413501 Adsorptive Separation of Xylene Isomers Using Zn2(BDC)2(DABCO) [MOF1] Metal Organic Framework

Wednesday, November 11, 2015: 9:33 AM
255D (Salt Palace Convention Center)
Sudeep Punnathanam and Arun Gopalan, Chemical Engineering, Indian Institute of Science, Bangalore, India

Adsorptive Separation of Xylene Isomers using Zn2 (BDC)2 (DABCO)  [MOF1]  Metal Organic Framework

Arun G and Sudeep N Punnathanam

            Isomeric forms of dimethylbenzene(xylene) especially the ortho and para isomers, find wide applications in the polymer, pharmaceutical and dye industries[1-3]. However, the separation of these isomers, especially the ortho isomer, remains a challenging task till date, due to the closeness of its melting and boiling points with the meta isomer[3]. The metal-organic framework MOF1, also known as Zn2 (BDC)2(DABCO), has been shown to selectively adsorb ortho-xylene from a mixture of xylenes[5]. In this work, Grand Canonical Monte Carlo(GCMC)[4] simulations  are used to study the adsorption of xylenes on MOF1 in order to understand the reasons for selectivty towards o-Xylene. MOF1 shows guest dependent framework flexibility[6], i.e., the structure of the adsorbent changes with the chemical nature and loading of the adsorbate. In the case of MOF1, two distinct structures, namely a large pore and a narrow pore, are observed. Comparison of GCMC simulations with experiments reveal that at high loading of xylenes, the MOF1 undergoes a structural transition from the large pore to the narrow pore structure. An examination of density distributions inside the pore reveal two adsorption sites for ortho-xylene but  only one for meta and para isomers. The presence of an additional adsorption site is the source of selectivity of MOF1 towards the ortho-isomer. The existence of this additional site is due to favorable alignment of the CH3 groups in the ortho isomer towards the oxygen atoms of the benzene dicarboxylate linkers which make up the pore walls of the adsorbent. Such favorable alignment is not possible with the meta and the para isomers.


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2. Neurath, A. R.., Design of Microbicide for Prevention of Sexually Transmitted Diseases Using A Pharmaceutical Excipient. AIDS Patient Care ST, 1999, 27(1), p. 11-21

3. Fabri, J., Graeser, Ulrich, and Simo, Thomas A, Xylenes, Ullmann's Encyclopedia of Industrial Chemistry. 2002: Wiley-VCH, Weinheim.

4. Frenkel, D., Smit, B., Understanding Molecular Simulation 2e, Academic Press, 2002.

5.Nicolau, M., Marco.P.M., et al., Single- and Multicomponent Vapor-Phase Adsorption

of Xylene Isomers and Ethylbenzene in a Microporous Metal – Organic Framework., J. Phys. Chem. C 2009, 113, p.13173–13179.

6. Dybtsev, D.N., H. Chun, and K. Kim, Rigid and Flexible: A Highly Porous Metal-Organic Framework with Unusual Guest-Dependent Dynamic Behavior. Angew. Chem., 2004. 43: p. 5033-6.

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