Rational modeling of the CPO of methane over platinum gauze: Elementary gas-phase and surface mechanisms coupled with flow simulations

The high-temperature catalytic partial oxidation of methane (CPOM) over a platinum gauze reactor was modeled by integrating 3D numerical simulations of the flow field coupled with heat transport as well as detailed micro-kinetic models including gas-phase and surface reaction mechanisms. Model results describe well CPO experiments over Pt-gauzes in the literature. The conversions of CH₄ and O₂ increase with an increased contact time and were constant in the temperature range of 1000–1200 K. The selectivity to CO linearly increases with temperature. H₂ was only observed above 1200 K, below this temperature H₂O was the only hydrogen-containing product. The contribution of heterogeneous steps in the overall process is prominent, but in the later stages of the reactor, gas-phase reactions become important at certain conditions of temperature, pressure and residence time. Simulations predicted significant gas-phase production of ethane and ethylene via methane oxidative coupling upon increasing the total pressure and residence time. Consequently, homogeneous and heterogeneous processes should be simultaneously implemented in order to accomplish a solid reactor modeling.     

Diffusion-weighted imaging of the spine using radialk-space trajectories

Introduction Diffusion-weighted MR imaging (DWI) of the spine requires robust imaging methods, that are insensitive to susceptibility effects caused by the transition from bone to soft tissue and motion artifacts due to breathing, swallowing, and cardiac motion. The purpose of this study was to develop a robust imaging method suitable for DWI of the spine. Methods and subjects A radialk-space spin echo sequence has been implemented, which is sell-navigating because each acquisition line passes through the origin ofk-space. Influence of cardiac motion and associated flow of cerebrospinal fluid is minimized by cardiac gating with a finger photoplethysmograph. The sequence has been tested on a 1.5T system. Diffusion-weighted images of six normal volunteers were acquired in the sagittal plane with 4b values between 50 and 500 s mm⁻². Because of the symmetries of the cord, diffusion measurements in the head-foot (HF) or left-right (LR) directions were sufficient to measure the dominant effects of anisotropy. Results The apparent diffusion coefficients (ADCs) measured, respectively, in the LR and HF directions were (0.699 ± 0.050) × 10⁻³ and (1.805 ± 0.086) × 10⁻³ mm² s⁻¹ in the spinal cord. (1.588 ± 0.082) × 10⁻³ and (1.528 ± 0.052) × 10⁻³ mm² s⁻¹ in the intervertebral disks, and (0.346 ± 0.047) × 10⁻³ and (0.306 ± 0.035) × 10⁻³ mm² s⁻¹ in the vertebrae of the cervicothoraeic spine. Conclusion Diffusion-weighted spin echo sequences with radial trajectories ink-space provide a means of achieving robust, high quality diffusion-weighted imaging and measuring ADCs in the spine. The application of the diffusion-weighting gradients in different directions allows diffusion anisotropy to be measured.     

LIQUID-LIQUID EXTRACTION OF Ag(I), Hg(II), Au(III) AND Pd(II) BY SOME OLIGOTHIA MACROCYCLIC LIGANDS INCORPORATING AROMATIC AND HETEROAROMATIC SUBUNITS*

ABSTRACT

A series of hydrophobic tri- to hexa-dentate sulfur containing macrocyclic ligands incorporating aromatic and heteroaromatic subunits have been studied with respect to their extraction properties toward Ag(I), Hg(II), Au(III), and Pd(II) in aqueous//organic systems. The stoichiometry of extracted species and their extraction constants have been determined. The different ligands are compared with structure related open-chain compounds. The influence of substitution, solvent, and anion on the extraction equilibrium is also discussed providing a basis for future design of selective extractants and for die development of improved separation methods. The extractability of the various metal ions strongly depends on the nature and the number of donor atoms of the corresponding ligands and on the properties of the metal ion itself. In some cases, simple open-chain ligands show extraction properties comparable to the present macrocycles. A trithia crown with incorporated benzo subunit highly prefers Ag(I) to Hg(II). Furthermore a distinct selectivity for Au(ni) and Hg(II) over Pd(II) with pyridine substituted macrocycles was found.     

