Continuous extraction of phenol and cresols from advanced pyrolysis oils

Abstract

Production of value-added chemicals will ultimately enable commercialization of biofuels. While bio-oils contain phenolic compounds, their separation has generally been difficult due to very wide product distributions. Advances in pyrolysis have produced oils with low oxygen and narrow product distributions that have made separation processes possible. We have demonstrated the continuous extraction of phenolic compounds from fast pyrolysis oils from switchgrass, produced using catalytic and/or tail-gas reactive pyrolysis, which enables distillation due to the absence of unstable oxygenated compounds. Having successfully distilled the bio-oil, the distillate was first subjected to batch extraction with 10 M KOH in varying ratios, and the yields of phenol and cresols were measured. Extraction yields of 15–20 wt% produced extracts where the proportion of measured phenolics consisted of > 50% phenol (i.e. “phenol selectivity”), an increase from 36% in the starting distillates. Washing the distillates with sodium bicarbonate before phenolic extraction helped to reduce excessive acid contamination. Countercurrent continuous extraction experiments using a Vigreux column attained steady-state after only a few minutes, although the phenol selectivity continued to increase for the duration of most experiments. Extraction yields ranged from 15 to 40 wt%.