Membranes

Novel hybrid membranes based on poly(ether-b-amide) copolymers and amine-modified mesoporous silica MCM-48 were prepared by the casting method. To the best of our knowledge, there is no evidence about the application of amine-modified MCM-48 silica in the fabrication of mixed matrix membranes (MMMs) based on PEBA copolymers. MMMs were characterized by FT-IR spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Modification of MCM-48 with the organosilane improved the compatibility with the polymeric matrix. In addition, the separation performance of prepared membranes was investigated by experiments of pure gas permeation. The incorporation of modified nanoparticles into the polymeric matrix improved the gas separation performance of the fabricated nanocomposite membranes. By comparing with pristine PEBA membranes, MMM with 2.5 % of APS-MCM-48 exhibited higher ideal selectivity for the gas pairs CO₂/CH₄ and CO₂/N₂.

Manufacturing and characterization of polysulfone and graphene oxide (PSU-GrO) fibers, obtained by electrospinning and evaluated for their potential use in water purification, is presented. Effect of electrospinning operation parameters on surface morphology, fiber diameter, hydrophobicity and flux permeate was established. Distance and voltage were the more significative parameters on fiber diameter, morphology and flow permeate. Evaluation of obtained membranes, for their potential use in water purification, indicates that there is an clear effect of fiber diameter on performance.

It has been shown that to increase the octane rating of gasoline, it is necessary employing acid catalysts in the olefin oligomerization reaction; in this way, this work presents the preparation of membrane sulfated zirconia–titania as acid catalyst; the membrane was prepared using the dip-coating method. The molar Zr/Ti ratio was 1; the samples were characterized by XRD, spectroscopy IR, and Raman. The analysis of X-ray diffraction shows good crystallinity at temperatures above 873 K. The catalytic performance of these materials was evaluated in the oligomerization of isobutene showing good activity and selectivity for the production of C₈ at 383 K and WHSV = 53 h⁻¹; the results show a good conversion for oligomerization of olefins.

In the present work, two supported liquid membranes, which used two new ionic liquids (ILs) as mobile phase, 1-(2-aminoethyl)-3-methylimidazolium trifluoromethanesulfonate ([AEMIm]Tf) and trioctylmethylammonium anthranilate ([TOMA])An, were studied characterizing their chemical structures by NMR and FTIR. Both the impregnation level and mass of the ILs in alumina tubular supports were determined by SEM-EDX mapping and gravimetric analysis. The permeation tests were carried out using pure gases at 25 °C and 1 bar. It was confirmed that in the ILs, [AEMIm]Tf and [TOMA]An, the amine groups reacted with CO₂, leading to the formation of carbamates. The IL [TOMA]An, which has the amine group at the anionic part, showed the best ideal permselectivity, reaching a selectivity of 92.

It is known that phenol is one of the highly toxic pollutants present in wastewaters, and nowadays, phenol is targeted for elimination by a high performance technology based on oxidizing agents and catalysts resistant to deactivation. In this work, we report the synthesis of catalytic membranes based on mixed Ce–Co oxides prepared by a coprecipitation method. Catalytic membranes are used as a catalyst and as separation media in removing phenol from aqueous effluents using Catalytic Wet Oxidation (CWO) technology and ozone pretreatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), and gas permeation tests were used for characterizing the catalytic membranes. A membrane reactor of contactor type facilitates the distribution of the oxidizing agent for mineralization of organic material in wastewater, at low temperatures. In this study, a removal of 75 % of phenol in a solution of 200 ppm was obtained after a reaction time of half hour with O₂ as oxidizing agent and a low content of mixed oxide load in the catalytic membrane.

A variety of nanochannels have been developed by several different experimental groups including that of Gokel at Missouri (St. Louis). These are selective for ions and also have potential in biomedical applications. Our group has performed molecular simulations of the transport of both chloride and sodium ions through these nanochannels assembled in lipid bilayers for which experimental data has been available. Results of these simulations are reviewed in terms of the validation of experimental models for transport and the potential for using other, more robust, platforms for these nanochannels is discussed.

This work uses 2D fluid dynamics and mass transfer simulations to evaluate the use of pulsatile flow in spiral wound reverse osmosis modules. The aim of pulsatile flow is to enhance mass transfer and increase the performance of the membrane modules, without significantly affecting pressure drop and energy losses. The synergies that exist between pulsatile flow and spacer filament-induced oscillations are explored. The results indicate that there is an optimal frequency that amplifies the perturbations. Flow pulsations at the optimal frequency (which is related to the natural oscillating frequency of the channel) cause vortex shedding at Reynolds numbers below 350, compared to values above 500 that would be necessary without pulsatile flow. This leads to an increase in mass transfer and permeate flux of the order of 12 % at those conditions.

When a gas flows through a polymeric membrane, the diffusion process is affected by the tortuosity factor (τ) and the chain immobilization factor (β) as two impedance elements which affect the diffusion in systems with large molecules. In this chapter, a thermodynamic framework to obtain values for the tortuosity and the chain immobilization parameters in semicrystalline polymeric membranes is presented. A thermodynamic expression for the factors τ and β in terms of the activation entropy and the cohesion energy of the polymeric structure was obtained. The model was applied to experimental data obtained for linear low-density polyethylene (LLDPE) membranes with different percentages of crystallinity and with different densities (0.94, 0.93, 0.92, 0.91, 0.90, and 0.87 g/cm³). Experimental measurements for diffusion and permeability of oxygen, methane, ethane, ethylene, propane, propylene, and helium were performed by the time-lag method. The temperature and pressure were of 30 °C and 1 bar, respectively, throughout all the diffusion and permeability analyses. Finally, to understand the differences between the parameters characterizing the immobilization of the chains and the tortuosity, with respect to the diffusion of gases, a thermodynamic analysis using helium was done.

