Marc Pera-Titus

Polyethylenimine (PEI) has been grafted on a 2D hexagonal mesostructured porous silica of MCM-41 type (LUS silica) using 3-glycidoxypropyltrimethoxysilane (GTMS) as a grafting agent to develop sorbents for CO₂ capture. The advantage of this tether is to create ethanolamine units upon reaction of the epoxy group with the amine functions of PEI. Two synthetic routes have been explored: (1) reaction of GTMS and PEI and then grafting on a calcined MCM-41 silica (M-1), and (2) grafting of GTMS on the silica and then reaction with PEI (M-2). In both cases, the grafted solids are well structured according to the XRD patterns. The amounts of glycidoxypropylsilane (GS) and PEI are 14 and 9 wt%, and 21 and 16 wt%, respectively, for samples M-1 and M-2. The CO₂ adsorption capacity of both materials has been tested at 303 K and 101 kPa and compared to a bare LUS silica sample impregnated with 25 wt% PEI (M-3-25). Samples M-1 and M-2 containing ethanolamine groups show higher CO₂ adsorption capacities, with loading of about 150 and 134 mgCO₂ / gPEI (36 and 43 mgCO₂ / g-sorbent), respectively, while the CO₂ adsorption capacity was about 55 mgCO₂ / gPEI (14 mgCO₂ / g-sorbent) for the impregnated solid M-3-25.

In this study, we present the results of a preliminary investigation on the influence of operating variables (temperature, sweep gas flow rate, and total feed vapor pressure) on xylene vapor mixture separation using tubular nanocomposite MFI-alumina zeolite membrane prepared by the pore-plugging synthesis technique. Within the detection limit of our analytical system, neither m- nor o-xylene was detected in the permeate stream, the membranes displaying therefore “infinite” p-xylene selectivity. The mixture's p-xylene flux displayed a maximum value of ca. 3.5 µmol·m⁻²·s⁻¹, corresponding to a mixture permeance of 11 nmol·m⁻²·s⁻¹·Pa⁻¹, at 473 K and for a feed composition 0.63 kPa p-xylene/0.27 kPa m-xylene/0.32 kPa o-xylene, being almost unchanged for sweep gas flow rates (N₂) higher than 20 mL(STP)/min and increasing with the total xylene vapor pressure at 1 : 1 : 1–3 p/m/o-xylene composition. The experimental p-xylene fluxes can be well predicted by a Maxwell-Stefan model, as expected for a mass transfer process driven by competitive adsorption / surface diffusion. Unlike film-like MFI membranes, the membranes presented here preserved their selectivity to p-xylene for total xylene pressures as high as 150 kPa. This behavior is attributed to the intimate contact between the alumina confining pores and MFI nanoparticles, reducing long-term stresses and thus preventing distortion of the MFI framework during p-xylene adsorption. These results open up potential applications of nanocomposite MFI-alumina for selective p-xylene separations at high loadings, for instance in pervaporation, where the use of film-like MFI membranes is discouraged.

The properties of condensed matter are strongly affected by confinement and size effects at the nanoscale. Herein, we measured by microvolumetry the increased solubility of H₂ in a series of solvents (CHCl₃, CCl₄, n‐hexane, ethanol, and water) when confined in the cavities of mesoporous solids (γ‐alumina, silica, and MCM‐41). Gas/liquid solubilities are enhanced by up to 15 times over the corresponding bulk values for nanoliquid sizes smaller than 15 nm as long as gas/liquid interfaces are mesoconfined in a porous network. Although Henry’s law constant apparently no longer applies under these confinement, the concentration of dissolved H₂ still increases linearly with increasing pressure in the range 1–5 bar. We discuss the role and main implications of surface excess concentrations at mesoconfined gas/liquid interfaces in enhancing gas solubility.

The kinetics of gas‐liquid catalytic reactions can be strongly promoted when these are performed in interfacial catalytic membrane reactors instead of other three‐phase reactors such as slurry stirrers or trickle beds. The well‐defined gas‐liquid‐catalyst contact in this system avoiding diffusional limitations is usually argued as the main reason for such enhancement. In this work, using nitrobenzene hydrogenation as a model reaction, we propose that this increased catalytic performance might also be attributed, at least partially, to increased gas solubilities in mesoconfined solvents (or simply “nanoliquids”) in interfacial contactors overcoming the values predicted by Henry's Law. To support this hypothesis, we provide experimental evidence of a dramatic increase of H₂ solubility in confined ethanol using mesoporous γ‐Al₂O₃ as confining solid. Gas‐liquid solubilities can be enhanced up to five times over the corresponding bulk values for nanoliquid sizes lower than 15 nm as long as the gas‐liquid interface is confined in a mesoporous array. In such a situation, the volume of the gas‐liquid interface is no longer negligible compared to the total volume of the confined liquid, and the high surface excess concentrations of the gas adsorbed on the liquid surface make solubility grow up dramatically. According to these measurements, we discuss how nanoliquids might form in catalytic membrane contactors, which gas‐liquid configuration in the reactor appears to be more appropriate, and how the structure of the mesoporous catalytic layer contributes to their increased gas solubilization performance. © 2008 American Institute of Chemical Engineers AIChE J, 2009