Bio-oil produced by fast pyrolysis of biomass is a potential source of low carbon, renewable hydrocarbon fuel. However, the properties such as low heating value, incomplete volatility, acidity, instability, and incompatibility with standard petroleum fuels significantly restrict its use as fuel. The undesirable properties of pyrolysis oil result from its chemical composition that mostly consists of different classes of oxygenated organic compounds. The elimination of oxygen is thus necessary to transform bio-oil into a liquid fuel that would be broadly accepted and economically attractive. Hydrodeoxygenation (HDO) or hydrotreating involves high-temperature, high-pressure
processing in the presence of hydrogen and catalyst to remove oxygen. HDO suffers from significant challenges such as coking, deactivation of HDO catalysts by the presence of water in the pyrolysis oil, requirement of significant quantities of hydrogen to remove oxygen, and economic availability of hydrogen at a scale suitable for distributed biomass conversion. An alternative economically feasible, less hydrogen dependent and decentralized process is required to convert bio-oil to refinery ready hydrocarbons.

A process of deoxygenation of bio-oil using solid-state, oxygen conductor based electrochemical cell is under investigation. The cell is operated at 500 – 550 °C to match the typical pyrolysis temperature for both physical and process integration of the two operations. The electrolysis process removes oxygen from the oxygenated organic molecule as well from steam to produce hydrogen in-situ. Thus, relatively small quantities of external hydrogen may be needed for deoxygenation, allowing for a distributed, small scale integrated upgrading unit. Mixtures of model compounds were tested using button cells and short stacks. The product from the electrochemical cell contained a suite of compounds with significantly lower oxygen content. Integrated testing of short stacks at the Pacific Northwest National Laboratory using a slip stream from a pyrolyzer shows that the product composition is similar to catalytic pyrolysis process. Additional tests are planned using improved electrode materials.

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