In recent years, the need to reduce energy consumption worldwide to move towards sustainable development has led many of the conventional technologies used in the industry to evolve or to be replaced by new alternatives. Oxygen is a compound with diverse industrial and medical applications. For this reason, obtaining it from air is one of the most interesting separations, traditionally performed by cryogenic distillation and pressure swing adsorption, two techniques which are very energetically expensive. In this sense, the implementation of membranes in a hollow fiber configuration is presented as a much more efficient alternative to carry out this separation. The aim of this work is to develop cost-effective multilayer hollow fiber composite membranes made of Matrimid and polydimethylsiloxane (PDMS) for the separation of oxygen and nitrogen from air. PDMS is used as a cover layer but can also enhance the performance of the membrane. In order to compare these two materials, three different configurations are studied. First, integral asymmetric Matrimid hollow fiber membranes were produced using the spinning method. Secondly, by using dip-coating method, a PDMS dense selective layer was deposited on a self-made polyvinylidene fluoride (PVDF) hollow fiber support. Finally, the performance of a dual-layer hollow fiber membrane of Matrimid and PDMS was studied. Membrane morphology was characterized by SEM and separation performance of the membranes was evaluated by mixed-gas permeation experiments. The novelty presented in this work is the manufacture of hollow fiber membranes and the way Matrimid is treated. This makes it possible to develop much thinner dense layers than in the case of flat-sheet membranes, which leads to higher permeance values. This is a key factor when implementing this technology on an industrial scale. Membranes prepared in this work were compared to the current state of the art, reporting quite good performance for the dual-layer membrane, reaching O₂ permeance of 30.8 GPU and O₂/N₂ selectivity of 4.7, with a thickness of about 5–10 μm (counting both selective layers). In addition, the effect of operating temperature on the membrane permeances has been studied experimentally; we analyze its influence on the selectivity of the separation process.

The growing interest in the production of biofuels has motivated numerous studies on separation techniques that allow the separation/concentration of organics produced by fermentation, improving productivity and performance. In this work, the preparation and characterization of new butanol-selective membranes was reported. The prepared membranes had a hollow fiber configuration and consisted of two dense selective layers: a first layer of PEBA and a second (outer) layer of PDMS. The membranes were tested to evaluate their separation performance in the selective removal of organics from a synthetic ABE solution. Membranes with various thicknesses were prepared in order to evaluate the effect of the PDMS protective layer on permeant fluxes and membrane selectivity. The mass transport phenomena in the pervaporation process were characterized using a resistances-in-series model. The experimental results showed that PEBA as the material of the dense separating layer is the most favorable in terms of selectivity towards butanol with respect to the other components of the feed stream. The addition of a protective layer of PDMS allows the sealing of possible pinholes; however, its thickness should be kept as small as possible since permeation fluxes decrease with increasing thickness of PDMS and this material also has greater selectivity towards acetone compared to other feed components.

Oxygen and nitrogen are two valuable and widely used products in industries, medical applications, and the food sector, for instance, so they present a significant market opportunity. Traditional methods to separate these gases are very energy-intensive. Therefore, in a world moving toward energy sustainability, membrane technology offers a more sustainable alternative. The aim of this work is to develop polymeric membranes with a hollow fiber configuration using Matrimid and ZIF-8 as fillers to improve the separation performance. As a first step, planar membranes with varying ZIF-8 content (0–20 wt %) were prepared using the casting solvent evaporation technique to determine the optimal Matrimid/ZIF-8 ratio. Subsequently, hollow fiber membranes of Matrimid and Matrimid/ZIF-8 were fabricated via the spinning method. The novelty of this work lies in incorporating ZIF-8 into Matrimid membranes in a hollow fiber configuration, as it is known that the inclusion of fillers in polymeric membranes allows improvements in their performance. Nevertheless, their production is quite challenging. The flat-sheet membranes prepared have shown that inclusion of ZIF-8 in Matrimid improves its O₂/N₂ selectivity by one point and that 5 wt % loading is the optimal point to see this enhancement. The same effect was observed in hollow fiber membranes, reaching an oxygen permeance of 2.16 GPU and an O₂/N₂ selectivity of around 6 (30 °C) for the Matrimid/ZIF-8 membrane, with a dense layer thickness of around 2 μm. All of these results were compared with those reported in the literature for the O₂/N₂ separation. Additionally, the impact of feed composition variations on membrane performance was analyzed.

The dehydration of ethylene glycol–water mixtures is a relevant challenge in the recovery and reuse of cooling liquids from industrial processes, particularly in the pharmaceutical sector. This work investigates the feasibility of using pervaporation with a hydrophilic polymeric membrane (PERVAP 4101, based on highly cross-linked poly­(vinyl alcohol)) to partially dehydrate mixtures containing up to 70 wt% water and maintain compositions close to the eutectic point (≈58 wt% ethylene glycol). Experimental tests were conducted in a laboratory-scale pervaporation unit at 60, 70, and 80 °C. The influence of feed composition and temperature on permeation flux, separation factor, and long-term stability was analyzed. A conditioning stage at 80 °C was found to be essential to achieve steady operation, resulting in high water selectivity (98.9–99.8 wt% water in permeate) and stable fluxes up to 4.2 kg m^–2 h^–1 during 30 h continuous tests. ATR–FTIR spectra of the pristine and conditioned membranes revealed only minor structural modifications, suggesting a slight reduction in crystallinity associated with increased permeability, which was later confirmed by DSC analysis. The experimental data were successfully correlated using a solution–diffusion model, considering the dependence of permeance on component activity and temperature. The apparent activation energies for water and ethylene glycol permeation were 34–42 and 43–58 kJ mol^–1, respectively. Results confirm that PERVAP 4101 membranes provide an efficient and stable route for ethylene glycol dehydration at high water contents, demonstrating potential for industrial implementation.