Temperature-programming profiles, types

Fig. 3.8 (a) Desorbed hydrogen (wt%) from the NaAlH milled for 5 h as a function of heating time while heating to 225, 300, 400 and 425°C. Quasi-Temperature Programmed Desorption (TPD) carried out in a Sieverts-type apparatus, (b) Temperature profile change as a function of time while heating to 225, 300 and 400°C in a Sieverts apparatus... 

The temperature programmed desorption profile for the adsorption of butadiene in place of cis-2-butene is shown in Fig. 1, curve c. Two sets of products are observed. The product below 210°C is unreacted butadiene, and the products above 210°C are carbon dioxide and water. The similarity in the evolution of the combustion products of butene and butadiene is an indication that their combustion proceeds via similar reaction mechanisms. The similarity in the desorption of butadiene suggests that in butene adsorption, butadiene desorption is desorption limited. Indeed, that both butene and butadiene adsorb on the same type of sites has been confirmed by sequential adsorption experiments. The results are shown in Table III. It was found that if the C4 hydrocarbons are adsorbed sequentially without thermal desorption between adsorptions, the amounts of the final desorption products are the same as those in experiments where only the first hydrocarbon... 

On MgO surfaces the presence of three different basic sites has been indicated from profiles of CO2 temperature programmed desorption [57]. The distribution of these basic sites depends on the thermal treatment of MgO. Moreover, from FTIR studies, four types of basic site are proposed for MgO (1) Mg-OH and three types of sites located at (2) edges, (3) vertices, and (4) pits on the MgO surface [58]. 

In principle, any type of magnetic or quadrupole mass spectrometer can be utilized for the analytical pyrolysis of organic materials, if a direct introduction system capable of producing a desired tempera-ture/time profile is available. For example, direct insertion probes (DIPs) and direct exposure probes (DEPs) are Avidely used for sample introduction and such probes are supplied with control units that allow heating and temperature programming of the sample up to 500-800°C. Therefore, such modules should be considered as the most readily available probes for Py-MS studies. 

Davidson [10] analysed a range of commercial PMMA copolymers by linear temperature programmed Py-EGA-IR to determine whether the evolution profiles of various pyrolysis gases against temperature were sufficiently distinctive to allow reliable identification of different types, and to distinguish between different batches of the same type. The results show that, with one exception, the different types and batches can be reliably identified, and reactions to account for some of the compounds evolved were presented. The potential value of Py-EGA-IR analysis of PMMA polymers for both production control and research is demonstrated. 

Using the values of Caq = 0.1 mol/1, Aj, Aj, Ej, and Ej as given in Type 1 reaetion, it is possible to solve Equation 6-146 with Equations 6-127 and 6-128 simultaneously for the temperature range of 260-400 K. A eomputer program was developed to determine the fraetional eonversion for different values of (-i a) over the temperature range of 260-400 K. Eigure 6-29 shows the reaetion profile of the eomputer results. 

Using the same values of the kinetic parameters as in Type 3, with CAO = 1 mol/1 and solving Equations 6-165, 6-127, and 6-128 simultaneously, it is possible to determine the fractional conversion XA. A computer program was developed to determine the fractional conversion for different values of (-rA) and a temperature range of 260-500 K. Figure 6-31 illustrates the reaction profile. 

The true temperature of a sample heated using a filament pyrolyzer can be quite different from the above profile temperature, significantly lower temperatures being recorded inside the samples [4]. In order to obtain a correct Teq, modern equipment uses a feedback controlled temperature system (see e g. [5] for a more detailed description of this type of pyrolyzer). Several other procedures for a precise temperature control of the filament are available, such as the use of optical pyrometry or thermocouples [6, 7], Special pyrolysis systems that allow programmed heated rates at different time intervals also are available [8]. 

The results of the test program, in terms of liquid-temperature data, are presented in Table I. A confidence level of approximately 0.1 R was established for these temperatures. Figure 4 presents a typical liquid-hydrogen temperature profile taken from one of the stratification tests. From the figure, it appears that the same type of stratification appearing in the NASA tests with combined heating is also present. Further, it is seen that the thermal layer has the same asymptotic behavior. 

---