Kohlen wassersto f f e / Modellierung / Pyrolyse / ReaktionskinetikThe pyrolysis of n-hexane -as well as the thermal decomposition of n-hexane with addition of propene and 1-butene -was studied at 819 K up to very high conversions. A reaction model, consisting of elementary reactions, was developed. With this model the experimental results including the formation of benzene and toluene can be described. Inhibition effects, the rates of formation of various products and the effects of products on the reacting system are discussed.

The kinetics of the thermal decomposition of n‐hexane and some hydrocarbon mixtures was studied experimentally in respect to the homogeneous formation of aromatics. Some 60 reaction products were identified, among them a number of precursor substances. An attempt has been made to extend our previous reaction model for the mathematical simulation of n‐hexane gas phase pyrolysis by addition of detailed pathways for the formation of benzene and toluene.

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Pyrolysis of 2,3-dimethyl butane (DMB) was carried out in a quartz flow reactor in the temperature range from 740 to 1032 K at normal pressure. The input concentration of DMB was 3.3 x mol/l using argon as diluent. Reaction time ranged between 3.1 and 3.9 s. The following products were analyzed by two-column gas chromatography: hydrogen, methane, ethene, propane, propene, butenes, butadiene, 2-methyl-2-butene, isoprene, benzene and toluene. Compared to thermal decomposition of n-hexane under similar experimental conditions, the main difference concerned the formation of ethylene, ethane and branched alkanes. A reaction model, based on elementary reactions, was developed to predict the experimental results and to verify our data basis of elementary reactions under different conditions. The model gives a quantitative description of the complex chemistry of the process. In addition, an algorithm is presented for model reduction. IntroductionThermal cracking of light naphtha feedstock is the most important process for producing olefins and diolefins. Production processes and equipment are designed on a purely empirical basis, mainly because a more profound knowledge of what happens on the molecular level is lacking. In this field, mechanistic modelling could help to predict, at least approximately, the reaction rates and product distribution of the complex chemical reaction system including its dynamics [32].In previous work [Z, 111, models were developed for the thermal degradation of n-hexane as an example of linear hydrocarbons. Up to 600 elementary reactions (ER) were needed to describe reaction rates and the formation of products up to high conversions. Moreover, with this model, the experimental results of pyrolysis of alkenes and n-hexane mixtures could be predicted. The experiments were carried out to investigate inhibition and acceleration effects on the overall reaction. This contribution presents an investigation on the pyrolysis of branched hydrocarbons. As a model substance, 2,3-dimethyl butane was used to investigate the influence of branched chain structures on decomposition. It was expected that, compared to nhexane, the decay mechanism of DMB would be less complex. Another aim was to test parts of our data basis of elementary reactions under conditions where C,-hydrocarbons are less important.It is generally accepted that thermal decomposition of hydrocarbons follows a radical reaction mechanism according to the Rice-Herzfeld scheme. The work of Niclause and Martin shows clearly that molecular reaction steps are of no importance whatsoever in thermal cracking [S, 61. Today, ESR and MS offer analytical tools to identify radical intermediates resulting from homolytic dissociation of C-C and C-H bonds. Capillary gas chromatography has reached a standard of development such that stable intermediate products can be quantitatively evaluated even in very small quantities 1261. Therefore, more and more precise experimental data become available which can be used for the development and verification of reacti...