**Cleanup and Conversion of Biomass Liquefaction Aqueous Phase to C 3–C 5 Olefins over Zn** *x***Zr** *y* **O** *z* **Catalyst**

**Stephen D. Davidson 1, Juan A. Lopez-Ruiz 1, Matthew Flake 1, Alan R. Cooper 1, Yaseen Elkasabi 2, Marco Tomasi Morgano 3, Vanessa Lebarbier Dagle 1, Karl O. Albrecht 4 and Robert A. Dagle 1,\***


Received: 14 October 2019; Accepted: 1 November 2019; Published: 6 November 2019

**Abstract:** The viability of using a Zn*x*Zr*y*O*z* mixed oxide catalyst for the direct production of C4 olefins from the aqueous phase derived from three di fferent bio-oils was explored. The aqueous phases derived from (i) hydrothermal liquefaction of corn stover, (ii) fluidized bed fast pyrolysis of horse litter, and (iii) screw pyrolysis of wood pellets were evaluated as feedstocks. While exact compositions vary, the primary constituents for each feedstock are acetic acid and propionic acid. Continuous processing, based on liquid–liquid extraction, for the cleanup of the inorganic contaminants contained in the aqueous phase was also demonstrated. Complete conversion of the carboxylic acids was achieved over Zn*x*Zr*y*O*z* catalyst for all the feedstocks investigated. The main reaction products from each of the feedstocks include isobutene (>30% selectivity) and CO2 (>23% selectivity). Activity loss from coking was also observed, thereby rendering deactivation of the Zn*x*Zr*y*O*z* catalyst, however, complete recovery of catalyst activity was observed following regeneration. Finally, the presence of H2 in the feed was found to facilitate hydrogenation of intermediate acetone, thereby increasing propene production and, consequently, decreasing isobutene production.

**Keywords:** biomass-derived aqueous phase upgrading; olefin production; oxide catalyst zinc–zirconia
