Interfaces pyrolyzer

Injection temperature Interface temperature Pyrolyzer temperature Injection volume Specificity ... 

Analytical pyrolysis requires heating of the sample at a temperature significantly higher than ambient. Commonly selected temperatures are between 500° C and 800° C, but for special purposes this temperature can be higher or lower. The pyrolytic process is done in a pyrolysis unit (pyrolyzer), which has a source of heat. The pyrolyzer is interfaced on-line or off-line with an analytical instrument, which is used for the measurement of the pyrolysis products. Common techniques applied for this purpose are gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS), mass spectrometry (MS), etc. Pyrolysis GC/MS (Py-GC/MS) is probably the most common technique in analytical pyrolysis. 

Other techniques utilize lasers for sample evaporation/pyrolysis and excitation such as laser induced desorption (LID) or laser microprobe mass analysis (LAMMA) (see e g. [1]). Some of the sample introduction procedures in Py-MS enhance the information obtained from Py-MS by the use of time-resolved, temperature-resolved, or modulated molecular beams techniques [10]. In time-resolved procedures, the signal of the MS is recorded in time, and the continuous formation of fragments can be recorded. Temperature-resolved Py-MS allows a separation and ionization of the sample from a platinum/rhodium filament inside the ionization chamber of the mass spectrometer based on a gradual temperature increase [11]. The technique can be used either for polymer or for additives analysis. Attempts to improve selectivity in Py-MS also were done by using a membrane interface between the pyrolyzer and MS [12]. 

Amorphous and semi-crystalline polypropylene samples were pyrolyzed in He from 388°-438°C and in air from 240°-289°C. A novel interfaced pyrolysis gas chromatographic peak identification system was used to analyze the products on-the-fly the chemical structures of the products were determined also by mass spectrometry. Pyrolysis of polypropylene in He has activation energies of 5-1-56 kcal mol 1 and a first-order rate constant of JO 3 sec 1 at 414°C. The olefinic products observed can be rationalized by a mechanism involving intramolecular chain transfer processes of primary and secondary alkyl radicals, the latter being of greater importance. Oxidative pyrolysis of polypropylene has an activation energy of about 16 kcal mol 1 the first-order rate constant is about 5 X JO 3 sec 1 at 264°C. The main products aside from C02, H20, acetaldehyde, and hydrocarbons are ketones. A simple mechanistic scheme has been proposed involving C-C scissions of tertiary alkoxy radical accompanied by H transfer, which can account for most of the observed products. Similar processes for secondary alkoxy radicals seem to lead mainly to formaldehyde. Differences in pyrolysis product distributions reported here and by other workers may be attributed to the rapid removal of the products by the carrier gas in our experiments. 

Procedures for Pyrolysis. In the pyrolysis-GC-mass spectrometry experiments, about 1 mg of polymer was weighed into a quartz tube which was inserted into the heating coil of the Pyroprobe. The latter fitted directly into the injection port of the Perkin-Elmer 990 GC. The GC was operated at a manifold temperature of 220°C, injector temperature of 210 °C, interface temperature of 255°C, He flow rate of 83 mL min"1, and FID detection. Samples were pyrolyzed at 600°, 650°, 700°, 750°, 800°, 850°, 900°, and 950°C at a heating rate of 20,000°C sec"1. All samples were held for 20 sec at the final temperatures. 

Pyrolysis and reforming of several types of common plastics (polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polyurethane, and polycarbonate) were studied qualitatively, using a micro-reactor interfaced with a MBMS. Each type of plastic pyrolyzed at 550-750°C. This was followed by steam reforming of vapors in a fixed bed of C-11 NK catalyst at 750-800°C. The composition of the product gas (mass spectrum) was observed for different values of the steam-to-carbon mtio and space velocity that changed depending on the size of plastic samples. Preliminary tests showed that at process conditions similar to those used for reforming natural gas, polymers were almost completely converted to hydrogen and carbon oxides. 

Pyrolyzer Oxygen Flow Reaction Interface Furnace (ml/min) Chamber... 

Fig. 8 Mechanism for ultrasound-induced polymta- chain scission (a) gradual bubble formation results from pressure variations induced by the acoustic field (b) rapid bubble collapse genc tes solvodynamic shear (c) small molecules pyrolyze to form radical byproducts up

As with Curie-point systems, the filament of a resistively heated pyrolyzer must be housed in a heated chamber that is interfaced to the analytical device. This interface chamber is generally connected directly to the injection port of a gas chromatograph, with column carrier gas flowing through it. The sample for pyrolysis is placed onto the pyrolysis filament, which is then inserted into the interface housing and sealed to ensure flow to the column (Figure 2.3). When current is supplied to the filament, it heats rapidly to pyrolysis temperatures and the pyrolysate is quickly swept into the analytical instrument. 

Viscous liquids, such as heavy oils, may be applied directly to the surface of a filament or may be pyrolyzed while suspended on the surface of a filler material, such as quartz wool inside a quartz tube. Lighter liquids, especially anything easily vaporized, will probably be evaporated from the filament by the heat of the interface before pyrolysis and are probably better studied using a furnace-type pyrolyzer. 

To be practical in these analyses, the pyrolyzer must have the ability to heat the sample material over a wide range of temperamres and to operate at lower temperatures without preheating the sample or introducing cold spots. Isothermal interfaces are usually a problem in that if they are hot enough to transfer all the pyrolysis products to the GC, they are probably too hot for the desorption steps, and volatiles will be lost while the sample is inserted into the unit. What is generally needed is a programmable interface or a separate heating zone for the desorption and pyrolysis steps. 

Curie-point pyrolyzers are generally not used in this stepwise fashion, since they are limited to one temperature per sample because of the way heating is controlled. Microfumaces, however, have been designed with a separate desorption zone, so that a sample may be manually lowered into a low-temperature zone for a first run, retrieved, and then lowered into the pyrolysis zone for a second run. Filament pyrolyzers are now available with a low-mass, programmable interface zone along... 

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