Two-step Ultra-low Acid/high Temperature Hot Water Pretreatment Of Cassava Residue And Enzymatic Hydrolysis To Prepare Fermentable Sugar

As the global crisis of shortage of fossil energy becomes more and more obvious,people are paying more and more attention to the development of sustainable clean energy.Among them,the study of biomass fuel ethanol has received extensive attention.Due to the fact that early starch alcohols are less raw materials and there is competition for grain,the study of lignocellulosic fuel ethanol has received extensive attention.However,due to the inherent compact structure of the lignocellulosic raw material,it cannot be directly converted to produce fermentable sugars.Therefore,in order to increase the yield of fermentable sugars,fermentable sugars are mostly extracted by pretreatment and enzymatic hydrolysis.In this paper,cassava residues from factory wastes are used as raw materials and treated with one-step ultra-low-acid(ULA-One-step),two-step ultra-low-acid(ULA-Two-step),one-step liquid hot water(HW-One-step)and two-step liquid hot water(HW-Two-step)synergetic enzymolysis.The pretreatment process was evaluated using the total sugar yield in the pretreatment and enzymatic hydrolysates and the concentration of inhibitors as indicators.And the component analysis,crystallinity analysis,FT-IR analysis,and thermogravimetric analysis were performed on the raw materials,pretreated solids,and enzymatic residues to explore the effect of different pretreatment methods on the content and structure of different components in cassava residues.The recoveries of glucose,xylose and total sugar reached 71.30%,72.88%and 70.33%,respectively,after ULA-One-step pretreatment synergistic enzymatic hydrolysis(0.01%(w/w)H2SO4,180 0C,20 min + 35 FPU/g),and the acid-insoluble lignin(AIL)recovery was 83.20%.After ULA-Two-step pretreatment followed by enzymatic hydrolysis(0.01%(w/w)H2SO4,180 ?,20 min + 0.05%(w/w)H2SO4,190 ?,10 min + 35 FPU/g),the recoveries of glucose,xylose and total sugar reached 72.97%,82.40%and 73.20%respectively,and the AIL recovery was 74.74%.The recoveries of glucose,xylose and total sugar reached 67.80%,73.74%and 67.75%,respectively,after HW-One-step pretreatment(190 ?,10 min + 35 FPU/g),and the recovery of AIL was 72.22%.The recoveries of glucose,xylose and total sugar reached 68.86%,76.40%and 68.95%,respectively,after HW-Two-step pretreatment(190 ?,10 min + 200 ?,10 min + 35 FPU/g),and the recovery of AIL was 69.18%.In addition,the contents of inhibitors(including formic acid,acetic acid,furfural,and 5-HMF)in the prehydrolysate of the four methods were all lower.The highest concentrations of forrmic acid,acetic acid,furfural,and 5-HMF were 1.03 g L-1,0.52 g·L-1,0.21 g·L-1,and 0.03 g·L-1,respectively,and were all far less than the limit of the inhibitors reported.Compared to single-step pretreatment,two-step pretreatment has higher total sugar yield,especially xylose.Compared with high-temperature hot water(HW)pretreatment,ultra-low-acid(ULA)pretreatment can not only reduce the temperature required for pretreatment but also have higher total sugar recovery.In addition,it does not increase the total inhibitor amount.The crystallinity and thermal stability of starch cassava residues after pretreatment with ULA and HW increased significantly.In addition,the corresponding carbonyl peak intensity of hemicellulose was obviously weakened,and most of the hemicellulose could be degraded in the pretreatment stage.The inherent compact structure of lignocellulose is destroyed,and the enzymatic conversion rate can be increased from 54.18%to 82.39%and 80.49%,respectively.The greater the degree of hemicellulose removal,the higher the corresponding enzymatic conversion rate,and the content of lignin and the index of crystallinity in the raw material of cassava residue have no obvious linear relationship with the enzymatic conversion rate.In addition,experiments show that cassava residue and remove starch from cassava residue(RSFCR)have the same suitable pretreatment process.The highest recoveries of glucose,xylose and total sugar after pretreatment and enzymatic hydrolysis of cassava residue were 94.01%,77.91%and 91.42%,respectively.The highest concentrations of formic acid,acetic acid,furfural and 5-HMF in the pretreatment hydrolysate were 1.10 g·L-1,1.01 g·L-1,,0.41 g·L-1 and 0.22 g·L-1,respectively.