Continuous extraction of phenol and cresols from advanced pyrolysis oils

Authors: Elkasabi, Yaseen; Mullen, Charles; Boateng, Akwasi

Submitted to: Springer Nature Applied Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2020
Publication Date: 3/2/2020
Citation: Elkasabi, Y.M., Mullen, C.A., Boateng, A.A. 2020. Continuous extraction of phenol and cresols from advanced pyrolysis oils. Springer Nature Applied Sciences. https://doi.org/10.1007/s42452-020-2134-4.
DOI: https://doi.org/10.1007/s42452-020-2134-4

Interpretive Summary: Pyrolysis is the process of heating materials in the absence of oxygen. We utilize the pyrolysis process to convert agricultural crops and wastes into a crude fuel intermediate (termed “bio-oil”) that is chemically similar to petroleum. One main difference is the higher oxygen content of bio-oil relative to petroleum. Some specialized pyrolysis processes produce bio-oil that is greatly reduced in oxygen content, though still considered an intermediate product. In the past, we have shown how these oils could be separated into oxygen-free and oxygenated fractions, the latter of which contains marketable compounds (phenolics) for various chemical applications. In this work, we demonstrated that the separation of phenolics could happen continuously, in a manner similar to that found industrially. The process parameters used to separate the phenolics allowed the separation to occur smoothly, such that no changes in the phenolic characteristics were observed over time. This work could help enhance adaptation of pyrolysis fuels by refineries.

Technical Abstract: Production of renewable value-added chemicals will ultimately enable commercialization of renewable biofuels. While bio-oils contain phenolic compounds, their separation has generally been difficult due to very wide product distributions. However, advances in pyrolysis have produced oils with low levels of oxygen and narrow product distributions that have made some 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 10M 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. A major issue is associated with the transfer of acidic components to the phenol extracts; 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 – 40 wt%.