Abstract:

In order to investigate the separation characteristics of typical oxygenate components of biomass pyrolysis oil in both macro- and micro-level, a series of molecular distillation experiments were conducted under different evaporation temperature and operation pressure using cotton stalk pyrolysis oil as raw material. It showed that the distilled fractions had higher H/C molar ratios and contained higher oxygen content than the residual fractions, while the residual fractions contained higher carbon contents with higher heating value and their H/C molar ratios was close to 1. The separation factor(α_{i, n}) was defined based on previous study and was used to evaluate the separation characteristics of typical compounds in micro-level. It showed that compounds with light molecular weights such as acetic acid, 1, 1-dimethoxy-propane, tetrahydro-2, 5-dimethoxy-furan were very easy to be distilled under all experiment conditions, while the distillation of 3-methyl-1, 2-cyclopentanedione was highly affected by the temperature and pressure in the experiment.It also indicated that monophenol compounds such as guaiacol, syringol and phenol could be distilled more easily than other compounds with large molecular weight, among which guaiacol was the easiest one to be distilled under 1 500 Pa and the phenol was less affected by temperature changes. It was much harder to distill diphenol than monophenol, among them, benzenediol showed comparatively poor distillation characteristics under the conditions of 2 500 Pa/50 ℃ especially. However, further lower the operation pressure could facilitate the evaporation of benzenediol largely. The changes of evaporation temperature and operation pressure had less effect on distillation of long-chain esters and carbohydrates than other compounds with large molecular weight.

Key words: biomass, biomass pyrolysis oil, molecular distillation, separation characteristics, separation factor