High-temperature high-pressure electrochemical hydrogenation of biocrude oil

Abstract

Hydrothermal liquefaction (HTL) occurs at high pressures (160–200 bar) and temperatures (300–350 °C), where the conditions in the reactor drive the conversion of wet biomass to biocrude oil (BC). Before drop-in, BC needs further upgrading (hydrogenation) to increase the energy content and decrease the concentration of heteroatoms. Normally this is done in hydrogenation reactors at high pressures and temperatures, which require an external high pressure H2 source. The main HTL by-product is process water (PW), which is either recirculated or cleaned before being disposed. Herein we investigated a membrane-less electrochemical method, which uses PW as hydrogen source and can be seamlessly integrated in HTL plants. We demonstrate a proof-of concept of a membrane-less electrochemical reactor that oxidizes PW at the anode and uses hydrogen in form of protons and electrons to hydrogenate BC at the cathode. We report BC upgrading (atomic H/C ratio increase up to 17 %) at high-pressure (up to 100 bar) and high-temperature (up to 200 °C), which mimic the conditions of an actual HTL plant. The proof-of-concept discussed here is a novel way of increasing the hydrogen content of biocrude oil within HTL reactor by using electricity, with no need of an external high-pressure H2 source.