Filtern
Dokumenttyp
Sprache
- Englisch (6) (entfernen)
Referierte Publikation
- ja (6) (entfernen)
Schlagworte
- Organic peroxide (6) (entfernen)
Organisationseinheit der BAM
Fireballs of liquid organic peroxides differ from those of liquid hydrocarbon fuels. Modified equations for predicting the fireball diameter, height, surface emissive power and the duration in dependence of the fuel mass are presented for di-tert-butyl peroxide. They base on 13 steel drum tests with fuel masses from 10 kg to 168 kg. Moreover, computational fluid dynamics simulations are performed using the laminar flamelet approach and a statistically turbulence treatment. Fireballs involving peroxide from 10 kg to 80 kg were simulated and their properties compared to the experimentally developed models. The deviations of each property are partially compensating each other leading to an adequate prediction of thermal safety distances for both, a time-independent and a time-averaged treatment. Simulations prove to be a good tool for predicting thermal radiation hazards of fireball scenarios.
The thermal radiation impact of organic peroxide fireballs is experimentally assessed using an infrared camera. Fireballs are generated while liquid peroxide filled steel drums are subjected to gas burner fire at different heating rates. Three large burning clouds are observed with varying flame characteristics. Thermal radiation properties are assessed by infrared images with the presented methods. Despite of the two-dimensional temperature fields, the flames are treated and characterized as three-dimensional objects. Fireball diameters and heights are calculated based on a representing radiating sphere with the same cloud volume. By the use of the solid flame model and assumptions for emissivity and transmissivity, heat fluxes and thermal radiation doses against distance are predicted. Thermal safety distances are presented based on the maximum irradiance and the allowed exposure time. The validation of the maximum and time-dependent radiation fields is achieved through heat flux sensors in varying distances to the fireball. The results prove the use of an infrared camera and a volume based size calculation to fully assess the thermal radiation hazards of fireballs.
Organic peroxides are capable to form fireballs with explosive violence. Only fireball models for liquid hydrocarbon fuels are available for the assessment of the thermal radiation properties. Because the development of such fireballs usually differ from those of organic peroxides the properties need to be characterized by modified equations. In this study liquid organic peroxide fireballs from 16 kg to 155 kg substance masses are characterized and compared to selected existing correlations. Flame characteristics and irradiances are measured with infrared cameras and heat flux sensors. All fireballs are consequences of simulated worst case scenarios where filled steel drums are engulfed by fire with varying heat impact. The differences of the given semi-empirical equations and the presented experimental work are explained. A new model is proposed for organic peroxide fireballs by modifying the constants of the known equations. The thermal radiation impact and safety distances are calculated and compared.
Organic peroxides are known for their decomposition behaviour and for considerable heat release connected with pressure build up. Efforts are required to run the industrial synthesis in semi-batch mode on safe condition. With the aim to use advantages as good heat transfer and small hold up, the synthesis of a peroxycarboxylic ester, namely tert-Butyl peroxy-2-ethylhexanoate (TBPEH), was transformed into continuous mode using a tube reactor with inner dimension of 1 mm. An appraisal of the critical diameter of the tube was done in advance. The use of an ultrasonic device allowed for specific reaction parameters a nearly complete conversion of the educts.
For the industrial production of chemicals a safe process design is required to avoid harm to people and
environment. It becomes tremendous important if one or more of the following points are characteristic for
the synthesis: high heat release, explosive atmosphere, presence of toxic and/or of thermal unstable substances.
One substance group, known for being unstable, is the group of organic peroxides. They are potential
high energetic substances. Many syntheses of organic peroxides are carried out in semi-batch
mode to control the heat release in a good manner. With the aim to increase process control, the advantages
of continuous reaction mode, combined with micro reaction technology, are used for the synthesis
of one specific organic peroxide in this work.
This approach is not only characterised by shorter residence time, good heat transfer, but also by smaller
quantities of managed chemicals, and, therefore, by a lower hazard potential. Often yield and selectivity
can be improved additionally.
For the study a peroxyester, namely tert-Butyl peroxy-2-ethylhexanoate (TBPEH), with known thermal
hazard potential was chosen. The two phase liquid/liquid reaction was carried out in three types of reactors.
A small scale tubular reactor, stressed by ultrasound, and two different micro structured reactors were
used. One of them had a meandering and the other a split-and-recombine channel structure. Synthesis
temperature was also varied.
From preliminary studies it was known that the side reaction of the involved carboxylic acid chloride to the
corresponding acid can become more important in continuous mode compared to semi-batch mode. The
effect of reactor type and temperature on selectivity and therefore yield of TBPEH was analysed and compared.
In result the reaction could be carried out in a safe manner. The high heat-exchanging efficiency of the
used reactors and the short residence time allowed synthesis temperature near the onset temperature of
decomposition of TBPEH. In relation to the results of the capillary tube and of the reactor with meandering
channel structure (MR), the results for the split-and-recombine reactor (SAR) showed the best trend line.
Further studies have to underline the result. Compared to the traditional reaction path (the semi-batch
mode), a higher space time yield could be achieved. This promising information is accompanied by the fact
of low reaction volumes. In consequence the productivity is low without a numbering up of reaction channels
or a scaling up of it. The nowadays existing philosophy of producing a specific quantity of product by a
company, followed by the transport to the costumer may change. Just organic peroxides, used in small
quantities, e.g. as initiators for polymerisation processes or as resin hardeners, provide the opportunity for
an on-demand-production.
Exothermic reactions involving organic peroxides carry a high potential hazard and must be considered with care. A safe handling requires, among others, the assessment of thermal process safety, for which safety characteristics like overall heat production and the resulting adiabatic temperature rise are essential. The article presents the results of the calorimetric investigation of the synthesis of four peroxycarboxylic esters, three tert-Butyl and one tert-Amyl peroxycarboxylic ester. In the two-step synthesis the second one clearly shows the higher exothermic potential. The overall heat production lies in the range of 126135 kJ/mol and is nearly independent of the carboxylic acid residual in the tert-Butyl peroxycarboxylic ester. The calculated adiabatic temperature rise is 7080 K. Influence of temperature and feed rate on the heat generation is discussed for one species. A grading of the synthesis with respect to temperature levels according to the criticality classes by Stoessel leads to the most critical for an exothermic reaction.