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Tetrafluoroethylene (TFE) is an industrial scale starting material e.g. for polymer production (PTFE, FEP). When ignited the chemically unstable TFE is capable to decompose in an explosive way. Explosion propagation through pipe systems of production plants have led to damage and fatalities within the last 7 decades.
Incident analyses identified compression heat a relevant source of ignition. Chemical plants consist of pipes, vessels, separating valves, strainers and other components. Before restarting the process after maintenance work different parts of the plant components could be filled with TFE, Nitrogen or Air at different initial pressures ranging from vacuum or atmospheric to TFE at operating pressure. Valve opening procedures may cause a temperature increase in the gas phase. Compression takes place at polytropic conditions. Heat losses cannot be neglected. Therefore the temperature development in the gas depends upon the surface-to-volume-ratio of the enclosure, geometrical influences, the state of gas flow, how fast the valve opens and the heat capacity of the gas being compressed.
In the present work initial test results from a 2.5” pipe will be compared with existing 1.1” pipe data. Geometrical effects will be briefly discussed as well as some first results concerning the influence of orifices are reported. Furthermore a method allowing for the identification of hazardous initial conditions is discussed.
The present contribution reports on specific aspects of safety engineering in heterogeneously catalysed oxidation reactions. Results for ethene-oxygen-mixtures in a continuous-flow micro reactor are reported related to the safety issues of the ethylene oxide process. Initial pressure is ranging from below 1 bar up to 10 bar at initial temperatures ranging from room temperature up to 673 K. Micro structured reactors offer an extended range of operating conditions. The key issue to be discussed in the present contribution is how to safely operate a micro reactor at conditions in conventional devices to be characterised as inside the explosion region. Within certain limits suppression of explosion inside a micro reactor can be achieved.
This holds true for chain reactions as well as runaway reactions. Nevertheless it is not possible to safely operate micro structured reactors at any condition. Therefore, explosion propagation through a Micro structured reactor and initiation of gas phase explosions by hot spots inside the reactor were investigated.
The investigation methods applied are subject to actual standardization.
Der vorliegende Beitrag behandelt spezifische Aspekte der Sicherheitstechnik bei heterogen katalysierten Oxidationsreaktionen. Ergebnisse von Explosionsuntersuchungen an Ethen-Sauerstoffgemischen in einem kontinuierlich betriebenen Mikroreaktor, die beispielsweise für den Ethylenoxidprozess relevant sind, werden vorgestellt. Der Anfangsdruck der untersuchten Eduktgemische lag zwischen 1000 hPa und 10000 hPa bei Anfangstemperaturen zwischen Umgebungstemperatur und einer Temperatur bis zu 673 K. Mikrostrukturierte Reaktoren bieten einen erweiterten Bereich von Betriebsbedingungen. Die Untersuchungen zielen auf den sicheren Betrieb eines Mikroreaktors bei Bedingungen, die bei konventionellen Reaktoren als innerhalb des Explosionsbereichs eingestuft werden, ab. In bestimmten Grenzen kann eine Unterdrückung von Explosionen in einem Mikroreaktor erreicht werden. Es ist jedoch nicht möglich, einen Mikroreaktor unter allen Bedingungen sicher zu betreiben. Aus diesen Gründen wurde die Explosionsausbreitung durch einen mikrostrukturierten Reaktor hindurch und die Zündung einer Gasphasenexplosion durch Hot-Spots in dem Reaktor untersucht. Die angewandten Untersuchungsmethoden sind Gegenstand aktueller Normungsaktivitäten.
Tetrafluoroethylene (TFE) is an industrial scale starting material e.g. for polymer production (PTFE, FEP). When ignited the chemically unstable TFE is capable of decomposing in an explosive way. Explosion propagation through pipe systems of production plants have led to damage and fatalities within the last seven decades.
Incident analyses identified compression heat a relevant source of ignition. Chemical plants consist of pipes, vessels, separating valves, strainers and other components. Before restarting the process after maintenance work, different parts of the plant components could be filled with TFE, nitrogen or air at different initial pressures ranging from vacuum or atmospheric to TFE at operating pressure. Valve opening procedures may cause a temperature increase in the gas phase. Compression takes place at polytropic conditions. Heat losses cannot be neglected. The temperature development in the gas depends upon the surface to volume ratio of the enclosure, geometrical influences, the state of gas flow, how fast the valve opens, and the heat capacity of the gas being compressed.
Laboratory scale tests (Meyer, 2009) revealed ignition of TFE/air due to compression heat. Tests in pipes of 28 mm inner diameter, i.e. already industrial scale, were performed by (Kluge et. al., 2016). In the present contribution initial test results from a 63 mm pipe will be compared with existing 28 mm pipe data. A description of the experimental setup as well as an explanation of the hazard diagram will be given.
Furthermore, a method allowing for the identification of hazardous conditions will be discussed.
Although catalytic reductions, cross-couplings, metathesis, and oxidation of C=C double bonds are well established, the corresponding catalytic hydroxylations of C–H bonds in alkanes, arenes, or benzylic (allylic) positions, particularly with O2, the cheapest, 'greenest', and most abundant oxidant, are severely lacking. Certainly, some promising examples in homogenous and heterogenous catalysis exist, as well as enzymes that can perform catalytic aerobic oxidations on various substrates, but these have never achieved an industrial-scale, owing to a low space-time-yield and poor stability. This review illustrates recent advances in aerobic oxidation catalysis by discussing selected examples, and aims to stimulate further exciting work in this area. Theoretical work on catalyst precursors, resting states, and elementary steps, as well as model reactions complemented by spectroscopic studies provide detailed insight into the molecular mechanisms of oxidation catalyses and pave the way for preparative applications. However, O2 also poses a safety hazard, especially when used for large scale reactions, therefore sophisticated methodologies have been developed to minimize these risks and to allow convenient transfer onto industrial scale.