Fundamental Study On Co-generation Of Bioethanol And Bio-oil From Lignocellulose

Sub-and supercritical liquefaction of lignocellulosic biomass into liquid bio-oil is particularly attractive but extremely challenging due to that the degradation products from sugar can react with lignin,resulting in low yield bio-oil and complexed functional groups in the bio-oil.In this context,three main components were converted separately to diminish the crosslinking reactions by integrated biological and thermochemical approach.Cellulosic bioethanol fermentation followed by hydrothermal liquefaction（HTL）of enzymatic residues for bio-oil production was investigated.A higher energy recovery of liquid products from lignocellulose as well as valorization of the cellulosic bioethanol waste residues was expected.Firstly,rice stalk（RS）was pretreated by the method of dilute sulfuric acid.The effects of various parameters,i.e.temperature,time,acid concentration and liquid-to-solid ratio,on chemical composition and physical structure of RS were explored.Around 66%hemicellulose and 25%lignin were removed with a cellulose content increased by 50%at an optimal conditions:temperature of 125°C,treatment time of30 min,concentration of 1.0%H₂SO₄ and a liquid-to-solid ratio of 20:1（m L:g）.XRD analysis showed that the crystallinity of cellulose was increased by 60%after pretreatment.The recalcitrant nature of lignocellulose was destroyed effectively after pretreatment,which contributed to the subsequent separate hydrolysis and fermentation（SHF）for bioethanol production.The results of enzymatic hydrolysis showed that the optimum enzymatic hydrolysis yield obtained was 72%at a liquid-to-solid ratio of 30:1（m L:g pretreated RS）,cellulase enzyme at a concentration of 50 FPU/g substrate,p H of 4.8 with hydrolysis time of 48 h and temperature of 50°C.The optimum conditions for bioethanol fermentation process occurred at 5.0 g/L of KH₂PO₄,2.0 g/L of（NH₄）₂SO₄,0.2 g/L of Mg SO₄·7H₂O and 6.0%of the precultured yeast solution with fermentation time of 24 h and temperature of 30°C,which achieved the maximum ethanol yield of 68%of the theoretical yield.HTL of enzymatic residues was conducted considering the effects of reaction temperature and residence time on the behavior of liquefaction process.The highest bio-oil yield of 31.6%was obtained at 320℃ and 40 min.Results showed that the most abundant component in the bio-oil was phenolic compounds followed by ketones.The higher heating values of the obtained bio-oil was 31.4 MJ/kg.In situ hydrogenation of enzymatic residues was proposed based on the aluminum and water reactions,which can provide in situ hydrogen.Catalytic hydro-liquefaction of enzymatic residues in situ with the assiated of Ni-Mo-S/γ-Al₂O₃ decreased the yield of phenolics and ketones in the bio-oil and increased the yield of hydrocarbons.In addition,the physicochemical properties of the bio-oil were improved.The energy recovery from co-generation of bioethanol and bio-oil was 55.9%,which was higher than single bioethanol production via SHF or bio-oil production via HTL.Simulation processes were carried out using Aspen Plus software for a biomass-based polygeneration system in which lignocellulosic bioethanol,xylose,bio-oil production were integrated in an existing combined heat and power（CHP）plant.Exergy analysis showed that the total exergy efficiency of the proposed polygeneration system was 67.4%,which was higher than that of the common bioethanol-CHP,bioethanol-xylose-CHP and bioethanol-biogas-CHP systems.