Scale invariants in the preparation of reverse high internal phase ratio emulsions

Abstract

8Reverse high internal phase ratio emulsions (HIPRE) are prepared with the system 9 water/Span80/dodecane to identify the influence of the process variables on droplet size 10 and polydispersity, and to study the influence of the process scale-up. After discussing 11 the most common scale invariants used in emulsification processes, we prepare 12 emulsions at two different scales following a complete factorial experimental design. 13Using the empirical models obtained with the statistical analysis of the results, we 14 determine the scale invariants for the system. Results from a previous study indicated 15 that the scale invariant for the preparation of HIPRE could be the stirring rate. However, 16 the results obtained in this work show that the scale invariant, based on droplet size, 17 could change depending on the conditions of emulsification. Only when the stirring rate 18 is high enough (> 1500 rpm), or when the surfactant-to-oil ratio is high and the total 19 addition time low, the scale invariant is indeed the stirring rate. The elevated shear 20 stress inside the mixer when the stirring rate is high is responsible of the small droplet 21 size obtained on both scales. However, for other values of the process variables, the 22 scale-invariant can be expressed as N·D  , where 0 <  < 0.5, and depends on other two oil ratio. We propose a methodology to determine these scale invariants and to calculate 25 the threshold values of surfactant-to-oil ratio and addition flow rate from which the 26 stirring rate is the scale invariant (when  → 0). 27Keywords: Scale-up, Reverse high internal phase ratio emulsion, Scale invariant, 28Droplet size, Stirring rate.