(111d) Zeolite/Polymer Composite Membranes for CO2 Capture From Flue Gas

Membrane technology provides a promising approach for CO₂
capture from post-combustion flue gas due to its smaller footprint and
potentially lower energy cost than the traditional amine scrubbing process.  Thin inorganic membranes with high
selectivity and flux have been conventionally supported by inorganic materials,
which are expensive and difficult for scale-up in a continuous manner and fabrication
into a high packing density in terms of high surface area/volume due to their
brittle nature. 

In this work, a thin zeolite seed layer (< 1 µm) has been
successfully deposited on a flexible polymer support for the first time, which
enables the continuous roll-to-roll fabrication of the membrane and the configuration
of spiral-wound membrane modules with a high packing density.  Zeolite-Y with pore size of about 7 Å was
specially selected for CO₂/N₂ separation from flue gas,
due to the preferential adsorption of CO₂ molecules with a larger
quadrupole moment and higher polarizability.  This is known as the "surface diffusion"
mechanism along with the blocking of N₂ molecules due to the
adsorbed CO₂ molecules.  In
addition, a polymer cover layer containing fixed polyamine and mobile amine
carriers was applied on top of the zeolite seed layer by knife-casting to
utilize the advantages of both inorganic and polymer membranes for CO₂
capture from flue gas.  The
thickness of polymer cover layer varied from 0.5 µm to 10 µm.  The separation performance of the
synthesized zeolite/polymer composite membrane was characterized under humid
flue gas composition at close to atmospheric feed pressure and 102^oC.  The resulting membrane showed a CO₂
permeance greater than 1100 GPU and a CO₂/N₂
selectivity above 400.  Based on the
transport results, a process and cost modeling study will be discussed in view
of achieving the DOE targets of < 35% increase on the cost of electricity
and < $40/tonne CO₂ captured for 2025.        

Considering the real application in a power plant, SO₂
tolerance of the aforementioned membrane was evaluated under different SO₂
concentrations in feed gas.  When SO₂
concentration in feed gas was below 1 ppm, the separation performance of the
composite membrane was not affected at all.  When 5-ppm SO₂ was supplied, a
reduction of CO₂ permeance was observed.  However, the CO₂permeance recovered back to about 80 ¨C 85% of its original
value within 24 hours after exposure to the feed gas without containing the SO₂,
which could be crucial if the up-stream SO₂ polishing step
fails.