Prediction of the Spatial Distribution of the Average Molecular Weights in Living Polymerisation Reactors using CFD Methods

Abstract

Polymerisation reactor design and mode of operation are particularly important for polymerisation processes where the lifetime of the growing 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 polymer produced, for example, molecular weight distribution. The strategies can only be devised for ideal reaction and reactor behaviour. Since neither are ideal, it is necessary to understand those factors which cause deviation from ideality. In this work, the influence of the spatial distribution of temperature and flow velocity is examined for an ideal classical living polymerisation reaction carried out in a tubular reactor under steady‐state reactor conditions using a computational fluid dynamics (CFD) code (PHOENICS) to explore the influence of the spatial distribution of species and temperature on the product with all other reactor features being ideal. Particular attention is given to the problem of describing the spatial distribution of the dispersity index (moments of the molecular weight distribution) of the polymer in addition to flow velocity, temperature, component concentrations and kinematic viscosity. Comparisons are made between the CFD predictions, simulations based on the ideal behaviour of the process, and the experimental results from a laboratory‐scale reactor. It is shown that the CFD predictions give a more realistic description of the tubular reactor behaviour for the conditions employed. The limitations of the CFD approach and the additional problems still needing to be addressed, such as mixing quality, are discussed.

Multiscale Modeling of Mixing Behavior in a 3D Atom Transfer Radical Copolymerization Stirred-Tank Reactor

“…Therefore, a laminar regime is employed in our CFD model. Similar assumption is also accepted by many other researchers . The corresponding governing equations under steady state condition are shown as follows:…”

“…Similar assumption is also accepted by many other researchers. [15][16][17]27] The corresponding governing equations under steady state condition are shown as follows:…”

Simulation of Polymer Reactors Using the Compartment Modeling Approach

“…In the last 20 years modeling approaches using CFD simulations to describe polymer reactors have overcome this challenge by using either simplified kinetics, as refs. 15–18 and Fox et al,19–21 and/or “user defined function”, as the group of Luo22–24 to take polymerization reaction into account, which is still numerical demanding. On the contrary, axial dispersion models describe hydrodynamics on macro scale with only one or two parameters, but allow for the implementation of complex polymerization kinetics on micro scale.…”

Computational Fluid Dynamics Simulation of Multiscale Mixing in Anionic Polymerization Tubular Reactors

“…For such polymerization systems, mixing shows multiscale behaviors, i.e., macroscopic‐scale and microscopic‐scale 14–16. On the one hand, macroscopic‐scale mixing can be described via reactor operation parameter distributions such as temperature, monomer concentration, and polymer concentration.…”

“…On the one hand, macroscopic‐scale mixing can be described via reactor operation parameter distributions such as temperature, monomer concentration, and polymer concentration. On the other hand, microscopic‐scale mixing can be investigated using polymer microscopic property profiles such as number‐average molecular weight ( M n ) and dispersity index (PDI) 9, 14, 15. Polymer molecular properties can be greatly influenced by polymerization operation parameters.…”