Mechanistic insights into aqueous phase propanol dehydration in H‐ZSM‐5 zeolite

Aqueous phase dehydration of 1‐propanol over H‐ZSM‐5 zeolite was investigated using density functional theory (DFT) calculations. The water molecules in the zeolite pores prefer to aggregate via the hydrogen bonding network and be protonated at the Brønsted acidic sites (BAS). Two typical configurations, i.e., dispersed and clustered, of water molecules were identified by ab initio molecular dynamics simulations of the mimicking aqueous phase H‐ZSM‐5 unit cell with 20 water molecules per unit cell. DFT calculated Gibbs free energies suggest that the dimeric propanol–propanol, the propanol–water, and the trimeric propanol–propanol–water complexes are formed at high propanol concentrations in aqueous phase, which provide a kinetically feasible dehydration reaction channel of 1‐propanol to propene. The calculation results indicate that the propanol dehydration via the unimolecular mechanism becomes kinetically discouraged due to the enhanced stability of the protonated dimeric propanol and the protonated water cluster acting as the BAS site for alcohol dehydration. © 2016 American Institute of Chemical Engineers AIChE J, 63: 172–184, 2017     

Fatty Acid Composition of Freshwater Wild Fish in Subalpine Lakes: A Comparative Study

In this study, the proximate and fatty acid compositions of the muscle tissue of 186 samples of fish belonging to fifteen species of freshwater fish harvested in subalpine lakes (bleak, shad, crucian carp, whitefish, common carp, pike, black bullhead, burbot, perch, Italian roach, roach, rudd, wels catfish, chub and tench) were investigated. Most of the fish demonstrated a lipid content in the fillet lower than 2.0 g 100 g^?1 wet weight (range 0.6–9.7). A strong relationship between feeding behavior and fatty acid composition of the muscle lipids was observed. Planktivorous fish showed the lowest amounts of n‐3 fatty acids (p < 0.05), but the highest monounsaturated fatty acid (MUFA) contents, in particular 18:1n‐9. Conversely, carnivorous fish showed the highest amounts of saturated fatty acids and n‐3 fatty acids (p < 0.05), but the lowest MUFA contents. Omnivorous fish showed substantial proportions of n‐3 fatty acids and the highest contents of n‐6 fatty acids. Principal component analysis showed a distinct separation between fish species according to their feeding habits and demonstrated that the most contributing trophic markers were 18:1n‐9, 18:3n‐3, 22:6n‐3 and 20:4n‐6. The quantitative amounts n‐3 polyunsaturated fatty acid in muscle tissues varied depending on the fish species, the lipid content and the feeding habits. Some species were very lean, and therefore would be poor choices for human consumption to meet dietary n‐3 fatty acid requirements. Nevertheless, the more frequently consumed and appreciated fish, shad and whitefish, had EPA and DHA contents in the range 900–1,000 mg 100 g^?1 fresh fillet.     

Identification of magnetic properties of few nm sized FePt crystalline particles by characterizing the intrinsic atom order using aberration corrected S/TEM

Hard-magnetic nanomaterials like nanoparticles of FePt are of great interest because of their promising potential for data storage applications. The magnetic properties of FePt structures strongly differ whether the crystal phases are face centered cubic (fcc) or face centered tetragonal (fct). We evaluated aberration corrected HRTEM, electron diffraction and aberration corrected HAADF-STEM as methods to measure the chemical degree of order S that describes the ordering of Pt and Fe atoms within the crystals unit cells. S/TEM experiments are accompanied by image calculations. The findings are compared with results obtained from X-ray diffraction on a FePt film. Our results show that STEM is a reasonable fast approach over HRTEM and electron diffraction to locally determine the chemical degree of order S.     

Effect of charge on anion and cation binding to poly(vinylbenzo-18-crown-6) in water

Complex formation constants, K, of cation to poly(vinylbenzo-18-crown-6) (P18C6) and to its monomeric analogue 4′-methylbenzo-18-crown-6 (MB 18C6) were measured in water potentiometrically or spectrophotometrically. The constants for Na⁺, K⁺ and Cs⁺ to P18C6, extrapolated to zero charge density, were found to be 2.4, 110 and 300 M^?1, respectively, and 27, 110 and ≈20 for MB18C6. Binding of K⁺ and of picrate anions to P18C6 was measured as a function of the number of K⁺ ions, Z, on the P18C6 chain. The charge effect (a decrease in K⁺ binding with increasing Z, and an increase in picrate binding) can be reasonably well-described by assuming the macroion to be a solvent- and ion-impenetrable sphere, the potential of which can be calculated by using a Debye-Huckel approximation. A linear plot is predicted and found (at least for picrate binding) between InK and Z, the slope yielding information on the radius of the P18C6 macroion. The cation effect on picrate binding to P18C6 was utilized to determine spectrophotometrically the order of binding of a series of cations to P18C6. The results were confirmed by using the dye, 2-(4′-hydroxybenzeneazo)benzoate which produces a much larger bathochromic shift on binding to P18C6 in water than does the picrate anion.     

Untersuchungskonzept zum Einfluss hoher Dehnraten auf die Zahnfußtragfähigkeit

Forschung im Ingenieurwesen - Der Einsatz von Getrieben in elektrifizierten Antriebssträngen und Flugzeugturbinen führt zu höheren Betriebsdrehzahlen und einer höheren Anzahl...