Algenol

About: Algenol is a based out in . It is known for research contribution in the topics: Adsorption & Fiber. The organization has 88 authors who have published 70 publications receiving 2878 citations.

Unexpected Molecular Sieving Properties of Zeolitic Imidazolate Framework-8.

Abstract: We studied molecular sieving properties of zeolitic imidazolate framework-8 (ZIF-8) by estimating the thermodynamically corrected diffusivities of probe molecules at 35 °C. From helium (2.6 A) to iso-C4H10 (5.0 A), the corrected diffusivity drops 14 orders of magnitude. Our results further suggest that the effective aperture size of ZIF-8 for molecular sieving is in the range of 4.0 to 4.2 A, which is significantly larger than the XRD-derived value (3.4 A) and between the well-known aperture size of zeolite 4A (3.8 A) and 5A (4.3 A). Interestingly, because of aperture flexibility, the studied C4 hydrocarbon molecules that are larger than this effective aperture size still adsorb in the micropores of ZIF-8 with kinetic selectivities for iso-C4H8/iso-C4H10 of 180 and n-C4H10/iso-C4H10 of 2.5 × 10(6). These unexpected molecular sieving properties open up new opportunities for ZIF materials for separations that cannot be economically achieved by traditional microporous adsorbents such as synthetic zeolites.

Exploring the Framework Hydrophobicity and Flexibility of ZIF-8: From Biofuel Recovery to Hydrocarbon Separations

Abstract: The framework hydrophobicity and flexibility of ZIF-8 are investigated by a detailed adsorption and diffusion study of a series of probe molecules including ethanol, 1-butanol, water, hexane isomers, xylene isomers, and 1,2,4-trimethylbenzene. The prospects for using ZIF-8 in biofuel recovery and hydrocarbon separations are discussed in terms of adsorption or kinetic selectivities. ZIF-8 shows extremely low water vapor uptakes and is especially suitable for vapor phase butanol-based biofuel recovery. The extraordinary framework flexibility of ZIF-8 is demonstrated by the adsorption of hydrocarbon molecules that are much larger than its nominal pore size, such as m-xylene, o-xylene and 1,2,4-trimethylbenzene. The calculation of corrected diffusion coefficients reveals an interesting spectrum of promising kinetic hydrocarbon separations by ZIF-8. These findings confirm that a molecular sieving effect tends to occur in the sorbate molecular size range of 4–6 A rather than around the nominal ZIF-8 pore size o...

Hybrid Zeolitic Imidazolate Frameworks: Controlling Framework Porosity and Functionality by Mixed-Linker Synthesis

Abstract: Zeolitic imidazolate frameworks (ZIFs) are a subclass of nanoporous metal–organic frameworks (MOFs) that exhibit zeolite-like structural topologies and have interesting molecular recognition properties, such as molecular sieving and gate-opening effects associated with their pore apertures. The synthesis and characterization of hybrid ZIFs with mixed linkers in the framework are described in this work, producing materials with properties distinctly different from the parent frameworks (ZIF-8, ZIF-90, and ZIF-7). NMR spectroscopy is used to assess the relative amounts of the different linkers included in the frameworks, whereas nitrogen physisorption shows the evolution of the effective pore size distribution in materials resulting from the framework hybridization. X-ray diffraction shows these hybrid materials to be crystalline. In the case of ZIF-8-90 hybrids, the cubic space group of the parent frameworks is continuously maintained, whereas in the case of the ZIF-7-8 hybrids there is a transition from a...

Adsorption of water and ethanol in MFI-type zeolites.

Abstract: Water and ethanol vapor adsorption phenomena are investigated systematically on a series of MFI-type zeolites: silicalite-1 samples synthesized via both alkaline (OH(-)) and fluoride (F(-)) routes, and ZSM-5 samples with different Si/Al ratios as well as different charge-balancing cations. Full isotherms (0.05-0.95 activity) over the range 25-55 °C are presented, and the lowest total water uptake ever reported in the literature is shown for silicalite-1 made via a fluoride-mediated route wherein internal silanol defects are significantly reduced. At a water activity level of 0.95 (35 °C), the total water uptake by silicalite-1 (F(-)) was found to be 0.263 mmol/g, which was only 12.6%, 9.8%, and 3.3% of the capacity for silicalite-1 (OH(-)), H-ZSM-5 (Si/Al:140), and H-ZSM-5 (Si/Al:15), respectively, under the same conditions. While water adsorption shows distinct isotherms for different MFI-type zeolites due to the difference in the concentration, distribution, and types of hydrophilic sites, the ethanol adsorption isotherms present relatively comparable results because of the overall organophilic nature of the zeolite framework. Due to the dramatic differences in the sorption behavior with the different sorbate-sorbent pairs, different models are applied to correlate and analyze the sorption isotherms. An adsorption potential theory was used to fit the water adsorption isotherms on all MFI-type zeolite adsorbents studied. The Langmuir model and Sircar's model are applied to describe ethanol adsorption on silicalite-1 and ZSM-5 samples, respectively. An ideal ethanol/water adsorption selectivity (α) was estimated for the fluoride-mediated silicalite-1. At 35 °C, α was estimated to be 36 for a 5 mol % ethanol solution in water increasing to 53 at an ethanol concentration of 1 mol %. The adsorption data demonstrate that silicalite-1 made via the fluoride-mediated route is a promising candidate for ethanol extraction from dilute ethanol-water solutions.