Isothermal-temperature ramp experiment

Fig. 13. Evaluation of kinetic parameters for the DOC model—NO oxidation (reaction R5 in Table II). Comparison of measured and simulated outlet NOx concentrations in the course of temperature ramp (2K/min) for two different space velocities (SV= 50,000 and 100,000 h-1). Lab experiment with isothermal monolith sample using synthetic gas mixture (100 ppm CO, 100 ppm C3H6, 500ppm NO, 8% 02, 8% C02, 8% H20, N2 balance).

At higher temperatures a significant amount of reaction may occur during the initial temperature ramp before approximate isothermal equilibrium has been attained. Some degree of correction for this is possible 16,17) by re-running the experiment on the reacted sample, under the same conditions, to obtain an estimate of the true baseline, as illustrated in Fig. 4. 

Radex Safety Calorimeter. The Radex calorimeter is a modular instrument that can simultaneously evaluate six different samples (size range 0.5 to 5 ml), or one substance under a variety of conditions. Each module is a separate entity with its own calibrated oven capable of being operated under an open, closed, or pressurized condition, with all temperature differences between the sample and the oven being stored in a microprocessor for further analysis. The Radex calorimeter is very versatile samples can be tested in either an isothermal or ramp mode. In the isothermal mode, each oven is heated to a preset temperature and held at that temperature throughout the experiment. In the ramp mode of operation, the oven is heated linearly to a preset temperature, or can be maintained at a given temperature for a predetermined time. The flexibility of oven function in the Radex calorimeter enables the user to determine the intrinsic stability of a chemical and to also compare the impact of such parameters as temperature, atmosphere, and impurities on the stability of a given substance. 

In this the way the effect of the rate of temperature ramping may be taken into account in the total cure profile. In such studies the empirical E data may be adequate, but for detailed kinetic modelling it is generally recognized that isothermal experiments are appropriate, and even they may have limitations, as discussed later. 

Isothermal NOx adsorption capacities were measured using varying amounts of NO as a feed in background gas [10% O2,10% H2O, 50 vppm SO2 and balance N2]. The space velocity was 25,000 h and measurements were taken over a variety of temperatures. Alternatively, the NOx adsorption capacity properties of the trap were measured in a temperature programmed experiment where NOx was passed over the trap as the temperature was ramped at 10 C min. ... 

Similar experiments, beginning with a partially covered surface, can be made to yield rates of adsorption, desorption and the equilibrium isotherms, all in one experiment. Such an all-embracing experiment starts with the adsorbent swept by a stream of inert containing enough adsorbate to cover say, half the sites at the initial temperature. At t=0 the flow is switched to a more concentrated stream of adsorbate and temperature ramping is initiated. 

The catalytic activity in decomposition of H2O-HAN (79 wt-%) mixture was followed by DTA-TGA to determine the onset of the decomposition and by means of a constant volume batch reactor using increase temperature mode or isothermal mode at 90 °C. The same catalyst to propellant ratio was used lOpL propellant and 16 mg catalyst for thermal analysis, 100 pL propellant and 160 mg catalyst for batch reactor experiments the temperature ramp was 10... 

In addition to these particular features of the soot combustion reactions, the reaction rate also depends on general variables, such as temperature for isothermal reactions and heating rate for ramp experiments, nature and partial pressure of gases in the stream, space velocity/residence time of gases in the solid bed, soot-to-catalyst ratio, and so on. 

In common with most thermal analysis techniques, DMA analyses can be performed under both ramped and isothermal temperature programmes. The outputs from an experiment are elastic (storage) modulus and viscous (loss) modulus, and tan 8, which is the ratio of viscous modulus over the elastic modulus. 

Although TPD is a versatile and useful technique widely available within the surface-science community, it does have some limitations. For one, because the experiments are carried out under vacuum, they can only probe irreversible reactions no readsorption of the desorbing products is possible. In addition, as the temperature is ramped during detection, the surface temperature and the reaction rates become coupled in a way difficult to separate or control. Of particular importance here is the fact that as the reactions proceed and the products desorb, the surface coverages decrease, so the rates at higher temperatures correspond to the new lower surface concentrations. In order to overcome this problem, isothermal kinetic experiments have been carried out using molecular beams [22,23],... 

