Fractionation Behaviors of Walnut Shell Bio-Oil Components Under Atmospheric Distillation

In this study, distillates of aqueous phase bio-oil (APB) and oil phase bio-oil (OPB) collected under different heating procedures were analyzed. The results showed that a variety of phenols in OPB with boiling points around 200 degrees C formed azeotrope, raising their boiling points to around 280 degrees C. Phenols fractionated in large quantities during the distillation of OPB were the main component of oil phase fraction, among which the overwhelming majority were phenol as well as its congeners and guaiacol as well as its congeners. Changing the heating procedure had a significant effect on the separation of these two compounds. It was notable that the content of phenol and its congeners was increased by 468% in the fraction heated at 320 degrees C and held for 15 min compared to crude OPB. The long heating time and the heating temperature above 140 degrees C were found to be necessary for coking of APB, which demonstrated that coking of APB during distillation could be avoided by changing the heating procedure. Summary of distillation behaviors for various high-value compounds provides guidance for process design and scale-up utilization of bio-oil.