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

Application of directly brewed compost extract improves yield and quality in baby leaf lettuce grown hydroponically

The aim of this work was to study whether the application of a directly brewed compost extract (added in the nutrient solution or by microsprinkler) could be used to improve the yield and quality of baby leaf red lettuce growing in a floating system, and to control the incidence of Pythium irregulare. Its e_ect on the quality of fresh-cut red lettuce was also studied. For this, two experiments were carried out over two growing cycles (winter–spring and autumn). The results showed that the use of compost extract added to the nutrient solution improved baby leaf lettuce growth and quality, reducing the nitrate content and enhancing the content of potentially health-promoting compounds such as phenols and flavonoids and the antioxidant capacity. Microbial quality was maintained during storage and the compost extract had no negative e_ect on the microbial load of the final product. In addition, application of the compost decreased the population of P. irregulare in the water. It is concluded that the application of directly brewed compost extract is of potential use in a sustainable soilless production system for baby leaf red lettuce, since it improves the yield and quality of the product and is able to control the incidence of P. irregulare.This work was supported by projects AGL2017-84085-C3-3-R and AGL2017-84085-C3-1-R from the Ministerio de Economía y Competitividad of Spain

Fitting approach to liquid–liquid displacement porosimetry based on the log-normal pore size distribution

Producción CientíficaLiquid-liquid displacement porosimetry (LLDP) has been used to characterize several UF membranes in a wide range of molecular weight cut-offs (MWCO). A new method to convert porosimetric data into pore size distributions and related information has been developed based on assuming log-normal pore size distributions. The results of this are in good agreement with those from the customary data conversion algorithm (as derived by Grabar and Nikitine). The proposed method can also be used when a reduced number of experimental data points is available, leading to a significant reduction of data acquisition time needed to complete a reliable analysis.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Polymeric films based on blends of 6FDA-6FpDA polyimide plus several copolyfluorenes for CO2 separation

Producción CientíficaThree emitting copolyfluorenes, based on 2,7-(9,9-dihexyl)fluorene and different aryl groups (1,4-bencene, PFH-B; 1,4-bencen-1,2,5-thiadiazole PFH-BT; 1,4-naphthalen- 1,2,5-thiadiazole, PFH-NT), showing diverse acceptor character, in different proportions were blended with a polyimide 6FDA-6FpDA to make a series of films. These copolyfluorene-polyimide blends were prepared and characterized in solid state, using several techniques. The fluorescence of conjugated polymers can be used as a tool to understand the formation of the membrane and also to increase permeability and selectivity in comparison to films without fluorescence. The relationship between the intrinsic fluorescence of conjugated polyfluorenes and their gas separation properties has been explored in order to establish the influence of the composition and the nature of the aryl group, in the conjugated polymer, on the gas separation performances. In all cases, a low proportion of copolyfluorenes (< 1%weight) gives better CO2/CH4 permselectivity properties than the original pure polyimide matrix. The best results were found for the samples that contain PFH-NT. This sample gives 25 % increase in the CO2 permeability with 15 % increase in CO2/CH4 selectivity. Finally, the loss of efficiency in conjugation mechanisms of absorption and emission of the samples could be explained on the basis of the π-staking of the polymer chains produced when a certain low percentage of conjugated polymers in the blend is surpassed. When this π- staking starts, gas permeation properties start to decline too.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Porosimetric characterization of polysulfone ultrafiltration membranes by image analysis and liquid–liquid displacement technique

Producción CientíficaStructural and surface properties of two commercial polysulfone ultrafiltration membranes have been evaluated by different techniques. Pore size distributions have been determined by Liquid–Liquid Displacement Porosimetry (LLDP) as well as by image analysis performed onto Field Emission Scanning Electron Microscopy (FESEM) images of the membrane surfaces. Fourier TransformInfrared Spectroscopy (FTIR) has been used to investigate membrane composition, and in particular, to obtain proper information on the presence of an additive within the membrane structure. Porosimetric results obtained by the two independent techniques compared reasonably well and the Molecular Weight Cut Off (MWCO) of the two membranes estimated from LLDP pore size distribution was found to be in good agreement with the nominal values given by manufacturers.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Alcohol reduction in red and white wines bynanofiltration of musts before fermentation

Producción CientíficaOne of the consequences of global warming is the early ripening of grapes which promotes a sugar content increase. Fermentation of their must leads to wines with an alcoholic degree higher than desired. The scope of this study is to select a nanofiltration (NF) technique to reduce the alcohol content of wines approximately 2 degrees by controlling the sugar content of grape must before its fermentation. For this purpose the performance of single-stage and two-stage NF processes using a spiral wound membrane unit were compared for white must (Spanish Verdejo) while for red must (Spanish Garnacha) a two-stage procedure was tested. During the singlestage NF intermittent backflush due to the osmotic pressure effect was tested. Results showed that backflushing had an undesirable effect because it increased the flux decay by disturbing the cake stabilization on the membrane. The corresponding wines obtained by adequate mixing of permeated and retained or control musts showed a 1 to 2 degrees alcohol reduction. Sensory evaluation and principal component analysis (PCA) revealed that there were no significant differences between the control and the filtered wines. Among the processes studied, the best NF technique was the two-stage process without backflush.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA248U13

