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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 12 (1989), S. 155-161 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The conversion of methanol over zeolite H-T was investigated in a fixed bed reactor. H-T was prepared from Na-T by ion exchange with HCl and NH4Cl solutions. The HCl solution caused appreciable dealumination. High yields of ethene were obtained with NH4Cl exchangeed zeolites Na-T with 45% decationization, high proprne yields with low HCl or NH4Cl Exchanged catalysts. Low methanol partial pressures and short residence times favoured the formation of lower olefins. Lowest coking rates were observed at a reaction temperature of 693 K. The catalytic activity decrased slowly with the number of reaction/regeneration cycles. The distribution of procucts 〉 C2 could be described by the most probable distribution of Schulz and Flory.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 17 (1994), S. 179-186 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The conversion of ethanol over H-ZSM-5 was studied as a function of ethanol partial pressure, reaction temperature, weight hourly space velocity and Si/Al ratio. The results obtained were in qualitative agreement with most of those in the literature. Combination with all published results to give a significant regression model was not possible due to the large scatter of the data from various scientific groups. In mechanistic investigations, temperature programmed reaction measurements of ethanol, diethyl ether and ethene were performed. The formation of ethene from ethanol via direct elimination or from diethyl ether as intermediate could be confirmed. In the conversion of ethanol/water mixtures, the product distribution did not change significantly up to a water content of 60 wt%. Then, a pronounced increase of ethene formation and a considerable decrease of the yields of aromatics was observed. When several reaction mixtures from syngas conversion to ethanol were converted over H-ZSM-5, the coking rate depended on the product distribution in the feed. Product mixtures from processes with higher amounts of compounds having an unfavourable C/H ratio led to rapid deactivation of the zeolite.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 16 (1993), S. 332-337 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effects of metal exchange between zeolites and alkali metals (Li, Na, K; zeolite Y, ZSM-5, T), alkaline earths (Mg, Ca, Sr, Ba; ZSM-5), transition metals (La, Ce, Cr, Mn, Fe, Co, Ni, Pd, Cu, Zn; ZSM-5) and aluminium (ZSM-5) on the conversion of ethanol were studied. Activities of the catalysts and selectivities for ethene, C3+ olefins, paraffins and arenes strongly depended on the cation, chosen for the modification. Only ethene was formed by alkali exchanged zeolites, the most active being Li-Y. This could be confirmed by a long-term ageing test with Li-Y pellets under semi-industrial conditions. The exchange of ZSM-5 with alkaline earths or transition metals permitted the formation of a wide variety of products, raning from high ethene to high aromatic yields. A correlation between certain product selectivities and electronegativity was only possible in a rough approximation.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 10 (1987), S. 323-329 
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The conversion of a number of alcohols, ethers, ketones, aldehydes, carboxylic acids, esters, and cyclic compounds and their mixtures on H-ZSM-5 at 673 K was investigated. These compounds can be easily converted to aromatic hydrocarbons if the C/H ratio of the molecule fragment, remaining after elimination of oxygen as water, is less than 0.62. At higher C/H ratios, coking of the catalyst increases, thus reducing its lifetime, a difficulty which can be overcome by hydrogenation of these compounds prior to their conversion over H-ZSM-5. A procedure is proposed for converting at least a part of organic waste chemicals to valuable products instead of burning them.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 71 (1978), S. 101-115 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The optimal construction of a periodical stirred tank reactor for a minimal molecular weight distribution of living polymers leads in the border-line case to a batch reactor with three phases of operation: filling of the reactor with initiator and monomer, formation of polymers, and emptying of the reactor.Therefore the periodical stirred tank reactor provides the means of producing living polymers with molecular weight distributions, nearly as narrow as those coming from the batch reactor. It combines the advantages of batch operation of living polymers with the technological advantages normally associated with the operation of a continuously stirred tank reactor.
