Reverse osmosis (RO) is widely used for water reclamation and is one of the most feasible technologies for addressing water scarcity around the world. RO membrane fabrication procedures are continually being optimized and modified to enhance the treatment performance and efficacy of the RO process. A review of the existing literature published on membrane fabrication revealed that a detailed and reproducible methodology consistent among prior studies was not available. Therefore, the primary objective of this study was to utilize techniques from prior research to develop a reliable lab-scale membrane fabrication process for studying the potable reuse applications of TFC RO membranes. Phase inversion was used to create a polysulfone (PSF) support layer on a non-woven fabric sheet. Then, the process of interfacial polymerization (IP) between amine and acyl chloride monomers was utilized to form a highly selective and ultrathin polyamide (PA) layer on the PSF support surface. The resulting membrane composition and performance was dependent on a wide range of parameters during the fabrication process. The optimal support materials, reactant types and concentration, and reaction conditions were determined through trial and error. The best performing membranes utilized N-methyl-2-pyrrolidone (NMP) as the solvent, Novatexx-2471 non-woven fabric for mechanical support, and 15 wt% PSF concentration for phase inversion. The optimal immersion duration was five minutes for the aqueous amine monomer solution during the IP process. The flux for membrane triplicates was 20.2  3.6 liters per square meter per hour (LMH) while the salt rejection was 96.8  2.0%. The relatively low standard deviation for flux and salt rejection indicates that the fabrication method developed herein is consistent. A commercial Dow Filmtec BW30 flat sheet PA-TFC RO membrane was tested for comparison and exhibited a flux of 44.9 LMH and a salt rejection of 98.5%. Thus, the membranes developed in this study achieved salt rejection on par with commercial membranes but exhibited a flux that was significantly lower. Furthermore, this study investigated modifications to the traditional TFC membrane using engineered silica nanomaterials with the goal of enhancing the membrane flux while maintaining high salt rejection. Two types of nonporous silicon dioxide nanoparticles (SDNPs), non-functionalized and amine functionalized, were dispersed in the aqueous and organic IP solutions. Ultrasonication of the non-functionalized SDNPs in the aqueous solution was observed to produce the most stable dispersion. Compared to the unmodified TFC membranes, the average flux of the SDNP-modified (TFC-NP) RO membrane triplicates was higher at 25.4  2.0 LMH with 0.1% (w/v) SDNPs incorporated in the PA layer. The salt rejection was lowered to 92.3  0.1% for the TFC-NP membranes. In addition, the membranes fabricated in this study were characterized using scanning electron microscopy (SEM), Fourier Transport Infrared Spectroscopy (FTIR), atomic force microscopy (AFM), and goniometry measurements. SEM images showed that the TFC-NP membranes contained larger spaces between ridges and valleys of the PA pore structure. FTIR confirmed the PA layer formation on the membranes fabricated herein but a spectral peak from the SDNPs was not observed for the TFC-NP membranes. AFM measurements indicated an increase in surface roughness of the modified membranes, likely because of the incorporation of SDNPs. The surface of TFC-NP membranes was found to be more hydrophilic than the unmodified TFC membranes based on contact angle measurements. Further optimization of the fabrication method developed herein is warranted before pursuing additional RO research topics, such as the disinfection byproduct precursor removal of TFC membranes.

Fresh water scarcity is an alarming issue for communities across the globe. The development of water recycling and reuse technologies has become crucial in expanding the limited water resources. Reverse osmosis (RO) is among the key processes that can treat wastewater to meet potable water reuse standards. Despite the advancements in RO membrane technologies, many challenges persist regarding the operation and maintenance of RO membranes, such as membrane fouling. Extensive research investigations have focused on developing RO membrane modifications to combat the decreased performance due to fouling. Polyethylenimine (PEI) is a promising polymer used for enhancing the anti-fouling properties of thin film composite (TFC) RO membranes. PEI, a positively charged polymer with high charge density, is commonly grafted on TFC RO membrane surfaces to produce smoother, more hydrophilic membranes to minimize fouling. However, little research is available on the optimal PEI placement within the composite RO membrane layers for enhancing antifouling properties. The current study aimed to investigate whether alternative positions within the membrane layers could yield better anti-fouling performance compared to incorporation PEI on the membrane surface. Unmodified (i.e., control) and PEI-modified TFC RO membranes were fabricated in the laboratory. The PEI-modified membranes were produced in two variations with regards to the position of PEI in the composite membrane layer. The first variation, named PEI-1, involved immersing the polysulfone (Psf) support layer of the membrane in an aqueous PEI solution, before the active polyamide (PA) layer was formed. The second variation, named PEI-2, consisted of immersing the fully formed TFC