The Filament or Platten Pyrolyser

The filament or platten pyrolyser is an electrically heated conductor having a relatively large usable surface area contained in a minimal volume. Figure 1 shows a recent example of the device which has been fabricated from a piece of Pyrotenax topped by a suitable finned cooling cap carrying a socket accepting a two-pin plug. The filament itself is initially a 2.5 ohmic length of 22 wire gauge platinum, chromel-alumel, nichrome or other resistance wire tightly machine-coiled to an internal diameter of 1.0 mm, tensioned across the central conductor and an extension of the sheath to a 2 ohmic length and spot-welded in place.

Obviously the length of the Pyrotenax barrel must be tailored for a particular injection port and the port itself reamered out so that the annular space between the inner wall of the injection port and the Pyrotenax outer sheath is no wider than 0.2 mm. This is to combat the probability of a back-pressure pulse, for when the pyrolyser is fired at a temperature of, say,

1 2 3 1 5 & 7 8 S 15 11 12 13 11 15 ii 17 18 13 20 21 22 23 24

Figure 1 A modern filament pyrolyser together with its modified chromatographic injection port. Inset: detail of mounted filament.

1 2 3 1 5 & 7 8 S 15 11 12 13 11 15 ii 17 18 13 20 21 22 23 24

Figure 1 A modern filament pyrolyser together with its modified chromatographic injection port. Inset: detail of mounted filament.

700°C there is a large local carrier gas expansion. Due to the dynamic resistance of the chromatographic column this must be accommodated in the direction of the gas flow to prevent both diffusion and the risk of reverse flow that passes the pyrolysate through the pyrolysis zone a second time with the risk of further thermal modification. This is absolutely essential to observe the terms of good practice. It must also be taken into account that there is a temperature coefficient of resistance which must be accommodated and suitable measures taken to ensure re-producibility.

Temperature control is best achieved by making the filament or platten one arm of a Wheatstone Bridge circuit and adjusting the balance to control final temperature. The system is calibrated by inserting the pyrolyser in a dummy column maintained under the chosen chromatographic operating conditions and observing the melting points of a series of inorganic salts. It should be noted that the current density applied to the filament must be conducive to rapid heat-up for it is essential to attain the pyrolysis temperature in a few milliseconds (if not microseconds) and ensure a hold for, say, no more than 1-2 s by means of associated timer circuitry. In that time the pyrolysis products are on-column and being separated - ideally the thermal profile should be a square wave.

These instrument combinations and their operations, described above, have been tried and tested by the writer in many laboratories throughout the world over many years and have proved easy to handle by laboratory technicians. Pyrolyses themselves are eminently reproducible provided that the sampling procedure is standardized (see below) and equipment is maintained in as near-sterile conditions as reasonably possible.

At best, the pyrolyser should be cleaned by heating at a higher temperature in an inert atmosphere between every shot. This serves two purposes: first, it removes traces of any residues and second, if cleaned on-column, the completeness of the pyrolysis is verified. In the event that this process is too time-consuming it is better conducted externally or under back-flush conditions.

The possibility of the heating substrate acting as a catalyst has never been completely negated despite a series of standardized experiments conducted by Jones on a variety of metals, both before and after gold-plating. A second hazard is found in the build-up of carbon on the filament itself; this modifies the pyrolysis surface.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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