Contents lists available at ScienceDirect Chemical Engineering & Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep Preparation of highly monodispersed emulsions by swirl flow membrane emulsification using Shirasu porous glass (SPG) membranes – A comparative study with cross-flow membrane emulsification Jophous Mugabi a , Shunji Tamaru a , Karatani Naohiro a , Roberto Lemus-Mondaca b , Noriyuki Igura a, ⁎ , Mitsuya Shimoda a a Laboratory of Food Process Engineering, Graduate school of Bioresource and Bioenvironmental Science, Faculty of Agriculture, Kyushu University, 744 Motooka, Nishi- Ku, Fukuoka city, Fukuoka 819-0395, Japan b Department of Food Science and Chemical Technology, Faculty of Chemical Sciences and Pharmaceutical, Universidad de Chile; Santos Dumont 964, Independencia, Santiago, Chile ARTICLE INFO Keywords: Swirl flow Cross-flow Membrane emulsification Oil-in-water emulsions High dispersed phase fluxes Sodium dodecyl sulphate (SDS) surfactant ABSTRACT Highly monodispersed oil-in-water (O/W) emulsions with narrow droplet size distribution (span) were prepared using swirl flow membrane emulsification at high dispersed phase fluxes (up to 15.6 m 3 /m 2 h) greater than the droplet dripping mode of droplet formation and at very low concentrations of sodium dodecyl sulphate (SDS) surfactant (as low as 0.01 wt.%). The swirl flow membrane emulsification method involved the generation of a centrifugal kind of flow in the continuous phase. This exerted higher radial shear stresses on the membrane wall which overcame the higher kinetic energy of the dispersed phase emerging from membrane pores when high dispersed phase fluxes were applied. The emulsions droplet size (d 50 ) was in the narrow range of 30.2 to 35 and span of 0.239 to 0.34 for swirl flow ME as compared to the highly polydispersed emulsions with d 50 in the range of 38.8–43.5 μm and span in range of 0.65–2.32 for the cross-flow ME method, for the 9.6 μm SPG membrane. 1. Introduction The membrane emulsification (ME) method is a drop-by-drop method of emulsion preparation which involves the permeation of the to-be dispersed phase fluid through the membrane pores to form dro- plets into the continuous phase fluid flowing at the membrane`s permeate side [1–3]. The emulsion droplets grow at the pore openings and detach upon reaching a certain size which is determined by the balance between the shear drag force acting on the droplets due to the flow of the continuous phase, the buoyancy of the droplet, the inter- facial tension and the inertial force due to the flow of the dispersed phase in the membrane pores [4]. Although, even in the absence of shear flow at the membrane surface, droplets can be spontaneously detached from a membrane whose pore openings have non-circular cross sections, entirely due to the action of interfacial tension but at lower production rates [5–8]. In ME method, the resulting emulsion droplet size is primarily controlled by the membrane pore size and therefore, emulsions with small droplet size and narrow droplet size distribution can be easily prepared at lower shear stresses, and low energy input (104–106 J/m 3 ), by choice of the appropriate membrane pore size and process parameters [4,9,10]. This renders the ME a sui- table method for preparing functional emulsions containing heat and shear sensitive ingredients such as proteins, starches and vitamins [4,11]. However, the ME method has not been widely adopted for commercial emulsion productions because of its low dispersed phase throughput, which greatly lowers the overall emulsion production rate [3,4,10,12]. In order for the ME method to be feasible for commercial scale emulsion production, the dispersed phase fluxes should be atleast above 0.1 m 3 /m 2 h[13]. However, in the conventional ME methods, the dispersed phase flux is typically restrained within the range of 0.001–0.1 m 3 /m 2 h depending on the membrane pore size in order to prevent the emulsification process from transitioning from the size- stable zone to the continuous outflow or jetting zone [4,14–16] and to avoid steric hindrance among droplets that may be formed simulta- neously at the adjacent pores [17]. This is because, in the conventional cross-flow ME method, the continuous phase is made to flow parallel to the axis of the porous membrane exerting weaker shear forces along the membrane wall, and thus as the dispersed phase flux is increased, the flow of the continuous phase liquid is gradually pushed away from the membrane wall by the higher kinetic energies of the radially extruding https://doi.org/10.1016/j.cep.2019.107677 Received 30 October 2018; Received in revised form 30 September 2019; Accepted 30 September 2019 ⁎ Corresponding author. E-mail address: igura@agr.kyushu-u.ac.jp (N. Igura). Chemical Engineering & Processing: Process Intensification 145 (2019) 107677 Available online 01 October 2019 0255-2701/ © 2019 Published by Elsevier B.V. T