Behavior of sulfur in biomass under hydrothermal conditions

Coworkers: Cheng Chang, Dr. David Baudouin

Hydrothermal conversion of wet biomass to liquid biofuels or biomethane is a promising route to reduce the impact of our society on the environment. The sulfur present in biomass is however an obstacle to the development of these technologies as it poisons the catalysts used downstream. This is the case in the catalytic Hydrothermal Gasification (cHTG) and for most catalytic upgrading processes downstream of a non-catalytic gasification process, such as Water gas shift, Fischer-Tropsch, methanol synthesis or CO/CO₂ methanation. In the case of Hydrothermal Liquefaction (HTL) of biomass for the production of biocrude, sulfur remains a problem for downstream upgrading/hydrotreating catalysts, as the presence of many heteroatoms represents a challenge for standard upgrading processes developed for the petrochemistry.

In this project, we aim to explore two new approaches to removing sulfur from such hydrothermal process streams: catalytic and selective Oxidative Desulfurization (ODS) and Thermochemical Sulfate Reduction (TSR). This study aims to devise reaction pathways and measure reaction kinetics, as well as identify materials that would catalyse the reactions, and optimize catalysts and processes. This work is done in collaboration with Prof. Matsumura at Hiroshima University, which will be using its micro-reactor coupled to in situ mass spectrometer.

The work done on TSR aims at better understanding the conversion of sulfate on the sulfur scavenger and/or gasification catalyst to limit or stop the deactivation of the latter by poisoning.  For the sulfur oxidation ot sulfate (ODS), the aim is to identify windows of operation at which a larger amount of sulfur is removed for the mainstream, by precipitation of sulfate in the sulfur trap, to decrease the demand on the sulfur scavenger, and hence decrease the amount required.

In addition to the impact on the biomass and catalysis community, these results shall benefit the geochemistry community interested in the chemistry of sulfate reduction or metal sulfide formation, as well as the pulping industry interested in increasing the efficiency of sulfur recycling from spent liquors.