Olefin selective pyrolysis

In the 1930s it was discovered that the pyrolysis of alkanes produced large quantities of olefins. This pyrolysis process is not very selective, but the costs of separation were cheaper, and scaleup was simpler and safer in making ethylene rather than acetylene so during the 1940s ethylene and other small olefins replaced acetylene as the major building block in chemical synthesis. We will consider the reactions and reactors used in olefin synthesis from alkanes in the next chapter. 

Most of the effort at China Lake was directed toward demonstrating, at the bench scale, that polymer gasoline could indeed be made noncatalytically from the olefins formed by the selective pyrolysis of municipal solid waste (MSW). Funding for the bench-scale demonstration was provided by the Industrial Environmental Research Laboratory (IERL) of the Environmental Protection Agency, beginning in 1975 (EPA-IAG-D6-0781). 

The combination of low residence time and low partial pressure produces high selectivity to olefins at a constant feed conversion. In the 1960s, the residence time was 0.5 to 0.8 seconds, whereas in the late 1980s, residence time was typically 0.1 to 0.15 seconds. Typical pyrolysis heater characteristics are given in Table 4. Temperature, pressure, conversion, and residence time profiles across the reactor for naphtha cracking are illustrated in Figure 2. 

Cracking temperatures are somewhat less than those observed with thermal pyrolysis. Most of these catalysts affect the initiation of pyrolysis reactions and increase the overall reaction rate of feed decomposition (85). AppHcabiUty of this process to ethane cracking is questionable since equiUbrium of ethane to ethylene and hydrogen is not altered by a catalyst, and hence selectivity to olefins at lower catalyst temperatures may be inferior to that of conventional thermal cracking. SuitabiUty of this process for heavy feeds like condensates and gas oils has yet to be demonstrated. 

The use of selectivity data as a means of identifying intermediates has been employed effectively. For example, in the dichlorocyclo-propanation of olefins, the selectivity of attack using CC12 generated by different methods (the pyrolysis and a elimination of chloroform) was found to be almost identical (Skell and Cholod, 1969a). This was... 

Neste Oy, Engineering Olefins FCCU light gasoline, EC pyrolysis gasoline Selective hydrogenation of C5, C6 and C7 diolefins to olefins 1 1995... 

Computer modeling of hydrocarbon pyrolysis is discussed with respect to industrial applications. Pyrolysis models are classified into four groups mechanistic, stoichiometric, semi-kinetic, and empirical. Selection of modeling schemes to meet minimum development cost must be consistent with constraints imposed by factors such as data quality, kinetic knowledge, and time limitations. Stoichiometric and semi-kinetic modelings are further illustrated by two examples, one for light hydrocarbon feedstocks and the other for naphthas. The applicability of these modeling schemes to olefins production is evidenced by successful prediction of commercial plant data. 

Maitlis et al (707) recently demonstrated the selective formation of C2-C3 olefins in the pyrolysis of [Cp Rh(CH2)CH3]j complexes suggesting the successive chain propagation with methylene and methyl species attached on the Rh ensembles. 

Figure 11 shows the high pressure gas purification system used to concentrate the olefins. The carbon dioxide was removed very selectively with a hot carbonate solution at a system pressure of about 3100 kPa. This resulted in a relatively pure stream of carbon dioxide being rejected. The semipurified pyrolysis gases then passed to the hydrocarbon absorber where the hydrocarbons other than methane were absorbed. The low molecular weight olefins were then boiled off the absorbing oil to result in a concentrated product stream. At this point in the process, several different uses for the olefins can be imagined (a) the olefins could be further... 

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