PYROLYSIS CHAMBER

Figure 11.1 shows the pyrogram of lead white pigmented linseed oil paint obtained at 610 °C with a Curie-point pyrolyser, with on-line methylation using 2.5% methanolic TMAH. The pyrolyser was a Curie-point pyrolysis system FOM 5-LX, specifically developed at FOM Amolf Institute (Amsterdam, the Netherlands), to reduce cold spots to a minimum. This means that the sample can be flushed before pyrolysis in a cold zone, and it also ensures optimum pressure condition within the pyrolysis chamber, thus guaranteeing an efficient transport to the GC injection system [12]. 

The column effluent passes through a pyrolysis chamber at 800°C and then through a conductivity detector. The solution is injected on to a gas chromatographic column (OV-10-Chromosorb W-HP1, 80-100 mesh,... 

Selavka et al. [36] have reported that for LC, a pyrolysis chamber temperature greater than 550°C gives rise to substantial baseline noise, which severely limits the detector s sensitivity and selectivity. Thus, LC-TEA is always performed in the nitroso mode (the pyrolyser is held at 550°C). 

The heat release temperature 7 liax in K as the pyrolysis chamber temperature at which... 

The combustion temperature 7 1[ax in K as the pyrolysis chamber temperature, at which the specific heat release rate is the maximum, i.e., Q(t) = Gmax-... 

Later researchers followed essentially the same process, substituting monomer precursors instead of the dimer, to produce PPV films. " The monomers were evaporated and the vapors carried into the pyrolysis chamber, where they were pyrolyzed at 800°C. The reactant species were then transported to the substrate maintained at 60°C to form the precursor polymer film. This film was then thermally converted to PPV at 150-320°C. - Scafer et al. have further shown that PPV can be produced via the dehydrogenation route introduced by Iwatsuki et al. They showed that soluble a-phenyl substituted poly-p-xylylene can be prepared by CVP of l-a-chlorobenzyl-4-methylbenzene. The parylene was then dehydrogenated by DDQ resulting in PPV. This process could be used to produce both segmented and unsegmented PPVs. The segmentation ratio was controlled by the molar ratio of the parylene to DDQ, in the... 

The semi-continuous type of reactor with the large capacity was comprised of a pyrolysis chamber, a catalytic cracking chamber and a separation and purifying section. The feed plastic material was melted and decomposed in the pyrolysis chamber held at the ambient pressure and at the temperature 723-783 K, and fed to the catalytic cracking chamber. A reflux condenser was used to separate and purify the products formed in the chamber and individual factors were obtained using fractional distillation apparatus [26]. Different types of reactors are being utilized depending on the type of feed and the expected products from the pyrolysis. 

Pyrolysis vessels are generally made from SS316 or 9Cr IMo steel. Maximum corrosion allowance should be made for the pyrolysis chamber as the metal will potentially be exposed to hydrochloric acid and hydrobromic acid that can cause pinholing of SS304. The pyrolysis chamber needs to have a relief valve or PSV (pressure safety valve) to vent to a safe location in case of a sudden pressure build-up. 

The pyrolysis chamber is generally heated with a high velocity gas burner. In order to avoid hot-spots, an impingement plate is used such that there is no flame impingement on the vessel itself. In newer designs however the chamber is heated indirectly with a hot air burner so that hot spots and flame impingement problems are eliminated. 

The carbonaceous coke formed during plastics pyrolysis is automatically scraped off and accumulates in the bottom of the pyrolysis chamber where it is reduced by attrition to a free-flowing black powder. The internal agitator/scraper constantly removes the carbonaceous char by-product before it acts as a thermal insulator and lowers the heat transfer to the plastic. The char residue produced is about 2-3% of the output for relatively clean polyolefln feedstocks and up to 8-10% for PET-rich feedstocks. 

Figure 15.5 Close-up of pyrolysis chamber of commercial plastics pyrolysis plant which can convert 10 tonne of unwashed, mixed plastics into 10000 L of diesel fuel per day. (Reproduced by permission of Ozmotech Pty Ltd)...

The core technology of the Thermofuel process is the catalytic reaction tower (or catalytic converter, Figure 15.7). The catalytic reaction tower contains a system of plates made from a special catalytic metal alloy. The metal plates are positioned so that the hot pyrolytic gases must travel a tortuous path, in order to maximize contact area and time. The catalyst chamber is heated to 220°C using the exhaust gases (not pyrolysis gases) from the furnace of the pyrolysis chamber. 

The catalyst chamber is the heart of the Thermofuel process and is directly responsible for the high quality of the output fuel from this process. The technology in and around this unit is highly proprietary since competitive processes do not have this type of longlife catalytic converter. Many other pyrolysis processes add zeolite catalysts directly to the pyrolysis chamber, however, these are expensive and quickly become fouled and deactivated. 

In the Thermofuel process the first reaction occurs in the pyrolysis chamber where the plastic is thermally pyrolyzed, causing random scission of carbon chain lengths. While secondary reactions occur in the catalytic converter (i.e. catalyst tower) where shorter carbon chains are reformed and further cracking of longer carbon chains occnrs such... 

In the Thermofuel process, carbon and coke deposits formed during the pyrolysis are continuously scraped from the pyrolysis chamber walls and reduced to a free-flowing black powder. Inorganic additives such as cadmium pigments from the plastics also end up in the char stream. The carbon matrix has a metal fixing effect and binds up the metal ions so that no leaching occurs after disposal. 

The Smuda process uses a reflux return where longer paraffin chains that condense shortly after exiting the main chamber are allowed to flow back to the main chamber (the reflux effect ). Also the heavies from the bottom of the distillation column flow back to the pyrolysis chamber for re-cracking (Figure 15.10b). 

In the Hitachi Process the low-boiling component of the gas flowing out from the top of the column of the pyrolysis chamber is cooled and condensed initially in the primary condenser, whereby kerosene is recovered. The low-boihng component of the gas passing through the first condenser without condensation is transferred to the second condenser where it is cooled for condensation, whereby gasoline is recovered. The decomposition gas portion remaining uncondensed from the second condenser is then sent to the gas combustion furnace by way of the water seal device and burned in the furnace [32, 33]. A mass... 

The basic setup of a NCD system is shown in Fig. 1. In almost all cases, only a portion of the entire SFC mobile phase is diverted to the CLND detector using a fused-silica capillary or restrictor [6-8,10,11]. Use of a restrictor minimizes the effects of the SFC decompressed carbon dioxide (CO2) and solvent composition on the pyrolysis reaction and chemiluminescence. The CO2 flow rate, dictated largely by the SFC outlet pressure, can affect the residence time of the solute in the pyrolysis chamber and the efficiency of the ozone reaction. The addition of modifiers to the SFC mobile phase (e.g., methanol) can compete for the available pyrolysis oxygen and can reduce signal response. High concentrations of modifier can dramatically affect the detection limits of some compounds [7]. Moreover, the sample concentration also appears to be limited by competition for oxygen, resulting in incomplete combustion. 

Fig. 1 Schematic diagram of SFC-CLND system (1) CO2 tank, (2) SFC pumping system, (3) autosampler, (4) modifier pump, (5) column, (6) UV detector, (7) pyrolysis inlet with linear restrictor, (8) pyrolysis chamber, (9) reaction cell,...

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