(82f) Catalytic Membrane Reactor for CO2 Hydrogenation Using H2-Containing Renewable Streams: Model-Based Feasibility Analysis

Catalytic membrane
reactor for CO₂ hydrogenation using H₂-containing renewable
streams: Model-based feasibility analysis

Robert Currie and David Simakov

Department of Chemical Engineering,
University of Waterloo, Waterloo, ON N2L 3G1, Canada

Converting CO₂ into
synthetic fuels and platform chemicals is an attractive pathway to decrease CO₂
emissions and to reduce our dependence on fossil fuels. Thermocatalytic
hydrogenation provides advantages of fast reaction rates and high conversion
efficiencies (as compared to electro-catalytic and photo-catalytic routes),
thus allowing for compact, high-throughput operation. The most fundamental
disadvantage is the requirement to supply a pure H₂ stream (water is
a source of H₂ in the electro- and photochemical CO₂
reduction). Natural gas reforming is obviously not an option, as this approach
will result in the overall positive carbon footprint. Water electrolysis using
renewable or surplus electricity is a possibility, but this technology requires
high capital investments and operation costs. This study assesses the
feasibility of using H₂-containing renewable streams, such as
biomass gasification product gases, as a source of H₂ for the thermocatalytic
CO₂ conversion to renewable natural gas (Sabatier reaction, CO₂
+ 4H₂ = CH₄ + 2H₂O).

It is suggested to use a H₂-selective
membrane to extract H₂ from a H₂-containing stream in
situ. The suggested Catalytic Membrane Reactor configuration is based on the
distributed H₂ supply via a H₂-selecive membrane along
the axial reactor dimension. The heat generated in the highly exothermic
Sabatier reaction is simultaneously removed using molten salt as a heat
transfer fluid. A dynamic mathematical model was formulated and analyzed by
numerical simulations. The model accounts for the heat exchange between the
reaction compartment and the cooling tube, for the mass exchange through the H₂-selective
membrane, as well as for catalyst deactivation. The reactor fed with a CO₂-rich
waste stream (biogas or landfill gas) without upstream CO₂
separation was analyzed. Effects of feed temperature, pressure, and space
velocity on the reactor spatiotemporal behaviour were investigated. Catalyst
deactivation was found to be significant but not severe, owing to the
distributed H₂ supply that leads to more uniform temperature
distribution and reduced rate of coking. The simulation results show that, with
a proper selection of operating parameters, it is possible to achieve CO₂
conversions over 80% after 1,000 h on stream, producing renewable natural gas
from a waste CO₂-rich stream and a H₂-containing biomass
gasification product gas.