Flow patterns and mass transfer performance of miscible liquid-liquid flows in various microchannels: Numerical and experimental studies

The advantages of miniaturized systems and the laminar flow regime that is present in microfluidic channels have opened a new range of applications in which the use of multiple streams with different reagents is exploited. However, further development of these microdevices needs deeper understanding on the phenomena involved in order to efficiently design such microsystems. In this work, we report the analysis of the solute mass transport performance in Y-Y-shaped microchannels as a function of the coupled influence of both the flow patterns and mass transport kinetics. With this objective, the influence of the following operation variables has been analyzed, the ratio between the residence and diffusion times (γ) and the volumetric ratio between the fluid phases (α), that was determined for three different geometric configurations. The performance of the devices was presented as the solute separation factor in the donor fluid and the concentration factor in the receiving phase. Results showed that the ratio α greatly impacts the solute concentration value reported in both phases for the same γ value, which in turn influences the solute mass flow at the channel outlets. Both the flow patterns and the concentration gradients developed inside the systems were numerically studied by using Computational Fluid Dynamics (CFD) techniques and experimentally analyzed by fluorescence microscopy with fluorescein employed as model solute. This study represents a thorough analysis of the phenomena that determine the performance of the separation of solutes between homogeneous flowing fluids in microdevices where the fluid dynamics are coupled with mass transfer phenomena and facilitates its extension to the general case where separation is enhanced by chemical reactions.Financial support from the Spanish Ministry of Economy and Competitiveness under the projects CTQ2015-72364-EXP/AEI and CTQ2015-66078-R (MINECO/FEDER) is gratefully acknowledged. Jenifer Gómez-Pastora also thanks the FPI postgraduate research grant (BES2013-064415). Cristina González-Fernández thanks the Concepción Arenal postgraduate research grant from the University of Cantabria

Non-enzymatic amperometric glucose screen-printed sensors based on copper and copper oxide particles

Non-enzymatic amperometric glucose sensors have gained much attention in the past decade because of the better chemical and thermal stability and biocompatibility compared to conventional sensors based on the use of biomolecules. This study focuses on a novel copper and copper oxide-based glucose sensor synthesized by an electrodeposition technique through a rigorous protocol which reports an excellent analytical performance due to its structure and its increased active area. In addition, the linear response range, detection limit and sensitivity were 0.5–5.0 mmol L−1, 0.002 mmol L−1, 904 μA mmol−1 L−1 cm−2, respectively. Results show a reliable electrode as it is chemically stable, exhibits rapid and excellent sensitivity, and it is not significantly affected by coexisting species present in the blood samples; furthermore, it reports a maximum relative standard deviation error (RSD) of 6%, and showed long operating life as the electrode was used for thousand measurements of 4.0 mmol L−1 glucose solution during three days.This research was funded by the Spanish Ministry of Science, Innovation, and Universities under the project RTI2018-093310-B-I00, grant Concepción Arenal from the University of Cantabria

Performance of continuous-flow micro-reactors with curved geometries. Experimental and numerical analysis

One of the major challenges in the design of micro-devices, when very fast reactions are carried out, is to overcome the limited performance due to the poor mixing efficiency of the reactants. Here, we report a holistic analysis of reactants mixing and reaction rate in liquid phase flow micro-reactors with curved geometries. In this sense, a mathematical model that accounts for momentum and mass conservation equations, together with species transport and chemical reaction rate under isothermal conditions, has been developed using computational fluid dynamics techniques (CFD). To validate the predictive model, four micro-reactor geometries with different radius and curved length (straight reactor, two types of serpentines and an Archimedean spiral) have been evaluated. Simulated results proved that mixing is promoted through the formation of Dean vortices as a consequence of the reduction of the radius of curvature and at the same time of the extension of the curve. Thus, the overall performance of the micro-reactor is improved because mass transport limitations are minimized and the process kinetics are greatly enhanced. Accordingly, the spiral micro-reactor reported the best performance by reducing by half the time required to obtain 95 % conversion when compared with the straight reactor. Simulated findings have been confirmed with the experimental analysis of the reaction between aqueous ammonium and hypochlorite ions. Very good agreement between simulated and experimental results has been achieved with an error lower than 10 %. Therefore, the robust model herein reported is a novel and valuable tool to assist in the optimum design of micro-reactors for fluid-phase isothermal applications.Financial assistance from the project RTI2018-093310-B-I00 (MCI/AEI/FEDER,UE) is gratefully acknowledged

Reverse electrodialysis: potential reduction in energy and emissions of desalination

