4. Conclusions
This study reports on CO2 adsorption behavior of zeolite
13X monoliths and beads under dry and humid conditions using both clean
and contaminated simulated flue gas feeds. As reported herein, zeolite
beads and monoliths experienced substantial drop in CO2breakthrough time after being saturated with humidity, on account of the
competitive adsorption which exists between CO2 and
water. On the other hand, a cooperative effect was observed when
SO2 and NO were introduced alongside the presence of
water. In those experiments, water led to the formation of NaOH clusters
which reacted with the acid contaminants to produce chemisorbents. In
turn, this gave rise to enhanced CO2 adsorption
capacity via carbonate formation on the additional active sites. This
being stated, all samples exhibited broader breakthrough fronts in the
contaminated runs compared to the clean-mode experiments, as a result of
added chemisorption because, although it did provide additional sites
for CO2 adsorption, the mechanism for chemisorption was
likely slower than that of physisorption, as it relied on the reaction
kinetics instead of mass transfer alone. Therefore, this study concluded
that zeolite materials – including binderless beads and 600 cpsi, and
800 cpsi monoliths – perform better under multicomponent flue gas
conditions from an adsorption capacity standpoint, but exhibit slightly
slower mass transfer kinetics. Moreover, this study indicated the
importance of examining adsorbent materials under realistic conditions
for successful implementation in scaled-processes and emphasized the
need for performing cyclic adsorption-desorption experiments using
multicomponent streams.