used to produce bioethanol as fuel additive. Ultrasonic and hydrothermal pretreatments followed by succes‐ sive alkali extractions were assembled into an integrated biorefinery process applied on cocksfoot grass to improve its enzymatic hydrolysis. Carbohydrates (cellulose and hemicelluloses) and lignin are the main constituents of cocksfoot grass, among which cellulose as a polymer of glucose is generally used in paper industry or hydrolyzed to produce bioethanol as fuel additive [3, 4]. With the benefit of a series of attractive characteristics and rich carbohydrate reserves, the cocksfoot grass wastes can be developed as useful industrial feedstock to gain additional economic benefits
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