Hydrocarbon cracking model

Taken together, these results support the hypothesis that EUV photoinduced hydrocarbon cracking, mediated by photoelectrons, is responsible for carbon contamination in EUV optics. This is referred to as the hydrocarbon cracking model. These results are supported by the model on a number of grounds. First, for a fixed amount of hydrocarbons in the vicinity of the mirror surface, the carbon growth increases with the number of photons and/or photoelectrons... 

In order to assess whether secondary reactions to form CO could be responsible for the experimental CO versus time curve shape, a series-parallel kinetic mechanism was added to the model. Tar and gas are produced in the initial weight loss reaction, but the tar also reacts to form gas. The rate coefficients used are similar to hydrocarbon cracking reactions. Fig. 5 presents the model predictions for a single pellet length. It is observed that the second volatiles maximum is enhanced. For other pellet lengths, the time of the second peak follows the same trends as in the experiments. While the physical model might be improved by the inclusion of finite rates of mass transfer, the porosity is quite large and Lee, et al have verified volatiles outflow is... 

The approach to hydrocarbon cracking taken by the Froment school is to model the actual elementary steps of radicals at the various molecular configurations [38]. These are relatively few initiation hydrogen abstraction from a primary, secondary, or tertiary carbon and radical decomposition by scission of a carbon-carbon bond in /3-position to the unpaired electron. Boolean relation matrices are used to reflect the structures of the hydrocarbon reactants by indicating the existence and location of all their carbon-carbon bonds. Computer software generates reaction networks on the basis of known rate coefficients and activation energies at the various positions. Froment states the number of components in naphtha cracking as around 200, that of radicals as 40, and that of elementary radical steps... 

The FCC unit comprises of two basic parts, a reactor/riser in which hydrocarbon cracking reactions occur and a regenerator in which catalyst regains its activity by burning coke deposited on it during cracking. More detailed description of the process is available in Avidan and Shinnar (1990). Recently, Dave and Saraf (2(X)2) reviewed the extensive literature available on modelling of industrial FCC units. 

Application of this model to the separation of hydrogen from hydrocarbon cracking gas has been attempted (Suzuki, I98S). Table 11.3 shows the conditions for calculation and Fig. 11.13.a and 11.13.b show the results for profiles of partial pressures and amounts adsorbed of carbon monoxide and nitrogen at purge ratios (ul/uh) of 0.11 and 0.1. Adsorption isotherm is of the Markham-Benton type. 

Dente and Ranzi (in Albright et al., eds.. Pyrolysis Theory and Industrial Practice, Academic Press, 1983, pp. 133-175) Mathematical modehng of hydrocarbon pyrolysis reactions Shah and Sharma (in Carberry and Varma, eds.. Chemical Reaction and Reaction Engineering Handbook, Dekker, 1987, pp. 713-721) Hydroxylamine phosphate manufacture in a slurry reactor Some aspects of a kinetic model of methanol synthesis are described in the first example, which is followed by a second example that describes coping with the multiphcity of reactants and reactions of some petroleum conversion processes. Then two somewhat simph-fied industrial examples are worked out in detail mild thermal cracking and production of styrene. Even these calculations are impractical without a computer. The basic data and mathematics and some of the results are presented. 

Willems, P, A., and Froment, G. F., Kinetic modeling of the thermal cracking of hydrocarbons. 

The combustion efficiency of benzene was monitored with an on-line real time mass spectrometer Ametek model Dycor 1000) tracking the parent mass peak for benzene. (Mass scans showed that as the parent peak was removed no peak above m/e = 40 appeared so the benzene was not just being cracked into a smaller unsaturated hydrocarbon but was being consumed.)... 

As a model for cracking of alkanes, the reaction of 2-methylpentane (16, 2MeP) over SbF5-intercalated graphite has been studied in a flow system, with the hydrocarbon being diluted in a hydrogen stream.104,105 A careful study of the product... 

For some widely practiced processes, especially in the petroleum industry, reliable and convenient computerized models are available from a number of vendors or, by license, from proprietary sources. Included are reactor-regenerator of fluid catalytic cracking, hydro-treating, hydrocracking, alkylation with HF or H2SO4, reforming with Pt or Pt-Re catalysts, tubular steam cracking of hydrocarbon fractions, noncatalytic pyrolysis to ethylene, ammonia synthesis, and other processes by suppliers of catalysts. Vendors of some process simulations are listed in the CEP Software Directory (AIChE, 1994). 

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