Conventional pyrolysis

Catalytic Pyrolysis. This should not be confused with fluid catalytic cracking, which is used in petroleum refining (see Catalysts, regeneration). Catalytic pyrolysis is aimed at producing primarily ethylene. There are many patents and research articles covering the last 20 years (84—89). Catalytic research until 1988 has been summarized (86). Almost all catalysts produce higher amounts of CO and CO2 than normally obtained with conventional pyrolysis. This indicates that the water gas reaction is also very active with these catalysts, and usually this leads to some deterioration of the olefin yield. Significant amounts of coke have been found in these catalysts, and thus there is a further reduction in olefin yield with on-stream time. Most of these catalysts are based on low surface area alumina catalysts (86). A notable exception is the catalyst developed in the former USSR (89). This catalyst primarily contains vanadium as the active material on pumice (89), and is claimed to produce low levels of carbon oxides. 

The products obtained using high energy for milliseconds are different from products produced by conventional pyrolysis at moderate temperatures for minutes or hours. The gaseous products are richer in unsaturates with acetylene predominating. 

In cases where R1 is a stabilizing group (entries 1-11) conventional pyrolysis is satisfactory, but the use of FVP has allowed the extension of the reaction to cases with R1 = H or alkyl (entries 13, 18-20) where conventional pyrolysis does not work. For R1 = C02Et, simply increasing the furnace temperature leads to loss of the ester group to give terminal alkynes and 1,3-diynes (entries 15, 17) as already noted in Section IV.B. The E-Z isomerization which occurs for styrylalkynes at higher temperatures (entry 20) was also noted previously in Section II.C. 

Saiz-Jimenez, C., Ortega-Calvo, J. J., and Hermosin, B. (1994). Conventional pyrolysis A biased technique for providing structural informations on humic substances Naturwis-senschaften 81, 28-29. 

Lowndes et al. [91] used the commercial CFD model Fluent to simulate flame spread along a conveyor belt. Fluent, at the time this modeling was conducted, did not contain a conventional pyrolysis model in the sense that is normally implied in the fire literature. Instead, the authors adapted a discrete phase model, which is intended to simulate the combustion of pulverized coal. 

The literature review of microwave-assisted or induced pyrolysis of plastics follows. In this section special attention is paid to the reactor configurations used, comparing them with the configurations found on more conventional pyrolysis equipment. The most important findings produced from this research are presented, including product yield, characteristics and composition. An analysis is presented to assess whether in any example there is evidence for nonthermal microwave effects promoting the pyrolytic reactions. 

Another material treated with microwave pyrolysis has been sewage sludge. Disposal of this material, which is a by-product in wastewater treatment processes, is a considerable problem and currently accounts for up to 60% of the operational cost of wastewater treatment plants. Microwave pyrolysis of sludge provides a rapid and efficient process with reduced process time and energy requirements compared with conventional pyrolysis [54]. 

Furthermore, the condensables from microwave pyrolysis contain less carcinogenic compounds than those produced in conventional pyrolysis [55] and the noncondensables have a higher concentration of CO and H2 (synthesis gas) after microwave pyrolysis than after conventional pyrolysis [56],... 

As mentioned above, the main difference between microwave and conventional pyrolysis is the initial sonrce of thermal energy and the way this is transferred to the plastic. Nonetheless, there are other differences, particularly when microwave pyrolysis is compared with flnidized-bed pyrolysis equipment in the latter, the primary reaction prodncts are carried ont of the reactor by a hot gas stream which enables these products to take part in secondary and tertiary reactions. On the other hand, in microwave pyrolysis, once the pyrolytic prodncts leave the carbon bed, they stop receiving heat by conduction from the hot carbon and come in contact with a relatively cold carrier gas. This has an important effect in the nnmber of consecntive reactions occnrring and therefore, on the natnre of the prodncts, as is shown in Section 3.2.2. 

The results shown in Table 21.1 do not imply that microwave pyrolysis is slower than conventional pyrolysis, but confirm the need to consider heat and/or mass transfer limitations because of the particle and size samples used in the experiments [26]. 

In terms of the individual compounds found in the condensable products, as with conventional pyrolysis, a-alkenes alkanes and dialkenes were the most abundant compounds. A large number of other aliphatic and aromatic compounds ranging from C3 to approximately 55 were also found, including methylcyclopentene, benzene, cyclohexene, toluene, ethylbenzene, xylene, propylbenzene and methyl-ethylbenzene. The analysis also showed that the condensables obtained at 500 and 700°C, although possessing similar levels of cleavage, showed important differences in the individual compounds present [85],... 

The main compounds in the noncondensable gaseous products were linear aUcenes and alkanes, ranging from Ci to C7 and accounted for almost 90% of the mixture, with the rest consisting mainly of cyclic aliphatic compounds. In terms of individual compounds, the gaseous mixture was composed of compounds similar to those found in the conventional pyrolysis of PE [72, 74, 92], with the difference however that negligible amounts of hydrogen were found [85],... 

The advantage of microwave pyrolysis over conventional pyrolysis methods do not rely on changes in chemical pathways, but in the advantages that have been mentioned previously. 

Scientific studies have found that the differences between microwave and conventional pyrolysis go beyond the obvious difference in the source of heat. Other differences arise from the very high rates of heat transfer from the microwave-absorbent to the waste, the amount heat received by the primary pyrolytic products once they leave the absorbent bed and the highly reducing environment. These three aspects have been shown to have an important effect in the final products since they modify the extent of secondary and tertiary reactions. Moreover, the scientific studies have shown that a nonthermal microwave effect in these processes is unlikely to exist. Tests have showed the potential of the microwave-induced pyrolysis process for the treatment of real plastic-containing wastes and it is believed that a commercial process could be developed, for example, to recover clean aluminium from plastic/aluminium laminates. Other materials, in particular tyres, coal and medical wastes are very good candidates to be treated/recycled using microwave pyrolysis and there have been a considerable number patents filed with this goal in mind. 

Conventional pyrolysis 5-30 min Medium 700-900 gases Charcoal, gases... 

The influence of wood variety (beech, chestnut, Douglas fir, redwood and pine) on the conventional pyrolysis characteristics has been investigated for a wide range of applied radiation intensities (front 28 to SOkW/m ), which correspond to final sample temperatures of 600-950K. 

A limitation of vacuum pyrolysis technology is heat transfer. Previous studies have shown that the rate of heat transfer is essentially the rate limiting step for pyrolysis reactions [2]. Conventional pyrolysis reactors such as multiple hearth furnaces, rotary kilns and screw type reactors exhibit overall heat transfer coefficients ranging from 10 to 60 [3], depending on the type of feedstock handled. The low thermal... 

It was shown that the conventional pyrolysis of the model compound generated a mixture of compounds suggesting that the importance of the mechanisms is A > B C. However, lignin provides a different matrix due to the cage effect of a large molecule. 

The aromatic acids released from different HA upon pyrolysis in the presence of TMAH probably represent original components of the HA structure released by the thermolytic action of TMAH (10,12,16,17). This observation is supported by the TMAH thermochemolysis data of Hatcher et al. (23) and Hatcher and Clifford (16) for a volcanic soil humic acid. In fact, the C-NMR spectrum of this particular HA (shown in Figure 4) clearly indicates that it is composed of only aromatic and carboxyl carbons. Conventional pyrolysis of these HA produced trace quantities of volatile products without the release of any significant compounds while pyrolysis in the presence of TMAH yielded mainly benzenecarboxylic acid methyl esters (Figure 5), in accordance with the NMR data. 

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