Editorial of the special issue on advanced electrochemical technologies for environmental applications

This special issue of Separation and Purification Technology gathers 27 articles, which are related to keynotes and oral or poster presentations at the 2nd European Workshop of Electrochemical Engineering entitled ‘New Bridges for a New Knowledge on Electrochemical Engineering’. The workshop was held from 1st to 5th October 2017 in Barcelona (Spain), as a Joint Event of the 10th World Congress of Chemical Engineering (WCCE10). This congress was promoted by the World Chemical Engineering Council (WCEC), the European Federation of Chemical Engineering (EFCE) and the European Society of Biochemical Engineering Sciences (ESBES) to approach researchers and specialists in all areas of chemical engineering and to improve their strategy for the development of innovative processes that will be vital for the society of tomorrow. The joint event was promoted by the Working Party on Electrochemical Engineering (WPEE) of the EFCE and co-organized with the Spanish Excellence Network on Environmental and Energy Applications of the Electrochemical Technology (thus being the 2nd Workshop of E3TECH Network). It took place at Fira de Barcelona, one of the most important trade fair institutions in Europe

Hollow Fiber Membranes of PCL and PCL/Graphene as Scaffolds with Potential to Develop In Vitro Blood—Brain Barrier Models

There is a huge interest in developing novel hollow fiber (HF) membranes able to modulate neural differentiation to produce in vitro blood–brain barrier (BBB) models for biomedical and pharmaceutical research, due to the low cell-inductive properties of the polymer HFs used in current BBB models. In this work, poly(ε-caprolactone) (PCL) and composite PCL/graphene (PCL/G) HF membranes were prepared by phase inversion and were characterized in terms of mechanical, electrical, morphological, chemical, and mass transport properties. The presence of graphene in PCL/G membranes enlarged the pore size and the water flux and presented significantly higher electrical conductivity than PCL HFs. A biocompatibility assay showed that PCL/G HFs significantly increased C6 cells adhesion and differentiation towards astrocytes, which may be attributed to their higher electrical conductivity in comparison to PCL HFs. On the other hand, PCL/G membranes produced a cytotoxic effect on the endothelial cell line HUVEC presumably related with a higher production of intracellular reactive oxygen species induced by the nanomaterial in this particular cell line. These results prove the potential of PCL HF membranes to grow endothelial cells and PCL/G HF membranes to differentiate astrocytes, the two characteristic cell types that could develop in vitro BBB models in future 3D co-culture systems.This research was funded by IDIVAL (INNVAL 17/20), MINECO/EIG-Concert Japan (X-MEM PCI2018-092929 project, International Joint Program 2018) and MINECO/Spain Feder (CTM-2016-75509-R project)

Phenomenological prediction of desalination brines nanofiltration through the indirect determination of zeta potential

The prediction of nanofiltration (NF) performance at environmentally relevant conditions, e.g.: highly saline brine solutions, is becoming of increasing interest for the recovery of waste materials in the water desalination industry. In this work, the prediction of the separation of sulfate and chloride contained in the retentate of reverse osmosis brackish water desalination by means of the commercial NF270 membrane is studied. Prior to theoretical modelling, streaming potential measurements were performed for aqueous single and binary mixtures of NaCl and Na2SO4 within the range of ionic strengths 1-100 mol/m3. Zeta potential values were obtained applying an extrapolation method from recent literature to allow the calculation of surface charge density under higher ionic strengths found in reverse osmosis desalination brines (100-1200 mol/m3). Then, the obtained surface charge density was used to simulate sulfate, chloride and sodium rejections by means of the Donnan steric pore model (DSPM), in the pressure range 2-20 bar. The good agreement between experimental and simulated rejection values allows validating the approach that enables the prediction of NF performance for the separation of monovalent and divalent anions, of interest for the purification of desalination brines before their further exploitation as a source of sodium chloride concentrated solutions.The authors gratefully acknowledge the funding for the projects CTM2016-75509-R and CTQ2015-66078-R

Effect of feed pressure and long-term separation performance of Pebax-ionic liquid membranes for the recovery of difluoromethane (R32) from refrigerant mixture R410A

The R410A refrigerant blend (GWP = 2088), a near azeotropic and equimass mixture of difluoromethane (R32, GWP = 675) and pentafluoroethane (R125, GWP = 3500), has been included in the HFC phase down road map established worldwide. In this context, the recovery of value-added R32 from R410A using membrane technology would be a breakthrough in the refrigeration and air conditioning sector, given that conventional distillation cannot be applied to this separation. For the first time, this work has taken advantage of the combination of ionic liquids and polymeric membranes for the separation of the constituents of the R410A mixture. Results show a remarkable improvement in terms of R32 permeability and R32/R125 selectivity in the composite membranes containing 40 wt % [C2mim][SCN] (αR32/R125 up to 14.5) and [C2mim][BF4] (αR32/R125 up to 11.0) with respect to the neat polymer membranes (αR32/R125 up to 6.9). Besides, the long-term stability was successfully tested for 25 days under high pressure conditions (7 and 12 bar), which makes these composite membranes excellent candidates for the development of membrane-based R32 separation and recovery processes.This research is supported by Project KET4F-Gas – SOE2/P1/P0823, which is co-financed by the European Regional Development Fund within the framework of Interreg Sudoe Programme, and Project PID2019-105827RB-I00, Ministerio de Ciencia e Innovación (Spain). The authors acknowledge the collaboration of Dr. Rosario Benavente (Institute of Polymer Science and Technology-CSIC) to perform the DSC experiments. Dr. Fernando Pardo, acknowledges the post-doctoral fellowship (FJCI-2017-32884, ‘Juan de la Cierva Formación’) from the Spanish Ministry of Science, Innovation and Universities

