Progress Towards Electrochemical Methods for Pyrolysis-Oil Hydrogenation

Abstract

Liquid fuels generation via flash pyrolysis of biomass followed by thermochemical upgrading has been a research topic for many years. The pyrolysis-oil produced from this process is a complex mixture of hundreds of organic and inorganic compounds. The reactive species in pyrolysis-oil complicate storage, transportation, and downstream processing because of secondary reactions. Currently these oils require a complex three-stage process operating at moderate temperatures between 433 and 678 K, and high hydrogen pressures of up to14,000 kPa. The process economics are limited by the high temperature and high pressure hydrogen requirement. Recent research suggests that the hydrogenation reactions can be performed using electrochemical reactors operating at much lower temperatures and pressures (293 K and 101 kPa) with no supplied dihydrogen. We have been exploring electrocatalytic upgrading of pyrolysis oil. Early tests show the feasibility of pyrolysis oil upgrading when tested in a flow cell configuration. 13C NMR and 1H NMR indicates a significant decrease in carbonyl and aromatic species post electrolysis (Figure 1) illustrating the viability of the approach. To better understand the influence of electrode catalysts on kinetics, probe molecules and probe molecule mixtures are being tested. The results indicate that Pd is the most active catalyst for electrochemical reduction of aldehydes and ketones, but was inactive for phenol reduction. However, Rh catalysts were active for phenol, but had lower activity for aldehyde and ketone reactions. Based on this research, a bi-metal catalyst is being developed and the experimental results will be presented. Reaction kinetics as well as the impact of site competition in mixtures will be discussed. Figure 1