Reactor pyrolysis products

Similar results are obtained from incineration of polymeric materials with octabromo- and pentabromodiphenyl ether (refs. 11,12). The temperature with the maximum PBDF-yield depends on the kind of polymeric matrix. All three bromo ethers 1-2 give the same isomer distribution pattern with preference for tetrabrominated dibenzofiirans. The overall yield of PBDF is lower for incineration of pentabromobiphenyl ether 2, 4 % at 700°C compared to 29 % for ether 1 at 500 °C (ref. 12). The preferred formation of tetrabrominated fiirans observed at all temperatures cannot be a result of thermodynamic control of the cyclisation reaction it is likely due to the special geometry of the furnaces. One explanation is that a spontaneous reaction occurs at approximately 400°C while the pyrolysis products are transferred to the cooler zones of the reactor details can be found elsewhere (ref. 12). 

A novel reactor for pyrolysis of a PE melt stirred by bubbles of flowing nitrogen gas at atmospheric pressure permits uniform temperature depolymerisation. Sweep-gas experiments at temperatures 370-410 C allowed pyrolysis products to be collected separately as reactor residue (solidified PE melt), condensed vapour, and uncondensed gas products. MWDs determined by GPC indicated that random scission and repolymerisation (crosslinking) broadened the polymer-melt MWD. 19 refs. USA... 

Catalytic upgrading of bio-oil was carried out over Ga modified ZSM-5 for the pyrolysis of sawdust in a bubbling fluidized bed reactor. Effect of gas velocity (Uo/U ,f) on the yield of pyrolysis products was investigated. The maximum yield of oil products was found to be about 60% at the Uo/Umf of 4.0. The yield of gas was increased as catalyst added. HZSM-5 shows the larger gas yield than Ga/HZSM-5. When bio-oil was upgraded with HZSM-5 or Ga/HZSM-5, the amount of aromatics in product increased. Product yields over Ga/HZSM-5 shows higher amount of aromatic components such as benzene, toluene, xylene (BTX) than HZSM-5. 

Attempts have also been made to obtain the radicals (CF3)3C and CeFs as products of vacuum pyrolysis of (CF3)3CI and CeFsI (Butler and Snelson, 1980b). However, only perfluoroisobutene was observed in an IR spectrum of pyrolysis products of (CF3)3CI. Thermolysis of CeFsl led to formation of CF4, CF3 and CF2 as a result of decomposition of the aromatic ring. This behaviour was explained as due to catalytic effects which take place on the platinum reactor surface. 

The most common type of commercial pyrolysis equipment is the direct fired tubular heater in which the reacting material flows through several tubes connected in series. The tubes receive thermal energy by being immersed in an oil or gas furnace. The pyrolysis products are cooled rapidly after leaving the furnace and enter the separation train. Constraints on materials of construction limit the maximum temperature of the tubes to 1500 °F. Thus the effluent from the tubes should be restricted to temperatures of 1475 °F or less. You may presume that all reactor tubes and return bends are exposed to a thermal flux of 10,000 BTU/... 

While the carbon arc method yields products in amounts that are easily characterized, there is a number of caveats of which one must be aware. Since the carbon arc operates at extremely high temperatures (>2000 °C) and emits copious amounts of light, there is the very real possibility of pyrolysis and/or photolysis of both substrate and products. These problems may be minimized by carrying out control experiments in which pyrolysis and photolysis products are identified and excluded. Maximum yields in carbon arc reactions are obtained when carbon and substrate are cocondensed. However, this technique can result in pyrolysis of substrate, which can be avoided by alternately depositing substrate and carbon on the cold reactor walls. Often both methods are employed in order to identify pyrolysis products. Since the carbon arc results in removal of macroscopic pieces of graphite from the rods, it is impossible to measure product yields based on actual carbon evaporated. 

Figure 57. Thermal black process a) Thermal black reactor b) Cooler c) Filler bricks d) Inlet for the feedstock e) Inlet for the fuel f) Outlet for the burned fuel g) Outlet for the pyrolysis products h) Carbon black outlet i) Blower...

