Mixed matrix membranes

In recent decades, mixed matrix membranes (MMMs) have attracted considerable interest in research laboratories worldwide, motivated by the gap between the growing interest in developing novel mixed matrix membranes by various research groups and the lack of large-scale implementation. This Special Issue contains six publications dealing with the current opportunities and challenges of mixed matrix membranes development and applications as solutions for the environmental and health challenges of 21st century society.Financial support by the Spanish Ministry for Science and Universities under project grant no. CTQ2016-76231-C2-1-R at the Universidad de Cantabria is gratefully acknowledged

Generación de mesoporos en la estructura del titanosilicato microporoso ETS-10

Estudio de la modificacion de la estructura del ETS-10 a traves de la creacion de mesoporos mediante tratamientos quimicos, dando lugar a un material con una estructura de poro jerarquizada que puede mejorar la interaccion entre el material inorganico y la matriz polimerica de una membrana mixta para la separacion de O2/N2. Caracterizacion mediante difraccion de rayos X, adsorcion de N2 y microscopia electronica de los materiales obtenidos

Effect of water and organic pollutant in CO2/CH4 separation using hydrophilic and hydrophobic composite membranes

Membrane technology is a simple and energy-conservative separation option that is considered to be a green alternative for CO2 capture processes. However, commercially available membranes still face challenges regarding water and chemical resistance. In this study, the effect of water and organic contaminants in the feed stream on the CO2/CH4 separation performance is evaluated as a function of the hydrophilic and permselective features of the top layer of the membrane. The membranes were a commercial hydrophobic membrane with a polydimethylsiloxane (PDMS) top layer (Sulzer Chemtech) and a hydrophilic flat composite membrane with a hydrophilic [emim][ac] ionic liquid–chitosan (IL–CS) thin layer on a commercial polyethersulfone (PES) support developed in our laboratory. Both membranes were immersed in NaOH 1M solutions and washed thoroughly before characterization. The CO2 permeance was similar for both NaOH-treated membranes in the whole range of feed concentration (up to 250 GPU). The presence of water vapor and organic impurities of the feed gas largely affects the gas permeance through the hydrophobic PDMS membrane, while the behavior of the hydrophilic IL–CS/PES membranes is scarcely affected. The effects of the interaction of the contaminants in the membrane selective layer are being further evaluated.This research was funded by the Spanish Ministry of Science and Innovation; project CTQ2016-76231-C2-(AEI/FEDER, UE) and project PID2019-108136RB-C31)

Pervaporación de mezclas de agua y alcohol con membranas polímero/materiales inorgánicos nanoporosos

Este Proyecto Fin de Carrera se centra en el estudio de la pervaporación de mezclas de agua y alcohol con membranas polímericas de quitosano y membranas mixtas de quitosano y el titanosilicato ETS-10. La pervaporación es un proceso de separación que utiliza membranas y que supone una alternativa eficiente a las técnicas de separación convencionales como es la destilación, basada en el equilibrio clásico líquido-vapor. El primer objetivo de este PFC ha sido el de montar y poner en funcionamiento la planta. El segundo paso fue el de preparar los dos tipos de membranas utilizados y caracterizarlos mediante técnicas de microscopía electrónica, termogravimetría y difracción de rayos X. En los experimentos de pervaporación posteriores se estudiaron los parámetros fundamentales de este proceso que son el flujo de permeación y el factor de separación y la influencia sobre ambos que tiene la variación de temperatura y la variación de la concentración de alcohol en la mezcla de alimentación. Después de esto se obtuvieron las siguientes conclusiones. Ambas membranas tienen un buen comportamiento en pervaporación. La interacción entre el quitosano y el ETS-10 en las membranas mixtas es buena y la adición del titanosilicato tiene como resultado un aumento en el flujo de permeación a costa de disminuir la efectividad de la separación. Otro efecto observado es que el incrementeo de la concentración de etanol en la alimentación supone una disminución en el flujo de permeación con un aumento en la separación. Un aumento de la temperatura produce un aumento del flujo pero la separación tiene diferente comportamiento para ambos tipos de membrana, aumentando la misma para las membranas mixtas, lo cual confirma que el ETS-10 tiene influencia en la membrana. Por último, los datos confirman una superación del equilibrio clásico líquido-vapor de la mezcla etanol/agua

