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Abstract: Nanoparticle silicalite-1 crystallization from clear solutions was followed by nitrogen adsorption at 77K, applied to the products collected from the synthesis solution at different times. Isotherm data were analyzed by t-plot/BET, density functional theory (DFT), and Saito–Foley methods. Variation in the micropore and mesopore/external areas and volumes of the products with time, were in strong agreement with a recent study, which indicated that nucleation that took place after an induction time, was accompanied by an aggregation of a population of smaller particles. A sharp decrease in external surface area was observed parallel to a significant increase in the micropore area of the solid product at this stage of synthesis, when a sudden jump in the effective diameter of the nanoparticles in solution was recorded. Although earlier appearance in the solid products, of small amounts of particles/regions with pore sizes in a range including the pore sizes of silicalite-1, was indicated by both the DFT and Saito–Foley analyses, variation of the Saito–Foley median diameter with synthesis time provided a clear evidence of the significance of this “induction time”, after which particles could grow at a constant linear rate. Nitrogen adsorption at 77K was shown to be a useful tool to monitor the nucleation and crystal growth of silicalite-1 nanoparticles. [Copyright &y& Elsevier]

Abstract: Gases from gasification processes contain H2S which is highly harmful for almost all catalyst materials and metal constructions such as in IGCC plants. Metal oxides and/or their admixtures are widely used for the removal of H2S from gases at high temperatures. These sorbents, however, suffer from several problems which adversely affect their performances. In this study, a new method was explored to prepare sorbents from nano-size (sub-micron) CuO supported on SiO2 materials. Three sorbents with 38.5 wt.%, 41.5 wt.% and 49.6 wt.% Cu contents were prepared and characterized. Results indicated that, the produced materials are mesoporous composite type materials of nano-size CuO and amorphous SiO2. The H2S adsorption characteristics of the prepared sorbents were studied in a laboratory scale fixed-bed reactor through sulfidation–regeneration cycles in the temperature range of 788–838 K at atmospheric pressure. The average sulfur uptake capacities of the sorbents, based on the breakthrough point H2S concentration of 20 ppm, were determined to be in the range of 2.38–2.91 g S/100 g sorbent after 3 cycles. Although the process at high temperatures appeared to disturb the structure of the sorbents to some extent, the drop in their sulfur adsorption capacities remained limited. [Copyright &y& Elsevier]

Abstract: Vapor phase adsorption isotherms of methyl tertiary butyl ether (MTBE) in silicalite-1 at temperatures in the range of 298–600K were measured using a gravimetric analysis system. A maximum saturation loading of 4mol/u.c. was measured. The diffusion coefficients as a function of loading at each temperature were calculated from the differential adsorption uptake data. Diffusivities were observed to increase with loading up to about 1mol/u.c., possibly due to significant adsorption on external surfaces of the particles. Above this value, diffusivities became independent of loading. Additionally, Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations were carried out to estimate the adsorption isotherms and the diffusion coefficients, and the results were compared to those of the experiments. The GCMC simulation results were in reasonable agreement with the experimental data, especially at higher pressures and lower temperatures, where the contribution of interparticle and surface adsorption became marginal. From the MD simulations, MTBE molecules were seen to move very slowly inside the crystal since they spend time at the channel intersections. These simulations were also extended to loadings higher than 4mol/u.c., in order to shed light on the higher adsorption capacities from aqueous solutions previously reported in the literature. The mobility of the MTBE molecules was observed to increase with loading beyond the value of 4mol/u.c., which deserves further investigation. [Copyright &y& Elsevier]

Abstract: Organic–inorganic hybrid (mixed matrix) membranes can potentially extend the separation performance of traditional polymeric materials while maintaining processing convenience. Although many dense films studies have been reported, there have been few reported cases of these materials being successfully extended to asymmetric hollow fibers. In this work we report the first successful production of mixed matrix asymmetric hollow fiber membranes containing metal-organic-framework (MOF) ZIF-8 fillers. Specifically, we have incorporated ZIF-8 into a polyetherimide (Ultem® 1000) matrix and produced dual-layer asymmetric hollow fiber membranes via the dry jet-wet quench method. The outer separating layer of these composite fibers contains 13wt% (17vol%) of ZIF-8 filler. These membranes have been tested over a range of temperatures and pressures for a variety of gas pairs. An increase in separation performance for the CO2/N2 gas pairs was observed for both pure gas and mixed gas feeds. [Copyright &y& Elsevier]

Polymeric hollow fiber membranes represent a high degree of process intensification closer to scaling-up. Metal-organic framework ZIF-7 and ZIF-8 continuous membranes were synthesized on the inner surface of a 520 μm outer diameter polysulfone hollow fiber using microfluidics. This provided a constant reactant concentration along the membrane for growing homogeneous, continuous and thin layers of ZIF-7 (2.4 μm) and ZIF-8 (3.6 μm) with good adherence. The high quality of the membranes and the zeolite-like sodalite porous structure of both MOFs with pore apertures of 0.30–0.34 nm allowed operation at high temperature (150 °C) and pressure (4 bar). High separation factors in CO 2 and H 2 containing mixtures were achieved. [ABSTRACT FROM AUTHOR]