    Notes: Die optimale Auslegung eines schwingenden Rührkesselreaktors zur Herstellung lebender Polymerer mit minimaler Uneinheitlichkeit führt im Grenzfall zu einem diskontinuierlichen Rührkesselreaktor mit drei Operationsphasen, nämlich dem Füllen mit Initiator und Monomeren, der Polymerisation und dem Leeren des Reaktors. Ein schwingender Rührkesselreaktor ermöglicht die Herstellung lebender Polymerer mit Molekulargewichtsverteilungen, die fast so eng sind, wie die aus diskontinuierlichen Rührkesselreaktoren. Es kombiniert die Vorteile der diskontinuierlichen Arbeitsweise mit den technologischen Vorteilen eines kontinuierlichen Rührkesselreaktors.
    Additional Material: 8 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 135 (1985), S. 183-191 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wurde die lebende anionische Polymerisation von Isopren mit n-Butyllithium in n-Heptan in einem idealen kontinuierlichen Rührkessel untersucht. Es konnte gezeigt werden, daß es oberhalb von Monomer- und Initiatoreingangskonzentrationen von 4 mol/l bzw. 0,02 mol/l nicht zur Ausbildung multipler stationärer Zustände im Hinblick auf die Umsätze des Monomeren und des Initiators sowie die Höhe der Molekulargewichte kommt, wie es Porter et al.6 forderten. Die Polyreaktion kann vielmehr auch in den genannten Konzentrationsbereichen durch die bekannte Kinetik nach Sinn1 beschrieben werden.
    Notes: The living anionic polymerization of isoprene with n-butyllithium in n-heptane in a continuous stirred tank reactor was investigated. It is shown that there exist no multiple steady states for monomer and initiator conversions and for molecular weights at monomer and initiator feed concentrations 〉4 mol/1 and 〉0,02 mol/1, respectively, as postulated by Porter et al.6, but that the results may well be described by the known model of Sinn1.
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 242 (1996), S. 47-64 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Auf der Basis einer früher erschienenen Arbeit von Chen und Lee wird ein Verfahren vorgestellt, das bei einer diskontinuierlichen, radikalischen, azeotropen Copolymerisation mit isothermer Fahrweise die Ermittlung optimaler Reaktionszeiten erlaubt, um vorgegebene Monomerumsätze und mittlere Polymerisationsgrade zu erzielen. Durch das Verfahren werden für die gegebenen Bedingungen der zulässige Bereich der Monomerkonzentrationen, ein geeigneter Initiator und seine Konzentration ermittelt, um das gesteckte Ziel in möglichst kurzer Reaktionszeit zu erreichen. Die Gültigkeit des Modells wurde am System Acrylnitril-Butadien in Chlorbenzol bei 343 K mit den Initiatoren 1,1′-Azocyclohexannitril (ACN) und 2,2′-Azoisobutyronitril (AIBN) getestet. Die Übereinstimmung zwischen theoretischen und experimentellen Werten ist zufriedenstellend. Es wird darauf hingewiesen, daß der Geleffekt in das Modell eingearbeitet werden kann, und daß das Verfahren auch auf radikalische Homopolymerisationen übertragbar ist.
    Notes: Based on an earlier paper of Chen and Lee, a procedure is developed to determine optimal reaction times for predetermined monomer conversions and number-average degrees of polymerization in an azeotropic free-radical batch copolymerization with one charge of monomers and initiator. The procedure allows for the calculation of the admissible range of monomer concentrations, the determination of an appropriate initiator and its most suited concentration to arrive at the goal in reaction times as short as possible. The validity of the model was tested in the free-radical copolymerization of acrylonitrile and butadiene in chlorobenzene at 343 K, using 1,1′-azocyclohexanenitrile (ACN) and 2,2′-azoisobutyronitrile (AIBN) as initiators. The agreement of theoretical and experimental data was satisfying. It is pointed out that the gel effect can be incorporated into the model, and that the procedure can also be used in the design of free-radical homopolymerizations.