Síntesis de membranas poliméricas con spin coater

Este Proyecto Fin de Carrera (PFC) se centra en la preparación de membranas poliméricas mediante la tecnología “spin coating” (recubrimiento por rotación). Esta técnica consiste en la fabricación de películas finas de espesor uniforme mediante la utilización de la fuerza centrífuga durante el proceso de deposición sobre un sustrato de una disolución polimérica. Las membranas prepararas pueden tener aplicación en la separación de gases, siendo esta una tecnología de menor coste energético y medioambientalmente limpia en comparación con los procesos tradicionales de separación. El objetivo principal de este PFC ha consistido en la puesta en marcha de la instalación de spin coating y establecer para la preparación de membranas poliméricas con esta técnica un manual que está disponible a partir de ahora en el laboratorio del Grupo de Investigación de Catálisis, Separaciones Moleculares e Ingeniería de Reactores (CREG) donde se ha realizado este proyecto. En la preparación de membranas poliméricas de polisulfona por spin coating se ha estudiado la influencia de distintas variables de diseño en la medida del espesor a lo largo y ancho de cada membrana utilizando la media aritmética y desviación estándar de estas medidas. Como variables de diseño se ha tomado el volumen y la concentración de la disolución depositada así como la velocidad de giro y tiempo de centrifugación de las dos etapas que componen el proceso (etapa 1 de inyección de la disolución polimérica y etapa 2 de distribución de la disolución en el sustrato). Se ha comprobado que a velocidades de giro altas, las membranas presentan un espesor más reducido y una mejor distribución superficial. La influencia del tiempo no es clara y los pesos apenas se ven afectados por los cambios de velocidad y tiempo. Se ha encontrado que la concentración de la disolución que afecta a la viscosidad es un parámetro importante para el control del espesor. Se ha puesto de manifiesto las ventajas que presenta el proceso spin coating con respecto al proceso tradicional sin rotación, tales como preparación de películas más delgadas y homogéneas así como un mayor control del proceso pudiéndose, obtener una amplia variedad de espesores entre 10 y 500 µm. Se ha preparado y caracterización membranas mixtas de polímero y ETS-10 utilizando la técnica spin coating. Se ha observado que para membranas mixtas, los espesores salen superiores a los de las poliméricas con las mismas condiciones de operación y se ha comprobado con la caracterización por microscopía electrónica el buen contacto entre la matriz polimérica y las partículas inorgánicas. Por último, se ha encontrado una mejora de separación de la membrana mixta en la separación de mezclas equimolares de O2/N2, a 35ºC con respecto a las poliméricas

Chitosan: polyvinyl alcohol based mixed matrix sustainable coatings for reusing composite membranes in water treatment: fouling characterization

This work aims at studying the potential of modifying the surface of used polyamide (PA) reverse osmosis (RO) commercial membranes by coatings made of renewable and biodegradable polymers, chitosan (CS) and polyvinyl alcohol (PVA), filled with Cu-ion-exchange layered AM-4 titanosilicate and UZAR-S3 stannosilicate to provide antifouling properties and enlarging life time of thin-film composite (TFC) membranes. The water permeation and fouling ratios were evaluated as a function of active layer material in the presence of model organic (BSA) and inorganic (NaCl) foulants. The mixed matrix membrane (MMM) coatings added on the active surface of the PA commercial membranes generally decreased the flux decline and increased the permeate flow recovery rate. The CS:PVA based coatings promote the reversible and not the irreversible fouling, especially CuAM-4CS:PVA. Beside, ATR-FTIR confirms the reversible nature of the BSA fouling and the irreversible nature of the NaCl fouling. These results may in the future open the possibility of renewing the useful lifetime of commercial RO membranes by a simple coating method in the light of the circular economy.Financial support from the Spanish Ministry of Science and Innovation under project PID2019-108136RB-C31 /AEI/10.13039/501100011033. MCIN/AEI/10.13039/501100011033 and the “European Union Next Generation EU/PRTR” for the Grant EIN2020-112319/AEI/10.13039/501100011033 are gratefully acknowledged. The Early Stage Researcher grant PRE2020-09765, funded by MCIN/AEI/ 10.13039/501100011033, is also thanked (A.T.C.)

Effect of humidity on CO2/N2 and CO2/CH4 separation using novel robust mixed matrix composite hollow fiber membranes: experimental and model evaluation

In this work, the performance of new robust mixed matrix composite hollow fiber (MMCHF) membranes with a different selective layer composition is evaluated in the absence and presence of water vapor in CO2/N2 and CO2/CH4 separation. The selective layer of these membranes is made of highly permeable hydrophobic poly(trimethyl-1-silylpropine) (PTMSP) and hydrophilic chitosan-ionic liquid (IL-CS) hybrid matrices, respectively, filled with hydrophilic zeolite 4A particles in the first case and HKUST-1 nanoparticles in the second, coated over compatible supports. The effect of water vapor in the feed or using a commercial hydrophobic PDMSXA-10 HF membrane has also been studied for comparison. Mixed gas separation experiments were performed at values of 0 and 50% relative humidity (RH) in the feed and varying CO2 concentration in N2 and CH4, respectively. The performance has been validated by a simple mathematical model considering the effect of temperature and relative humidity on membrane permeability.This research was funded by the Spanish Ministry of Science, Innovation and Universities (www.ciencia.gob.es) under project CTQ2016-76231-C2-1-R

