Study On Effects Of Acidity,Alkalinity And Pretreatment On The Production Of Hydrothermal Bio Oil From Agricultural Waste Cotton Stalk

Hydrothermal liquefaction technology is an effective way to realize the high-value utilization of biomass resources.Its reaction conditions are mild and energy consumption is low,which can promote the energy utilization of agricultural solid waste.In this paper,the agricultural waste cotton stalk was treated by hydrothermal liquefaction with more mild reaction conditions to prepare bio oil.The catalytic effect of homogeneous and heterogeneous acid-base on hydrothermal liquefaction and the effect of pretreatment on the tissue structure of raw materials were systematically investigated to explore its influence on the formation of hydrothermal bio oil from agricultural waste cotton stalk.The main research contents include:Firstly,the effects of different homogeneous acids and bases（H₂SO₄,HCl,HNO₃,Na OH,KOH,Na₂CO₃and K₂CO₃）on the hydrothermal preparation of bio oil from cotton stalk were investigated.The results showed that the promotion effect of homogeneous alkali on the formation of bio oil was better than that of homogeneous acid.Under the condition of homogeneous acid-base and cotton stalk co hydrothermal,there are abundant functional groups in the obtained bio oil,the calorific value increases from 23.32 MJ·kg^-1to 27.22 MJ·kg^-1,and the O content decreases from 31.86%to23.71%,which promotes the deoxidation effect of hydrothermal process and improves the content of aromatic components such as phenols.In particular,the addition of alkali can improve the light component content of bio oil,remove some nitrogen and sulfur heteroatoms,and effectively adjust the composition of bio oil.Secondly,on the basis of fully understanding the effects of homogeneous acid-base on the formation and components of cotton stalk hydrothermal bio oil,the hydrothermal preparation of cotton stalk bio oil was further studied with heterogeneous nano oxides（Al₂O₃,Zn O,Ce O₂,Ti O₂,Si O₂,Mg O）as catalysts.The results show that the energy recovery rate of bio oil is affected by the synergistic effect of acid and alkali sites on the oxide surface,and has a"U-shaped"relationship with base value/acid value.When the base value/acid value is high（about 1.1）or low（about 0.3）,the energy recovery rate of catalytic hydrothermal bio oil is high（11.27%）.Among the nano oxides in the experimental range,the addition of Ce O₂obtained the highest yield of bio oil,which was 7.96%.The addition of nano oxide effectively reduced the formation of macromolecular compounds with high boiling point in bio oil,increased the content of H from 5.73%to 6.44%,and increased the saturation of bio oil.Finally,in order to further study the effect of acid-base on the formation of hydrothermal bio oil from cotton stalk at the level of raw material tissue structure,some acid-base pretreatment methods were selected to investigate the effect of pretreated cotton stalk on the formation activity of hydrothermal bio oil.It was found that the main objects of alkaline pretreatment such as urea/alkali,alkali/ethanol and alkali and ball-milling were hemicellulose and lignin,and the lignocellulosic tissue structure of cotton stalk was looser after treatment.Under the conditions of reaction time of 1 h and2 h,the pretreatment improved the yield of bio oil.After pretreatment,the H/C ratio of hydrothermal bio oil increased from 1.12 to 1.18,the saturation of bio oil increased,the content of S decreased from 0.26%to 0.02%,the content of aromatic components decreased,and the content of aliphatic components such as ketones increased.Pretreatment not only changed the tissue structure of cotton stalk,but also improved its reaction activity in hydrothermal process to a certain extent.