Three-layer spacer configurations for feed channels in spiral wound membrane modules are analyzed. The simulation results indicate that complex flow structures are generated by the presence of spacers, which favor the mass transfer in the vicinity of the membrane sheets. By making a comparison with conventional two-layer configurations, it was found that three-layer arrangements of circular spacers with immersion grades of 0.5, 0.6, and 0.7 result in higher average mass transfer coefficients, suggesting a feasible implementation of this type of spacer configurations in full-scale membrane modules.

Membranes are the most sensitive unit to the damaging effect of biofouling in reverse osmosis equipment. Biofouling is defined by many variables and elements, including a surface-deposited organized microbial ecosystem showing complex functional and structural characteristics, known as biofilm. Biofilm formation results from the excretion of an extracellular protective matrix by microorganisms. Biofilm blocks reverse osmosis (RO) membranes, decreasing the permeability and, consequently, the rate at which water can be desalinated. The nutritional and microbial parameters of water samples from the Cortes Sea, and specifically from the coast of Guaymas, Sonora, México, were determined. The water samples were used to isolate marine microorganism present in this ecosystem. A modified growth medium was developed to represent this specific sea environment. Finally, several artificial biofouling-related experiments were carried out in order to reproduce, and then, analyze the potential membrane damage caused by biofouling. A discrepancy was found between the salinity in the water samples from the Guaymas coast and the standard salinity expected for the Pacific Ocean. Several causes for this variability and its effect on the physical and chemical parameters are proposed, and the potential impact on desalination plants due to the microbial population, which will ultimately be responsible for biofouling on RO membranes, is analyzed.

The treatment of reject water from a nanofiltration system by photo-oxidation with ultraviolet light and titanium dioxide (TiO₂) showed that degradation efficiency of the organic micropollutants (OMPs) varied depending on the reaction time analyzed. Thus, compounds such as diclofenac and ibuprofen exhibited greater than 95 % degradation within the first 15 min, while less than 65 % of naproxen and gemfibrozil was degraded after 15 min of reaction time. Salicylic acid had the lowest degradation efficiency in 15 min (<45 %) of all of the compounds studied. In addition to radical recombination, suspended particles limit potential homogeneous illumination in the reaction system while the presence of organic material causes parallel hydroxyl radical-consuming reactions, which may be responsible for low degradation efficiencies under these conditions.

This chapter describes the application of membrane bioreactor (MBR) technology for the treatment of wastewater to be used subsequently for indirect recharge in the Mexico Valley aquifer. Using a laboratory-scale system, four cleaning regimes were evaluated: co-current water and air applied intermittently; countercurrent water and air applied intermittently; co-current air applied continuously; and system operated without cleaning, which demonstrated that the cleaning regime (direction and frequency of application of the cleaning agent) influences permeate quality. The co-current flow with constant aeration was found to be the best methodology. A strategy of operation was thus defined, taking into consideration the hydrodynamic factors of the membrane. In addition, the removal efficiency of four emergent pollutants (ibuprofen, salicylic acid, naproxen, and diclofenac) was determined using MBR treatment. The results show that biodegradation and sorption phenomena are the main removal mechanisms for these emerging pollutants (removal >75 %). It was determined that, through the use of membrane bioreactor treatment, a permeate may be obtained which meets the physical–chemical standards established by the Mexican regulations for indirect recharge of the aquifer with treated wastewater named NOM 0014 CONAGUA.

The development of new membranes for gaseous separations has been focused on the improvement of their gas transport properties in order to obtain highly pure products, higher gas flows to be treated, and materials that are more resistant to the operation conditions. In the present study, the comparison between two commercially available membranes for the sweetening process of natural gas and one membrane synthesized at the Instituto Mexicano del Petróleo (IMP) is carried out. The size of plants, their investment, operation, and gas processing costs are analyzed. It was found that the IMP membrane required less permeation area, lower investment, maintenance, and operation costs and promoted methane loss savings in the permeation stream and a lower gas processing cost.

Many regions of the world face significant water supply issues due to its scarcity. In the state of Sonora, Mexico, there is physical scarcity of water, a grave problem that has generated social conflict in recent years. The Instituto Tecnológico de Sonora (ITSON) is making a significant bet on desalination technologies within its research and development projects and has incorporated the study and analysis of technical aspects of desalination in Chemical Engineering course programs, as well as in undergraduate, MSc, and PhD thesis topics. This work summarizes the Consejo Nacional de Ciencia y Tecnología (CONACyT, Mexican National Science and Technology Council) Fellowship Research Project that is underway at ITSON, which aims to improve the understanding of reverse osmosis membrane biofouling with applications in desalination, specifically for Mexican Pacific coast seawater. As a preliminary study, an experimental system has been developed to test membranes and spacers, both commercial and produced in the laboratory through 3D printing techniques. The results indicate that variations in the design and dimensions of the spacers can lead to better productivity in terms of observed rejection and permeate flux. Therefore, it is necessary to test new spacer designs in order to optimize the results.

In the newly established Morelia Unit of the Materials Research Institute (IIM) of the National Autonomous University of Mexico (UNAM) several investigations on polymeric materials with applications in membrane technology are being conducted. The new materials developed via ring-opening metathesis polymerization (ROMP) as well as polycondensation have potential environmental and energy applications such as gas separation (Scheme 16.1), proton exchange membranes for low temperature fuel cells, (Scheme 16.2), and the recovery of heavy metals from aqueous solutions (Scheme 16.3), among others. In the short term, the research will focus on generating more sustainable routes for producing polymers from renewable raw materials (Scheme 16.4). In particular, the inclusion of natural sources such as vegetable oil derivatives for obtaining new or already known polymeric materials will be considered.