Potential Adsorbent for Light Hydrocarbon Separation: Role of SBA-15 Framework Porosity

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.