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Ways to Optimize Solid-Liquid Mixing

Abstract

This white paper presents a number of mixing technologies and techniques employed in solid dispersion and dissolution.

The aim of this paper is to provide practical information on the efficient use of specialty mixing equipment for the preparation of low, medium and high viscosity solid-liquid mixtures under low and high shear conditions.

Introduction

Whether mixed into liquid in the form of powders, pellets, granules, flakes, crystals or fibers, solids often represent a processing challenge. Manufacturers generally prefer to deal with only fluids in their mixing operation mainly for convenience. Compared to solids, liquids are easier to handle and mix with other liquid ingredients. For example, within the paper industry, chemicals are commonly shipped in roughly 50% concentrated form. Water is simply added to achieve the dilute solution required for process needs or making of the finished product.

This convenience of course comes at a price. In fact, tremendous savings may be obtained if raw materials are ordered in solid form instead of liquid form. Significant amounts can be saved in shipping costs alone, especially with large volume requirements of slurries or solutions that are mainly water in composition. The key is to have an efficient and repeatable in-house mixing process for dispersing solids into liquid.

Then there are those formulations that require solid-liquid mixing no matter what which manufacturers cannot escape from. Depending on the properties of the solid(s) and the liquid vehicle, the mixing operation can be a straightforward batch or continuous process or it can involve several stages and require different types of mixers. From dispersing fillers into a viscous composite or dissolving solid polymers into solvent to wetting out hydrophobic powders or breaking up agglomerates of pigments, the degree of mixing difficulty varies from one specific application to another.

To structure our discussion in this paper, we use viscosity and shear intensity as the categories within which we enumerate a number of ways to optimize solid-liquid mixing.