Liquid-Liquid Mass Transfer In a Rotor-Stator Spinning Disc Reactor

Liquid-liquid mass transfer in a rotor-stator spinning disc reactor

Frans Visscher, John van der Schaaf, Mart de Croon, and Jaap C. Schouten

Laboratory of Chemical Reactor Engineering, Eindhoven University of Technology, The Netherlands

Introduction

High gas-liquid and liquid-solid mass transfer rates can be achieved in the rotor-stator spinning disc reactor (SDR) [1, 2]. Here we demonstrate high liquid-liquid mass transfer rates in this new type of reactor using the extraction of benzoic acid from n-heptane to water. A benzoic acid in n-heptane flow was continuously contacted in the SDR with a benzoic acid free water flow. The steady state benzoic acid concentrations in both liquids were measured by UV-VIS spectroscopy. The experimental setup is shown in Figure 1.

 

Figure 1. Schematic drawing of the rotor-stator spinning disc set-up. The rotor is located at 1.0 10^-3 m from the top and bottom stator. Water is fed to the top of the reactor near the axis. n-Heptane with benzoic acid is fed through an inlet in the bottom stator near the rim of the disc.

Results

The overall liquid-liquid mass transfer coefficient, k_La_Lε_ORG, was determined for a total volumetric liquid flow ranging from 4.5 10^-6 m³ s^-1 for an organic to aqueous ratio of 1:1, to 17.2 10^-6 m³ s^-1 at a ratio of 1:7. The multiphase flow pattern was determined through high speed imaging of the bottom stator.

Figure 2. The influence of rotational disc speed on the holdup inside the reactor. Pictures are made through the bottom stator, with a total flow rate of 4.7 10^-6 m³ s^-1. Water appears blue because of water soluble ink, n-heptane appears white.

Upon increasing the rotational disc speed the continues n-heptane spiral (in white) breaks up into spiralling droplets due to the enlarged shear force that is present between the rotor and the bottom stator. This causes an increase of the interfacial area.

Figure 3 The overall liquid-liquid mass transfer rates in the rotor-stator spinning disc reactor are increasing with an increase of the rotor speed and with the flow ratio. Values are calculated assuming plug flow behavior for both phases.

Figure 4 At higher rotational disc speed, a stronger shear stress is acting on the liquids between the rotor and the stator. This causes an increase of the overall mass transfer coefficient. The overall liquid-liquid mass transfer rates are calculated assuming ideally mixed behavior.

 

Conclusion

These liquid-liquid mass transfer rates are at least 25 times higher compared to those in packed columns, and at most 15 times higher compared to mass transfer rates in state of the art microchannels. This implies that both the process volume and the process time of current equipment could be decreased.

 

References

[1]  Meeuwse, et al. (2010) Chemical Engineering Science, 65(1), 466-471.

[2]  Meeuwse, et al. (2010) Industrial & Engineering Chemical Research, 49(21), 10751-10757.