Pulse-mode pyrolysis

Pulse-Mode Pyrolysis. Sample is in direct contact with a hot wire, thus minimizing secondary reactions. Although the temperature profile is reproducible, the exact pyrolysis temperature cannot be measured. Another disadvantage is that the sample weight cannot be known accurately. This is also known as Curie point pyrolysis. 

Levy, R.L., Fanter, D.L. and Wolf, C.L. (1972) Temperature rise time and true pyrolysis temperature in pulse mode pyrolysis gas chromatography . Anal. Chem., 44, 1, 38-42. 

Phenol-formaldehyde resins Pulsed mode pyrolysis - Phenol, methyl-substituted phenols Cleavage of phenol-methylene bond and subsequent hydrogen abstraction [85]... 

Pulse-mode pyrolyzers include resistively-heated electrical filaments or ribbons and radio frequency induction-heated wires [841,842,846,848,849]. The filament or ribbon-type pyrolyzers are simple to construct. Figure 8.45, and typically consist of an inert wire or ribbon (Pt or Pt-Rh alloy) connected to a high-current power supply. Samples soluble in a volatile solvent are applied to the fileutent as a thin film. Insoluble materials are placed in a crucible or quartz tube, heated by a basket-lilce shaped or helical wound filiunent. The coated filament is contained within a low dead volume chamber through which the carrier gas flows, sweeping the pyrolysis products onto the column. The surface temperatui of the filament is raised rapidly from ambient temperature to He equilibrium pyrolysis temperature. This... 

Pyrolysis may be performed using continuous-mode or pulse-mode instruments. In the first instance, the material must be introduced rapidly into the furnace at a predetermined temperature, which is maintained throughout the pyrolysis. Common modem pulse-mode instruments allow very rapid sample heating within a specified time. There are three different types of pulse-mode pyrolyzers ... 

There are several procedures to perform pyrolysis flash pyrolysis (pulse mode), slow gradient heating pyrolysis (continuous mode), step pyrolysis, etc. Commonly, the pyrolysis for analytical purposes is done in pulse mode. This consists of a very rapid heating of the sample from ambient temperature, targeting isothermal conditions at a temperature where the sample is completely pyrolysed. Controlled slow temperature gradients are also possible in pyrolysis, but their use in analytical pyrolysis is limited. Step pyrolysis heats the sample rapidly but in steps, each step following a plateau of constant temperature kept for a limited time period. 

PGC can be classified into two distinct types, depending on the method in which heat is applied to the sample static-mode (furnace) reactors and dynamic (filament, pulse-mode) reactors. Furnace-type pyrolysis systems are seldom used in forensic laboratories. The most common pyrolysis systems used are the Curie... 

In this type of system a resistively heated platinum or nichrome wire coil or ribbon is used to rapidly heat the sample. The wire is continuously swept with carrier gas, whereupon the pyrolysis vapors are transported into the chromatographic column. Heating times are relatively large (up to 20 s) for this system, which may lead to nonrepeatable pyrograms and secondary reactions. The pyrolysis conditions, sample size, and location must be carefully controlled to obtain repeatable data. Two possible heating modes are available for this system pulse mode or programmed mode. For most forensic applications the pulse mode has been used. 

Continuous or pulse mode (flash pyrolysis) step mode (temperature-programmed pyrolysis)... 

Pyrolysers can be divided into two main categories on the basis of their mode of operation, i.e. the continuous type, where the sample is supplied to a furnace preheated to the final temperature, and pulse mode reactors in which the sample is introduced into a cold furnace which is then heated to the final pyrolysis temperature. In the analytical pyrolysis of solid and some liquid materials mainly pulse mode pyrolysers are used and the following sections will focus on a few of the most popular pyrolysis techniques utilizing this mode of operation. However, for pyrolytic studies of liquid and gaseous samples continuous pyrolysers are applied. 

Infrared spectra of polymers are also obtained in a rapid screening mode by pulse pyrolysis-FTIR using solid samples (ca. 0.1-0.5 mg) that are placed "as is" into the Pyroprobe-Pyroscan-FTIR system for semi-quantitative, qualitative information. The vapor phase IR spectrum in Figure 3a is that from a pulse pyrolysis (750 C for 10 sec) of a 100 mg sample of solid poly(styrene). The thermal decomposition of poly(styrene) to its slyrene... 

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