(627a) Carbon Dioxide Fixation in Two Plug Flow Reactors in Series Over a Copper Based Methanol Synthesis Catalyst in the First Reactor and a Cobalt Based Fischer-Tropsch Synthesis Catalyst in the Second Reactor

Utilization of CO₂ as a raw
material is of interest not only as carbon source but also because of
its impact on the environment through the greenhouse effect. There have been
various attempts to fixate CO2, such as (1) Hydrogenation of CO₂ to methanol
over methanol synthesis catalysts; (2) hydrogenation of CO₂ to
hydrocarbon fuels over Fischer-Tropsch synthesis (FTS) catalysts.

Hydrogenation of CO₂ over cobalt
based catalysts under FTS reaction conditions have been conducted by
various researchers. Activity data clearly showed that CO₂ is readily
hydrogenated over cobalt based catalysts. However, because the cobalt catalysts
have low water gas shift (WGS) activity and high hydrogenation activity, the
products for the FT CO₂ hydrogenation are methane rich short
chain paraffins which are not commercially attractive. Based on our group research,
if the cobalt catalyst is mixed with a WGS catalyst, the product distribution
for FT CO₂
hydrogenation is beneficially changed.

Copper based catalysts
are very active in both WGS and methanol synthesis reactions. For the
production of methanol from synthesis gas, it appears that the pathway to
methanol formation is through CO₂ as an intermediate. Hydrogenation of CO₂ to methanol
with the by-product of carbon monoxide over copper containing catalyst is a widely studied subject. However, a
series reactors configuration can be used for the hydrogenation of CO₂ to methanol
and hydrocarbon fuels by combining methanol synthesis, reverse-WGS and FTS
reactions.

In
our study, CO₂ fixation over copper and cobalt based catalysts under
different reaction conditions were carried out in two plug flow reactors. The
two PFR reactors are combined in series: the copper based
catalyst in the first reactor and the cobalt based catalyst in the second
reactor. For CO₂
hydrogenation over the copper based catalyst, the main products are methanol
and carbon monoxide. The chemical equilibrium for both the reverse-WGS and
methanol synthesis reactions limits the CO₂
conversion at the reaction conditions. The product distribution, catalyst
activity and selectivity of CO₂
hydrogenation between only one PFR reactor with cobalt catalyst and the two PFR
reactors in series (first with copper catalyst and second with cobalt catalyst)
are compared. Based on the experimental data and thermodynamic considerations,
a potential
optimized process design for CO₂ hydrogenation is suggested to fixate CO₂ to both methanol and
hydrocarbon fuels.