Used for Pyrolysis

Analytical pyrolysis requires heating of the sample at a temperature significantly higher than ambient, commonly between 500° C and 800° C. For special purposes this temperature can be higher. The pyrolytic process is done in a pyrolysis unit (pyrolyser) which commonly interfaces with an analytical instrument (see Section 1.2). The analytical instrument is used for the measurement of the pyrolysis products. It is also possible to perform off line pyrolysis (no direct interface to an analytical instrument), followed by the analytical measurement. The pyrolysers have a source of heat where the sample is pyrolysed. The pyrolysis products are usually swept by a flow of gas from the pyrolyser into the analytical instrument. 

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. 

There are several construction principles for pyrolysers, such as inductively heated, resistively heated filament, furnace type, and radiative heated. The principles of construction for the main types of pyrolysers will be discussed in Section 4.2 to Section 4.6. 

FIGURE 4.1.1. The simplified scheme of a pyrolyser (based on the design of a heated filament system made by CDS Inc.). 

Because pyrolysis is frequently a complex process, there is no precise rule to indicate which Teq temperature should be chosen for a given sample. The ceiling temperature Tq (see Section 3.1), which may be seen as a recommended temperature for pyrolysis, was not proven in practice as a reliable guidance for the choice of Teq. For this reason, in the specialized literature the description of the pyrolysis products of a certain material 

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Laser desorption is commonly used for pyrolysis/mass spectrometry, in which small samples are heated very rapidly to high temperatures to vaporize them before they are ionized. In this application of lasers, very small samples are used, and the intention is not simply to vaporize intact molecules but also to cause characteristic degradation. 

Most importantly, biomass pyrolysis will be carried out at remote locations, and in distributed manner. Thus, the catalysts should be cheap and simple to use. Acidic clays, silica aluminas and H-FAU type zeolites are relatively cheap and robust materials, can be mixed easily with heat carriers, and used for pyrolysis. Efficient contact between the solids (catalyst and biomass) to maximize catalytic action is one of the challenges that need to be overcome. 

The fiwdstocks used for pyrolysis vary widely and range from light saturated hydrocarbons such as ethane, propane, and even ethane/propane blends, to heavier petroleum cuts such as petrochemical naphtha and light and heavy gas oils. In this respect, the situation is clearly in favor of fight hydrocarbons in the United States, a country that is rich in natural gases containing methane as well as ethane and propane, and vHiich still mainly uses the latter two to manufacture ethylene, hi Europe and Japan, by contrast, petroleum cuts traditionally supply the steam cracker feedstocl (Table Zl). 

Typically two major types of rotary kilns are used for pyrolysis processes either internally or externally heated systems. For internally heated kilns a heat exchanger based on steam-... 

Similarly, microwaves have been used for pyrolysis of coal, which is known to have very poor microwave absorption, by mixing it with inorganic oxides (very good microwave receptors) or with carbon. After the initial stages of pyrolysis the coal undergoes some graphitization, turning into carbon black that further absorbs microwaves [48, 49]. 

A reactor constructed of stainless steel 410 was used for pyrolysis since it contained no nickel. The coke layer formed during pyrolysis was usually thin and greyish. Less frequently, a piece of black coke was found on the surface. The metal surface (Surface C) was always grey. Figure 5 shows the two types of coke formed at Surface A in the stainless steel 410 reactor. The black (less frequent) coke appeared to be a floe of fine filaments, about 0.05 / m in diameter, with occasional 0.4- m filaments. The predominant deposit seems to be platelets of coke that include metal crystallite inclusions, the lighter area. The metal particles in the coke deposits, as detected by EDAX, were chromium rich compared with the bulk metal, as reported in Table III. Some sulfur also was present in the deposit the sulfur was present, no doubt, because of the prior treatment of the surface with hydrogen sulfide. Surfaces B and C for the stainless steel 410 reactor are also shown in Figure 6. Surface B indicated porous coke platelets. Surface C was covered mostly with coke platelets, and cavities existed on the surface. Metal crystallites rich in iron apparently were pulled from the metal surface and were now rather firmly bound to Surface B. Surface C was richer in chromium than the bulk metal. 

INSTRUMENTATION USED FOR PYROLYSIS - Resistively heated filament pyrolyzers... 

Laser pyrolyzers are practically the only type of radiative heating pyrolyzer with certain applicability. Attempts were made in the past to use a strong light/heat source and focus the beam with lenses [20] to achieve the desired power output. However, the laser as a radiative energy source is much more convenient. The laser beam can be focused onto a small spot of a sample to deliver the radiative energy. This provides a special way to pyrolyze only a small portion of a sample. A variety of laser types were used for pyrolysis purposes normal pulsed, Q-switched, or continuous wave (cw) [21], at different energy levels. More common are the normal pulsed high-power lasers. 

In addition to the compounds that have a structure compatible with that of the polymer, some Ci6 molecules were tentatively identified in the pyrolysate of Brij . These molecules were either incorrectly identified (by using mass spectral library search), or they are an impurity in the sample used for pyrolysis. Other dodecyl ethers were detected in the pyrolysate, but they were more difficult to identify unambiguously,. The generic formula for these ethers is shown below ... 

Fiffure 4. Current vessel design used for pyrolysis at the University of Waterloo. 

On the other hand there has been very little uniformity in the methods used for pyrolysis and hence different parts of the pyrolysates are always studied. 

The same laboratory apparatus and tubular reactors used for pyrolysis of ethane (1) were employed in this investigation. The gas chromatograph and the method of product analysis used by Herriott (6) were modified, however, in order to obtain a more accurate analysis of the gaseous products up to butane. This was... 

Figure 4. Concentration profile for Incoloy 800 reactor used for pyrolysis of ethane and propane after hydrogen sulfide treatment...

Figure 5. Concentration profile for 304 stain less steel reactor used for pyrolysis of...

The oil and gas yield from a rapid processing pyrolysis plant is about 37% or about 2.7 kcal return per kilocalorie invested. Since the plant analyzed in the study was processing city wastes, there was no energy or economic charge for biomass material. However, if tropical dry-wood is used for pyrolysis about 5 kcal of wood is required to produce 1 kcal of oil. 

A pyrex tube, 5 mm id, 30 cm long, was used for pyrolysis. Samples (4-5 mg) were placed in aluminum pans as used for differential scanning calorimetry, folded to fit inside the tube, and located centrally by 3 mm diameter pyrex glass rods of appropriate length either side of the sample pan. Teflon plugs with 1.5 mm diameter stainless steel inlet and outlet tubes conducted the dry nitrogen carrier gas (50 ml/min) through the system to the gas cell. A temperature ramp of 5 °C/min from ambient to 500 °C was... 

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