Solvent-mediated extraction of phenolics from mid-level oxygen content pyrolysis oils

Authors: Elkasabi, Yaseen; Mullen, Charles; Strahan, Gary

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2024
Publication Date: 4/25/2024
Citation: Elkasabi, Y.M., Mullen, C.A., Strahan, G.D. 2024. Solvent-mediated extraction of phenolics from mid-level oxygen content pyrolysis oils. BioEnergy Research. https://doi.org/10.1007/s12155-024-10756-1.
DOI: https://doi.org/10.1007/s12155-024-10756-1

Interpretive Summary: Pyrolysis is a high-temperature process for converting crop waste into oils ('bio-oils'). These bio-oils are made of many different chemicals and have the potential to become high value. In order for that to happen, we need ways to separate bio-oils into different types of chemicals. Depending on the process conditions used, the oxygen content of bio-oils will vary. We have recently produced oils with about 15-20% oxygen, a moderate level, but also a unique composition compared with those produced at other pyrolysis conditions. Therefore these oils will require new methods of separation, which we have tested in this work. We found that these moderate level oxygen bio-oils can separate even without heating or boiling the oils, which is what was typically required previously. We also found that, once the bio-oil is separated into categories of chemicals, these groups can more easily react to form higher value chemicals. These findings can help make better use of agricultural wastes, which can provide more sources of revenue for bio-oil refiners.

Technical Abstract: Technologies for producing renewable fuels and chemicals rely on the production of stable intermediates. For thermochemical technologies, pyrolysis of biomass produces oils that must compromise between carbon yield and oil quality. Bio-oil extraction has largely focused on regular bio-oils (~33 wt% O) and partially deoxygenated oils (< 12 wt% O). Mid-level oxygen (MLO) bio-oils produced from switchgrass were characterized for their ability to separate into phenolic-rich fractions. Toluene-soluble portions of the oils underwent NaOH extraction to extract one-ring phenolics, while toluene-insoluble portions were fractionated with isopropyl alcohol (IPA). While phenolic extraction proceeded without distillation (having been a prerequisite for partially deoxygenated bio-oils), the efficiency of extraction was less than optimal, owing to the presence of other oxygenated compounds in the hydrocarbon-rich fraction. Both IPA insoluble and soluble fractions underwent solvent liquefaction reactions with base additives. While water as a reaction medium produced greater concentrations of phenols than methanol, addition of sodium carbonate produced narrower product distributions of phenols and inhibited formation of benzenediols.