Pressure and Cross-Flow Dependent Interfacial Fouling of Mesoporous PES-PUMA Membranes During Water-in-Oil Emulsion Separation

Water-in-oil (W/O) emulsion treatment is challenging because efficient membrane separation requires simultaneous control of oil transport, water rejection, interfacial interactions, and fouling resistance. However, the coupled effects of operating pressure and cross-flow hydrodynamics on membrane pore accessibility, foulant-layer evolution, and the permeability-rejection trade-off during cyclic W/O emulsion treatment remain insufficiently understood. In this study, an electrospun mesoporous polyurethane–melamine/polyethersulfone (PES-PUMA) membrane was evaluated for the separation of stabilized W/O emulsions under different operating pressures and feed flow rates. At an ultra-low pressure of 20 kPa, the membrane achieved an oil permeate flux of 36.5 ± 2.7 L m−2 h−1 and water rejection of 93.1 ± 2.1%. Increasing the operating pressure to 100 kPa increased the oil permeate flux to 87.6 ± 3.5 L m−2 h−1 while decreasing water rejection to 78.2 ± 1.8%. Increasing the cross-flow rate from 0.05 to 0.5 mL s−1 increased the oil permeate flux from 23.4 ± 0.7 to 90.7 ± 2.1 L m−2 h−1 while decreasing water rejection from 95.3 ± 2.1% to 78.4 ± 1.2%. Quadratic regression models revealed significant nonlinear relationships between hydraulic operating conditions and both separation responses, providing a quantitative description of the pressure- and flow-dependent performance trade-off. Higher cross-flow reduced foulant-layer thickness and favored more reversible fouling, whereas increasing operating pressure promoted pore constriction and compact foulant deposition. These findings establish a quantitative pressure–cross-flow–transport–fouling relationship, demonstrating that hydraulic conditions jointly regulate membrane permeability, water rejection, foulant-layer development, and fouling reversibility. This study therefore provides mechanistic and quantitative insight into optimizing the operation of the established PES–PUMA membrane to balance separation performance and fouling resistance during W/O emulsion treatment.