KINETIC-MODEL FOR FORMATION OF AROMATICS IN THE HIGH-TEMPERATURE CHLORINATION OF METHANE

A detailed thermochemical kinetic model consisting of 165 reversible r eactions has been developed to describe catalyzed polymerization of me thane under adiabatic conditions. The model, an extension of that prev iously proposed (Weissman and Benson, 1984, 1989), was tested against available experimental data for CH3Cl pyrolysis in the absence and pre sence of CH4 in the temperature range 1260-1310 K (Weissman and Benson , 1984). Predictions of major product yields are reasonable although p redictive inadequacies are discussed. Product distributions in the CH4 /Cl-2 reaction were studied as a function of inlet/mixing temperature (T-0 = 750-900 K), reactor pressure (P-R = 1.0-5.0 atmospheres) and CH 4:Cl-2 mole ratio (1.0-2.0). Product distribution is shown to be a str ong function of inlet temperature and reactant mole ratio. Choice of t hese parameters define the ''window'' of accessible reaction condition s experimentally available for useful product formation. Commercially attractive C-2 yields (C2H2, C2H4), with minimal soot formation (as id entified by the yields of precursor molecules, styrene and naphthalene ), are predicted under ''ideal'' conditions. On the basis of the propo sed model, the simulations indicate in situ mixing of preheated CH4 an d Cl-2 feeds is required. The latter must be achieved on millisecond t ime-scales in order to provide a homogeneous mixture at the onset of r eaction. Only limited homogeneous formation of high molecular weight p roducts is predicted at the residence times and temperatures considere d, suggesting that the significant yields of soot observed experimenta lly may be a consequence of heterogeneous and/or mixing effect contrib utions. The effects of the latter experimental ''perturbations'' on ho mogeneous product formation, neglected in the simulations which were c onducted under ''ideal'' conditions, are considered in detail.