RO membrane in an aqueous PEI solution to incorporate PEI on the surface of the active PA layer. The PEI used in the study for membrane modification had branched configuration with molecular weight of 1200 g/mole. The laboratory-scale TFC RO membranes produced herein were characterized and tested for water flux, salt rejection, and fouling behavior. The water flux and salt rejection, commonly referred to as permselectivity, of all the membranes produced were evaluated in a crossflow filtration unit. On the other hand, the fouling tests were conducted in a dead-end membrane filtration unit because of operational limitations of the crossflow unit. The PEI-1 membrane produced a water flux of 18.7 LMH (L/m2hr) and a stable salt rejection of 82.1%. The PEI-2 membrane resulted in a water flux of 22.4 LMH and a salt rejection of 85.2%. These results indicate that incorporating PEI on the membrane PA active surface layer achieved better permselectivity compared to PEI-1, which is the membrane with PEI incorporated inside the structure (i.e., incorporated on the Psf support layer). However, both PEI-modified membranes exhibited lower permselectivity performance compared to the unmodified control membrane, which produced a water flux of 23.9 LMH and salt rejection of 88.2%. To test fouling of the unmodified and PEI modified RO membranes, bovine serum albumin (BSA) was chosen as a model foulant based on preliminary investigations conducted herein to compare BSA to sodium alginate. After the foulant was introduced in the feed, the unmodified membrane exhibited a 31.8% total fouling ratio, the decrease in flux from the foulant solution compared to running clean DI water. However, a 90.7% flux recovery ratio was achieved when a final DI water rinse was performed. The PEI-1 membrane had a 39.7% total fouling ratio and a 81.6% flux recovery ratio after rinsing with DI water. The PEI-2 membrane showed a 43.1% total fouling ratio as a result of BSA fouling and a 94% flux recovery ratio when rinsed with DI water at the end of the fouling test. Water contact angle (WCA) analysis confirmed that the PEI-2 membrane had the most hydrophilic surface (WCA 25.1°) compared to the control membrane (WCA 52.9°). The higher hydrophilicity of PEI-2 aligns with its higher flux recovery results, which indicated reduced membrane fouling. Furthermore, the PEI-2 membrane had a drastically lower WCA than those reported in the literature for PEI-modified membranes, which ranged from (63° – 80°). In conclusion, the increased flux recovery and surface hydrophilicity of the PEI-2 membrane indicated that the best anti-fouling performance would likely be obtained when PEI is grafted onto the surface of the active PA membrane surface. Future research is warranted to optimize the PEI-2 membrane by exploring the effect of PEI concentration, molecular weight, and structural configuration (i.e., branched versus linear), on anti-fouling performance of the membranes.

[ES] La presente tesis doctoral se centra en el desarrollo de nuevas membranas de separación de gases, así como su empleo in-situ en reactores catalíticos de membrana para la intensificación de procesos. Para este propósito, se han sintetizado varios materiales, como polímeros para la fabricación de membranas, catalizadores tanto para la metanación del CO2 como para la reacción de síntesis de Fischer-Tropsch, y diversas partículas inorgánicas nanométricas para su uso en membranas de matriz mixta. En lo referente a la fabricación de las membranas, la tesis aborda principalmente dos tipos: orgánicas e inorgánicas. Con respecto a las membranas orgánicas, se han considerado diferentes materiales poliméricos, tanto para la capa selectiva de la membrana, así como soporte de la misma. Se ha trabajado con poliimidas, puesto que son materiales con temperaturas de transición vítrea muy alta, para su posterior uso en reacciones industriales que tienen lugar entre 250-300 ºC. Para conseguir membranas muy permeables, manteniendo una buena selectividad, es necesario obtener capas selectivas de menos de una micra. Usando como material de soporte otro tipo de polímero, no es necesario estudiar la compatibilidad entre ellos, siendo menos compleja la obtención de capas finas. En cambio, si el soporte es de tipo inorgánico, un exhaustivo estudio de la relación entre la concentración y la viscosidad de la solución polimérica es altamente necesario. Diversas partículas inorgánicas nanométricas se estudiaron para favorecer la permeación de agua a través de los materiales poliméricos. En segundo lugar, en cuanto a membranas inorgánicas, se realizó la funcionalización de una membrana de paladio para favorecer la permeación de hidrógeno y evitar así la contaminación por monóxido de carbono. El motivo por el cual se dopó con otro metal la capa selectiva de la membrana metálica fue para poder emplearla en un reactor de Fischer-Tropsch. Con relación al diseño y fabricación de los reactores, durante esta tesis, se desarrolló el prototipo de un microreactor para la metanación de CO2, donde una membrana polimérica de capa fina selectiva al agua se integró para evitar la desactivación del catalizador, y a su vez desplazar el equilibrio y aumentar la conversión de CO2. Por otro lado, se rediseñó un reactor de Fischer-Tropsch para poder introducir una membrana metálica selectiva a hidrogeno y poder inyectarlo de manera controlada. De esta manera, y siguiendo estudios previos, el objetivo fue mejorar la selectividad a los productos deseados mediante el hidrocraqueo y la hidroisomerización