Preparation of oil-in-water nanoemulsions at large-scale using premix membrane emulsification and Shirasu Porous Glass (SPG) membranes

Nanoemulsions are increasingly used in cosmetics, pharmaceutics and food. They are produced usually by low or high energy techniques. In this study, a process involving moderate pressure in the range 10-60 bar was proposed as an alternative, in particular for the encapsulation of sensitive actives or applications that require a precise droplet size control. Oil-in-water (O/W) nanoemulsions were prepared by premix membrane emulsification (PME) using a set-up with a controlled high pressure syringe pump and 125mm long SPG membrane. A coarse emulsion (premix) was injected through the membrane with pore size between 0.2 and 0.8 mu m in order to reduce and homogenize the droplet size. The effect of several parameters was investigated: process parameters (scalability, cycle number, membrane pore size, flowrate) or formulation (oil and surfactant concentrations). Nanoemulsions were prepared at large scale up to 500 mL at production rate up to 200 mL/min, pressure below 60 bar and one cycle. The droplet size was linearly related to the membrane pore size and highly monodisperse nanoemulsions of around 260 nm in diameter and stable for 9 months at room temperature were achieved with the smallest pore size membrane (0.2 mu m). Moreover, the mechanisms involved in PME for nanoemulsions were discussed, such as flow through the membrane pores and droplet disruption by wall shear stress inside the membrane porous structure.