Salinity gradient energy harvesting by reverse electrodialysis (RED) is a promising renewable source to decarbonize desalination. This work surveys the potential reduction in energy consumption and carbon emissions gained from RED integration in 20 medium-to-large-sized seawater reverse osmosis (SWRO) desalination plants spread worldwide. Using the validated RED system’s model from our research group, we quantified the grid mix share of the SWRO plant’s total energy demand and total emissions RED would abate (i) in its current state of development and (ii) if captured all salinity gradient exergy (SGE). Results indicate that more saline and warmer SWRO brines enhance RED’s net power density, yet source availability may restrain specific energy supply. If all SGE were harnessed, RED could supply ~40% of total desalination plants’ energy demand almost in all locations, yet energy conversion irreversibility and untapped SGE decline it to ~10%. RED integration in the most emission-intensive SWRO plants could relieve up to 1.95 kg CO2-eq m−3. Findings reveal that RED energy recovery from SWRO concentrate effluents could bring desalination sector sizeable energy and emissions savings provided future advancements bring RED technology closer to its thermodynamic limit.This research was funded by the LIFE programme (LIFE19 ENV/ES/000143) and the Spanish Ministry of Science, Innovation and Universities (RTI2018-093310-B-I00 and CTM2017-87850-R, and the FPI grant awarded to C.T., PRE2018-086454)

Optimized copper-based microfeathers for glucose detection

Diabetes is expected to rise substantially by 2045, prompting extensive research into accessible glucose electrochemical sensors, especially those based on non-enzymatic materials. In this context, advancing the knowledge of stable metal-based compounds as alternatives to non-enzymatic sensors becomes a scientific challenge. Nonetheless, these materials have encountered difficulties in maintaining stable responses under physiological conditions. This work aims to advance knowledge related to the synthesis and characterization of copper-based electrodes for glucose detection. The microelectrode presented here exhibits a wide linear range and a sensitivity of 1009 µA∙cm−2∙mM−1, overperfoming the results reported in literature so far. This electrode material has also demonstrated outstanding results in terms of reproducibility, repeatability, and stability, thereby meeting ISO 15197:2015 standards. Our study guides future research on next-generation sensors that combine copper with other materials to enhance activity in neutral media.This research was funded by the Spanish Ministry of Science, Innovation, and Universities under the project PDC2022-133122-I00

Thin-film composite matrimid-based hollow fiber membranes for oxygen/nitrogen separation by gas permeation

In recent years, the need to reduce energy consumption worldwide to move towards sustainable development has led many of the conventional technologies used in the industry to evolve or to be replaced by new alternatives. Oxygen is a compound with diverse industrial and medical applications. For this reason, obtaining it from air is one of the most interesting separations, traditionally performed by cryogenic distillation and pressure swing adsorption, two techniques which are very energetically expensive. In this sense, the implementation of membranes in a hollow fiber configuration is presented as a much more efficient alternative to carry out this separation. The aim of this work is to develop cost-effective multilayer hollow fiber composite membranes made of Matrimid and polydimethylsiloxane (PDMS) for the separation of oxygen and nitrogen from air. PDMS is used as a cover layer but can also enhance the performance of the membrane. In order to compare these two materials, three different configurations are studied. First, integral asymmetric Matrimid hollow fiber membranes were produced using the spinning method. Secondly, by using dip-coating method, a PDMS dense selective layer was deposited on a self-made polyvinylidene fluoride (PVDF) hollow fiber support. Finally, the performance of a dual-layer hollow fiber membrane of Matrimid and PDMS was studied. Membrane morphology was characterized by SEM and separation performance of the membranes was evaluated by mixed-gas permeation experiments. The novelty presented in this work is the manufacture of hollow fiber membranes and the way Matrimid is treated. This makes it possible to develop much thinner dense layers than in the case of flat-sheet membranes, which leads to higher permeance values. This is a key factor when implementing this technology on an industrial scale. Membranes prepared in this work were compared to the current state of the art, reporting quite good performance for the dual-layer membrane, reaching O2 permeance of 30.8 GPU and O2/N2 selectivity of 4.7, with a thickness of about 5–10 μm (counting both selective layers). In addition, the effect of operating temperature on the membrane permeances has been studied experimentally; we analyze its influence on the selectivity of the separation process.This work was supported by the Spanish AEI through the project PID2019-104369RB-I00 and the European Union through the projects “HYLANTIC”-EAPA_204/2016, which is co-financed by the European Regional Development Fund in the framework of the INTERREG Atlantic program, and the Project ENERGY PUSH SOE3/P3/E0865, which is co-financed by the European Regional Development Fund (ERPF) in the framework of the INTERREG SUDOE Programme

High performance flow-focusing droplet microreactor. Extractive separation of rare earths as case of study