Separation of CO2-N2 gas mixtures: Membrane combination and temperature influence

Novel mixed matrix membranes (MMM) with different characteristics are experimentally evaluated in a two-stage membranes-in-series bench-scale setup for the separation of CO2-N2 gas mixtures. For stage 1, a high permeability (higher than 1000 Barrer) and low selectivity (about 5–10) membrane is chosen: the [emim][Ac]-Chitosan (IL-CS) hybrid membrane developed in our laboratory and the Pervap 4060 (Sulzer) composite membrane. For stage 2, we chose our Zeolite A/PTMSP MMM, whose selectivity is higher than 20 even at up to 343 K, the CO2 permeability not lower than 5000 Barrer, which allows skipping the use of the intermediate compressor. The influence of membrane intrinsic properties (i.e. selective membrane material), number of modules in series, and feed concentration on separation performance is evaluated experimentally. In this system, a 10% CO2 feed is concentrated to 43%, 26 and 40% for the Zeolite A/PTMSP MMM – Zeolite A/PTMSP MMM, IL-CS – Zeolite A/PTMSP and Pervap 4060 – Zeolite A/PTMSP in stage 1 and stage 2, respectively. The agreement of the experimental results with a mathematical model at the low CO2 feed concentration of flue gas allows estimating the membrane area needed for each membrane material to achieve a given CO2 purity and removal efficiency. The very large membrane areas needed to reach the 90% CO2 purity and removal efficiency target are drastically reduced if the CO2 removal efficiency required is set to 70%, especially for the combinations with different membranes in each stage, which gives scope for attempting further development of novel membrane materials for CO2capture processes.This work is partially based on a concept from Eliot S. Gerber (U. S.A.), for which he is gratefully acknowledged. The authors are also grateful for the financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under project CTQ2012-31229. A.F.B. and C.C.C. also thank the MINECO for the Early Stage Researcher (BES2013-064266) and ‘‘Ramón y Cajal” (RYC2011-0855) contracts, respectively

Use of Chitosan as Copper Binder in the Continuous Electrochemical Reduction of CO2 to Ethylene in Alkaline Medium

This work explores the potential of novel renewable materials in electrode fabrication for the electrochemical conversion of carbon dioxide (CO2) to ethylene in alkaline media. In this regard, the use of the renewable chitosan (CS) biopolymer as ion-exchange binder of the copper (Cu) electrocatalyst nanoparticles (NPs) is compared with commercial anion-exchange binders Sustainion and Fumion on the fabrication of gas diffusion electrodes (GDEs) for the electrochemical reduction of carbon dioxide (CO2R) in an alkaline medium. They were tested in membrane electrode assemblies (MEAs), where selectivity to ethylene (C2H4) increased when using the Cu:CS GDE compared to the Cu:Sustainion and Cu:Fumion GDEs, respectively, with a Faradaic efficiency (FE) of 93.7% at 10 mA cm−2 and a cell potential of −1.9 V, with a C2H4 production rate of 420 µmol m−2 s−1 for the Cu:CS GDE. Upon increasing current density to 90 mA cm−2, however, the production rate of the Cu:CS GDE rose to 509 µmol/m2s but the FE dropped to 69% due to increasing hydrogen evolution reaction (HER) competition. The control of mass transport limitations by tuning up the membrane overlayer properties in membrane coated electrodes (MCE) prepared by coating a CS-based membrane over the Cu:CS GDE enhanced its selectivity to C2H4 to a FE of 98% at 10 mA cm−2 with negligible competing HER. The concentration of carbon monoxide was below the experimental detection limit irrespective of the current density, with no CO2 crossover to the anodic compartment. This study suggests there may be potential in sustainable alernatives to fossil-based or perfluorinated materials in ion-exchange membrane and electrode fabrication, which constitute a step forward towards decarbonization in the circular economy perspective.This research was funded by the Spanish Ministry for Science and Innovation, grant numbers PID2019-108136RB-C31, PID2019-108136RB-C32, PID2020-112845RB-I00 and EIN2020-112319. A.M.M. also acknowledges the Ministry for the Early Stage researcher contract (FPI grant no. BES-2017-080795)

Past, present and future of membrane technology in Spain

The following review aims at analyzing the contribution of Spanish researchers to membrane science and technology, with a historical compilation of the main milestones. We used a bibliometric analysis based on the Scopus database (1960?2020) dealing with 8707 documents covering the different disciplines and subject areas where membranes are involved. Furthermore, the information has been updated to the present moment of writing this manuscript in order to include the latest research lines and the different research groups currently active in Spain, which may lead the way to the development of the field in the coming years