Experimental Validation of a Novel Model for the Micromixing Intensity

Experimental validation of a novel model for the micromixing intensity in a rotor-stator spinning disc reactor

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

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

Introduction

The characteristic timescale for micromixing are determined for a rotor-stator spinning disc reactor. This reactor consists of a rotating disc which is enclosed by two stationary discs and a cylindrical housing and is shown in Figure 1.

Figure 1. Rotor-stator spinning disc reactor configuration. Upon rotation of the rotor, the shear forces between the rotor and the stator cause high turbulence intensity.

Previous research showed that intense mixing of multiphase processes can be achieved in this reactor (Visscher, van der Schaaf et al. 2011). For a chemical process with competing reactions, the yield and selectivity are influenced by the mixing efficiency at micro scale in a reactor (Baldyga and Pohorecki, 1995). The mixing at micro scale can be characterized with the iodide-iodate reaction system (Fournier, Falk et al. 1996b;Fournier, Falk et al. 1996a). This reaction system is based on two parallel reactions that are competing for the acidic protons.

 

Reaction 1:	H2BO3- + H+ ⇌ H3BO3	(pseudo instantaneous)
Reaction 2:	5 I‑ + IO3- + 6 H+ ⇌ 3 I2 + 3 H2O	(fast reaction)
Reaction 3:	I- + I2 ⇌ I3-	(pseudo instantaneous)

                                               

The Dushman reaction (Reaction 2) is fast, in the same range of the micromixing process, but is much slower than the pseudo-instantaneous neutralization reaction (Reaction 1). Therefore the product distribution of the reactions 1 and 2 can be used to represent the mixing intensity at micro scale. This product distribution at the reactor outlet can be determined by measuring the triiodide concentration with in-line UV-VIS spectroscopy.

The product distribution is correlated to the timescale of the micromixing process through a novel model which is applicable for ideally mixed systems. This correlation is a function of turbulence intensity, and operational conditions like the specific proton donor, volumetric flow rates, concentrations, and the reactor temperature. The trends predicted by the model are validated using the rotor stator spinning disc reactor.

Reference List

Visscher, F., van der Schaaf, J., de Croon, M.H.J.M., and Schouten, J.C., 2011 Liquid-liquid mass transfer in a rotor-stator spinning disc reactor. Annual AIChE meeting 2011, Minneapolis, MN.

Baldyga, J. and Pohorecki, R., 1995. Turbulent micromixing in chemical reactors -- a review. The Chemical Engineering Journal and the Biochemical Engineering Journal 58, 183-195.

Fournier, M.C., Falk, L., and Villermaux, J., 1996a. A new parallel competing reaction system for assessing micromixing efficiency - Experimental approach. Chemical Engineering Science 51, 5053-5064.

Fournier, M.C., Falk, L., and Villermaux, J., 1996b. A new parallel competing reaction system for assessing micromixing efficiency--Determination of micromixing time by a simple mixing model. Chemical Engineering Science 51, 5187-5192.