Patricia A. P. Mendes

Separation of Hexane Isomers on Rigid Porous Metal Carboxylate-Based Metal-Organic Frameworks

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 differences in terms of separation.

Ethnobotany in the Center of Portugal (Santarém)

In recent years, the interest in the practical applications of local people’s knowledge has been renewed. The potential uses of ethnobotanical information can be used for new marketable purposes. In order to keep alive the ancient relationship of useful flora amongst our people, we carried out ethno-botanical research in the Center of Portugal (Santarem). Useful plants and traditional remedies and other uses are inventoried. Morphological aspects of the most important taxa are registered. A palynological investigation on the honeybee nectar and pollen sources gathering strategies using honey and pollen loads has been developed in the central part of Portugal (Santarem). All the data collection was compared with the results of floristic surveys in the region.

Dynamics of a Fixed Bed Adsorption Column in the Kinetic Separation of Hexane Isomers in MOF ZIF-8

A fixed bed adsorption mathematical model has been developed to describe the kinetic separation of hexane isomers when they flow through a packed bed containing the microporous Metal-Organic Framework (MOF) ZIF-8 adsorbent. The flow of inert and adsorbable species through the fixed bed is modeled with fundamental differential equations according to the mass and heat conservation laws, a general isotherm to describe adsorption equilibrium and a lumped kinetic mass transfer mechanism between bulk gas phase and the porous solid. It is shown that a proper combination of two characteristic times (the residence time of the gas in the fixed bed, \(\tau _{fb}\) and the characteristic time of diffusion of solutes into the pores \(\tau _{dif}\)) can lead to very different dynamics of fixed bed adsorbers where in a limiting case can gives rise to a spontaneous breakthrough curves of solutes. The numerical simulations of an experimental breakthrough curve with the developed mathematical model clearly explain the complete separation between linear n-Hexane (nHEX) and the respective branched isomers: 3-Methyl-Pentane (3MP) and 2, 2-Dimethyl-Butane (22DMB). The separation is due to significant differences in the diffusivity parameters \(\tau _{dif}\) between 3MP and 22DMB and the residence time of the gas mixture \(\tau _{fb}\) within the fixed bed. This work shows the importance of mathematical modelling for the comprehension and design of adsorption separation processes.