In a parallel experiment, the extent of the reaction a is measured using the partial heat to a particular time divided by the total heat of the isotherm plus the residual heat of a subsequent 10°/min ramp. Figures 5 and 6 show the observed relationship of In a and In t to a. As expected for a similar degree of advancement a, the ionic mobility a increases with temperature. Similarly for the same value of a, the dipolar mobility increases. An increase in dipolar mobility corresponds to a shorter relaxation time. Thus t decreases as temperature increases. Somewhat unexpected, both In a and In t exhibit a nearly linear dependence on a. Curvature in the In a and In t versus a plot is most pronounced for small values of a and at the highest temperature. There is no evidence of a break in the In <7 or In T dependence on a which would indicate gel. 

The Transformation of Cubic ice to Hexagonal Ice. In this set of experiments the transformation of the cubic fraction of the frozen pure water droplets was investigated as a function of annealing time at several different temperatures between 228 and 263 K. Emulsified droplets of Jvm 10 pm were cooled at a rate of 10 K min to 223 K, and then the temperature was rapidly ramped to the isothermal transformation temperature (Ttrans)-While the frozen droplets were held at Ttrans 0.2 K, the diffraction pattern between 20 = 39.3° to 44.3° was monitored. This covers the exclusive ice Ih reflection at 26 43.5° and the reflection common to both ice Ic and ice h at 20 40°. 

If the set of runs in a TS-BR experiment is appropriately spaced and sufficiently dense, triplets of conversion-rate-temperature can be obtained for any point within the enveloping curves on Figure 5.2. Conversion is obtained from interpolations on Figure 5.1 rates are obtained from slopes or numerical differentials of the same data. The corresponding temperatures are obtained for the ramping rate and clock time from Figure 5.3. An unlimited number of such triplets can be generated and sub-sets of isothermal or other constrained data can be selected, or sieved out, from this overall set for specific purposes. 

Output temperatures during the TS-PFR experiment on the oxidation of carbon monoxide. Due to the configuration of the reactor it was possible to maintain almost isothermal conditions during each ramping. Output temperatures deviatedfrom the ramp temperature only at high conversions, where the heat of reaction could not be fully removed from the reactor. 

Figure 9 The calorimetric response for vapour sorption of an amorphous drug substance with a glass transition temperature of about 95 °C. The experiment was performed in an isothermal microcalorimeter coupled with a vapour perfusion device at 25°C. A linear RH ramp was imposed at 5% RH h. The resulting signal shows initial moisture adsorption, recrystallisation and subsequent moisture desorption...

Because of their simple construction and operation, furnace pyrolyzers are frequently inexpensive and relatively easy to use. Since they are operated isothermally, there are no controls for heating ramp rate or pyrolysis time. The analyst simply sets the desired temperature and, when the furnace is at equilibrium, inserts the sample. Although this simplicity may lose its attractiveness as soon as the analyst requires control over heating rate or time, there are some experiments and sample types that capitalize on the design of a furnace. Liquid, especially gaseous samples, are pyro-lyzed much more easily in a furnace than by a filament-type pyrolyzer. Because filament pyrolyzers depend on applying a cold sample to the filament and then... 

Ramped DSC experiments were carried out on samples taken after the first heat-up phase, at the end of the Dewar experiment, and at the end of the isothermal heat flow calorimetry experiment. Similar results were obtained in all cases — that is, a strong exothermic peak with a heat release of around 1140 J and an onset temperature of around 160°C. It can be seen that the shape of the curves obtained (Figure A2.5) as well as the heat released and onset temperature are nearly identical to that obtained from the DSC experiment on the mixture of reactants (Figure A2.2, page 198). Thus the exothermic peak from the mixture of reactants is not due to the process reaction, as originally postulated, but is caused by the decomposition of the reaction product. This was further confirmed when a DSC experiment was eventually carried out on a sample of the product taken during pilot plant manufacture. 

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