The Ziegler Natta catalysts are mostly heterogeneous in nature and adsorption processes are most likely to occur during polymerization reactions. Various kinetic schemes have been proposed assuming that polymerization centers are formed by the adsorption of metal alkyl species on the surface of a crystalline transition metal halide and then chain propagation occurs between the adsorbed metal alkyl and monomers. Langmuir Hinshelwood rate law for adsorption and reaction on solid is frequently adopted for this kind of reaction scheme. The rate expression for the heterogeneous Ziegler–Natta catalyzed polymerization process can be derived by using following model.

 

Assuming the rate of initiation and termination to be equal and that the overall rate is summation of rate of propagation and transfer, the overall rate can be derived as:

 

 

Industrial processes

Most polymerization processes are carried out in the liquid phase in batch reactor or CSTR and only few are continuous. For continuous process plug flow or fluidized bed with low residence time is used. Long residence time should be avoided in batch /CSTR as it is associated with many disadvantages such as catalysts decay and accumulation, polymer degradation, production of non-uniform polymer etc.