Oxidative Dehydrogenation of a C4 Raffinate‐2 towards 1,3‐Butadiene in a Two‐Zone Fluidized Bed

The oxidative dehydrogenation of a C4 raffinate‐2 consisting of n‐butane, 1‐butene, and 2‐butene was conducted in a two‐zone fluidized bed reactor using a Mo‐V‐MgO catalyst. This study reports the influence of the operating conditions temperature, hydrocarbon inlet height, and oxygen/hydrocarbon molar ratio on the product distribution, in particular on the formation of 1,3‐butadiene. Axial concentration profiles were measured to elucidate the reaction sequence in the fluidized bed.     

Comparison of exhaust emissions and their mutagenicity from the combustion of biodiesel, vegetable oil, gas-to-liquid and petrodiesel fuels

Efforts are under way to reduce diesel engine emissions (DEE) and their content of carcinogenic and mutagenic polycyclic aromatic hydrocarbons (PAH). Previously, we observed reduced PAH emissions and DEE mutagenicity caused by reformulated or newly developed fuels. The use of rapeseed oil as diesel engine fuel is growing in German transportation businesses and agriculture. We now compared the mutagenic effects of DEE from rapeseed oil (RSO), rapeseed methyl ester (RME, biodiesel), natural gas-derived synthetic fuel (gas-to-liquid, GTL), and a reference petrodiesel fuel (DF) generated by a heavy-duty truck diesel engine using the European Stationary Cycle. Mutagenicity of the particle extracts and the condensates was tested using the Salmonella typhimurium mammalian microsome assay with strains TA98 and TA100. The RSO particle extracts increased the mutagenic effects by factors of 9.7 up to 17 in strain TA98 and of 5.4 up to 6.4 in strain TA100 compared with the reference DF. The RSO condensates caused up to three times stronger mutagenicity than the reference fuel. RME extracts had a moderate but significantly higher mutagenic response in assays of TA98 with metabolic activation and TA100 without metabolic activation. GTL samples did not differ significantly from DF. Regulated emissions (hydrocarbons, carbon monoxide, nitrogen oxides (NO_x), and particulate matter) remained below the limits except for an increase in NO_x exhaust emissions of up to 15% from the tested biofuels.     

Preparation of diastereomerically pure 9-carboxybicyclo[6.1.0]nonane derivatives

Reactions of cyclooctene ( 1 ) with dibromocyanoacetic esters and copper(I) bromide give (8–10) : 1 mixtures of isomers ( 2 , 3 ), not stereochemically pure compounds as reported by others. The stereochemistry is elucidated by independent synthesis of one diastereomer ( 3a ). Carbenoid addition of alkoxycarbonylmethylene to 1 and 1,5-cyclooctadiene leads also to exo/endo adduct mixtures. Methods are developed to generate diastereomerically pure compounds ( exo -7a , exo -8, endo -9 , exo -10 , endo -10 ) from these. Endo esters of this series undergo very facile base catalyzed epimerization.     

Universelle Energiekennzahlen für Deutschland — Teil 2: Verbrauchskennzahlentwicklung nach Baualtersklassen

