This review is devoted to the application of bulk synthetic polymers such as polysulfone (PSf), polyethersulfone (PES), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF) for the separation of oil-water emulsions. Due to the high hydrophobicity of the presented polymers and their tendency to be contaminated with water-oil emulsions, methods for the hydrophilization of membranes based on them were analyzed: the mixing of polymers, the introduction of inorganic additives, and surface modification. In addition, membranes based on natural hydrophilic materials (cellulose and its derivatives) are given as a comparison.

The work is focused on the study of the influence of the cellulose type and processing parameters on the structure, morphology, and permeability of cellulose films. The free volume of the cellulose films was evaluated by the sorption of n-decane, which is a non-solvent for cellulose. The structural features of the membranes and their morphology were studied using X-ray diffraction, IR spectroscopy, SEM, and AFM methods. The characteristic features of the porous structure and properties of cellulose films regenerated from cellulose solutions in the N-methylmorpholine-N-oxide (NMMO) and cellophane films were compared. Generally, cellulose films obtained from solutions in NMMO have a higher permeability and a lower rejection (as measured using Orange II dye) as compared to cellophane films. It was also found that the cellulose films have a higher ultimate strength and modulus, whereas the cellophane films are characterized by higher elongation at break.

Cellulose composite membranes have been fabricated by casting a cellulose solution in N-methylmorpholine oxide on a nonwoven polyester support. The membranes have been tested for nanofiltration of aprotic solvents. The solvent permeability has changed from 0.11 ± 0.02 to 2.5 ± 0.4 kg/(m² h bar) in the following order: DMSO > NMP > DMFA > THF > acetone, which can be attributed to a decrease in viscosity of the fluids. The rejection of the anionic dyes Orange II (MW 350) and Remazol Brilliant Blue R (MW 626) has been found to range within 15–85% and 42–94%, respectively, on the solvent nature. Sorption experiments have revealed a noticeable difference between certain solvents in interaction with the membrane material: a lower degree of cellulose swelling in THF (37%) and a higher degree in DMSO (230%). In addition, it has been found that the rejection of solutes by the composite membranes correlates with the degree of cellulose swelling. A rejection of ≥90% has been achieved for Remazol Brilliant Blue R, which has the larger molecule, at a cellulose swelling ratio of 100% or higher. Thus, it has been concluded that polymer swelling leads to narrowing the porous structure of the cellulose layer of the composite membrane and, hence, improvement in separation parameters.

The dissolution of cellulose in the [Emim]OAc ionic liquid mixed with DMSO as a cosolvent has been studied, and the possibility of fabricating composite cellulose membranes for the nanofiltration of organic media has been explored. It has been shown that the addition of DMSO to [Emim]OAc leads to a decrease in the dissolution time, which has a minimal value at a solvent ratio of 1 : 1. Composite membranes on a poly(ethylene terephthalate) support have been synthesized. The cellulose content in the casting solution was 6, 8, 12, or 16 wt %. It has been found that the rejection factor of the Remazol Brilliant Blue R dye (626 g/mol) varies from 42 to 82% depending on the composition of the casting solution.

The weak point of ionic liquids is their high viscosity, limiting the maximum polymer concentration in the forming solutions. A low-viscous co-solvent can reduce viscosity, but cellulose has none. This study demonstrates that dimethyl sulfoxide (DMSO), being non-solvent for cellulose, can act as a nominal co-solvent to improve its processing into a nanofiltration membrane by phase inversion. A study of the rheology of cellulose solutions in diluted ionic liquids ([EMIM]Ac, [EMIM]Cl, and [BMIM]Ac) containing up to 75% DMSO showed the possibility of decreasing the viscosity by up to 50 times while keeping the same cellulose concentration. Surprisingly, typical cellulose non-solvents (water, methanol, ethanol, and isopropanol) behave similarly, reducing the viscosity at low doses but causing structuring of the cellulose solution and its phase separation at high concentrations. According to laser interferometry, the nature of these non-solvents affects the mass transfer direction relative to the forming membrane and the substance interdiffusion rate, which increases by four-fold when passing from isopropanol to methanol or water. Examination of the nanofiltration characteristics of the obtained membranes showed that the dilution of ionic liquid enhances the rejection without changing the permeability, while the transition to alcohols increases the permeability while maintaining the rejection.

For the first time, the effect of the side-chain in polyalkylmethylsiloxane towards pervaporative removal of methyl tert-butyl ether (MTBE) from water was studied. The noticeable enhancement of separation factor during the pervaporation of 1 wt.% MTBE solution in water through the dense film (40–50 µm) can be achieved by substitution of a methyl group (separation factor 111) for heptyl (161), octyl (169) or decyl (180) one in polyalkylmethylsiloxane. Composite membrane with the selective layer (~8 µm) made of polydecylmethylsiloxane (M10) on top of microfiltration support (MFFK membrane) demonstrated MTBE/water separation factor of 310, which was 72% greater than for the dense film (180). A high separation factor together with an overall flux of 0.82 kg·m⁻²·h⁻¹ allowed this M10/MFFK composite membrane to outperform the commercial composite membranes. The analysis of the concentration polarization modulus and the boundary layer thickness revealed that the feed flow velocity should be gradually increased from 5 cm·s⁻¹ for an initial solution (1 wt.% of MTBE in water) to 13 cm·s⁻¹ for a depleted solution (0.2 wt.% of MTBE in water) to overcome the concentration polarization phenomena in case of composite membrane M10/MFFK (T_exp = 50 °C).