Propane cracking models

The basic conversion rate data for the present study are from experiments on propane cracking made several years ago by one of the authors (K. D. Williamson). The conversion/time/temperature data have been published in graphical form (2). We believe these to be superior to any high-temperature cracking rate data available. The range of decompositions covered (0-80%) is extended by recourse to some older propane data available to us but not previously published. These latter data are of somewhat poorer quality. Previously unpublished data on n-butane and n-hexane conversion (0-99% decomposition) from the Williamson study are used to verify the model. 

Thus the high conversion data indicate, at least conditionally, that the EE model is useful even beyond the maximum decompositions used in commercial propane cracking. 

Keywords Propane cracking Density fimctional methods BMK Thermochemistry Kinetics CCSD(T) calculations Composite models... 

Table 8.1 shows the stochastic model solution for the petrochemical system. The solution indicated the selection of 22 processes with a slightly different configuration and production capacities from the deterministic case, Table 4.2 in Chapter 4. For example, acetic acid was produced by direct oxidation of n-butylenes instead of the air oxidation of acetaldehyde. Furthermore, ethylene was produced by pyrolysis of ethane instead of steam cracking of ethane-propane (50-50 wt%). These changes, as well as the different production capacities obtained, illustrate the effect of the uncertainty in process yield, raw material and product prices, and lower product... 

In commercial practice, propane is often cracked at percent decompositions above 90%. C4+ paraffins are commonly cracked at 90% to nearly 100% decomposition. A kinetic model fitting decomposition data in the 90+% range should, therefore, be valuable. 

Mechanistic modeling has been useful in studying pyrolysis kinetics at low conversion (4,5,6). Few attempts have been reported at the high conversion levels of commercial cracking (7). This stems from the large number of species and free radicals and of their associated reactions, which increases substantially with conversion and leads to excessive computation time. In addition, when one considers that precise pyrolysis mechanisms, for even a simple feedstock such as propane (8), are still subject to dispute, it is clear that more empirical models will continue to dominate commercial applications. 

The model includes several reactions which account for cocracking effects. Examples of this type of reaction include the reverse reactions of R-l and R-4 and the reaction R-17. R-17 predicts more ethylene and less heavier products from cocracking ethane and propane than from separate cracking. 

The cracking of propane to produce ethylene is represented by the simplified kinetic model ... 

Berner, U., Faber, E., Scheeder, G. Panten, D. 1995. Primary cracking of algal and landplant kerogens kinetic models of isotope variations in methane, ethane and propane. Chemical Geology, 126(3/4), 233-245. 

As a model for cracking of alkanes, the reaction of 2-methylpentane (MP) over SbFs-intercalated graphite has been studied in a flow system, the hydrocarbon being diluted in a hydrogen stream. A careful study of the product distribution vs time on stream showed that propane was the initial cracking product whereas isobutane and isopentane (as major cracking products) appear only later. 

Koyama, H. and Dranoff, J. S., Modeling the Thermal Cracking of Ethane and Propane in a Non-Isothermal Vertical Pneumatic Transport Reactor , Ind. Eng. Chem. Res., 31, 2,265(1992). 

The results given in Section 9.3.2 for the thermal cracking of naphtha and of a mixture of ethane-propane were obtained with very detailed radical kinetic schemes for these processes [Willems and Froment, 1988a, b]. The present problem formulates ethane cracking in terms of a drastically simplified molecular model containing 7 reactions. This reaction scheme and the corresponding kinetic model was derived from the radical scheme developed by Sundaram and Froment [1977]. Table 1 gives the kinetic parameters of these reactions. It should be mentioned that the kinetic parameters for the reverse reactions (2) and (5) were obtained from equilibrium data. Table 2 is the matrix of stoichiometric coefficients ay defined by... 

Sundaram,K.M. and G.F.Froment. "Modelling of Thermal Cracking KineticsoThermal Cracking of Ethane,Propane and Their Mixtures" Chem.Eng.Sci. v32 (1977) 601-609. 

Modeling of thermal cracking of propane was performed by Sundaram and Froment [46] on the basis of experimental work by Van Damme et al. [47]. The kinetics of mercury-photosensitized decomposition of propane was studied in a pair of papers by Papic and Laidler [14, 15] in the seventies. 

DFT, ab initio and model chemistry calculations have been performed on the chain initiation, propagation and termination reactions for the cracking of propane. From the methodological point of view, it was shown that the DFT BMK results of enthalpies of formation and energies of activation are very similar to the experimental values, with rms error of about 2 kcal/mol. For reactions involving... 

Sundaram, K. M. and G. F. Froment, 1977. Modeling of thermal cracking kinetics. 1. Thermal cracking of ethane, propane and their mixtures. Chemical Engineering Science, 32, 601. 

In the work of Lobera et al. (2008), Li et al. (201 la), and Fsgoo s et al. (2011), cracking of propane was also included in their kinetic models. They all used power-law models and assumed that the reaction was first order to propane. It is worth mentioning that the C—C break from both... 

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