(655b) Minimize Losses During Scale Up of Multiphase Stirred Tank Reactors Through Better Understanding of Hydrodynamics

Stirred reactors are commonly used for carrying out catalytic hydrogenation in the process industries. The catalytic hydrogenation is a complex process involves four phases gaseous(H₂), organic, aqueous and solid (catalyst). A number of competing mass transfer and kinetic rate processes contribute to the overall process performance. The kinetic parameter stay the same on scale-up however other processes such as mass transfer and mixing intensity are usually lower in pilot/plant scale reactors compared to the laboratory scale reactors. This leads to lower conversion and selectivity on scale-up. In a stirred reactor, better mass transfer and mixing intensities can be achieved by selecting proper combination of agitator system, baffle arrangements & operating speed.

In this study Computational Fluid Dynamics (CFD) based models were used to understand the impact of impeller system design, baffle arrangement & operating speed on the reactor hydrodynamics. Multiphase CFD models were used to evolve various performance parameters such as gas-liquid interfacial area, power dissipation, mixing patterns. Multiple configurations were tested and compared with the lab scale reactor and an un-optimized pilot scale agitator design. An optimized design of impeller system & baffle arrangement showing mass transfer rates comparable with lab scale reactor was selected.

The optimized design showed 75% conversion as against the 27% conversion shown by the un-optimized design. The observed conversion with optimized design was in good comparison with the 80% conversion levels observed in the lab scale reactor. Thus, better understanding of reactor hydrodynamics is required for successful scale-up of multiphase stirred reactor. CFD models can be successfully employed to quickly analyze various scenarios and optimize the reactor design