Abstract
In this study, a rotating membrane emulsification setup incorporating a 6.1μm pore diameter SPG membrane was used to produce O/W emulsions of average droplet sizes between 23.4 and 216.6μm. All emulsions consisted of 10vol% of sunflower oil or silicone oil stabilised by 1wt% Tween 20. The transmembrane pressure (0.1–1.8bar), rotational speeds (100–2000RPM) annular gap width (5–45mm), dispersed and continuous phase viscosity were all investigated as to their effect on emulsion droplet size and dispersed phase flux. Modification of the dispersed phase flow properties alters the droplet size with four regions being suggested; a decrease in size (as droplet coalescence is minimised), a plateau (size-stable zone), a gradual increase in size (due to transfer of mass via droplet neck) and then a rapid increase (due to jetting). The importance of Taylor vortices development was seen with larger droplets formed in their absence; typically at low rotational speeds, narrow vessel diameters and more viscous continuous phases. It was concluded that the flow behaviour of each phase requires careful consideration to understand the likely formation mechanism(s) during operation. Across the pressure and viscosity ranges investigated, the dispersed phase flux ranged between 50 and 12,500Lm−2h−1 and pore activity was within the range of 0.5–2.7%.
Highlights
At the newly created interfaces formed droplets can quickly coalesce through a ‘back-reaction’ that increases emulsion droplet size
The aim of this study is to gain insight into how O/W emulsion droplet size and production rate are affected by the flow behaviour of the dispersed phase and continuous phase
The effect of transmembrane pressure, shear rate, dispersed and continuous phase viscosity on the final droplet size and flux has been investigated for a rotating membrane emulsification system
Summary
At the newly created interfaces formed droplets can quickly coalesce through a ‘back-reaction’ that increases emulsion droplet size. At the most fundamental level, the process entails passing dispersed phase through the pores of a membrane into the continuous phase This is commonly achieved via the application of pressure. The flux largely depends on properties related to the membrane as well as the pressure applied and dispersed phase viscosity Some of these can be chosen by the operator and the process can be optimised depending on whether droplet size or throughput is the main priority [11]. The aim of this study is to gain insight into how O/W emulsion droplet size and production rate are affected by the flow behaviour of the dispersed phase (flow through the membrane) and continuous phase (flow within the processing vessel). This study is designed to further current understanding of the droplet formation mechanisms involved within this process, which in turn should allow for the development of approaches to precisely formulate specific emulsion microstructures
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