Screening separation studies with equimolar quaternary mixtures
of hexane isomers, namely, n-hexane/3-methylpentane/2,3-dimethylbutane/2,2-
dimethylbutane (n-HEX/3MP/23DMB/22DMB), in the temperature range of
343–423 K and partial pressures up to 10 kPa have been performed using three
rigid porous metal (III/IV) carboxylate-based metal–organic frameworks
(MOFs) with different composition and topology. These carboxylate-based
MOFs are denoted as MIL-100(Cr), MIL-125(Ti)-NH2 and MIL-127(Fe).
Adsorption study results revealed that all the isomers were adsorbed on
MIL-100(Cr) and MIL-125(Ti)-NH2, with adsorption amounts reaching 24 and
12 wt%, respectively, and the order of adsorption being similar to the normal
boiling point of the compounds, that is, n-HEX > 3MP > 23DMB > 22DMB,
with selectivity of adsorption never exceeding three (i.e. selectivities between
the extreme compounds n-HEX and 22DMB). It is worth noting that adsorption
of branched isomers is practically excluded on MIL-127(Fe), which exhibits a
strong molecular sieve effect of the adsorbed n-HEX with the loading capacity
reaching a maximum of 7 wt%. Finally, an alternative strategy, which involved
probing the effect of post-synthetic functionalization on the coordinatively
unsaturated metal sites of the MIL-100(Cr) using functional group ethylamine or
N-methylethylenediamine showed no significant differenc
