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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: Metal oxides, are widely used as sorbents to remove H2S from hot gases produced by gasification processes. These oxides, however, suffer from several problems such as low capacity, sintering, evaporation, low duration and mechanical strength. Pure metal oxides or their admixtures loaded on inert materials have been used to overcome these problems. In this study, Cu/SBA-15 type sorbents were prepared by the wet impregnation method, in which copper and SBA-15 are active and support material, respectively. The prepared sorbent samples contained 21.97% and 40.2% Cu by weight. The H2S removal characteristics of the samples were investigated by using a laboratory scale fixed bed reactor through sulfidation–regeneration cycles in the temperature range of 788–838 K. Characterization results showed that the preparation method does not have a serious destructive effect on the structure of the support material. The average breakthrough point sulfur uptake capacities of the sorbents with 21.97% Cu and 40.22% Cu were determined to be 0.63 and 1.57 g S/100 g adsorbent, respectively, after three cycles. The XRD and nitrogen adsorption analysis indicated that the structures of the sorbents were destructed to some extent during the sulfidation–regeneration cycles. Changes in the sulfur up take, however, were not comparable and remained limited. [Copyright &y& Elsevier]

A modification in the gas separation performance of zeolitic imidazolate framework (ZIF)-supported hollow fiber (HF) membranes by means of an imine-condensation functionalization reaction carried out by microfluidics is reported. The accommodation of voluminous amine molecules in the SIM-1, Zn(4-methyl-5-imidazolecarboxaldehyde)2, also known as ZIF-94, sod structure during the functionalization reaction caused the ZIF atoms to be rearranged in a less dense rho structure, with a wider pore diameter and a diminished CO2 affinity. These changes had effects on the membrane performance, resulting in an enhanced CO2 permeance while maintaining a good permeance–selectivity balance. ZIF aldehyde-containing SIM-1 membranes were earlier prepared on the inner side of polymeric P84® HF using a microfluidic approach. The SIM-1 membranes displayed very interesting results in the separation of gas mixtures of great relevance to the natural gas field. High selectivities in the separation of He/CH4 (160), H2/CH4 (136) and CO2/CH4 (38) mixtures were achieved, and these are the first SIM-1 membranes with such a high separation performance to the best of our knowledge. These SIM-1 membranes were in situ stepwise functionalized with long-chain amine solutions, namely, hexyl- and nonylamine. Microfluidics allowed the easy sequential implementation of this post-reaction step in the membrane fabrication procedure. An imine-condensation reaction took place between the aldehyde groups in the 4-methyl-5-imidazolecarboxaldehyde ligand forming SIM-1 and the corresponding amines. The extent of the reaction was analyzed by FTIR, TGA and XRD, together with the changes in the textural properties and the adsorption capacities. [ABSTRACT FROM AUTHOR]

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]

The field of metal–organic framework based mixed matrix membranes (M4s) is critically reviewed, with special emphasis on their application in CO2 capture during energy generation. After introducing the most relevant parameters affecting membrane performance, we define targets in terms of selectivity and productivity based on existing literature on process design for pre- and post-combustion CO2 capture. Subsequently, the state of the art in M4s is reviewed against these targets. Because final application of these membranes will only be possible if thin separation layers can be produced, the latest advances in the manufacture of M4 hollow fibers are discussed. Finally, the recent efforts in understanding the separation performance of these complex composite materials and future research directions are outlined. [ABSTRACT FROM AUTHOR]

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]

Zeolitic imidazolate framework-93 (ZIF-93) continuous membranes were synthesized on the inner side of P84 co-polyimide hollow fiber supports by microfluidics. MOFs and polymers showed high compatibility and the membrane exhibited H2–CH4 and CO2–CH4 separation selectivities of 97 (100 °C) and 17 (35 °C), respectively. [ABSTRACT FROM AUTHOR]