    Additional Material: 7 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 2335-2347 
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vinylphenyloxy- and allyloxy-substituted silyl ketene acetals are presented as new functionalized initiators for group transfer polymerization (GTP). All initiators initiated GTP of butyl acrylate in tetrahydrofuran with tetrabutylammonium cyanide as catalyst to yield butyl acrylate macromonomers with number-average molecular weights somewhat lower than those calculated for an ideal living polymerization and with polydispersities of about 1,8-2,6. For the metal-free anionic polymerization, functionalized initiators were obtained introducing allyloxy and vinylbenzyl groups into tetrabutylammonium diethyl malonate. Both compounds initiated a very rapid polymerization of butyl acrylate in tetrahydrofuran with high monomer conversion. The number-average molecular weights of the macromonomers, produced in a semi-batch procedure, reached nearly theoretical values, the polydispersities were about 1,2. In all macromonomers the functionality with respect to terminal vinyl and allyl groups was near one, so that they can be used with other monomers to form graft copolymers, e. g., in a free-radical polymerization.
    Additional Material: 1 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 197 (1996), S. 921-935 
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The polymerization of vinyl acetate (VA), methyl methacrylate (MMA), and methyl acrylate (MA) in ethyl acetate and tetrahydrofuran solution was initiated by the two-component initiating systems Fe(III) 2-ethylhexanoate or Co(II) acetylacetonate and pentamethyldisiloxane as co-initiator. Whereas Fe(III) 2-ethylhexanoate initiated the polymerization of all three monomers also in the absence of the siloxane, with an activity increasing from VA to MA, Co(II) acetylacetonate was completely inactive under these conditions. Addition of the siloxane co-initiator raised the monomer conversions with both transition metal initiators, particularly pronounced for MMA and MA. Number-average degrees of polymerization for poly(vinyl acetate) and poly(methyl acrylate) amounted to some hundred or less, but increased to several thousand for poly(methyl methacrylate). Electron spin resonance (ESR) spin trap experiments with N-tert-butyl-α-phenylnitrone (PBN) revealed that the transition metal compounds and the siloxane undergo a reaction in which free radicals are produced by oxidative cleavage of the co-initiator to generate hydrogen atoms which initiate the polymerization. With Fe(III) 2-ethylhexanoate PBN adducts of carbon-centered radicals are observed in the absence and in the presence of the monomers. By way of contrast, with Co(II) acetylacetonate only the hydrogen atom adduct to PBN is observed in the absence of the monomers. Co(acac)2 is likely to form a new complex with the co-initiator and the spin-trap molecules. The co-ordinated PBN competes with the two parent ligands of the complex for the liberated hydrogen atoms, however, due to favorable reaction rate the PBN-H adduct is formed preferably. The PBN adducts of carbon-centered radicals replace the PBN-H adduct when the monomers are added to the initiator solution, i.e. the H atoms are now preferably trapped by the monomer molecules.
    Additional Material: 14 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 197 (1996), S. 1055-1069 
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The propagation rate coefficient kp for the free-radical polymerization of 1,3-butadiene was determined as a function of temperature in the range of 30-60°C in bulk and as a function of the concentration of 1,3-butadiene in chlorobenzene at 50°C using a combination of a UV flash-lamp induced polymerization and a measurement of the molecular weight distribution of the produced polymer by size exclusion chromamgraphy. Differences of up to around 45% resulted even for the same concentrations and temperatures when these measurements were compared with recent determinations of kp of 1,3-butadiene in chlorobenzene in which just such an experimental setup was used. This finding was essentially attributed to large differences in the radical termination rates which prevailed in the reaction volumes under the current conditions of the pulse-induced polymerization experiments. Moreover, in the vicinity of bulk concentrations of 1,3-butadiene in chlorobenzene, kp apparently decreases with concentration.
    Additional Material: 6 Ill.
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