This work advances the knowledge of the design and manufacture of microdroplet reactors for reactive liquid–liquid systems assisted by advanced simulation techniques (CFD). The mathematical model is based on the integrated analysis of the fluid dynamics for multiphase systems, passive mixing of reactants inside and outside the microdroplet and interfacial reaction rate. To validate the results obtained with the predictive model a spiral microdevice with droplet generation using flow-focusing geometry has been designed and fabricated by additive manufacturing. First, the influence of fluid flowrate, hold-up and viscosity on the droplets frequency and size has been evaluated with the model and assessed experimentally. Next, the performance in the separation of a binary Dysprosium-Lanthanum system has been tested, working with a dispersed aqueous phase containing the rare earth elements (REEs) solution and a continuous organic phase constituted of a solution of the extractant Cyanex® 572 in Shellsol® D70. The extraction experiments have been conducted at residence times between 3 and 60 s to generate aqueous phase monodispersed droplets with high interfacial area that varies between 61.4 and 49.2 cm2·cm−3 depending on the operating conditions. At pH 1, 90 % of dysprosium has been extracted, and almost complete separation of both REEs has been achieved. Very good agreement between simulated and experimental results has been reached with an error lower than 12 %. Therefore, here we provide the tools to design and predict the microdroplet enhanced performance of extractive liquid–liquid microreactors.Financial assistance from the Project PDC2022-133122-I00 funded by MCIN/AEI /10.13039/501100011033 and the European Union Next Generation EU/PRTR is gratefully acknowledged. G. González-Lavín also thanks the FPU postgraduate research grant FPU21/03297 funded by MCIN/AEI/ 10.13039/501100011033 and ESF+. The authors thank Dr Gerardo Prieto from the University of Santiago de Compostela for the interfacial tension measurements

Generalized disjunctive programming model for optimization of reverse electrodialysis process

Reverse electrodialysis (RED), an emerging electrochemical technology that uses ion-selective membranes to directly draw electricity out from salinity differences between two solutions, i.e., salinity gradient energy (SGE), has the potential to be a clean and steady renewable source to reach a sustainable water and energy supply portfolio. Although RED has made notable advances, full-scale RED progress demands more techno-economic and environmental assessments that consider full process design and operational decision space from module- to system-level. This work presents an optimization model formulated as a Generalized Disjunctive Programming (GDP) problem to define the cost-optimal RED process design for different deployment scenarios. We use a predictive model of the RED stack developed and validated in our research group to fully capture the behavior of the system. The problem addressed is to determine the RED plant's topology and the working conditions for a given design of each RED stack which renders the cost-optimal design for the defined problem and scenario. Our results show that, compared with simulation-based approaches, mathematical programming techniques are an efficient and systematic approach to provide decision-making support in early-stage applied research and to obtain design and operation guidelines for full-scale RED implementation in real scenarios.Project LIFE19 ENV/ES/000143 funded by the LIFE Programme of the European Union. Grant PDC2021-120786- I00 funded by MCIN/AEI/10.13039/501100011033 and by the “European Union NextGenerationEU/PRTR”. Grant PRE2018-086454 funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”

A generalized disjunctive programming model for the optimal design of reverse electrodialysis process for salinity gradient-based power generation

Reverse electrodialysis (RED) is an emerging electro-membrane technology that generates electricity out of salinity differences between two solutions, a renewable source known as salinity gradient energy. Realizing full-scale RED would require more techno-economic and environmental assessments that consider full process design and operational decision space from the RED stack to the entire system. This work presents an optimization model formulated as a Generalized Disjunctive Programming (GDP) problem that incorporates a finite difference RED stack model from our research group to define the cost-optimal process design. The solution to the GDP problem provides the plant topology and the RED units´ working conditions that maximize the net present value of the RED process for given RED stack parameters and site-specific conditions. Our results show that, compared with simulation-based approaches, mathematical programming techniques are efficient and systematic to assist early-stage research and to extract optimal design and operation guidelines for large-scale RED implementation.This work was supported by the LIFE Programme of the European Union (LIFE19 ENV/ES/000143); the MCIN/AEI/10.13039/501100011033 and “European Union NextGenerationEU/PRTR” (PDC2021–120786-I00); and by the MCIN/AEI/10.13039/501100011033 and “ESF Investing in your future” (PRE2018–086454)

Cost-optimal design of reverse electrodialysis process for salinity gradient-based electricity generation in desalination plants

Salinity gradient-based technologies offer a solution for desalination plants seeking clean, uninterrupted elec tricity to support their decarbonization and circularity. This work provides cost-optimal designs of a large-scale reverse electrodialysis (RED) system deployed in a desalination plant using mathematical programming. The optimization model determines the hydraulic topology and RED units’ working conditions that maximize the net present value (NPV) of the RED process recovering salinity gradient energy between brine and treated waste water effluents. We examine how electricity, carbon and membranes prices, desalination plant capacity, and membrane resistance may affect the NPV-optimal design’s competitiveness and performance. We also compare the conventional series-parallel configuration and the NPV-optimal solution with recycling and added reuse alternatives. In the context of soaring electricity prices and strong green financing support, with the use of high-performing, affordable membranes (~10 €/m2 ), RED could save 8 % of desalination plant energy demand from the grid, earning 5 M€ profits and LCOE of 66–126 €/MWh, comparable to other renewable and conventional power technologies. The optimization model finds profitable designs for the entire range of medium-capacity desalination plants. The findings underscore the optimization model effectiveness in streamlining decisión-making and exploiting the synergies of full-scale, RED-based electricity in the energy-intensive water sector.This work was supported by the LIFE Programme of the European Union (LIFE19 ENV/ES/000143); the MCIN/AEI/10.13039/ 501100011033 and “European Union NextGenerationEU/PRTR” (PDC2021-120786-I00); and by the MCIN/AEI/10.13039/ 501100011033 and “ESF Investing in your future” (PRE2018-086454)