Subcritical Water-Assisted Emulsification of Decane / Water: Influence of Surfactants

Abstract

A finely monodispersed oil-in-water (O/W) emulsion was obtained under high temperature and pressure conditions (240 o C and 10 MPa). A coarse emulsion stabilized by Tween 20 was prepared in advance from the decane / water system to be treated under the subcritical conditions. The treated coarse emulsion was thereafter mixed with the aqueous solution including surfactants to improve the monodispersity of the oil droplets. The subcritical condition could supply sufficient energy to produce finely dispersed oil droplets (~233 nm in diameter).

Subcritical Water-Assisted Emulsification of Oil / Water: The Effect of the Solubility of the Organic Solvent and Surfactants

“…In the first, the mixture of oil/water was emulsified under subcritical conditions and Tween 20 was used as surfactant A and B, according to the previous publication [7]. The results using a variety of organic solvents are summarized in Table 2.…”

“…The size of the oil droplets and their dispersity in general depend on the emulsification technique. Previously, the oil droplets in emulsions have been prepared by homogenizers, ultrasound homogenizers, rotor stator systems, microchannels [3], a membrane emulsification technique [4] or subcritical water-assisted emulsification [5][6][7][8]. Subcritical water is water that maintains its liquid state at elevated temperatures under pressurized conditions; i.e.…”

“…a fluid with much energy. This property is advantageous for the supply of sufficient energy during emulsification, to yield finely dispersed oil droplets of 300 nm diameter [7].…”

“…The former property of subcritical water suggested that organic solvents could be solubilized in water even at high concentrations [9]. The types of organic solvents such as fatty acids (oil phase) and non-fatty acids (oil phase) were likely to affect the emulsification process: the size distribution and dispersity [5][6][7][8]. The miscibility (solubility) of the organic solvent in water also was likely to affect the emulsification process due to the alteration of the surfactant orientation, as shown by work already reported using immiscible organic solvents [7,8] with that of miscible solvents [5,6].…”

“…The types of organic solvents such as fatty acids (oil phase) and non-fatty acids (oil phase) were likely to affect the emulsification process: the size distribution and dispersity [5][6][7][8]. The miscibility (solubility) of the organic solvent in water also was likely to affect the emulsification process due to the alteration of the surfactant orientation, as shown by work already reported using immiscible organic solvents [7,8] with that of miscible solvents [5,6]. It is, therefore, considered that the investigation of the emulsification mechanism from the aspects of the miscibility of the oil in the water phase and the effect of the surfactants might give a better insight into the formation mechanism of finely dispersed oil droplets.…”