The residence time is calculated based on the fluidizing gas velocity, assuming that the "free volume" (i.e. the volume of the expanded bed minus the volume of the sand) is fully utilized. At the temperature, total reactor gas flow rates, and sand bed volumes used, the residence time was about 0.5-1.0 sec. A typical operation began by washing the sand in 10% HNO3 and distilled water to remove impurities, such as iron, which may act as catalysts, and then calcined at 850° C for at least 12 hours to remove any sulfides and carbonates. The coal feed is then begun and pyrolysis products then exit the pyrolyser to a set of two cold traps fitted with cellulosic thimble filters maintained at 0° C. The outlet gas temperature after the first trap is 30-34° C. Much of the light char formed is entrained in the exit gas and carried into these traps, with most of it in the first trap. 

For the processes of different reactor types, kiln and retort pyrolysis processes are characterized by a relatively low capital investment. However, they suffer from unfavorable economics, due to the high processing costs compared with the value of the oil product obtained. Also, the characteristics of this process are relatively long residence times of waste in the reactor, poor temperature control due to large temperature gradients across their internal dimensions, fouling walls of the reactor by carbon residue and low liquid product quahty due to the production of a diverse number of pyrolysis products. 

Laboratory-scale pyrolysers can be used for producing oils for analytical purposes. Many scientific and technical publications report on the pyrolysis of well-characterized polymers in open or closed reaction vessels, furnace-heated tubes, fixed-bed and fluidized-bed reactors. The pyrolysis products are generally analysed off-line, being condensed in cooled traps. 

The pyrolysis products, together with the fluidizing gas (i.e. the noncondensable pyrolysis gases), leave the reactor via a cyclone, where dry carbon soot and filler materials are precipitated. A cooling system and an electrostatic precipitator condense the liquid fraction of the pyrolysis products. The waste heat is used to heat up the fluidizing gas. A stream of pyrolysis products is branched off the main product cycle and refined in the rectification unit described for the smaller test plant. 

Li et al. [16] also stndied the influence of pyrolysis temperature on the pyrolysis products derived from solid waste in a rotary kiln reactor. They used an externally heated laboratory-scale rotary kiln pyrolyser (Figure 19.8). The length of the rotary kiln was 0.45 m with an internal diameter of 0.205 m. Kiln rotation speed can be adjusted from 0.5 to 10 rpm. The raw materials used in this study were polyethylene (PE), wood and waste tyres. The results obtained by Li et al. [16] reiterated that as the reaction temperature profile changes so does the product yield (Figure 19.9). 

It should be noted that Equations 1, 2, 3, 4, and 5 imply a homogeneous kinetic system. Coking in tubular reactors results from a combination of homogeneous and heterogeneous processes. As the kinetics of these processes are not well understood and as the quantitative yield of coke is several orders of magnitude smaller than other pyrolysis products, it is more convenient to model coke formation separately based on commercial operating data. 

Production of Coke and Other Pyrolysis Products From Acetylene, Butadiene, and Benzene in Various Tubular Reactors... 

Analysis obtained by mass spectrometry. The above sample of pyrolysis product was obtained at 835°F, 300 psig, in a continuous-flow coil reactor, residence time 45 min. 

The test rig is equipped with a feedstock hopper suitable to low-bulk-density biofuels and the biomass is fed continuously into the sand bed of the reactor via an injector screw which can feed fuel either into the bottom of the bed or to about 1 meter above the air distributor. The maximum fuel mass flow rate is 90 kg/h. The feeding system consists of two screw feeders in series separated by a rotary valve. The second screw has a higher feeding rate thus it will remain almost empty and therefore is not likely to be blocked by pyrolysis products. Steam can be added to the primary air as a gasification agent. 

The combustion of the pyrolysis products starts in the reactors Dense bed 1 and Dense bed 2. These two reactors model the cylindrical zone at the bottom part of the combustor. The block Flame 1 represents the core of this bottom part. The blocks Flame 2 - Flame 4 cover the upper... 

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