(548v) Kinetic Parameter Estimation for Electrocatalytic Hydrogenation of Model Compounds Derived from Fast Pyrolysis of Biomass

Authors: 
Das, S., MSU
Saffron, C. M., Michigan State University
According to the DOE’s Billion-ton report published in 2016, there is not enough biomass (that can be produced at less than $60/ton) in the U.S. to meet the annual energy demands for the U.S. transportation sector. Biofuel made using one billion tons of biomass, available by 2040, would not result in the complete displacement of petroleum-derived transportation fuels consumed in 2017. In this context, carbon and energy efficiency are paramount for maximizing the scale of displacement. Cellulosic fermentations to produce ethanol are inherently carbon and energy inefficient, as biomass’s lignin is not converted into liquid fuels and one-third of the carbohydrate carbon is lost as carbon dioxide during fermentation.

An alternative biofuel production strategy is proposed that combines fast pyrolysis with localized electrocatalytic hydrogenation (ECH) and centralized petroleum refining to produce a gasoline-like fuel. In this regard, a comparative study of the energy, mass, and carbon flux through these two processes was performed. Pyrolysis-electrocatalysis processes potentially overcome the carbon and energy inefficiencies that limit cellulosic ethanol. ECH of bio-oil, the liquid product of fast pyrolysis, at a localized depot is a key component of the proposed biofuel production scheme. ECH utilizes renewable electricity from wind turbines or solar photovoltaics to split water and make in situ hydrogen and subsequently catalyze the reduction of reactive aromatic compounds. As bio-oil is a complex mixture of hundreds of organic compounds, ECH has been primarily studied by analyzing individual representative compounds present in bio-oil, such as phenol, syringol, and guaiacol. An unwanted side reaction associated with ECH is the hydrogen evolution reaction, which adversely impacts the Faradaic efficiency. Faradaic and voltage efficiency impacts the number of membrane-electrode stacks required to fully saturate bio-oil, therefore a mechanism for determining the overall reaction rate is needed. In this regard, a kinetic model has been developed to estimate the kinetic rate constants for the electrochemical and catalytic surface reactions for the ECH of phenol as a model bio-oil compound. Experiments were performed in a two compartment cell with the cathodic and anodic chambers separated by a proton exchange membrane. Ru/ACC was employed as the catalytic cathode while a Pt wire was used as the anode. Bulk species concentration data were collected at regular intervals of time to estimate the reaction rate constants by means of non-linear sequential parameter estimation in Matlab. The developed model includes equations to characterize the diffusion of bulk species to the catalyst surface as well as equations to describe the adsorption, desorption, and surface reactions occurring on the cathode. The next step is to perform the same analysis for other representative bio-oil compounds to better characterize the electrocatalytic hydrogenation of biomass-derived bio-oil. This leads to a better understanding of the process and serves as a crucial step towards scale-up of ECH as a keystone of novel pyrolysis-based bioenergy systems.