Filament pyrolyser

Figure 11.2 Py/silylation GC/MS chromatograms of aged linseed oil pyrolysed in the pre sence of HMDS, (a) Pyrogram obtained with a microfurnace pyrolyser pyrolysis temperature 600 °C furnace pressure 14 psi purge flow 0.5 ml min (b) Pyrogram obtained with a resistively heated filament pyrolyser pyrolyser interface I80°C transfer line 300°C valve oven 290°C. 1, Hexenoic acid, trimethylsilyl ester 2, hexanoic acid, trimethylsilyl ester 3, heptenoic acid, trimethylsilyl ester 4, heptanoic acid, trimethylsilyl ester 5, octenoic acid, trimethylsilyl ester 6, octanoic acid, trimethylsilyl ester 7, nonenoic acid, trimethylsilyl ester 8, nonanoic acid, trimethylsilyl ester 9, decanoic acid, trimethylsilyl ester 10, lauric acid, trimethylsilyl ester 11, suberic acid, trimethylsilyl diester 12, azelaic acid, trimethylsilyl diester 13, myristic acid, trimethylsilyl ester 14, sebacic acid, trimethylsilyl diester 15, palmitic acid, trimethylsilyl ester 16, stearic acid, trimethylsilyl ester...

Figure 11.3 Chromatograms of linseed oil mature films some of which contain pigments, obtained after (a) pyrolysis/methylation and (b) pyrolysis/silylation, at 600°C with a resistively heated filament pyrolyser. Reprinted from j. Anal. Appl. Pyrol., 74, Chiavari et at., 6, Copyright 2005 with permission from Elsevier...

Figure 11.4 Chromatogram relative to a mature linseed oil paint sample containing a high amount of sulfates, obtained by pyrolysis/silylation with a resistively heated filament pyrolyser at 600° C...

Figure 11.8 THM GC trace of bleached beeswax. FAME, fatty acid methyl ester obtained with a resistively heated filament pyrolyser at 550°C MeO FAME, methyl ester of methoxy fatty acid ME, alkyl methyl ether DiME, dimethoxyalkane EtC, hydrocarbon X Y, carbon chain length number of double bonds. Reprinted from J. Anal. Appl. Pyrol., 52, Asperger et al., 1, 13, Copyright 1999 with permission from Elsevier...

Furnace, Curie-point or heated filament pyrolysers linked to packed column or capillary column gas chromatograph. GC-MS or GC-FT-IR interfaces. 

The attaining of Teq temperature by the sample is not controlled solely by the heat source of the pyrolyser but also by the sample properties and the pyrolyser construction. This is caused by the variations in the process of heat transfer to the sample from the heat source. For example, the sample characteristics such as the mass m and the specific heat c will influence the increase of the sample temperature by the formula A T = Q/(m c). In addition, phase changes and exothermic and endothermic chemical reactions in the sample may play an important role in temperature rise. To diminish the variations determined by these processes, a very small sample size is recommended. A study done on the temperature variation of a filament pyrolyser [4] showed a decrease of the nominal temperature of the filament for the first part of the THT, when the sample load increased, due to heat absorption by the sample. 

TABLE 4.1.1. The isoprene/dipentene ratio as a function of temperature for the pyrolysis of Kraton 1107 in an inductively heated or a resistively heated filament pyrolyser. 

Resistively heated filament pyrolysers were used for a long time in polymer pyrolysis [9], A schematic drawing of a common filament pyrolyser is shown in Figure 4.1.1. The principle of this type of pyrolyser is that an electric current passing through a resistive conductor generates heat in accordance with Joule s law ... 

There are several advantages of the resistively heated filament pyrolysers compared to other types. They can achieve very short TRT values, the temperature range is large, and Teq can be set at any desired value in this range. Several commercially available instruments are capable of performing programmed pyrolysis, and autosampling capability is also available (such as the CDS AS-2500). 

Another problem with the filament pyrolysers is the possibility that the filament may be non-uniformly heated over its length. This may determine different Teq s in different points of the filament. If the sample is not always placed in the same point of the filament in repeated experiments, this may introduce a rather drastic reproducibility problem. In spite of these disadvantages, the resistively heated filament pyrolysers are among the most common ones, and very good reproducibility has been reported frequently [12]. 

