Samples of mesoporous silica SBA-15 with and without controlled framework microporosity
were prepared under microwave hydrothermal conditions. These samples were evaluated
for their ability to separate ethane and ethylene by obtaining their equilibrium adsorption
isotherms using volumetric adsorption at 303 and 323 K, respectively. The data obtained
were analyzed using the Langmuir−Freundlich adsorption isotherm model. Although the
mesoporous silica samples showed a higher adsorption capacity for ethylene, it was found
to decrease upon reduction in the adsorbent's framework microporosity. Likewise, the isosteric
heats of adsorption estimated by the Clausius−Clapeyron equation are higher for ethylene
as compared to those for ethane and were also found to depend on framework microporosity.
The sample with higher microporosity displayed strong affinity for ethylene and is comparable
with those reported for π-complexation-based systems. This affinity was observed to weaken
on the sample with lower microporosity and absent altogether on the micropore-free SBA-15 sample. Furthermore, the affinity of the micropore-free SBA-15 framework for ethylene
and ethane was observed to be similar to and comparable with those obtained on MCM-41
type mesoporous silica. The thus-obtained trend has revealed the importance of framework
microporosity in designing a SBA-15-based adsorbent for ethane/ethylene separation.
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