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PDF Text:

LIQUID­SOLID MASS TRANSFER

IN A ROTOR­STATOR SPINNING DISC REACTOR

Marco Meeuwse, John van der Schaaf and Jaap C. Schouten*

Laboratory of Chemical Reactor Engineering, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands Email: j.c.schouten@tue.nl; website: www.chem.tue.nl/scr

Summary

Liquid-solid mass transfer coefficients in a rotor-stator spinning disc reactor are reported that were determined from measurements of reaction rates of the heterogeneously catalysed oxidation of glucose. The overall reaction rates are limited by both liquid-solid mass transfer and the intrinsic oxidation kinetics at the operating conditions used. The liquid-solid mass transfer increases with increasing rota- tional disc speed. The estimated liquid-solid mass transfer coefficient kLS increases from 1.5 · 10−4 m s−1 at 49 rad s−1 to 3 · 10−4 m s−1 at 181 rad s−1, which is at least a factor 3 higher than in conventional reactors.

Keywords

Process intensification, Novel reactor technologies, Multiphase reactors, Spinning disc reactor

Introduction

There is an increasing demand in the chemical industry for smaller, safer, and more cost efficient versatile reactors. In multiphase reactions, gas-liquid and/or liquid-solid mass transfer are often rate limiting and determine the size of the reactor. A higher mass transfer rate can increase the reactor performance and the reactor can be made smaller. Meeuwse et al.1 showed that in a rotor-stator spinning disc reactor, the gas-liquid mass transfer rates are up to a factor 10 higher than in conventional gas-liquid reactors.

The rotor-stator spinning disc reactor consists of a rotating disc between two stator walls, at 1 mm distance. With a catalytically active disc, this new reactor type can also be used for heterogeneously catalysed reactions, making use of the high liquid-solid surface area available per unit reactor volume. In this study, we have estimated the rate of liquid-solid mass transfer in the rotor-stator spinning disc reactor with a heterogeneous catalyst deposited on the disc.

Experimental

The experimental setup is shown in Figure 1. Operating conditions and dimensions are indicated in the figure. Glucose is oxidized to gluconate by using a 20 wt% Pt/C catalyst coating on the bottom of the rotating disc. Glucose is present in excess in the reactor (0.5 mol l−1) and is therefore not rate determining. The kinetics of the reaction are an intricate function of the oxygen concentration2,

* To whom all correspondence should be addressed

because of catalyst overoxidation. Low oxygen concentra- tions of 5 and 25 vol.% are therefore used here.

The overall reaction rate coefficient Kov is a function of the volumetric liquid-solid mass transfer coefficient and the intrinsic kinetics reaction rate coefficient and can be calculated from the decrease in oxygen concentration:

liquid-solid mass transfer term. The temperature in the

Figure 1. Schematic drawing of the experimental setup of the rotor-stator spinning disc reactor.

⎛Cin ⎞⎛ ⎞−1 Kov=φL⎜ O2 −1⎟=⎜ 1 + 1 ⎟

V⎜Cout ⎟ ka kηC

⎝lsls r cat⎠

The rotational disc speed in the reactor only influences the

R⎝O 2



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 Supercritical Fluid Extraction 121.pdf Page 001
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