The reproducibility of the results for heated filament pyrolysers (CDS Pyroprobe 1000) and Curie point pyrolysers (Horizon Instruments) was reported for several samples [34]. This included several synthetic polymers, dammar resin, chitin, an insect cuticle, a hardwood (cherry), a seed coat (water lily), lycopod cuticle (fossil Eskdalia), as well as several organic geological samples. All samples were pyrolysed at 610° C for 5 s in a flow of helium. The residence time in the pyrolyser before pyrolysis was kept constant and the temperature of the sample housing was 250° C. Other parameters such as the temperature of the transfer line to the analytical instrument were also the same. Both systems were connected to a GC/MS system for the pyrolysates analysis. 

Table 4.7.2. The area counts for the chromatographic peaks corresponding to several syringyl derivatives from cherry hardwood pyrolysate [34] for a filament pyrolyser (samples F1, F2, F3) and a Curie point pyrolyser (samples C1, C2, C3).

Figure 5.2.1 is not to scale and shows in more detail the connection from the pyrolyser (as a filament pyrolyser) to the GC, the injection port, and the pneumatic system of the GC. In this diagram a piece of deactivated fused silica passes through the injection port of the GC and goes directly into the pyrolyser. In other systems the injection port is not bypassed and the pyrolysate is carried into the injection port through the transfer line and further into the analytical column. Also, some systems have the capability to automatically isolate the GC when the insertion probe is removed and air can penetrate into the GC. 

By scanning the temperature in a filament pyrolyser, the technique allows the separation of non-polymeric impurities from a polymer or composite material. Time-resolved filament pyrolysis has a series of useful applications as an analytical tool or even in some structure elucidations. As an example, it can be used [48] to differentiate the existence of more labile groups in a polymer structure. A typical variation of the total ion trace in a time-resolved pyrolysis MS for a composite material is shown in Figure 5.4.3. 

Table 9.1.2. Yield (wt.) % of different components from kraft lignin at 65(f C in a filament pyrolyser.

The Py-GC/MS analysis of the browning polymer from glucose and ammonia (from diammonium phosphate) is shown in Figure 11.2.1. The pyrolysis was performed at 600° C for 10 sec. in a filament pyrolyser (CDS 1000), and the separation was done on a Carbowax column 60 m long, 0.32 mm i.d. and 0.25 pm film thickness, with temperature gradient of the GC oven between 40° C and 240° C. 

Ericsson [280] investigated the temperature—time profile of home-built and commercially available filament pyrolysers. 

Disadvantages of resistively heated filament pyrolysers are difficult automation and the fact that the pyrolysis temperature is difficult to control, as the thermal properties of the sample and filament vary with sample size and filament ageing. Consequently, in spite of constant energy supply to the filament, the temperature attained by the sample during the transient period of pyrolysis is not accurately fixed. The temperature of the surface, which may act catalyti-cally, is difficult to measure. 

In the case of filament pyrolysers, the parameters which pertain specifically to the sample were identified [533]. These factors are method and uniformity of sample deposition, region of sample deposition, sample thickness, sample-to-filament contact, but also catalytic effects, nature of carrier gas, flowrate, pyrolysis chamber temperature and purity of solvents used in sample deposition. Important parameters are also the temperature-time profile (TTP), which depends upon TRT, THT as well as Teq. Reproducibility is enhanced if the entire sample experiences the same TTP and if the primary products... 

Modem PyFTlR equipment allows thermal evolution, vaporisation and pyrolysis directly in the FTTR. In direct PyFTIR the sample is located <3 mm below the beam [833,834]. Washall et al. [833] have described a cylindrical interface equipped with KBr windows, for connection of a ribbon filament pyrolyser to FTIR. Also sample cells with ZnSe windows are available for insertion into the light path of a Fourier transform infrared spectrometer for direct FTTR measurement of intricate solids. 

May and co-workers [11] have used this Curie point filament pyrolyser to produce Py-GC for various polymers. 

Voigt employed the platimun filament pyrolyser. This unit is attached directly to the gas inlet of Ae gas chromatograph for the examination of ethylene - propylene copolymers. 

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