Design and development of a pyrolysis probe for short path thermal desorption.

摘要

Pyrolysis is the process of heating a substance to high temperature in the absence of oxygen so it does not burn but rather the thermal energy causes dissociation of chemical bonds. It has been widely employed as an analytical tool where it is combined with gas chromatography (GC) and its ancillary techniques (Mass Spectrometry, Fourier transform infrared spectroscopy, etc.) Analytical pyrolysis has been applied in a variety of areas such as microbial classification, protein identification, food packaging material identification, and forensics.;State of the art commercial pyrolysis instruments have intrinsic disadvantages that undermine widespread application. Most pyrolysis systems are dedicated attachments to a GC which preclude using the system for other injection techniques. Furthermore, commercial pyrolysis instruments are essentially probes inserted into the GC injector or are extensions to the GC injector. Pyrolysis releases high molecular weight, non-volatile residues into the GC injector which can foul the system and lead to sample to sample cross contamination problems.;The objective of this research is to design and develop a pyrolysis probe attachment for Short Path Thermal Desorption which would remedy the disadvantages of current commercial systems. Specifically, the new pyrolysis probe should combine the features of Short Path Thermal Desorption, have a quick setup, not be prone to injector contamination, be easily movable and transferable, accurate and precise.;A prototype has been built in our laboratory and subjected to mechanical and engineering tests. In the first demonstration of the new pyrolysis probe, virgin high density polyethylene (HDPE) was analyzed by pyrolysis-direct thermal desorption (DTD)-GC-MS. A very strong peak of ethylene (primary pyrolysis product) was evolved in the pyrogram followed by a homologous series of oligomers up to C40 thereby validating the instrument. Pyrolysis studies on other model polymers such as polystyrene (PS), ethylene vinyl alcohol (EVOH), ethylene vinyl acetate (EVA), and polyethylene terephthalate (PET) were also proved successful in revealing their monomers, oligomers, important decomposition products, and additives. The pyrolysis chamber and sample tube was very clean after each run and no cross contamination was detected between injections, proving the superiority of this novel pyrolysis system over existing commercial instruments.