Pyrolysis systems

Nitrogen gas pyrolysis system was designed and set up to transform the PAN hollow fiber membrane into PAN-based carbon hollow fiber membrane. The instrument involved in this system is illustrated in Fig. 5.3. Caibolite (Model CTF 12/65/550) wire wound tube furnace with the Eurotherm 2416CC temperature control system is used for the pyrolysis of the PAN hollow fiber membrane. The furnace can be operated at a maximum temperature of 1200°C and has the abihty to control the heating rate and the thermal soak time during the pyrolysis process. 

A PAN hollow fiber bundle is inserted into a quartz tube, where both ends of the tube are fitted with Pyrex socket. The front Pyrex socket is used to channel nitrogen gas into the tube and the back socket is used to purge the volatile compounds evolved during pyrolysis. Then the quartz tube is inserted into the Carbolite furnace. All the connections must be properly tightened up in order to prevent the air from entering the quartz tube, which can interrapt the inert gas pyrolysis process. 

However, before pyrolysis, the PAN hollow fber must be subjected to the thermo-stabilization or preoxidation process in air or oxygen. This is necessary in order to cross-link the PAN chains and to prepare a PAN aromatic ladder stracture that can withstand high temperatures during the pyrolysis process. For this purpose air is introduced to the quartz tube and the hollow fiber is heated at 250°C for 30 min in air. 

After thermo-stabilization, air in the tube is purged by nitrogen to prevent the oxidation from occurring during the high temperature pyrolysis process. The hollow fiber is then heated to a required pyrolysis temperature and under the required conditions. The resulting carbon membrane is cooled down to ambient temperature in nitrogen atmosphere. Table 5.2 shows the pyrolysis conditions required for the preparation of the PAN caibon hollow fiber membrane. 

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Thermal and Photochemical Reactions. Unsubstituted ethyleneimine has astonishing thermal stabihty. The reaction of ethyleneimine diluted with argon proceeds to give a mixture of unidentified compounds only at temperatures above 400°C (339). In a flow pyrolysis system under pressures of <1.33 kPa (<10 mm Hg) on quartz wool, isomerization to give /V-methylenemethylamine and ethylideneimine was observed only ia the temperature range 510—535°C. Higher temperatures result ia fragmentation (340). 

Fig. 9. Lurgi-Rhurgas flash pyrolysis system, where 1 is a lift pipe 2, primary pyrolysis reactor 3, screw feeder 4, secondary pyrolysis reactor 5 and 7,...

The fuel may be sohd waste or gas or oil from a gasifier or pyrolysis system. 

Figure 12.8 Mia ocolumn size exclusion chromatogram of a styrene-aaylonitrile copolymer sample fractions ti ansfeired to the pyrolysis system are indicated 1-6. Conditions fused-silica column (50 cm X 250 p.m i.d.) packed with Zorbax PSM-1000 (7p.m 4f) eluent, THF flow rate, 2.0 p.L/min detector, Jasco Uvidec V at 220 nm injection size, 20 nL. Reprinted from Analytical Chemistry, 61, H. J. Cortes et al, Multidimensional chromatography using on-line microcolumn liquid chromatography and pyrolysis gas chromatography for polymer characterization , pp. 961 -965, copyright 1989, with peimission from the American Chemical Society.

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]. 

Plot the selectivity to C4H8 as a function of ethane conversion. Does it behave like a secondary or primary product Consult the paper by Dean (1990), and describe additional reactions which lead to molecular weight growth in hydrocarbon pyrolysis systems. While some higher molecular weight products are valuable, the heavier... 

The photolysis of trimethyl boron at temperatures up to 300 °C may occur by reactions (1)—(3) of the pyrolysis process112. Subsequent steps which lead to hydrogen formation in the pyrolysis system are much less important [CH4 H2 a 2 1 under pyrolysis conditions, 9 1 in photolysis system]. 

Crandall et al. first showed that hexamethylbicyclopropylidene 39 rearranges at 400 °C in a flow pyrolysis system to yield a 10 1 mixture of two isomeric hexa-methylmethylenespiropentanes 98 and 99 (Scheme 18) [49,50] formed via tri-methylenemethane diradical intermediates. In close analogy to this result, the photolysis of the diazo compound 100 did not only give permethylbicyclopro-pylidene 24a,but a 45 55 mixture of 24a and 101, and upon flash vacuum pyrolysis at 400°C only 101 was formed (the yields were not reported) (Scheme 18) [98]. 

