Programmed-temperature heating

Table II. Peak temperature of sulfur containing model compounds during programmed temperature heating (25 C/min from 250 to 875 C)...

The techniques referred to above (Sects. 1—3) may be operated for a sample heated in a constant temperature environment or under conditions of programmed temperature change. Very similar equipment can often be used differences normally reside in the temperature control of the reactant cell. Non-isothermal measurements of mass loss are termed thermogravimetry (TG), absorption or evolution of heat is differential scanning calorimetry (DSC), and measurement of the temperature difference between the sample and an inert reference substance is termed differential thermal analysis (DTA). These techniques can be used singly [33,76,174] or in combination and may include provision for EGA. Applications of non-isothermal measurements have ranged from the rapid qualitative estimation of reaction temperature to the quantitative determination of kinetic parameters [175—177]. The evaluation of kinetic parameters from non-isothermal data is dealt with in detail in Chap. 3.6. 

Programmed- temperature split Liquid sample from syringe into cold inlet heat programming vaporises sample. Small fraction to column Concentrated samples thermally labile Broad, some focusing required 0.1-2 0.01-10... 

There are two basic approaches to direct mass-spectral analysis of volatile additives, namely constant-temperature heating and temperature-programmed heating (sometimes called thermolysis-mass spectrometry,... 

For capillary GC, the split/splitless inlet is by far the most common and provides an excellent injection device for most routine applications. For specialized applications, there are several additional inlets available. These include programmed temperature vaporization (PTV) cool on-column and, for packed columns, direct injection. PTV is essentially a split/splitless inlet that has low thermal mass and a heater allowing rapid heating and cooling. Cool injection, which can be performed in both split and splitless mode with the PTV inlet, reduces the possibility of sample degradation in the inlet. Capabilities of the commonly available inlets are summarized in Table 14.3. 

Figure 12.4 Scheme of an ideal DSC curve for the study of an endothermic process by the dynamic method. Also shown are the programmed temperature (fp) line and the zero line. The zero line is obtained in a separate experiment, where the sample and the reference crucibles are empty and the heating program used in the main experiment is maintained. 

MECHMOD A utility program written by Turanyi, T. (Eotvos University, Budapest, Hungary) that manipulates reaction mechanisms to convert rate parameters from one unit to another, to calculate reverse rate parameters from the forward rate constant parameters and thermodynamic data, or to systematically eliminate select species from the mechanism. Thermodynamic data can be printed at the beginning of the mechanism, and the room-temperature heat of formation and entropy data may be modified in the NASA polynomials. MECHMOD requires the usage of either CHEMK1N-TT or CHEMKIN-III software. Details of the software may be obtained at either of two websites http //www.chem.leeds.ac.uk/Combustion/Combustion.html or http //garfield. chem.elte.hu/Combustion/Combustion. html. 

Inside the column oven, the solvent flows through 0.75 m of 0.009 in. I.D. conditioning coil, through a low dead-volume tee containing a thermocouple to monitor solvent temperature, and then to the column. The column oven, with a 425 0 maximum temperature, is heated by two 2-kilowatt wire wound heaters which are controlled with a Gulton Model 2GB Controller which provides either Isothermal or programmed temperature control. 

A thermochemical method that simultaneously measures differences in heat flow into a test substance and a reference substance (whose thermochemical properties are already well characterized) as both are subjected to programmed temperature ramping of the otherwise thermally isolated sample holder. The advantage of differential scanning calorimetry is a kinetic technique that allows one to record differences in heat absorption directly rather than measuring the total heat evolved/... 

The French CEA cooperates with the US DOE under the GEN IV umbrella to develop a thermochemical (iodine-sulphur process) cycle to produce clean Hj from heat from nuclear plants. The US also has a US 6.5 million nuclear energy program to convert hydrogen from high temperature heat nuclear sources (and solar) with a projected cost competitive with gasoline. 

I. Chromathermography. The term coined by Zhukhovitskii et al(Ref 41) for a chromatographic analysis in which a stream of air is applied while the firnace(which heats consecutive sections of the adsorbing column, and causes desorption) is moved down the column. The air stream thus distributes the components at different spots of the temperature field, and keeps them separated. The method, first proposed in 1951, was discontinuous(Ref 41 45), but later(Ref 46), the continuous modification, called "thermal dynamic method was devised (Compare with "programmed temperature gas chromatography listed unde r item D)... 

Figure 27.5 TG-MS data for a trace for a Mo2C1.0>, catalyst. The solid line corresponds to the weight loss, the dotted line to the temperature program used (heating rate 1 Ks 1). He gas mixed with 50% hydrogen was used as carrier gases, (a) H2 He (1 1) (b) H20 (c) CO ...

The chemical equilibrium program is used in the adiabatic mode to calculate temperatures, heats and (crude) pressures for decomposition and oxidation. Stull (Chemical Engineering Progress, Loss Prevention, Vol. 4, p. 16, 1970) showed that these parameters are rough measures of potential reactive hazard. 

Our first task in applying any of these rigorous tray-to-tray programs is to select logical, yet accurate specifications. This is the hit line of why you must first run a shortcut fractionation method. Why You need and must input accurate specifications such as top and bottom temperatures, heat duties, number of trays, reflux rate, and other such data. These rigorous programs simply will not converge until you input these mandatory and accurate specifications. All of this specification data is derived in the shortcut fractionation method Hdist. 

Harris and Habgood, in their standard work on programmed temperature GC [605] have shown that the retention time of a component under programmed temperature conditions is a function of the retention behaviour of the solute under isothermal conditions and the programming rate. The latter they defined as the heating rate (rT ... 

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