Aqueous extractive upgrading of bio-oils created by tail-gas reactive pyrolysis to produce pure hydrocarbons and phenols

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

Submitted to: ACS Sustainable Chemistry & Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2015
Publication Date: 11/2/2015
Publication URL: https://handle.nal.usda.gov/10113/61639
Citation: Elkasabi, Y.M., Mullen, C.A., Boateng, A.A. 2015. Aqueous extractive upgrading of pyrolysis bio-oils to produce pure hydrocarbons and phenols in high yields. ACS Sustainable Chemistry & Engineering. 3(11):2809-2816.

Interpretive Summary: Pyrolysis refers to 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. Our specialized pyrolysis process (tail-gas reactive pyrolysis, or TGRP) produces bio-oil that is greatly reduced in oxygen content, though still considered an intermediate product. This research shows how simple and inexpensive extraction processes can be performed on TGRP bio-oil to separate oxygen-free compounds, as well as other compounds deemed profitable (e.g. phenols). A simple base metal catalyst such as nickel can be used to upgrade the extracts into fuel-grade compounds. Compared to the TGRP process, traditional methods for bio-oil are more costly because they require chemically removing the oxygen and the traditional process produces carbon dioxide and carbon monoxide, both of which contribute to environmental hazards globally.

Technical Abstract: Tail-gas reactive pyrolysis (TGRP) of biomass produces bio-oil that is lower in oxygen (~15 wt% total) and significantly more hydrocarbon-rich than traditional bio-oils or even catalytic fast pyrolysis. TGRP bio-oils lend themselves toward mild and inexpensive upgrading procedures. We isolated oxygen-free hydrocarbons by extraction of TGRP bio-oil distillates. Extraction proceeded by adding aqueous sodium hydroxide to distillates, resulting in a hydrocarbon layer and a phenolic salts layer. The hydrocarbons consist primarily of mono- and bicyclic aromatics, are essentially free of oxygen (< 1.0 wt %), and possess low moisture (< 1.0 wt %) and low acidity (TAN < 5.0 mg KOH/g). The phenolic salts can be re-acidified to produce phenols with low moisture (~2.5 wt %) and with narrow product distribution. The aqueous phase byproduct contains organic acids and precipitated sodium chloride. The hydrocarbon layer can be upgraded via mild hydrogenation with sponge nickel base metal catalyst in water, producing naphtha compounds appropriate for direct use as drop-in fuel and/or refinery blendstock. Furthermore, using only hydrogenation eliminates CO and CO2 production that normally accompanies hydrodeoxygenation.