(685b) Catalytic Gasification of Biomass in Supercritical Water

The use of renewable sources of
energy such as biomass is an alternative that has the potential to reduce our
reliance on imported oil while addressing environmental concerns. Among the
technologies that convert biomass into fuels, Supercritical Water Gasification
(SCWG) has been suggested to process wet feedstocks because of the ability of
water to dissolve organic components of plant materials at supercritical
conditions, promoting formation of gases such as H₂ and CH₄,
and limiting the amount of tar and char formed as residues.

Metal catalysts can improve SCWG
efficiency in a variety of ways. Some catalysts promote the cleavage of C-C
bonds, which is crucial to achieve higher gasification yields. Others promote
reactions in the gas-phase changing product composition towards H₂
production, such as water-gas shift. This research project aims to determine
which metal catalysts are more effective to conduct SCWG, and the conditions
where catalytic effects are maximized.

We gasified cellulose and lignin as
model compounds for biomass in supercritical water, and avoided catalytic
effects from the reactor walls by using quartz reactors. We ran experiments in
the absence of catalysts and in the presence of nickel, iron or copper wires to
evaluate their effects on product yields. In order to determine how
experimental conditions affected catalysis, we varied temperature from 400 to 725
°C, biomass loading from 5.0 to 33.3 wt
%, and water density from 0.08 g/ml to 0.18 g/ml.

The results indicate that high
temperatures, low loadings and high water densities promoted catalytic
activity. Nickel increases yields of the gas products (H₂ in
particular) at all conditions studied, while iron and copper increase yields
only at specific conditions. When CH₄ and energetic yields are also
taken into account, iron is more effective at high temperatures and copper at
low biomass loadings.