HETEROPHASE STEP-GROWTH POLYMERIZATION IN A CONTINUOUS TUBULAR REACTOR

Abstract

The interfacial process is a well-established industrial process for the production of Bisphenol A polycarbonates. However, there is a dearth of kinetic analyses of the interfacial process in a tubular reactor, which offers greater overall control of this process. In the interfacial process, Bisphenol A dissolved in a dispersed aqueous phase reacts with phosgene in the continuous organic phase producing oligomers that undergo further reaction in the organic phase to produce polymers. This process was carried out in a tubular reactor at a constant pressure of 85 PSI and a constant temperature of 35°C. The kinetics of the mass transfer and reaction and the solubility of reactants were used to develop a mathematical model of the interfacial process in a tubular reactor. The parameters were optimized using proprietary plant data and the model simulations compared to the experimental data proved to be quite accurate. The developed model was used to investigate the heterophase kinetics of this system. A key parameter controlling the interfacial process in a tubular reactor is the dispersed aqueous droplet size. The droplet size determines the total surface area for mass transfer, and decreasing this droplet size from 10&mu;m to 5&mu;m results in an increase of molecular weight by about 130%. Also, the mass transfer coefficient of BPA (k_L2) determines whether the processes at the interface are diffusion controlled or reaction controlled. The system exhibits diffusion controlled behavior when k_L2 is approximately 1.0 × 10<super>-7</super> m/s. Conversely, the system exhibits reaction controlled behavior when k_L2 is around 4.0 × 10<super>-6</super> m/s. The chain length distribution in the interfacial process follows Flory's most probable distribution. This functional group model was then expanded to a copolymerization system for siloxane-polycarbonate copolymers. For the copolymerization process, the key parameters shown to have a significant effect on the copolymer composition (mean sequence length and sequence length distribution) is the feed composition and reactivities of the comonomers.