A STUDY OF MACROSEGREGATION IN LOW-DENSITY POLYETHYLENE AUTOCLAVE REACTORS BY COMPUTATIONAL FLUID DYNAMIC MODELING

Flow and reaction in a typical commercial scale autoclave LDPE reactor were modeled by a three-dimensional computational fluid dynamic (CFD) k-epsilon model in order to shed light on the macrosegregation effect s that can occur in these reactors. It is shown that the CFD model pre dicts significant differences from CSTR behavior. Results are discusse d in terms of the effects of macro- and microscale inhomogeneities of concentration and temperature on free radical polymerization kinetics. The observed nonidealities in terms of minima in the initiator consum ption curves and multiple steady states are explained on the basis of competing turbulent transport and chemical kinetics. Microsegregation effects are shown to be negligible in comparison to macrosegregation e ffects. Given the fact that the CFD model is based an reactive scalar and energy balances without adjusted parameters in the three-dimension al flow field of the entire reactor, it is tentatively concluded that commercial-scale LDPE vessel reactors can have significant macrosegreg ation effects beyond a certain steady-state adiabatic operating temper ature that is specific to the initiator being used.