Research On Characteristics Of Bio-oil Separation And Its Fractions Based On Molecular Distillation

Bio-oils made from lignocellulosic biomass through fast pyrolysis usually contain high moisture and oxygen contents,together with high thermal instability,which means they cannot be used until modified and upgraded by certain means.Bio-oils are rich in chemical compounds,and it is difficult to reach a high overall conversion efficiency with a single modification method.Therefore,pre-separation is required to optimize the upgrading route for fractions with different characteristics and improve the overall utilization efficiency of bio-oil.Molecular distillation is suitable for separating and extracting the mixture components with high thermal sensitivity,because it proceeds under low operating temperature with short proceeding time.In this paper,the research on the characteristics of separation and its products based on bio-oil molecular distillation under a series of temperature and pressure conditions is carried out.A series of molecular distillation experiments under different evaporation temperature and pressure was proceeded,the macro and micro characteristics of bio-oil separation products under different experiment conditions were explored.The study found that the distillate fraction contains a higher H/C molar ratio and oxygen content,which increases with decreasing temperature and vacuum,and the residual fraction contains a higher heating value and carbon content,and the H/C molar ratio is close to 1;Typical oxygenate compounds with light molecular weights such as acid,aldehyde,furan are all enriched in the distillate fraction and the residual fraction is rich in phenolic compounds.Based on the GC-MS distribution of the compounds in each separation fraction,a separation factor to evaluating the distillation capacity of 18 typical oxygenates in bio-oil semiquantitatively was defined.The results show that,except for cyclopentanedione,typical oxygenate compounds with light molecular weights such as acid,aldehyde,furan maintain extremely strong distillation capacity under all experimental conditions;the distillation capacity of benzenediol,a typical monophenolic compound,is significantly lower than phenol compounds among phenolic compounds as its separation factor is as low as 0.224 at 2500Pa/50 ?,but its distillation capacity can be significantly improved by reducing the operating pressure;the distillation capacity of laevoglucose among sugar compounds is significantly higher than the other two sugars,due to the distillation of sugars not as sensitive to pressure change as phenolic compounds,reducing the pressure has less effect on improving their distillation capacity than benzenediol.Exploring the characteristics of the separation products under different conditions and the distillation performance of typical compounds serves as important references for optimizing the separation route of bio-oil and regulating the separation conditions.Based on the above-mentioned molecular distillation of the residual distillate oil,through further characterization it was found that the main components were phenols and esters,rich in guaiacol and its derivatives especially,containing a large number of oxygen-containing functional groups and structures such as aromatic rings,C=O,C-O.Then,the residual distillate oil was used as the raw material to prepare the carbon electrode at 5 different carbonization temperatures.Galvanostatic(GCD)charge-discharge test showed that the specific capacitance of the residueoil carbon electrode at the carbonization temperature of 800 ? was the highest.Compared to the curve of the bean pulp carbon electrode at a carbonization temperature of 800 ?,the residue-oil carbon electrode has better electric double layer capacitor's characteristics;after 10000 cycles of charge-discharge tests it was found that the residue-oil carbon electrode has better circulation stability with the specific capacitance retention rate at stable state around 170%,which indicates that the residual distillate oil obtained by bio-oil molecular distillation has certain application potential as a raw material of carbon electrode for supercapacitors.