Kinetics of Desorption of Hexane from the Microporous Metal Organic Framework

The kinetics of desorption of hexane from the microporous metal framework RPM 1 has been studied using a pulse mass analyzer. In this method a small sample of organic liquid was injected into a heated carrier gas that passes through a packed bed of adsorbent. The change in mass of the bed with time was observed following the adsorption of the pulse. RPM 1 is a microporous material of the general formula [M3(bpdc)3(bpy)] ·4DMF·H2O, where M is either Co or Zn, bpdc is biphenyl dicarboxylate and bpy is 4,4′-bipyridine. The pores are channels of larger supercages (11 x 11 x 5 Å) connected by smaller windows of approximately 8 Å diameter. The desorption of hexane was well represented by a combination of two first order processes. Activation energies determined for the two processes over a temperature range of 373 to 473 K were 56 and 63 kJ/mol for RPM 1 (Co). The two activation energies are similar to isosteric heats of adsorption measured independently in earlier work at corresponding coverages. Similar values were found for RPM 1 (Zn). The pulse mass analyzer was found to be an effective way to investigate the dynamics of adsorption processes.