Influence of heating temperatures on the component distribution of distillates derived from walnut shell bio-oil

Influence of heating temperatures on the component distribution of distillates distilled from walnut shell bio-oils was studied. Meanwhile, distillates were further separated into water-soluble and water-insoluble fraction to characterize product distribution. The results showed that distillate fraction yield increased with strengthening heating temperature from 120 to 300 ℃. Aromatic hydrocarbons (e.g. naphthalene) and carboxylic acids (e.g. acetic acid) significantly concentrated in water-insoluble fraction as heating temperatures were below 240 ℃. Notably, the relative concentration of aromatic and carboxylic compounds in the water-insoluble fraction derived from 300 ℃ was 13.86 and 3.15 times higher than that of crude bio-oil, respectively. Large amounts of phenols such as phenol and guaiacol was distilled as heating temperatures exceeded 240 ℃, which induced enhanced yield of water-insoluble fraction. Moreover, the moisture of all the water-soluble fractions was higher than 60%, which demonstrated the water-soluble fraction remarkably concentrated moisture. In addition, undetected components (e.g. butyl 2-ethylacetate and cyclopentanone) in crude bio-oil surprisingly existed in distillates and the total moisture of distillates was higher than that of crude bio-oils, which proved esterification and polycondensation reactions occurred in bio-oil distillation process. Furthermore, the component distribution of distillates also indicated modifying heating temperatures effectively enriched commodity chemicals. Note that water-insoluble fraction distilled from 300 ℃ exhibited relative concentration of phenol, guaiacol, 4-methyl-2-methoxyphenol, 4-ethyl-2-methoxyphenol and 4-propyl-2-methoxyphenol was 109%, 160%, 84%, 53% and 444% higher than that in crude bio-oil, respectively.