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  • 1
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 54 (1989), S. 253-254 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0887-624X
    Keywords: acrylic acid ; phenothiazine ; p-methoxyphenol ; inhibition, mechanism of ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Inhibition of acrylic acid by p-methoxyphenol fits a conventional stoichiometric mechanism but phenothiazine inhibits acrylic acid via a completely different, catalytic cycle which does not depend on the presence of oxygen. We propose that this mechanism may involve a pair of single electron transfer reactions between free radicals, phenothiazine N-radicalcation, and phenothiazine itself, the latter being cyclically regenerated. Arrhenius equations were derived for the rates of disappearance of inhibitor and oxygen in acrylic acid stabilized with phenothiazine and with p-methoxyphenol and also with phenothiazine in the absence of oxygen. The practical implication of high oxygen to p-methoxyphenol consumption ratios is quite important: if commercial acrylic acid (usually stabilized with p-methoxyphenol) is inadvertently heated during storage, the limiting substance determining the onset of polymerization will be the dissolved oxygen and not p-methoxyphenol unless oxygen (air) is being supplied to and dissolved in the liquid at a rate sufficient to overcome the rate of its consumption.
    Additional Material: 2 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 12 (1993), S. 111-114 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The most common cause for runaway polymerizations of glacial acrylic acid (AA) is overheating of the material due to mechanical failure, human error, or nearby fire. Under such circumstances, dissolved oxygen (D.O) is consumed more rapidly than the AA stabilizer, p-methoxyphenol (MEHQ), and “oxygen stravation” is the immediate cause of polymerization onset. From the known kinetics of oxygen disappearance, it is possible to calculate D.O. concentrations during a heatup period and to predict the time remaining until that concentration becomes unacceptably low. This information provides guidance for the timely activation of an emergency response shortstop inhibitor injection system so that there is enough time for adequate mixing of the inhibitor, phenothiazine (PTZ), to prevent or mitigate the polymerization.
    Additional Material: 4 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 60 (1996), S. 2481-2487 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The lengths of polymerization induction periods for butyl acrylate (BA) in the presence of air were measured at temperatures from 54 to 122.5°C. The kinetics of MEHQ and oxygen consumption at 80 and 100°C are characterized by their own induction periods followed by sharply accelerated rates immediately prior to the BA polymerization. It is proposed that these phenomena are consistent with an “intrinsic” BA radical formation rate that is extremely slow compared to the ultimate rate of radical production from the decomposition of peroxides. These oligomeric peroxides build up during the induction period and, at its end, rapidly decompose with a resulting “radical cascade effect,” causing the accelerated inhibitor and oxygen consumption followed rapidly by BA polymerization. Thus, confirmation that a supply of BA has a normal MEHQ concentration may not be sufficient to ensure its stability. Strict adherence to the storage conditions and shelf life recommended by the supplier6 is absolutely vital to storage safety, especially because uncontrolled poly-merization of BA has the potential to be violent (polymerization exotherm rates higher than 1000°C/min were observed). © 1996 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Process Safety Progress 12 (1993), S. 47-48 
    ISSN: 1066-8527
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Vinyl acetate monomer and acrylic acid and its esters are stabilized with phenolic polymerization inhibitors. Oxygen is needed for these stabilizers to work effectively in acrylic monomers, but is not necessary for vinyl acetate monomer, and actually destabilizes it at elevated temperatures.
    Additional Material: 1 Tab.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Plant/Operations Progress 8 (1989), S. 105-108 
    ISSN: 0278-4513
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The details of an unscheduled polymerization of acrylic acid initiated by indirect heating have been characterized by in-depth analysis of the polymer, kinetic and thermodynamic calculations, and heat and material balances on the system. The data fit together to give a consistent picture of the polymerization scenario. The fact that the acrylic acid polymerization was not violent was primarily due to the presence of about 10 ppm phenothiazine, which delayed the onset of free radical polymerization until about 2 to 3 hours after the monomer had reached its boiling point. Since much of the acrylic acid was converted to dimer during this induction period, the ultimate energy release was greatly limited. Other moderating factors were a relatively slow heatup of the tank contents in the external heat exchange recycle loop, free vapor venting, and the incursion of fire monitor water into the tank.
    Additional Material: 4 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The major features of polymerization induction periods for acrylic acid inhibited with phenothiazine and p-methoxyphenol have been characterized at 100°C, including duration of the induction periods, and rates of inhibitor disappearance, molecular oxygen absorption, and peroxide formation. Surprisingly, thermally produced radicals react more rapidly with phenothiazine than with oxygen since there is no detectable oxygen absorption or peroxide for mation during phenothiazine-induced induction periods. Thus, phenothiazine has been used to estimate the thermal rate of radical formation. Phenothiazine's effectiveness as an inhibitor is not directly affected by oxygen, although it does undergo oxygen-promoted, noninhibition-related side reactions. p-Methoxyphenol, on the other hand, depends entirely on the presence of oxygen to function as an inhibitor. Compared with equivalent concentrations of p-methoxyphenol, induction periods obtained with phenothiazine are very long, and the rate of inhibitor disappearance is slower by at least an order of magnitude. The characteristics of p-methoxyphenol inhibition reflect a greater radical flux deriving from the significant rates of oligomeric peroxide formation and decomposition which we measured during p-methoxyphenol-induced induction periods at 100°C. MEHQ is an effective inhibitor at ambient temperatures in part because of the greater stability of the peroxides at these lower temperatures.
    Additional Material: 5 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Plant/Operations Progress 6 (1987), S. 188-189 
    ISSN: 0278-4513
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Polymerization inhibitors are used in the processing and storage of acrylic acid. Depending upon the inhibitor and the conditions, it is sometimes imperative that oxygen be present for inhibitor “activation.”
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0449-296X
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A group of substituted phenols, quinone, and tropone were used to retard AIBN-initiated ethyl acrylate polymerization in ethyl propionate solution at 44.7°C. in the absence of oxygen. It was concluded that the efficiency of retardation depended upon the ability of the terminator to stabilize a positive charge on its reaction site in the transition state. Tropone was found to be a particularly good retarder. The radical-trapping efficiency of 2,2-diphenyl-1-picrylhydrazyl in this system was found to be 50-60%.
    Additional Material: 1 Ill.
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