Comprehensive Evaluation Of The Liquid Fraction During The Hydrothermal Treating Of Rapeseed Straw And Effect Of The Treatment On Enhancing Enzymatic Hydrolysis Of Residues

The requirement for efficient and green conversion technologies has prompted hydrothermal processing as a promising treatment option for sustainable biorefinery industry.The treatment has been applied to process plenty of lignocellulose materials,yielding abundant high value-degraded products,especially the products in the liquid fraction.Therefore,it is essential to systematically evaluate the degraded products in aqueous fraction by comprehensive analysis and structural characterization during the treatment.In addition,exploration of the relation between the composition changes and the fermentation yields can enhance efficiency of the enzymatic hydrolysis of the residues.Rapeseed straw was hydrothermally treated at temperatures ranging from 145 °C to205 °C for various retention times(15min,30 min,60min and 120 min),and the degraded polysaccharides and lignin products in aqueous phase were systematically evaluated by comprehensive analysis and structural characterization.Results showed that with an increase of severity,the polysaccharides were gradually depolymerized resulting in products with low molecular weight.The maximum yield of oligosaccharides(99.94 g/kg)accompanying a relatively low level of monosaccharides(17.77 g/kg)was obtained at a high temperature(190 °C)for a short retention time(15 min).In these cases,monosaccharide degradation components were increased,and the S/G ratio largely decreased from 4.6 in L145–60 to 1.8 in L205–60,accompanied by strong condensation of lignin with an increased of severity.The degraded polysaccharides had a linear backbone of(1→4)-linked β-D-xylopyranosyl xylan decorated with branches based on 2D NMR spectra analysis.The yields of the degraded constitutions have a incomplete linear correlation with the treatment severity.Effect of hydrothermal treatment on enzymatic hydrolysis of residues was further studied.Results showed that with an increase of pretreatment severity,hemicelluloses were gradually removed,and temperature higher than 190 °C led to destroy crystalline structure and partial delignification,which could be proved by the FR-IR spectra and the increase of the thermal stability of the residues.The microstructure of the material was partially destroyed and spherical particles appeared on the surface of the treated samples under the harsh treatmentconditions.X-ray diffraction spectra showed that with the degradation of the hemicellulose and amorphous cellulose,the crystallinity of residues gradually increased from 28.9% to51.4%.Chemical composition analysis of residues illustrated that more than 95% of the hemicelluloses were removed,cellulose of the rapeseed straw increased from 35.01% to60.08% and insoluble lignin rapidly increased from 12.70% to 34.47%.The glucose yield increased with an increase of severity and higher saccharification ratio(96-99%)was achieved under relatively lower temperature(190 °C)and short retention time(15-30 min).The rapeseed straw was hydrothermally treated based on high-valued products.Effect of hydrothermal treatment on liquid fractions and efficiency of enzymatic hydrolysis of residues were comprehensively studied.These results would provide some valuable information in the commercial exploitation of rapeseed straw for the large-scale production of bio-based chemicals in the biorefinery industry.