Removal of methylparaben using emulsion liquid membrane: Stability, kinetics, and process optimization

The main goal of this study was to develop and optimize an emulsion liquid membrane (ELM) system for effective removal of methylparaben (MeP) from aqueous solutions. This study investigates the extraction of MeP from aqueous solutions using the ELM method, focusing on optimizing key operational factors that influence process efficiency. Aliquat 336® (methyltricaprylammonium chloride), a quaternary ammonium-based ionic liquid, was examined as an extractant due to its strong affinity for MeP, enabling efficient transport through the membrane phase. As well, changes in emulsification energy (1000–5000 J) , surfactant concentration (1–5% w/v Span 80) , and internal-to-organic phase volume ratios (1:1 to 1:5) were studied to assess water-in-oil (W/O) emulsion stability, a crucial factor for system performance. In experimental results, the extraction efficiency (E) of MeP was greatly affected by factors such as the type of stripping agent, ionic strength (I), emulsification conditions, phase volume ratios, and stirring speed. With its optimal I and favorable electrostatic interactions, potassium chloride (KCl) proved to be the most effective stripping agent, achieving a maximum extraction efficiency (E max ) of 92.6% within 5 min under optimal conditions (2000 J emulsification energy, 3% w/v Span 80, 1:3 internal-to-organic phase ratio, and 300 rpm stirring speed). Kinetic modelling confirmed that the extraction process follows a first-order kinetic model, with a rate constant (k) of 0.045 min⁻¹, indicating that mass transfer dominates in the initial stage before reaching equilibrium. Also, it emphasized the importance of precise operational control, as high stirring speeds (>400 rpm) or excessively large internal phase volumes (>1:2 ratio) can cause emulsion instability and reduce efficiency by up to 30%.