The Co-production Of Aldehydes And Alcohols From Bagasse Based On PPAWS Pretreatment System

Biomass is a renewable resource,the use of which to produce furfural platform compounds is important for exploring biomass energy,alleviating current energy crisis and combating global climate change.The current use of biomass to prepare furfural is mainly through the hemicellulose degradation pathway,but it results in the low-efficiency utilization of cellulose and lignin fractions.In this study,a PPAWS（i.e.pressurised-phosphoric acid-acetone-water）system was used to pretreat sugarcane bagasse,obtaining high-yield furfural in a short time and cellulose-rich hydrolysis residue.The residue was then subjected to enzymatic saccharification and anaerobic fermentation to produce butanol,enabling the multi-component utilization of lignocellulose and the combined production of aldehyde-alcohol multi-products.Firstly,PPAWS pretreatment of sugarcane bagasse was carried out to investigate the effects of external factors（temperature,time,pressure）,internal factors（solid-liquid ratio,acid dosage,acetone ratio）and co-catalysts（ZnCl₂,AlCl₃）on furfural yield,lignin removal and cellulose retention.The results showed that the reaction temperature（>160℃）,reaction time（<10 min）and system pressure（≥1.5 MPa）were favourable for furfural yield and lignin removal.Among the internal factors,the solid-to-liquid ratio and acid dosage had a more significant effect on the furfural output.In the presence of applied external pressure,acetone was used as a solvent to facilitate furfural production,while achieving efficient lignin dissolution and effective retention of cellulose fraction.The addition of AlCl₃ was more effective in the yield of furfural than ZnCl₂.Under the optimum reaction conditions,the furfural yield was up to 72.7%,the cellulose content in the hydrolysis residue was 92.6%,the cellulose retention was 82.5%and the lignin removal was 93.4%.In addition,the experiments were conducted to elucidate the mechanism of the influence of pressure environment on the reaction system by online monitoring of the PPAWS pretreatment process using xylan as the substrate.It was found that the external pressure applied to the reactor was beneficial to increase the furfural yield,probably due to the fact that additional pressure increased the spatial site resistance of the acid-catalyzed conversion of acetone to the enol form,hindering the hydroxylaldehyde condensation reaction and thus inhibiting the reaction of furfural with acetone.In addition,a prediction model for different hydrolysis working conditions was developed by machine learning methods for the pretreatment liquid phase products.Compared with random forest（R²=0.7946）,the BP neural network（R²=0.9932）has better prediction accuracy for the hydrolysis process.Secondly,the enzymatic saccharification of the hydrolysis residue was carried out,and the enzymatic effect of both wet and dry residues was investigated in comparison.The results showed that the wet material had better enzymatic performance at a solid-liquid ratio of 1:20 and an enzyme loading of 20 FPU/g dry matter,with nearly 100%enzymatic digestion at a glucose concentration of 50.2 g/l for 72 h.The effect of acetone on the enzymatic saccharification process was also investigated,with the enzymatic saccharification system being promoted when the acetone content was≤0.1%and inhibited when it was>0.5%.The effect of acetone on the enzymatic saccharification process was also investigated.Finally,the hydrolysate was treated with anaerobic fermentation after enzymatic digestion and the experiments were conducted to evaluate the fermentation performance of the hydrolysate using the standard medium as a reference.It was found that the fermentation performance of the hydrolysate was comparable to that of the standard medium,with the butanol yield of 8.46 g/l,total solvent yield of 14.37 g/l,solvent conversion rate of 0.29 g/g,and total solubility yield of 0.20 g/l/h after 72 h of fermentation.This study will provide reference to the multi-component utilization of lignocellulosic biomass and the co-production of diversified products and promote the large-scale and efficient clean utilization of biomass resources in China.