Short-time Atmospheric Glycerol Organosolv Pretreatment And Thick-mash Ethanol Fermentation Of Sugarcane Bagasse

To realize the cellulosic bioethanol industrialization,it is necessary to approach the ‘THREE-HIGH'?High-titer,high-conversion and high-productivity?technical level of the starchy ethanol production.Hereinto,some strategies such as construction of effective pretreatment and adoption of fed-batch thick-mash fermentation have demonstrated robust advantages.Accordingly,this thesis has focused on these points as below.First,the water washing pattern of atmosphere glycerol organosolv pretreatment of sugarcane bagasse constructed previously in our lab was investigated.The optimal condition was as follows: 150 mL boiling water was added into the reactor when cooking temperature descended to ¹30 °C.Then the slurry was filtered with a G1 sand core funnel followed by wash twice?200 m L × 2?with tap water.In the substrate,residual glycerol accounted for 0.39%,which was too low to influence adversely the downstream enzymatic hydrolysis and fermentation.The water washing method presented a promise to reduce the glycerol and water use,together with the energy consumption.Second,a new atmospheric glycerol organosolv?AGO?pretreatment was explored to reduce the pretreatment time.The pretreatment temperature of 240 °C and time of 20 min was selected to build a short-time AGO pretreatment process,in which 70% lignin removed from the sugarcane bagasse while cellulose kept above 80%.However,the pretreated substrate presented a limited hydrolyzability.To further improve the substrate hydrolyzability,sodium hydroxide was used as catalyst to reconstruct the AGO pretreatment process.The pretreatment condition was selected in the reaction system of 10 g feedback / 140 g glycerol as below: 0.3 g NaOH?0.2%,w/w?,240 °C and 10 min.Under controlled condition,the removal rate of lignin was 75%,and the recovery of cellulose and hemicellulose was 88% and 80%,respectively.That is,the cellulose was 57% with 10% of the residual lignin in pretreated substrate.Interestingly,no significant furan fermentation inhibitor was found during the AGO pretreatment.The substrate?10–20%,w/v?reached 80–90% for 72 h enzymatic hydrolysis at 6 FPU·g^-1 substrate of the enzyme loading,indicating of the good hydrolyzability at thick-mash enzymatic hydrolysis.With modern analytic?SEM,AFM,CLSM,FT-IR and XRD?,the good substrate hydrolyzabilty was correlated with appealing structural features of alkaline-catalyzed AGO pretreated substrate.Finally,thick-mash ethanol production from the alkaline-catalyzed AGO pretreated substrate was explored with fed-batch semi-simultaneous saccharification fermentation.Under controlled condition(15%?w/v?of substrate concentration,6 FPU·g^-1 dry matter of enzyme loading,30 mg·g^-1 dry matter of Tween 80),the glucose yield reached 72 g·L^-1 for 48 h enzymatic hydrolysis.Further feeding the dried substrate equivalent with 5%?w/v?of substrate concentration each at 12 h,18 h,24 h and 30 h of enzymatic hydrolysis,to make the solid concentration equivalent with 35%?w/v?.The enzymatic hydrolysis reached 132 g·L^-1 of the glucose yield at 72 h with 60% of cellulose conversion.Based on all the above,the fed-batch semi-simultaneous saccharification fermentation of ethanol was carried out at optimized condition(pre-hydrolysis 48 h,yeast extract 16 g·L^-1,fermentation temperature 37 oC,inoculation size 10%?v/v?).And the ethanol yield achieved at 60.66 g·L^-1 for 48 h with 59% of cellulose-to-ethanol conversion.