An expert system for hydrocarbon pyrolysis reactions

The behaviour of complex chemical reactions such as the cracking of hydrocarbons may be represented by a set of differential equations each of which corresponds to a mass balance over a single elementary species, reactant or product. The simulation of the overall reaction is achieved by numerical integration of this set of equations. For reactions such as combustion and pyrolysis of organic molecules the number of elementary reactions is very large indeed and in order to produce a viable model of the reaction it is necessary to produce a subset that approximates to the behaviour of the real system.We have developed an expert system on a VAX11/780 that generates reaction mechanisms on the basis of a generator of elementary reactions that is constrained by rules relating to initial conditions and kinetic and thermodynamic data. Chemical species are represented by PROLOG lists that can be manipulated in a variety of ways in order to generate reactions such as dissociation, abstraction, combination etc. The emphasis of the system is on eliminating unproductive reactions at an early stage in order to avoid the generation of hundreds of redundant reactions.The mechanisms generated so far for small acyclic hydrocarbons compare favourably with those produced by human experts. It appears that some relatively straightforward extensions of the existing system will result in a powerful tool for the investigation of complex reactions and the evaluation of kinetic data.