(771c) Membrane Contactors for Post Combustion Carbon Dioxide Capture: Wetting Resistance On Long Time Scales

Carbon dioxide
(CO₂) is one of the largest contributors to the greenhouse effect.
Because of the raise of the energy needs, the CO₂ concentration in
the atmosphere could increase by a factor of 2 from today to 2100 if no action
is engaged to reduce emissions. Postcombustion CO₂
capture by gas-liquid absorption in a chemical solvent is usually considered as
the easiest way to remove CO₂ from power plants. In place of packed
columns, which show a large footprint and may be subject to several
disadvantages such as flooding, foaming, channelling and entrainment, membrane contactors, which are based on hydrophobic microporous hollow fibers, have recently attracted increased attention.

Membrane contactors are indeed
considered as one of the most effective strategy for intensified gas-liquid
absorption processes. A major complication has however to be taken into account
when a membrane contactor is used for gas-liquid absorption purposes: the
gradual wetting of the membrane by the solvent can significantly increase the
mass transfer resistance and annihilate the interest in terms of process
intensification. The influence of wetting on membrane contactors performances
is well documented, essentially through simulation studies but, surprisingly,
no comparison of the wetting resistance of different types of hollow fibers over long time scales (i.e. months) has been
reported.

 In this study, post-combustion CO₂
capture by absorption in a chemical solvent (MonoEthanolAmine,
MEA) has been investigated based on laboratory scale experiments under steady
state conditions. Two standard membrane contactor materials (microporous polypropylene PP and polytetrafluoroethylene
PTFE) have been compared to two novel composite hollow fiber
materials, which show a dense skin layer on the liquid side in order to prevent
wetting (a polymethylpentene, PMP and a Teflon-AF
dense skin coated on a microporous PP fiber). The four different membrane contactors have been
tested over 1000 hours for CO₂ absorption in a 30% MEA solution. The
results in terms of stability of the CO₂ capture efficiency over
time and the overall mass transfer performances are presented and discussed. A
spectacular wetting protection effect of the dense skin membranes is obtained
(Figure 1). Microporous membrane materials show a
significant decrease of the capture efficiency over time; a very large decrease
of the capture efficiency is observed with PP after 100 hours contact time with
the solvent, while a slight decrease only is obtained after 300 hours for the
PTFE membrane. The interest of the different types of fibers
for process intensification purposes with a special emphasis on long time use
is discussed. More specifically, it will be shown that dense skin composite fibers only can ensure a significant intensification factor
(higher than 4) to be attained on long time scales.