(311a) Breathing Effects In the Adsorption and Separation of Xylene Isomers on the Metal Organic Framework MIL-53
AIChE Annual Meeting
Tuesday, November 18, 2008 - 12:33pm to 12:54pm
Xylene isomer separation is one of the most important bulk scale adsorptive separation processes. Currently, faujasite based adsorbents are used in this process. Recently, we discovered that MIL-47 is a very effective adsorbent for the liquid phase separation of para-xylene from the other xylene isomers . MIL-47 is a porous terephthalate built from infinite chains of V4O6 octahedra, held together by the dicarboxylate groups of the terephthalate linkers . In this way a 3-dimensional microporous framework with 1-dimensional diamond shaped channels with free internal diameter of about 0.85 nm is formed.
In the present work, adsorption and separation of xylene isomers on a similar structure, MIL-53, was investigated. Low coverage adsorption properties were determined using gas phase pulse chromatography, vapor phase adsorption isotherms were obtained by gravimetry and the separation of C8 alkylaromatics (o-xylene, p-xylene, m-xylene and ethyl benzene) was evaluated by performing breakthrough experiments.
Zero coverage adsorption enthalpies were found to be comparable to those obtained on MIL-47. However, adsorption isotherms showed completely different behavior. All C8 alkylaromatics have 2-step isotherms and show hysteresis. This is attributed to breathing of the MIL-53 framework, as reported before by Llewellyn et al . This breathing effect strongly influences the separation of the C8 alkylaromatics in breakthrough conditions.
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