Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2019
Publication Date: 1/1/2020
Citation: Elkasabi, Y.M., Wyatt, V.T., Jones, K.C., Strahan, G.D., Mullen, C.A., Boateng, A.A. 2020. Hydrocarbons extracted from advanced pyrolysis bio-oils: characterization and refining. Energy and Fuels. 34(1):483-490. https://doi.org/10.1021/acs.energyfuels.9b03189.
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. Specialized pyrolysis processes (either catalytic pyrolysis or tail-gas reactive pyrolysis) produce bio-oil that is greatly reduced in oxygen content, though still considered an intermediate product. We have shown how simple and inexpensive extraction processes can separate the bio-oils into two fractions: an oxygen-free fraction that is close to fuel compounds (hydrocarbons), and a fraction made of commercially-valued compounds called phenolics. In this work, we showed how the hydrocarbon fraction can be further upgraded into fuel-grade compounds, using simple, inexpensive nickel catalysts. Amongst the most important results is that 1) toxic compounds like benzene can be removed down to below regulatory limits, and 2) the sulfur found in the hydrocarbon fraction can be eliminated down to below regulatory levels. These results could enable the adaptation of renewable fuels into standard refineries, since similar processes were used to achieve the results.
Technical Abstract: Advanced pyrolysis processes, such as catalytic fast pyrolysis (CFP) and tail-gas reactive pyrolysis (TGRP) allow for separation into phenolic and hydrocarbon fractions. The hydrocarbon fraction, while free from oxygen (<2 wt%), still requires further upgrading to become a finished blendstock. In particular, the hydrogen deficiency, molecular weight distribution, and benzene content require further treatment, and biomass feedstocks like guayule carry over significant amounts of sulfur (~500 ppm), even after catalytic hydrodeoxygenation (HDO). Utilizing both upstream separation steps and catalytic hydrogenation, we successfully upgraded each fraction according to its needed product changes, including desulfurization. After fractional distillation of the hydrocarbon fraction, sulfur levels ranged from 80 – 700 ppm, with respect to decreasing volatility. All fractions contained primarily one-ring aromatics, eventually increasing to two-ring aromatics. The lightest fraction contained 6 wt% benzene, and fraction 2 (143 – 163 degree C) required minimal treatment, as it consisted of nearly 100% BTEX. Sponge nickel catalyst eliminated sulfur in all fractions down to below 10 ppm, with the exception of the hydrocarbon distillation residue which went from 760 to 120 ppm, indicating the sulfur remained labile even after biomass pyrolysis. Hydrogenation primarily produced naphtha and/or tetralin, which can be used to improve combustibility of jet fuels.