(656d) Oxidation of L-Methionine in a Rotor-Stator Spinning Disc Reactor

Oxidation of L-Methionine in
a Rotor-Stator Spinning Disc Reactor

Arnab
Chaudhuri¹ , Koen Kuijpers¹, Parimala Shivaprasad^1,2, Emma
Anna Carolina Emanuelsson², Timothy Noël¹, John van der
Schaaf¹

¹Department of Chemical
Engineering, TU Eindhoven, 5612 AZ, Eindhoven, Netherlands

²Department of Chemical
Engineering, University of Bath, BA2 7AY, Bath, United Kingdom

Process intensification (PI) is a promising
pathway to achieve sustainable chemical production while also improving the
safety of traditional chemical processes ^[1]. The rotor-stator spinning
disc reactor (rs-SDR) is one such PI reactor which consists of a
rotating disc enclosed by a stator. Reaction intensification is caused by the
high shear force on the feed as a result of the velocity gradient between the
rotor and the stator; resulting in high rates of mass and heat transfer ^[2].
This leads to rs-SDR being a particularly interesting reactor for photochemical
applications where photon transfer and mass transfer of the activated species are
often limited (e.g. for high concentration). In this study, we demonstrate the
potential of a photo-rs-SDR for applications towards photochemical reactions. The
oxidation
of L-methionine with methylene blue as the catalyst (Figure.1) was chosen as
the model reaction. The gas-liquid mass transfer limitations^[3] of this systems makes
it particularly applicable for the photo-rs-SDRs and demonstrates the potential
for improvements in productivity.

Figure 1: Reaction
scheme

The rs-SDR was illuminated using a solar light
simulator (AM1.5G), to ensure no light limitations. The reaction was carried
out by co-feeding the reaction solution and oxygen at the bottom of the
reactor. Samples were collected after a single pass through the reactor and the
reaction conversion was measured using HPLC.

Figure 2: Schematic
representation of the reactor set-up

A few of the results obtained are presented in
this abstract. Two different configurations were used for the photo-rs-SDR, one
with illumination on the dispersed region and one with illumination on the thin
film side. As illustrated in Fig 3, the dispersed region seemed to provide better
conversions. This is most likely since the mass transfer rates are higher in
this region and this allows for more oxygen in the liquid phase, leading to
improvements in reaction rates. As the liquid flow rates are increased for
constant gas flowrates, the conversions obtained are quite low regardless of
the reactor configuration.

Figure 3: Effect of
spinning speed and gas-liquid flowrate on reaction conversion

Figure 4: Visual
studies of flow regimes in the photo rs-SDR indicated that uniform distribution
of gas could be achieved with increased rotation speed.

Visual studies (Fig 4) of the reactor illustrated
that for 1:1 gas to liquid flow ratios, uniform distribution of gas could be
achieved throughout the illuminated section of the reactor for the dispersed configuration.
This further indicates that the contact between gas and liquid phases in this
region was quite high and improved with rotation speeds.

Quite high conversions were achieved in this
reactor with residence times of 10 mins. This indicates that the productivity
of L-methionine oxidation can be improved. The effect of rotation speed, gas-liquid
flowrate and catalyst concentration were investigated on the reaction
conversion. We have also investigated these parameters under more light
limiting conditions.  Additionally, the results were compared to two conventional
reactors which are currently used in photochemistry: batch and microflow.

To the best of the authors’ knowledge, this is
the first study of a successful synergistic reaction system using photochemistry
with the rs-SDR. We are currently investigating the potential of the photo
rs-SDR for targeted applications in pharmaceuticals and the fine chemical
industries.   

References

[1] Vlachos, D.G. and S. Caratzoulas,
Chemical Engineering Science 2010, 18-29.

[2] Meeuwse, M., J. van der Schaaf, and
J.C. Schouten, AIChE Journal 2012, p. 247-255.

[3]Emmanuel, N., Mendoza, C., Winter, M., Horn,
C. R., Vizza, A., Dreesen, L,& Monbaliu, J. C. M., Organic Process
Research & Development, 2017,p. 1435-1438.