UMIST Polymer Engineering Report
S F Bush
Introduction
Earlier works (Ref 1, Appendix A) on the cracking of hydrocarbons and chlorination of hydrocarbons has provided a general mechanism and explicit rate expressions for the formation of carbon which have been found to be consistent with observations in a number of practical cases. The purpose of this note is to consider how the treatment might be extended to combustions where oxygen rather than chlorine is the oxidant and where the temperatures involved are likely to cause cracking.
References
Ref 1: S F Bush, Mechanism of Cracking and Carbon Formation, Norwegian Institute of Technology, 16th August 1977.
Invited paper to the Norwegian Institute of Technology Conference on Steam Cracking, Trondheim, 16th-17th August 1977.
S F Bush
Summary
What follows is an approximate mechanism and derived rate expressions determined by the need to see broadly what is going on in a very complex system. For a detailed prediction of the cracking pattern of any of dozens of feedstocks, the computer based methods described in Bush and Dyer (Ref 9) are required. In the following, some necessarily approximate generalisations have been made in the interests of understanding the meaning of the overall activation energy and pre-exponential parameters of carbon formation found experimentally.
References
Ref 9: S F Bush and P Dyer, The experimental and computational determination of complex chemical kinetics mechanisms, Proceedings of the Royal Society, A. 351 33-53 (1976).
Paper published in the Proceedings of the Royal Society (A. 351, 33-53) 15th January 1976.
S F Bush with P Dyer
Thanks are due to the late Mr C A J Young, FRS, who communicated the paper.
Summary
Methods for the experimental and computational analysis of complex kinetics problems are described. Two examples which have been applied to industrial-scale design and operation are taken: high temperature chlorocarbon rearrangement and hydrocarbon cracking. Surface mechanisms are included within the treatment.
The experiments were based mainly on the continuous-flow uniform reaction cell which allowed precise control over physical conditions up to the temperature limit of interest, 1000 oC. The computational treatment is based on the development of a mathematical model system which permits a model structure to be varied at will, enabling radically different mechanisms to be rapidly examined. Using the methods, many thousands of computations have been carried out on a variety of systems of widely differing structures for the purposes of both research and design.
In Appendix A the model structure was used. In Appendix B the minimisation of the sum of squares by Gauss’s method was used.
See also the other items in this section Mathematics & Computation.
