Zg. Meszena et Af. Johnson, Prediction of the spatial distribution of the average molecular weights inliving polymerisation reactors using CFD methods, MACROMOL TH, 10(2), 2001, pp. 123-135
Full Paper: Polymerisation reactor design and mode of operation are particu
larly important for polymerisation processes where the lifetime of the grow
ing species is long compared to the mean residence time of reactants in the
reactor. For these reasons, reactor control strategies can be devised for
living polymerisation processes in order to tailor the nature of the polyme
r produced, for example, molecular weight distribution. The strategies can
only be devised for ideal reaction and reactor behavior. Since neither are
ideal, it is necessary to understand those factors which cause deviation fr
om ideality. In this work the influence of the spatial distribution of temp
erature and flow velocity is examined for an ideal classical living polymer
isation reaction carried out in a tubular reactor under steady-state reacto
r conditions using a computational fluid dynamics (CFD) code (PHOENICS) to
explore the influence of the spatial distribution of species and temperatur
e on the product with all other reactor features being ideal. Particular at
tention is given to the problem of describing the spatial distribution of t
he dispersity index (moments of the molecular weight distribution) of the p
olymer in addition to flow velocity, temperature, component concentrations
and kinematic viscosity. Comparisons ate made between he CFD predictions, s
imulations based on the ideal behaviour of the process, and the experimenta
l results from a laboratory-scale reactor. It is shown that the CFD predict
ions give a more realistic description of the tubular reactor behaviour for
the conditions employed. The limitations of the CFD approach and the addit
ional problems still needing to be addressed, such as mixing quality, are d
iscussed.