Hydrocarbon pyrolysis, kinetics

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. 

In studying pyrolysis kinetics, Liliedahl et al. (1991) determined the RTD of their apparatus by pulse-injection of a gaseous hydrocarbon tracer. 

Tsang Chemical Kinetic Database for Hydrocarbon Pyrolysis [406]... 

W. Tsang. Chemical Kinetic Database for Hydrocarbon Pyrolysis. Ind. Eng. Chem. Res., 31 3-8,1992. 

Table n. Kinetics for representative reaction pathways for hydrocarbon pyrolysis... 

Ross and Shu [38], discussing the computer modelling of hydrocarbon pyrolysis for olefin production, classify reaction models in four categories in order of increasing sophistication empirical, semi-kinetic, stoichiometric and mechanistic. Most concepts of this classification are included in Table 3 with, however, a more classical meaning of the word stoichiometry. 

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. 

A few years later, a third type of reaction was added to the scheme, the isomerization of large radicals by internal abstraction of H atoms (9). This was shown (41) to account satisfactorily for the product distribution arising from the pyrolysis of long chain hydrocarbons (e.g., n-Ciel ). Very little has happened in the approximately 25 years since the last of these contributions to alter our conceptual understanding of the kinetics of hydrocarbon pyrolysis. Instead, the very extensive research done since then has generally been devoted to determining the quantitative kinetic parameters associated with the elementary step reactions of the pyrolysis chain. Much of this work has been summarized in some recent books (62) and reviews (26, 51). 

One new field related to hydrocarbon pyrolysis of small ring compounds (3- and 4-membered rings) has been developed in the past decade, and that is the subject of biradicals. These are discussed briefly. In the present article, I consider in some detail the present status of our experimental and theoretical understanding of these step reactions and how they relate to the very practical problems of kinetic modeling of pyrolysis systems. 

Savage PE (2000) Mechanisms and kinetics models for hydrocarbon pyrolysis. J Anal Appl Pyrolysis 54 109-126... 

In our previous study, (1 ) the introduction of large amounts of hydrogen into a hydrocarbon pyrolysis system was found to enhance the rate of pyrolysis and to result in increased yields of ethylene. The role of hydrogen was discussed in terms of the reaction kinetics and mechanism where hydrogenolysis of higher olefins into ethylene has an important role. In this connection, hydrogenolysis of 1-butene ( ) and isobutene (3) had been investigated to demonstrate the kinetics o consecutive demethylation of the olefins into ethylene. 

Other kinetic treatments were presented [385-387] which tested the kinetics of the liquid hydrocarbon pyrolysis to PO thermal degradation. 

Flame or Partial Combustion Processes. In the combustion or flame processes, the necessary energy is imparted to the feedstock by the partial combustion of the hydrocarbon feed (one-stage process), or by the combustion of residual gas, or any other suitable fuel, and subsequent injection of the cracking stock into the hot combustion gases (two-stage process). A detailed discussion of the kinetics for the pyrolysis of methane for the production of acetylene by partial oxidation, and some conclusions as to reaction mechanism have been given (12). 

Chemical vapor deposition (CVD) of carbon from propane is the main reaction in the fabrication of the C/C composites [1,2] and the C-SiC functionally graded material [3,4,5]. The carbon deposition rate from propane is high compared with those from other aliphatic hydrocarbons [4]. Propane is rapidly decomposed in the gas phase and various hydrocarbons are formed independently of the film growth in the CVD reactor. The propane concentration distribution is determined by the gas-phase kinetics. The gas-phase reaction model, in addition to the film growth reaction model, is required for the numerical simulation of the CVD reactor for designing and controlling purposes. Therefore, a compact gas-phase reaction model is preferred. The authors proposed the procedure to reduce an elementary reaction model consisting of hundreds of reactions to a compact model objectively [6]. In this study, the procedure is applied to propane pyrolysis for carbon CVD and a compact gas-phase reaction model is built by the proposed procedure and the kinetic parameters are determined from the experimental results. 

E. B. Ledesma, N. D. Marsh, A. K.Sandrowitz, and M. J. Womat, Global kinetic rate parameters for the formation of polycycUc aromatic hydrocarbons [PAH] from die pyrolysis of catechol A model compound representative of soUd fuel moieties. Energy Fuels 16(6), 1331—1336... 

There are a large number of chain reactions that are significant in industrial processes or play an important role for the environment. Classes of chain reactions that are relevant industrially include hydrogen/halogen reactions and pyrolysis of hydrocarbons, which are both discussed below, and free-radical polymerization discussed in many textbooks on kinetics. As an example of a chain reaction of significant environmental consequence, we will discuss formation of nitric oxide from fixation of atmospheric nitrogen. 

E. Ranzi, M. Dente, A. Goldaniga, G. Bozzano, and T. Faravelli. Lumping Procedures in Detailed Kinetic Modeling of Gasification, Pyrolysis, Partial Oxidation, and Combustion of Hydrocarbon Mixtures. Prog. Combust. Sci. Techn., 27 99-139, 2001. 

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