• Energy Research

This article describes a modification of the conventional membrane crystallization technique in which a membrane is used to dose the solvent/antisolvent composition to generate supersaturation and induce crystallization in a drug solution. Two operative configurations are proposed: (a) solvent/antisolvent demixing crystallization, where the solvent is removed in at higher flow rate than the antisolvent so that phase inversion promotes supersaturation and (b) antisolvent addition, in which the antisolvent is dosed into the crystallizing drug solution. In both cases, solvent/antisolvent migration occurs in vapor phase and it is controlled by the porous membrane structure, acting on the operative process parameters. This mechanism is different than that observed when forcing the liquid phases through the pores and the more finely controllable supersaturated environment would generate crystals with the desired characteristics. Two organic molecules of relevant industrial implication, like paracetamol and glycine, were used to test the new systems. Experiments demonstrated that, by using antisolvent membrane crystallization in both configurations, accurate control of solution composition at the crystallization point has been achieved with effects on crystals morphology.

Salinity gradient energy is currently attracting growing attention among the scientific community as a renewable energy source. In particular, Reverse Electrodialysis (RED) is emerging as one of the most promising membrane-based technologies for renewable energy generation by mixing two solutions of different salinity. This work presents a critical review of the most significant achievements in RED, focusing on membrane development, stack design, fluid dynamics, process optimization, fouling and potential applications. Although RED technology is mainly investigated for energy generation from river water/seawater, the opportunities for the use of concentrated brine are considered as well, driven by benefits in terms of higher power density and mitigation of adverse environmental effects related to brine disposal. Interesting extensions of the applicability of RED for sustainable production of water and hydrogen when complemented by reverse osmosis, membrane distillation, bio-electrochemical systems and water electrolysis technologies are also discussed, along with the possibility to use it as an energy storage device. The main hurdles to market implementation, predominantly related to unavailability of high performance, stable and low-cost membrane materials, are outlined. A techno-economic analysis based on the available literature data is also performed and critical research directions to facilitate commercialization of RED are identified.

In this work, innovative use of Salinity Gradient Power (SGP) as renewable energy source for indirect production of hydrogen is addressed. A lab-scale reverse electrodialysis (RED) unit, fed with different NaCl solutions mimicking highly concentrated brine (5M), Reverse Osmosis retentate (1M), seawater (0.5 M) and brackishwater (0.1M), was coupled to an alkaline polymer electrolyte (APE) water electrolysis cell. SGP-RED unit, equipped with 27 cell-pairs, reached at bestan Open Circuit Voltage (OCV) of 3.7 V and maximum gross power density of 3.2 Wm2 MP (membrane pair) when feeding the low concentration compartment (LCC) with 0.1 M NaCl and the High Concentration Compartment (HCC) with 5 M NaCl. The single-cell APE water electrolys isunit, operated at 1.8V, attained a current density of 120 mAcm2 under the following configuration: 10% w/w KOH electrolyte, highly conductive anion selective membrane composed of inert low-density polyethylene, finely milled anion selective particles and water-soluble poly(ethyleneglycol-ran-propyleneglycol), non-Platinum catalysts (NiCo2O4 and NiFe2O4) loading of 10 mgcm2 and 15% w/w polymerbinderatbothcathodeandanode, and operational temperature of 65 °C. The integrated system resulted in a maximum hydrogen production rate of 44 cm3 h1 per cm2 of electrode surface area.

Reverse electrodialysis (RED) is one of the most promising membrane-based processes for renewable energy generation from mixing two solutions of different salinity. However, the presence of Mg2+ in natural water has been shown to drastically reduce open circuit voltage (OCV) and output power of RED. To alleviate this challenge, commercial cation exchange membranes (CEM) supplied by Fujifilm Manufacturing Europe B.V. (The Netherlands) were chemically modified by polypyrrole (PPy)/chitosan (CS) composites under controlled Pyrrole (Py) concentration (0.025-1 M) and polymerization time (0-8 h). The modified membranes were physically characterized by FTIR, SEM and EDX along with the determination of key electrochemical properties like ion exchange capacity, ionic conductivity, monovalent selectivity and swelling degree. The monovalent selectivity (Na+ vs Mg2+) of the modified membranes, evaluated based on flux of ions by diffusion dialysis, indicated up to 3-fold improvement compared to pristine membranes inline with the enhanced OCV (up to 20%) during RED test in mull-ion solution. This was obtained without significant change in membrane and interface resistances as depicted by electrochemical impedance spectroscopy. The modified membranes displayed power densities in the range of 0.6-1.5 W/m(2) MP (MP: membrane pair) with more than 42% improvement compared to pristine membranes during RED test with mull-ion solutions. Although there is a gap for further improvement, these findings highlight a promising use of conducing polymers to design a highly selective and conducive membrane for RED.

Although desalination market is today dominated by Seawater Reverse Osmosis (SWRO), important technological issues remain unaddressed, specifically: relatively low water recovery factor (around 50%) and consequent huge amount of brine discharged, and energy consumption (3-5 kWh/m3) still far from the minimum thermodynamic value (~1 kWh/m3). Herein, the energy performance of an innovative systems combining SWRO, Membrane Distillation (MD) and Reverse Electrodialysis (RED) for simultaneous production of water and energy is investigated. The valorization of hypersaline waste brine by Salinity Gradient Power production via RED and the achievement of high recovery factors (since MD is not limited by osmotic phenomena) represent a step forward to the practical implementation of Zero Liquid Discharge and low-energy desalination. The analysis is supported by lab-scale experimental tests carried out on MD and RED over a broad set of operational conditions. Among the different case studies investigated, exergetic efficiency reached 49% for the best scenario, i.e. MD feed temperature of 60°C, MD brine concentration of 5M NaCl, RED power density of 2.2 W/m2MP (MP: membrane pair). Compared to the benchmark flowsheet (only SWRO), up to 23% reduction in electrical energy consumption and 16.6% decrease in specific energy consumption were achieved when including a RED unit. The analysis also indicates that optimization of thermal energy input at the MD stage is critical, although it can potentially be fulfilled by lowgrade waste heat or solar-thermal renewable sources. Overall, the proposed integrated system is coherent with the emergent paradigm of Circular Economy and the logic of Process Intensification.

This repository contains the Dataset of the Journal article "Energy duty in direct contact membrane distillation of hypersaline brines operating at the water-energy nexus" published on Journal of Membrane Science. 

In the context of global climate crisis and growing world population there is the urgent need for viable technical solutions to harvest energy from alternative, renewable and continuous sources and to recover pure water at affordable costs. Herein, we capitalize on the study of direct contact membrane distillation technology treating hypersaline solutions simulating reverse electrodialysis outgoing mixed streams, in the logic of valorising the otherwise environmentally threating brine, in an integrated system operating at the water-energy nexus. Experimental results in terms of transmembrane water flux and dissolved salts rejection, indicate that DCMD is a feasible option to treat feed solutions with concentrations as high as 228 g L? 1 total dissolved solids, while recovering pure water from brines which are practically impossible to be dewatered through reverse osmosis. Specific thermal energy consumptions and gain to output ratios, calculated under different feed compositions and flow rates for polypropylene and polyvinilidenefluoride membranes, indicated the possibility to tailor the thermal energy requirements of the MD stage by controlling the ratio between the streams at different salinity that are partially mixed in the RED unit and to potentially adapt it to the available amount of heat.