The effect of humidity on the CO2/N2 separation performance of copolymers based on hard polyimide segments and soft polyether chains: Experimental and modeling

In this work, we studied two copolymers formed by segments of a rubbery polyether (PPO or PEO) and of a glassy polyimide (BPDA-ODA or BKDA-ODA) suitable for gas separation and CO2 capture. Firstly, we assessed the absorption of water vapor in the materials, as a function of relative humidity (R.H.), finding that the humidity uptake of the copolymers lies between that of the corresponding pure homopolymers values. Furthermore, we studied the effect of humidity on CO2 and N2 permeability, as well as on CO2/N2 selectivity, up to R.H. of 75%. The permeability decreases with increasing humidity, while the ideal selectivity remains approximately constant in the entire range of water activity investigated. The humidity-induced decrease of permeability in the copolymers is much smaller than the one observed in polyimides such as Matrimid® confirming the positive effect of the polyether phase on the membrane performance.Finally, we modeled the humidity-induced decrease of gas solubility, diffusivity and, consequently, permeability, using a suitable approach that considers the free volume theory for diffusion and LF model for solubility. Such model allows estimating the extent of competition that the gases undergo with water during sorption in the membranes, as a function of the relative humidity, as well as the expected reduction of free volume by means of water molecules occupation and consequent reduction of diffusivity. Keywords: CO2 capture, Humid gas permeation, Transport properties in polymeric membranes, Water vapor sorption, Modelin

A systematic study of ammonia recovery from anaerobic digestate using membrane-based separation

Producción CientíficaAmmonia recovery from synthetic and real anaerobic digestates was accomplished using hydrophobic flat sheet membranes operated with H2SO4 solutions to convert ammonia into ammonium sulphate. The influence of the membrane material, flow rate (0.007, 0.015, 0.030 and 0.045 m3 h−1) and pH (7.6, 8.9, 10 and 11) of the digestate on ammonia recovery was investigated. The process was carried out with a flat sheet configuration at a temperature of 35 °C and with a 1 M, or 0.005 M, H2SO4 solution on the other side of the membrane. Polytetrafluoroethylene membranes with a nominal pore radius of 0.22 µm provided ammonia recoveries from synthetic and real digestates of 84.6% ± 1.0% and 71.6% ± 0.3%, respectively, for a membrane area of 8.6 × 10−4 m2 and a reservoir volume of 0.5 L, in 3.5 h with a 1 M H2SO4 solution and a recirculation flow on the feed side of the membrane of 0.030 m3 h−1. NH3 recovery followed first order kinetics and was faster at higher pHs of the H2SO4 solution and recirculation flow rate on the membrane feed side. Fouling resulted in changes in membrane surface morphology and pore size, which were confirmed by Atomic Force Microscopy and Air Displacement Porometry.Junta de Castilla y León - FEDER (VA088G19, CLU 2017-09 y UIC 071)Ministerio de Ciencia e Innovación (proyecto: PID2019-109403RB-C21/AEI/10.13039/501100011033

Recent advances in membrane-based biogas and biohydrogen upgrading

Producción CientíficaBiogas and biohydrogen, due to their renewable nature and zero carbon footprint, are considered two of the gaseous biofuels that will replace conventional fossil fuels. Biogas from anaerobic digestion must be purified and converted into high-quality biomethane prior to use as a vehicle fuel or injection into natural gas networks. Likewise, the enrichment of biohydrogen from dark fermentation requires the removal of CO2, which is the main pollutant of this new gaseous biofuel. Currently, the removal of CO2 from both biogas and biohydrogen is carried out by means of physical/chemical technologies, which exhibit high operating costs and corrosion problems. Biological technologies for CO2 removal from biogas, such as photosynthetic enrichment and hydrogenotrophic enrichment, are still in an experimental development phase. In this context, membrane separation has emerged as the only physical/chemical technology with the potential to improve the performance of CO2 separation from both biogas and biohydrogen, and to reduce investment and operating costs, as a result of the recent advances in the field of nanotechnology and materials science. This review will focus on the fundamentals, potential and limitations of CO2 and H2 membrane separation technologies. The latest advances on membrane materials for biogas and biohydrogen purification will be systematically reviewed.Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación (AEI)/10.13039/501100011033 - (projects PID2019- 109403RB-C21)Junta de Castilla y León y Fondo Europeo de Desarrollo Regional (FEDER) - (grant CLU2017-09, UIC082, CL-EI-2021-07 and UIC 315