(257e) Horizontal and Vertical Gas-Liquid-Solid Slurry-Taylor Flow: Liquid-Solid Mass Transfer Measurements Via Ion Exchange Resin

In multiphase micro-reaction
technology the solid catalyst is usually immobilized on the reactor walls,
which not only leads to rather small catalyst amounts per unit volume but more
seriously impinges on its flexibility. The catalyst removal in case of
deactivation or change of operation is difficult, even impossible without
damage to the reactor wall. Furthermore the coating process itself is specific
for each catalyst and requires therefore additional development time.

A new approach to join
beneficial properties of Taylor-flow with the operational flexibility of
conventional slurry reactors is the slurry-Taylor flow where catalyst particles
are suspended and kept in motion by the internal circulations in the liquid
slugs.

The concept of a three phase
slurry micro-reactor was first applied by Enache et
al. [1] for gas-liquid-solid vertical flow. In contrast to other recent studies
[2, 3, 4] on liquid-liquid horizontal flow where solid
particles are placed in the dispersed liquid phase, we investigate gas-liquid horizontal
and vertical flow with the solid localised (in general) in the continuous
phase.

We were able to show that the
performance of this new contact mode is comparable to a laboratory stirred tank vessel under semi-batch conditions [5] and we concentrate
now on hydrodynamics and mass-transfer properties.

We identified different flow
regimes by varying the fluids flow rates, solid charge and flow direction
(figure 1).

Here we discuss our first
results regarding the liquid-solid mass transfer capacity of slurry-Taylor
flow. We
chose to work with ion exchange resins as suspended particles [6] and apply and
compare two different measurement strategies to follow the neutralization of
caustic soda and thereby the ion exchange rate: we use a pH color indicator
(figure 2) which allows not only to estimate the time required to reach a
specific pH-value but also to detect the region of transfer positioned in the
liquid slug which is especially interesting for heterogeneous flow regimes.
Also we measure the change of conductivity with electrodes consisting of two
platinum wires, connected to an alternating current source. Several of these
electrodes are placed along the tube length which allows us to follow the
sodium concentration online. Both methods are used to calculate liquid-solid
mass transfer coefficients for different fluid flow rates, particle diameters
and charges with the aim to propose a correlation law.

 SHAPE  \* MERGEFORMAT

Figure
1) Examples for some typical flow patterns for horizontal (A, C) and vertical
(B, D) flow. Materials : gas phase: N₂,
liquid phase : EtOH, solid phase: SiO₂,
40-76 µm, impregnated with NiO₂, solid charge 5g/L (C, D) and 10 g/L
(A,B). PFA tube, d_tube=1.65mm. Total velocity 47 mm/s (A, B) and 150 mm/s (C, D).

Figure 2)
Example of liquid-solid mass transfer measurement using a pH color indicator:
gas phase: N2, liquid phase: H₂O, initially 0.01 mol/l NaOH, 0.1 g/L cresol red, solid phase: Dowex
50WX8, 200-400 mesh; PFA tube, d_tube=1.65mm;
total velocity 120 mm/s; complete color change and thus due to the usage of
cresol red neutralization can be detected after a residence time of ≈40
seconds.

REFERENCES

[1] D.I. Enache,
G.J. Hutchings, S.H. Taylor, R.Natividad, S.Raymahasay, J.M. Winterbottom,
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6295-6303.

[2] A. Ufer, D. Sudhoff,
A. Mescher, D. W. Agar, Suspension catalysts in a
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167 (2011) 468-474.

[3] K. Olivon,
F. Sarrazin, Heterogeneous reaction with solid
catalyst in droplet-flow millifluidic device, Chem. Eng.
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[4] G. K. Kurup,
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[5] A.-K. Liedtke, F. Bornette, R.
Philippe, C. de Bellefon, Gas?liquid?solid ??slurry Taylor''
flow: Experimental evaluation through the catalytic hydrogenation of
3-methyl-1-pentyn-3-ol, Chem. Eng. J. in press, corrected proof.

[6] V. G. Pangarkar,
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