(Invited) Electrochemical Upgrading of Bio-Oil

Biomass is a potential renewable source for liquid fuels and most commodity chemicals. Non-edible lignocellulosic biomass residue such as agricultural and forest wastes can be converted to liquid fuels via bio-oil production by fast pyrolysis. A variety of challenges related to unwanted characteristics of bio-oil need to be overcome for practical use of this approach. One such challenge is the high oxygen content (35 – 40 wt%) of bio-oil. The conventional approach to remove oxygen is the hydro-deoxygenation process that uses high pressure hydrogen. Typical bio-oil is biphasic and only the organic phase is processed in subsequent upgrading steps, leaving behind valuable carbon-containing material in the aqueous phase. Ceramatec and its partners, Pacific Northwest National Laboratory (PNNL), Technology Holding LLC, and Drexel University, are investigating an electrochemical process to remove oxygen from bio-oil components without the use of hydrogen. Model compounds have been tested using an oxygen ion conducting ceramic membrane based electrochemical cells operated in the temperature range of 500 – 600 °C. Under an applied electric potential, only oxygen ions are transported through the membrane. In addition to direct removal of oxygen from the oxygenated hydrocarbons, indirect removal of oxygen via reaction with hydrogen that is generated by the electrolysis of steam present in the feed is also expected to aid in the electrodeoxygenation (EDox) process.

Feasibility tests were performed using water soluble model compounds, guaiacol that has two oxygen containing functional groups, a phenolic (−OH) and methoxy (−OCH₃) groups and syringol that has a phenolic and two methoxy groups. These compounds are produced by pyrolysis of lignin. The selected model compound is co-fed with steam without using external hydrogen in the feed. A button cell configuration was used as the test vehicle with a nickel-cermet cathode and a ferrite-cobaltite perovskite anode. The results show that the EDox process produces a variety of compounds that have lower or no oxygenated functional groups. The liquid products were analyzed using GC-MS. Analysis shows that, on weight basis, a reduction of 25% and 47% of oxygen content occurred for guaiacol and syringol feed. Gas phase hydrocarbon products such as methane, ethane, propane, and propene were also identified but not included in estimating oxygen removal.

A deoxygenation trial of aqueous phase from the pyrolysis of yellow pine oil received from PNNL was also performed. Based on the analysis of liquid products collected, over 24% of oxygen removal was accomplished.

Test system modifications are planned to allow complete mass balance of the process. Electrode materials and test conditions will be modified to evaluate the effect on oxygen removal and product selectivity.

Acknowledgment:  This material is based upon work supported by the Department of Energy under Award Number DE-EE0006288.

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