Die universellen Energiekennzahlen für Deutschland beinhalten bis dato 1/4 Million Gebäude‐Energieverbrauchskennzahlen der BRUNATA‐METRONA‐Gruppe aus den vergangenen sechs Jahren. Deren Datenaufbereitung umfasst die rückwirkende Revision respektive Normierung aller Energiekennzahlen anhand neuer ortsgenauer Klimafaktoren des Deutschen Wetterdienstes. Eine Auswahl von 110.000 Energiekennzahlen von gas‐ und ölbeheizten Gebäuden — davon etwa die Hälfte mit Baujahr nach 1977 — werden statistisch gemäß ihrer Kennzahlenentwicklung nach Baualtersklassen aufgeschlüsselt. Betrachtet wurden dabei nur nominell wärmetechnisch unsanierte Mehrfamilienhäuser bis 1994 und Neubauten ab 1995. Es wird belegt, dass die Mediane der heutigen Energiekennzahlverteilungen der bis in die 1960‐er Jahre gebauten Gebäude relativ konstant um 155 kWh/(m2a) liegen. Für diesen Bauzeitraum fallen die Energiekennzahlen für rund 90 % des Bestandes (5 bis 95 % Quantil) zwischen 100 und 260 kWh/(m2a). Seitdem fallen die Mediane stetig auf aktuell bis 85 kWh/(m2a). Der stärkste relative Rückgang ergibt sich für die Baujahre von 1994 nach 1995 mit Inkrafttreten der Wärmeschutzverordnung 1995. Die Standardabweichungen der Verteilungen haben sich gegenüber den Gebäuden aus den 1960‐er Jahren von über 50 kWh/(m2a) bis auf heute an nähernd 25 kWh/(m2a) etwa halbiert. Eine Gegenüberstellung der empirisch ermittelten Verbrauchskennzahlverteilungen mit den typischen Mindestanforderungen der vergangenen Wärmeschutzverordnungen und aktuellen Energieeinsparverordnungen schließen sich an. Mathematische Parametrierungen der empirischen Kennzahlverteilungen für Modell‐ und Hochrechnungen der Energieeffizienzentwicklung werden mitgeliefert. Universal Energy ratings for Germany — (Part 2): Evolution of rating distributions according to year of building construction. To date, “Universal Energy Ratings” for Germany contain about a quarter of a million energy consumption ratings recorded by the BRUNATA METRONA Group within the recent six year period. Data processing comprises a retro perspective review and normalisation of all energy ratings according to new, localised climate factors from the German weather service. A subset of 110.000 energy ratings concerning gas‐ and oil‐heated buildings only — half of those built past 1977 — has been analysed statistically by creating energy rating distributions depending on construction year, focussing exclusively on unrenovated objects (according to 1995 standards) built prior to 1995 and new buildings constructed in 1995 or later. It is shown, that the median values of rating distributions from about 1900 up into the 1960ies appear relatively constant around 155 kWh/(m2a). For building construction years within this time interval 90 % of today’s energy ratings (5 % to 95 %‐percentiles) fall into the range between 100 and 260 kWh/(m2a). For construction years after the mid 1960ies the median values continuously decrease to about 85 kWh/(m2a) today. Their corresponding standard deviations decreased by a factor of two from above 50 kWh/(m2a) to about 25 kWh/(m2a). The most distinct relative decrease occurred between 1994 and 1995 when the WSVO’95 was activated. This work adds a direct comparison between the recorded today energy ratings and the typical requirement levels of the various heat insulation regulations, WSVO, and Building Energy Conservation Ordinances, EnEV, concerning building construction years starting from 1977. We also present parameterization functions for the most important rating distributions that could be utilized for general model calculations and extapoletions to picture future energy efficiency evolution.     

Salicylidene‐imine–zirconium(IV) complexes in combination with methylalumoxane as catalysts for the conversion of hexa‐1,5‐diene: adjusting of the catalytic activity

A variety of substituted schiff base complexes of the composition (“salen”)ZrCl₂(thf) ( 1 – 21 ) were synthesized, with methylalumoxane (“MAO”) activated and used for a systematic study of their catalytic activity towards hexa‐1,5‐diene (“salen”: substituted salicylidene–ethylene‐iminato ligands). Main product of the catalytic cycle is methylenecyclopentane. Dimers are only formed in minor amounts. The catalytic activity and selectivity of the Ziegler–Natta systems strongly depend on the nature and the position of the peripheric substituents in the Schiff base ligands. Electron‐withdrawing substituents in para‐position to the phenolato oxygen (5‐position) decrease the catalytic activity. Improved activity and selectivity were obtained with electron‐donating substituents in 5‐position. Altering the ethylene bridge causes a lowering of the activity or inactivation. According to the x‐ray analysis the metal center in the related complex (L)ZrCl₂ ( 22 ) (L: N′,N′‐bis(ethylene)‐N′‐methyl‐N,N′′‐bis(benzoylacetonato‐imine) has a pentagonal‐bipyramidal environment. The pentadentate schiff base ligand lies in the plane, and both chloro groups occupy the axial positions. In contrast to the catalytically active salene complexes 22 can not rearrange to form a species in which the both chlorides are cis to each other. Consequently 22 is catalytically inactive.