(395bf) A New Flexible Cu-Based MOF for Separation of Linear and Branched C4-Hydrocarbons

Authors: 
Staudt, R., University of Applied Science Offenburg
Lange, M., aInstitut für Nichtklassische Chemie



A new flexible Cu-based MOF for Separation of linear and branched C4-hydrocarbons

M. Langea, M. Kobalzb, A. Möllera, H. Krautscheidb, R. Staudtc

aInstitut für Nichtklassische Chemie e.V.,Permoserstr. 15, 04318 Leipzig, Germany bUniversität Leipzig, Institut für Anorganische Chemie, Johannisalle 29, 04103 Leipzig, Germany cUniversity of Applied Sciences Offenburg, Badstr. 24, 77652 Offenburg, Germany

Recently, a new Cu-based MOF material (overall formula 3 [(Cu2(H-Metrz-ia)2] 1) with SBUs in paddle wheel structure was reported[1]. 1 possesses a three-dimensional pore system with two different windows of 0.27-0.35 nm and 0.44-0.50 nm as determined from X-ray single crystal structure analysis. The calculated solvent accessible pore volume reaches 50 % (PLATON[2]).
In this study, adsorption measurements were performed with both linear and branched alkanes
and alkenes in order to assess the effect of structural flexibility on the separation of C4- alkanes/alkenes from the gas phase. The pure component adsorption of n-butane and isobutane on 1 was measured gravimetrically in a temperature range from 283 to 313 K and at pressures up to 300 kPa.
Sorption measurements show a stepwise pore filling, which is typical for flexible MOFs [3] (Fig. 1, left). By sorption of n- and isobutane, the framework opens and a maximum in loading is reached at 2.97 mmol g-1 and 3.12 mmol g-1, respectively, which results in similar pore volumes for both sorptives. In contrast, the equilibration times for n- and isobutane are significantly different (Fig. 1, right). Thus, the material has the potential to separate linear

from branched C4-isomers on the basis of adsorption kinetics.

Fig. 1: Sorption isotherm of n-butane on 1 up to 250 kPa at 298 K (left) with a broad adsorption-desorption- hysteresis in the low pressure region, which is typical for flexible MOFs. The comparison of equilibria for n- and isobutane on 1 (right) show no thermodynamic separation effect, but the uptakes indicates a high potential for kinetic separation (insert).

Hence, kinetic measurements, like uptake experiments, breakthrough curves etc., will be presented to determine sorption rates. These are used as a basis for the calculation of effective selectivities. In addition, mixture measurements with time-resolved analysis of the gas phase composition will give detailed information about the adsorption process of n- and isobutane mixtures.

References:

[1] J. Lincke: Dissertation, Universität Leipzig, 2012. [2] PLATON, A. L. Spek: J. Appl. Cryst. (2003), 36, 7.

[3] J. Lincke, D. Lässig, J. Möllmer, C. Reichenbach, A. Puls, A. Möller, R. Gläser, G. Kalies, R. Staudt, H. Krautscheid: Micropor. Mesopor. Mater. 2011, 142, 62-69.