Figure 1. Occidental Research Corporation s flash pyrolysis system. Adapted from Ref, 12...

Figure 27.1 (a) C02 Laser Pyrolysis System, (b) Detail of the gas nozzle, R = gas mixture of reactant gases Ig = coaxial flow of inert gas, usually argon. 

Generally, most pyrolysis systems have produced similar yields. Thus, it is important that any successful pyrolysis plant make provisions for selling the byproducts, especially the char. 

Firestone Tire Rubber Company performed a major cooperative research program with the U.S. Bureau of Mines in the early 1970s. They developed a 10 tire per day laboratory pyrolysis unit. In their studies they determined average yields of pyrolysis products per tire as follows 1 gallon oil, 7 pounds char, 3 pounds gas (57 scf), and 2 pounds steel and ash. Generally, most pyrolysis systems have produced similar yields. 

Feedstocks for various industrial pyrolysis units are natural gas liquids (ethane, propane, and n-butane) and heavier petroleum materials such as naphthas, gas oils, or even whole crude oils. In the United States, ethane and propane are the favored feedstocks due, in large part, to the availability of relatively cheap natural gas in Canada and the Arctic regions of North America this natural gas contains significant amounts of ethane and propane. Europe has lesser amounts of ethane and propane naphthas obtained from petroleum crude oil are favored in much of Europe. The prices of natural gas and crude oil influence the choice of the feedstock, operating conditions, and selection of a specific pyrolysis system. 

Figure 3. Global reaction network for asphaltene and resid pyrolysis systems [7].

Several models which are based on mechanistic chemistry similar to that shown in Table V have appeared in the literature to describe hydrocarbon pyrolysis systems. The publications of Froment (45,46) are an example of this type of modelling. 

LaMarca, C., Kinetic Coupling in Multicomponet Pyrolysis Systems, Ph.D. Dissertation, Univ. of Delaware, 1992. 

To begin the exploration of actual reaction pathways in complex pyrolyses of aromatic substances, we have carried out a detailed experimental and theoretical analysis of the liquid-phase pyrolysis of bibenzyl. This pyrolysis system has been studied by others (44,45,46), and the general kinetic features of this reaction system are now rather well agreed on. Complete details of this work will appear elsewhere (38a) and a few implications of this work of particular relevance to coal reactions will be discussed here. 

Figure 9. Diagram of possible variation of viscosity of pyrolys-ing systems with temperature of pyrolysis. System A pyrolysis of coal to give coke of fine-grained mosaics, 1 pm diameter ...

Fig. 3.2 Setup of the spray pyrolysis system (1) temperature controller (2) peristaltic pump (3) temperature switch (4) chronometer (effective spraying and total time) (5) spray nozzle (6) motor for lateral and circular displacement (7) heating chamber (8) heating plate (9) lateral displacement support (10) generator (11) spray solution (12) carrier gas (N2) (13) connection to thermocouples (14) transmission gear (15) rotating system (16) flowmeter for the carrier gas (N2) (after Correa-Lozano et al. 1996)...

Coal pyrolysis is a very old technique (dating back to the eighteenth century), based on relatively inelegant technology. Most pyrolysis systems in use in the late 1800s and early 1900s were in Europe and had as their objective the production of smokeless fuel (char) for domestic use. However, within a short time it was realized that the coal tar fraction contained valuable chemical products. However, as inexpensive petroleum appeared on the scene, interest in coal byproducts faded. A detailed review has been published.29... 

Attachment of the Pyrolysis System. The attachment of a pyrolyzer to a GC system should be made so that minimum dead volume remains in the system. Dead volume can be tested for by injection of methane into the GC column a tailing methane peak indicates the existence of dead volume. Such voids drastically reduce resolution and may also trap polar or more volatile fragments. The system should also be tested for contamination from previous runs by firing the pyrolyzer without sample. Generally, such a blank run should be made from time to time to ensure the absence of memory effects. A typical configuration of the so-called on-line approach is presented in Fig. 4.7.4. 

In the on-line approach, helium is recommended as the carrier gas to avoid the risk of an explosion in the pyrolysis system. Before pyrolysis, the GC system is optimized with respect to linear gas flow velocity in the column and methane peak shape (indication of dead volumes). Column connections should be made as specified by the column manufacturer. 

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