Mixing control in a continuous-flow microreactor using electro-osmotic flow

Ramil Siraev,Dmitry Bratsun,Pavel Ilyushin,Anna Samoilova,Alexander Nepomnyashchy

doi:10.1051/mmnp/2021043

Abstract

In recent years, pharmaceutical production has been stimulating the gradual miniaturization of continuous-flow chemical reactors. This process eventually resulted in the emergence of a new generation of microreactors. The advantages of these new reactor types are the flexible production that allows us to quickly reconfigure the scheme, small reactant quantities used for the synthesis, the control of the main reaction parameters with high accuracy. Nevertheless, a decrease in the thickness of the channels where the species contact and react forces us to search for new non-mechanical mechanisms for mixing. This problem is relevant for the slow reaction occurring in a slot where diffusion alone cannot provide mixing at reasonable distances from the entrance. It is also true for the fast reaction that takes place in a frontal manner. In this work, we consider the efficiency of mixing the reactants induced by electro-osmotic flow in a Hele-Shaw configuration with non-uniform zeta potential distribution. As a test reaction, we take the neutralization reaction with simple albeit non-linear kinetics. The reaction occurs between two miscible solutions, which are initially separated in space and come into contact in a continuous-flow microreactor. The reaction proceeds frontally, which prevents the efficient mixing of the reactants due to diffusion. Using direct numerical simulations of 2D and 3D flows, we demonstrate that the zeta potential applied to boundaries can effectively control the mixing rate of fluids by lengthening the front of the reaction. This approach makes it possible to increase the yield of the reaction product.

Highlights

Revolution in chemical technologies revolves around microreactors with the continuous flows of the reactant solutions and reaction products
The beginning of the 2000s, with the introduction of new technologies based on continuous-flow reactors, saw significant changes in fine organic synthesis
These findings show that the reactants are mixed slower in a continuous-flow reactor with the stationary distribution of zeta potential

Summary

Introduction

Revolution in chemical technologies revolves around microreactors with the continuous flows of the reactant solutions and reaction products. Continuous-flow microreactors have a small reactor zone and provide a high flow rate for a solution that maintains quick mixing of the reactants and efficient reaction behavior. They contain a special reactor zone with a convective flow for more efficient mixing This process increases the product output and decreases the reaction behavior rate. The reactor zone should be of an appropriate size and have a specific orientation for convection, while the diffusion works properly in small-sized microchannels If we neglect these requirements, no mixing occurs. One has to accelerate the reaction by an additional stirring of the reactive mixtures These systems reveal new aspects: for example, chemoconvective instability can occur in the gravity field due to the effect of the concentration-dependent diffusion of the reactants [6,7,8].

Mathematical formulation

Batch reactor: contribution of diffusion and EOF to mixing

Controlling a continuous-flow microreactor using EOF mechanism

Conclusion