Thermodynamic Modeling and Validation of the Temperature Influence in Ternary Phase Polymer Systems

The effect of the temperature, as a process variable in the fabrication of polymeric membranes by the non-solvent induced phase separation (NIPS) technique, has been scarcely studied. In the present work, we studied the influence of temperature, working at 293, 313 and 333 K, on the experimental binodal curves of four ternary systems composed of PVDF and PES as the polymers, DMAc and NMP as the solvents and water as the non-solvent. The increase of the temperature caused an increase on the solubility gap of the ternary system, as expected. The shift of the binodal curve with the temperature was more evident in PVDF systems than in PES systems indicating the influence of the rubbery or glassy state of the polymer on the thermodynamics of phase separation. As a novelty, the present work has introduced the temperature influence on the Flory–Huggins model to fit the experimental cloud points. Binary interaction parameters were calculated as a function of the temperature: (i) non-solvent/solvent (g12) expressions with UNIFAC-Dortmund methodology and (ii) non-solvent/polymer (χ13) and solvent/polymer (χ23) using Hansen solubility parameters. Additionally, the effect of the ternary interaction term was not negligible in the model. Estimated ternary interaction parameters (χ123) presented a linear relation with temperature and negative values, indicating that the solubility of the polymers in mixtures of solvent/non-solvent was higher than expected for single binary interaction. Finally, PES ternary systems exhibited higher influence of the ternary interaction parameter than PVDF systems

Hydrogen separation from multicomponent gas mixtures containing CO, N2 and CO2 using Matrimid asymmetric hollow fiber membranes

The application of hollow fiber membranes for the separation of industrial gas mixtures relies on the correct characterization of the permeation of the involved gaseous components through the hollow fiber membranes. Thus, this study is focused on the characterization of the permeation through Matrimid® hollow fiber membranes of four gas mixtures containing H2 (H2/N2, H2/CO, H2/CO2), and the quaternary gas mixture H2/N2/CO/CO2, working at a constant temperature of 303 K and pressures up to 10 bar. The main differences and similarities in the gas permeation properties of hollow fibers with respect to flat membranes, as well as in the permeation of gas mixtures with respect to pure gases, are discussed. Our results suggest that for mixtures containing H2 and CO2 hollow fiber membranes perform better than flat membranes given that a lower depression in the permeability of H2 has been observed. At 2.3 bar feed pressure, ideal selectivity values obtained for H2/N2, H2/CO and H2/CO2 gas pairs were 74.4, 42.6 and 5 respectively, with a H2 permeance of 50.2×10−8 m3(STP) m−2 s−1 kPa−1. The specific behavior observed in the permeation through hollow fiber has been explained by a combination of different phenomena such as hollow fiber membrane substructure resistance, CO2 induced plasticization and competitive sorption effects between the components of the gaseous mixtures

Integration of stable ionic liquid-based nanofluids into polymer membranes. Part II: gas separation properties toward fluorinated greenhouse gases

Membrane technology can play a very influential role in the separation of the constituents of HFC refrigerant gas mixtures, which usually exhibit azeotropic or near-azeotropic behavior, with the goal of promoting the reuse of value-added compounds in the manufacture of new low-global warming potential (GWP) refrigerant mixtures that abide by the current F-gases regulations. In this context, the selective recovery of difluorometane (R32, GWP = 677) from the commercial blend R410A (GWP = 1924), an equimass mixture of R32 and pentafluoroethane (R125, GWP = 3170), is sought. To that end, this work explores for the first time the separation performance of novel mixed-matrix membranes (MMMs) functionalized with ioNanofluids (IoNFs) consisting in a stable suspension of exfoliated graphene nanoplatelets (xGnP) into a fluorinated ionic liquid (FIL), 1-ethyl-3-methylpyridinium perfluorobutanesulfonate ([C2C1py][C4F9SO3]). The results show that the presence of IoNF in the MMMs significantly enhances gas permeation, yet at the expense of slightly decreasing the selectivity of the base polymer. The best results were obtained with the MMM containing 40 wt% IoNF, which led to an improved permeability of the gas of interest (PR32 = 496 barrer) with respect to that of the neat polymer (PR32 = 279 barrer) with a mixed-gas separation factor of 3.0 at the highest feed R410A pressure tested. Overall, the newly fabricated IoNF-MMMs allowed the separation of the near-azeotropic R410A mixture to recover the low-GWP R32 gas, which is of great interest for the circular economy of the refrigeration sector.European Regional Development Fund | Ref. KET4F-Gas-SOE2/P1/P0823Agencia Estatal de Investigación | Ref. PID2019-105827RB-I00/ AEI / 10.13039/501100011033Ministerio de Ciencia, Innovación y Universidades | Ref. FJCI-2017-32884Laboratório Associado para a Química Verde | Ref. FCT/MCTES UIDB/50006/202