Minimum thermal stability temperature

MPDA M-phenylene diamine MTST minimum thermal stability temperature... 

Good heat transfer on the outside of the reactor tube is essential but not sufficient because the heat transfer is limited at low flow rates at the inside film coefficient in the reacting stream. The same holds between catalyst particles and the streaming fluid, as in the case between the fluid and inside tube wall. This is why these reactors frequently exhibit ignition-extinction phenomena and non-reproducibility of results. Laboratory research workers untrained in the field of reactor thermal stability usually observe that the rate is not a continuous function of the temperature, as the Arrhenius relationship predicts, but that a definite minimum temperature is required to start the reaction. This is not a property of the reaction but a characteristic of the given system consisting of a reaction and a particular reactor. 

In most of the studies discussed above, except for the meta-linked diamines, when the aromatic content (dianhydride and diamine chain extender), of the copolymers were increased above a certain level, the materials became insoluble and infusible 153, i79, lsi) solution to this problem with minimum sacrifice in the thermal properties of the products has been the synthesis of siloxane-amide-imides183). In this approach pyromellitic acid chloride has been utilized instead of PMDA or BTDA and the copolymers were synthesized in two steps. The first step, which involved the formation of (siloxane-amide-amic acid) intermediate was conducted at low temperatures (0-25 °C) in THF/DMAC solution. After purification of this intermediate thin films were cast on stainless steel or glass plates and imidization was obtained in high temperature ovens between 100 and 300 °C following a similar procedure that was discussed for siloxane-imide copolymers. Copolymers obtained showed good solubility in various polar solvents. DSC studies indicated the formation of two-phase morphologies. Thermogravimetric analysis showed that the thermal stability of these siloxane-amide-imide systems were comparable to those of siloxane-imide copolymers 183>. 

Some halo-substituted anilines are of limited thermal stability, tending to eliminate hydrogen halide which may catalyse further decomposition. To avoid decomposition during distillation, this should be conducted in the presence of solid alkali or magnesium oxide at minimum temperature (under relatively high vacuum) and/or with exclusion of air by inert gas. Individually indexed compounds are 4-Bromoaniline, 2296... 

The thermal stability of acidic OH groups in a-cages is shown in Figure 2. The curve for REY zeolite shows 2 characteristics—viz., a significant minimum in the curve at temperatures between 350° and 500°C, and the height of the second part of the curve is half that of the first part of the curve. All 3 REY zeolite samples (B, C, and D) showed these characteristics. 

Thermal Stability. Pyranyl foams are crosslinked aromatic polymers, and, therefore, their thermal stability is good in comparison with polyurethane foams. The maximum service temperature for low-density pyranyl foams is 135°C (275 F), but higher temperatures are possible for short periods. The minimum temperature to which the foam has been subjected is -78°C (-108 F) (1). 

It is also possible to use the data given in ref. 28 to calculate the monomer concentration at all P/Po-levels. In the present calculations, no corrections have been made for the particle size or the surface tension, due to the presence of emulsifier (1 g ammoniumlaurate per 1 H O). If the rate of dehydrochlorination is plotted against the concentration instead of P/PQ, Figure 3 is obtained. Compared to Figure 1, the 45°C series now becomes almost identical with the polymers at 55°C, except at the lowest monomer concentration. The relations between the rate of dehydrochlorination and polymerization temperature at constant monomer concentration will therefore show a plateau below 55 C, see Figure 4. A minimum is only indicated for monomer concentrations below about 10 g VC per 100 g PVC. At temperatures above 55°C, the thermal stability decreases with increasing polymerization temperature. 

Photochemical reactivity of drug formulations is an important aspect to consider during development, production, storage, and use of pharmaceutical preparations. However, photochemical stability of drug substances is rarely as well documented as thermal stability of the compounds. For instance, in order to obtain a high sterility assurance level of the product, a parenteral preparation is sterilized in its final container if possible. Steam sterilization at minimum temperature of 121°C for... 

At the mesopause, there is again an extreme temperature (a minimum) at a height of 85 km. The temperature above the equator ranges between 190 and 200 K, at intermediate geographic latitudes it is 170 to 210 K and at higher latitudes, 130 to 230 K (the higher and lower values correspond to the summer and winter, respectively) [9, 16]. The layer is thermally stabilized. 

Separations are possible in gas chromatography if the solutes differ in their vapor pressure and/or intensity of solute-stationary phase interactions. As a minimum requirement the sample, or some convenient derivative of it, must be thermally stable at the temperature required for vaporization. The fundamental limit for sample suitability is established by the thermal stability of the sample and system suitability by the thermal stability of column materials. In contemporary practice an upper temperature limit of about 400°C and a sample molecular weight less than 1000 is indicated, although higher temperatures have been used and higher molecular weight samples have been separated in a few instances. 

Another class of thermally stable materials with electroactivity are polyacene quinone radical (PAQR) polymers. The thermal stability of PAQR polymers was. studied up to 1200°C under helium. The electrical conductivity was found to go through a minimum at about 500"C, showing that the original synthetic structure of a PAQR polymer is unique and thermally sensitive and that the negative temperature dependence of e.c. makes it similar to degenerate semi-metals [237]. 

Since the heat of evaporation of acetic acid of -1-23.7 kJ/mol is low compared with the overall heat formed in the oxidation ( 1300kJ/mol for TA), it is clear that considerable amounts of acetic acid need to be evaporated in order to maintain thermal stability. The amount of acetic acid that can be evaporated is directly related to the vapor pressure in the effluent gas flow. Since the vapor pressure is only a function of temperature, the actual operation temperature in the oxidation reactor is determined by the temperature required to obtain the required vapor pressure for safe heat removal in the reactor. Though counterintuitive, it means that higher operation temperatures are typically safer to operate for this catalyst system. For the TA process, this leads to a minimum operation temperature of around 180 °C. Higher temperatures are even better from a heat integration perspective but yield more unwanted by-products and overoxidation to CO2. 

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