**4. Conclusions**

In this study we demonstrated a cleanup process, previously reported using batch processing, here adapted to continuous flow liquid–liquid extraction. Aqueous phases, rich in carboxylic acids, were obtained from several liquefaction processes, including HTL, FP, and SP, and evaluated for cleanup and catalytic upgrading. Future advances to the cleanup process are required in order to improve hydrocarbon retention. Cleaned feedstocks were converted to primarily C4 and C5 olefins, and CO2 over a Zn*x*Zr*y*O*z* mixed oxide catalyst. The reaction network appears consistent with previous reports using model ethanol and acetic acid feedstocks. Carboxylic acids are converted primarily to iso-olefins over Zn*x*Zr*y*O*z* catalyst. Specifically, iso-butene is produced from acetic acid, a primary constituent from the biomass-derived aqueous phase. Conversion of acetic acid and propionic acid over Zn*x*Zr*y*O*z* involve cross-coupling reactions and produce branched C5 olefins. Non-participating hydrocarbons in the feedstock (e.g., sugars, polyols) are not believed to participate in the reaction mechanism through ketone intermediates and contribute to catalyst deactivation. 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.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4344/9/11/923/s1, Table S1: LC analysis of USDA-FP feedstock after key steps of clean up protocol, Table S2: LC analysis of KIT-SP feedstock after key steps of clean up protocol, Table S3: ICP analysis of USDA-FP feedstock after key steps of clean up protocol, Table S4: ICP analysis of KIT-SP feedstock after key steps of clean up protocol, Figure S1: KIT-SP feedstock A) Initial B) During Carbon Treatment, After Third Carbon Treatment ~72 h C) After All Carbon Treatment, Five Carbon Treatments ~120 h, Table S5: Summary of dilute feedstock cleanup.

**Author Contributions:** S.D.D. lead most experiments, data analysis, and operations. J.A.L.-R. contributed to the development of the cleanup protocol. M.F. synthesized and prepared the Zn*x*Zr*y*O*z* catalyst. A.R.C., Y.E., and M.T.M. provided the major feedstocks studied in this work (PNNL-HTL, USDA-FP, and KIT-SP respectively). V.L.D., K.O.A., and R.A.D. lead conceptualization, project administration, and funding acquisition.

**Funding:** This work was financially supported by the U.S. Department of Energy's (DOE) Bioenergy Technologies Office under Contract DE-AC05-76RL01830 and in collaboration with the Chemical Catalysis for Bioenergy Consortium (ChemCatBio), a member of the Energy Materials Network (EMN), and was performed at Pacific Northwest National Laboratory (PNNL). PNNL is a multi-program national laboratory operated for the DOE by Battelle Memorial Institute.

**Acknowledgments:** The authors thank Teresa Lemmon for analytical support of this work and collaborators at NREL for providing dilute feedstocks. ARS acknowledges the help of Mark Schaffer and Neil Goldberg for operation of the pyrolysis system. The views and opinions of the authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.
