Browsing by Author "Mendes, Patrícia A.P."
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- Adsorption equilibrium and dynamics of fixed bed adsorption of CH4/N2in binderless beads of 5A zeolitePublication . Silva, José A.C.; Ferreira, Alexandre; Mendes, Patrícia A.P.; Cunha, Adelino F.; Gleichmann, Kristin; Rodrigues, AlírioThe sorption equilibrium of methane (CH4) and nitrogen (N2) in binderless beads of 5A zeolite is presented between 305 and 373 K and pressures up to 3 bar in a static electronic microbalance. The adsorbed amount of CH4 and N2 is around 1.6 and 1.02 mol/kgads, respectively, at 305 K and 3 bar. A comparison of these values with the ones in literature shows that the adsorption capacity of the 5A binderless beads is 20% higher than that of the 5A binder commercial materials. The CH4 and N2 adsorption isotherms were fitted with the simplest Langmuir model with a prediction of the maximum amount adsorbed for both compounds of 5.0 mol/kg. The heats of sorption are -16.6 and -15.1 kJ/mol for CH4 and N2, respectively. In the overall pressure and temperature range the isotherms of N2 seems practically linear. However, it was observed that the experimental data of N2 at low coverage (below 0.2 bar) deviates slightly from Type I isotherms. Thereafter, the binary sorption of CH4 and N2 has been investigated in a fixed bed adsorber at 313 and 343 K and total pressures up to 5 bar for 50(CH4)/50(N2) and 75(CH4)//25(N2) mixture ratios diluted in an inert helium stream. A mathematical model was formulated to compute the dynamic behavior of the fixed bed adsorber using the extended binary Langmuir model, showing close agreement with the measured binary breakthrough experiments in the partial pressure range of the components above 0.2 and below 3 bar. © 2015 American Chemical Society.
- A complete separation of hexane isomers by a functionalized flexible metal organic frameworkPublication . Mendes, Patrícia A.P.; Horcajada, Patricia; Rives, Sébastien; Ren, Hong; Rodrigues, Alírio; Devic, Thomas; Magnier, Emmanuel; Trens, Philippe; Jobic, Hervé; Ollivier, Jacques; Maurin, Guillaume; Serre, Christian; Silva, José A.C.The separation ability of branched alkane isomers (nHEX, 3MP, 22DMB) of the flexible and functionalized microporous iron(III) dicarboxylate MIL-53(Fe)-(CF3)2 solid is evaluated through a combination of breakthrough experiments (binary or ternary mixtures), adsorption isotherms, X-ray diffraction temperature analysis, quasi-elastic neutron scattering measurements and molecular dynamics simulations. A kinetically controlled molecular sieve separation between the di-branched isomer of hexane 22DMB from a mixture of paraffins is achieved. The reported total separation between mono- and di-branched alkanes which was neither predicted nor observed so far in any class of porous solids is spectacular and paves the way towards a potential unprecedented upgrading of the RON of gasoline.
- Dynamics of a fixed bed adsorption column in the kinetic separation of hexane isomers in MOF ZIF-8Publication . Mendes, Patrícia A.P.; Rodrigues, Alírio; Almeida, João P.; Silva, José A.C.A fixed bed adsorption mathematical model has been developed to de- scribe the kinetic separation of hexane isomers when they flow through a packed bed containing the microporousMetal-Organic Framework (MOF) ZIF-8 adsorbent. The flow of inert and adsorbable species through the fixed bed is modeled with fun- damental 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, fb and the characteristic time of diffusion of solutes into the pores 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 mathemati- cal 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 dif between 3MP and 22DMB and the residence time of the gas mixture fb within the fixed bed. This work shows the importance of mathematical modelling for the comprehension and design of adsorption separation processes.
- Single and multicomponent adsorption of hexane isomers in the microporous ZIF-8Publication . Mendes, Patrícia A.P.; Rodrigues, Alírio; Horcajada, Patricia; Serre, Christian; Silva, José A.C.Single, binary and ternary breakthrough experiments of hexane (C6) isomers n-hexane (nHEX), 3-methylpentane(3MP), and 2,2-dimethylbutane (22DMB) were performed in the microporous zinc methyl-imidazolate metal–organic framework ZIF-8, covering the temperature range between 313 and 423 K and partial pressures up to 20 kPa. Adsorption equilibrium isotherms for nHEX were collected from single component breakthrough experiments who show that the sorption behavior of linear nHEX is totally different than the one observed for the branched isomers. Indeed, while nHEX is retained in the bed the branched paraffins spontaneously breakthrough leading to an efficient separation with a remarkable working capacity (25 wt%) for nHEX at 313 K and partial pressure 10 kPa. Langmuir isotherm is found to reasonably describe the adsorption equilibrium data of nHEX while the heat of sorption reaches 32.8 kJ/mol with Langmuir equilibrium affinity constants ranging from 1.73 to 0.0624 kPa 1 between 313 and 423 K, respectively. The ternary experiments (nHEX/3MP/22DMB) show a complete separation between nHEX and the branched isomers together with an adsorbed amount of nHEX similar to the one found in single component experiments. In the binary experiments (3MP/22DMB) the separation and sorption capacity is negligible. A fixed bed adsorption dynamic model is used to demonstrate that the complete separation of nHEX from the branched paraffins is due to a spontaneous breakthrough ofthe branched paraffins due to its lower diffusivity values when compared with nHEX.