de olefinas y parafinas con la ayuda de la alta presión parcial de hidrógeno. / [CA] La present tesi doctoral es centra en el desenvolupament de noves membranes de separació de gasos, així com el seu ús in-situ en reactors catalítics de membrana per a la intensificació de processos. Per a aquest propòsit, s'han sintetitzat diversos materials, com a polímers per a la fabricació de membranes, catalitzadors tant per a la metanació del CO2 com per a la reacció de síntesi de Fischer-Tropsch, i diverses partícules inorgàniques nanomètriques per al seu ús en membranes de matriu mixta. Referent a la fabricació de les membranes, la tesi aborda principalment dos tipus: orgàniques i inorgàniques. Respecte a les membranes orgàniques, diferents materials polimèrics s'ha considerat com a candidats prometedors, tant per a la capa selectiva de la membrana, així com com a suport d'aquesta. S'ha treballat amb poliimides, ja que són materials amb temperatures de transició vítria molt alta, per al seu posterior ús en reaccions industrials que tenen lloc entre 250-300 °C. Per a aconseguir membranes molt permeables, mantenint una bona selectivitat, és necessari obtindre capes selectives de menys d'una micra. Emprant com a material de suport altre tipus de polímer, no és necessari estudiar la compatibilitat entre ells, sent menys complexa l'obtenció de capes fines. En canvi, si el suport és de tipus inorgànic, un exhaustiu estudi de la relació entre la concentració i la viscositat de la solució polimèrica és altament necessari. Diverses partícules inorgàniques nanomètriques es van estudiar per a afavorir la permeació d'aigua a través dels materials polimèrics. En segon lloc, quant a membranes inorgàniques, es va realitzar la funcionalització d'una membrana de pal¿ladi per a afavorir la permeació d'hidrogen i evitar la contaminació per monòxid de carboni. El motiu pel qual es va dopar amb un altre metall la capa selectiva de la membrana metàl¿lica va ser per a poder emprar-la en un reactor de Fischer-Tropsch. En relació amb el disseny i fabricació dels reactors, durant aquesta tesi, es va desenvolupar el prototip d'un microreactor per a la metanació de CO2, on una membrana polimèrica de capa fina selectiva a l'aigua es va integrar per a així evitar la desactivació del catalitzador i al seu torn desplaçar l'equilibri i augmentar la conversió de CO2. D'altra banda, un reactor de Fischer-Tropsch va ser redissenyat per a poder introduir una membrana metàl¿lica selectiva a l'hidrogen i poder injectar-lo de manera controlada. D'aquesta manera, i seguint estudis previs, el objectiu va ser millorar la selectivitat als productes desitjats mitjançant el hidrocraqueix i la hidroisomerització d'olefines i parafines amb l'ajuda de l'alta pressió parcial d'hidrogen. / [EN] The present thesis is focused on the development of new gas-separation membranes, as well as their in-situ integration on catalytic membrane reactors for process intensification. For this purpose, several materials have been synthesized such as polymers for membrane manufacture, catalysts for CO2 methanation and Fischer-Tropsch synthesis reaction, and inorganic materials in form of nanometer-sized particles for their use in mixed matrix membranes. Regarding membranes manufacture, this thesis deals mainly with two types: organic and inorganic. With regards to the organic membranes, different polymeric materials have been considered as promising candidates, both for the selective layer of the membrane, as well as a support thereof. Polyimides have been selected since they are materials with very high glass transition temperatures, in order to be used in industrial reactions which take place at temperatures around 250-300 ºC. To obtain highly permeable membranes, while maintaining a good selectivity, it is necessary to develop selective layers of less than one micron. Using another type of polymer as support material, it is not necessary to study the compatibility between membrane and support. On the other hand, if the support is inorganic, an exhaustive study of the relation between the concentration and the viscosity of the polymer solution is highly necessary. In addition, various inorganic particles were studied to favor the permeation of water through polymeric materials. Secondly, as regards to inorganic membranes, the functionalization of a palladium membrane to favor the permeation of hydrogen and avoid carbon monoxide contamination was carried out. The membrane selective layer was doped with another metal in order to be used in a Fischer-Tropsch reactor. Regarding the design and manufacture of the reactors used during this thesis, a prototype of a microreactor for CO2 methanation was carried out, where a thin-film polymer membrane selective to water was integrated to avoid the deactivation of the catalyst and to displace the equilibrium and increase the CO2 conversion. On the other hand, a Fischer-Tropsch reactor was redesigned to introduce a hydrogen-selective metal membrane and to be able to inject it in a controlled manner. In this way, and following previous studies, the aim is to enhance the selectivity to the target products by hydrocracking and hydroisomerization the olefins and paraffins assisted by the presence of an elevated partial pressure of hydrogen. / I would like to acknowledge the Spanish Government, for funding my research with the Severo Ochoa scholarship. / Escorihuela Roca, S. (2019). Novel gas-separation membranes for intensified catalytic reactors [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/121139