Validation of the scale-up process of highly-concentrated emulsions

Abstract

Emulsions are dispersions of two immiscible liquids, one of which is dispersed as tiny droplets -dispersed phase- in the other one -continuous phase. The decisive parameter to characterise an emulsion is the dispersed phase volume fraction ϕ. This study is focused on highinternal- phase-ratio emulsions (HIPRE), which are defined by ϕ exceeding 0.74, defined as the ratio in which the spheres of the dispersed phase are monodispersed undistorted forming the most compact packing. In this work, water-in-oil (W/O) emulsions are constituted by a 90 % wt/wt (88 % vol/vol) of water dispersed in the continuous phase (dodecane and surfactant Span 80). The first goal of this work is the validation of empirical models obtained previously from central composite designs which apparently predict the emulsion properties given some fixed preparation and composition conditions. Actually, three of these conditions are studied: the stirring rate of the impeller and the addition flow rate, as preparation factors; and the surfactant concentration (surfactant-to-dodecane ratio), as composition variable. The characterisation of the emulsions is carried out testing their viscoelastic behaviour -rheological tests-, the stability over time –by measuring changes on the back scattering- and droplet size –determined through images obtained with an optical microscope. To do the validation of the models, additional experiments are carried out following a simple design in the experimental range of the variables. The preparation of the emulsions is simple and in this step is where the different factors are varied in order to analyse their effects on the emulsion. The continuous phase –organic one, in which surfactant concentration is varied from one experiment to another- is introduced into the jacketedtank at 25 ºC and then, the impeller is set at a fixed stirring rate and the dispersed phase -wateris added at a constant flow rate. In this method, emulsions are formed thanks to the energy input provided by the stirrer...