A novel process is presented to generate electricity from low-grade heat by combining a Reverse Electrodialysis membrane with an Adsorption desalinator in a closed-loop system. A Reverse Electrodialysis membrane generates electricity by controlled mixing of two salt solutions of different concentrations. An Adsorption desalinator restores the initial salt gradient by utilising low-grade heat for the separation. In this study the process is designed from optimising the salt and material selection to the development of the real system application. Energy and exergy efficiencies of the proposed system show the potential of this novel renewable energy technology. The efficiencies of 227 salts with a range of different valences and 10 adsorption materials have been investigated over a large number of system parameters. The results show that the optimised system can achieve an exergy efficiency of up to 30 %. Moreover, high salt concentrations do not significantly increase the specific energy consumption of the Adsorption desalinator, which allows operating the Reverse Electrodialysis membrane at the optimal salt concentrations.

Adsorption heat transformers use low-grade heat to produce potable water and provide cooling at the same time. In this study, we present a comprehensive performance analysis for an experimental system featuring the world's smallest design using silica gel, which is commonly used as benchmarking material. We analyse the system performance in a thorough cycle analysis that quantifies the influence of isosteric heating times and cycle times onto the adsorption working capacity. In addition, the performance is assessed through common performance indicators for desalination as well as cooling. We found that the system achieved a Specific Daily Water Production of up to 10.9 kg w /(kg sg d) at 80°C. The combination of cooling and desalination is discussed highlighting advantages as well as disadvantages, which are often neglected. The results show that silica gel has a high performance in desalination, which decreases by more than 60 % if cooling is desired as well.

Closed-loop Reverse Electrodialysis is a novel technology to directly convert low-grade heat into electricity. It consists of a reverse electrodialysis (RED) unit where electricity is produced exploiting the salinity gradient between two saltwater solutions, coupled with a regeneration unit where waste-heat is used to treat the solutions exiting from the RED unit and restore their initial composition. One of the most important advantages of closed-loop systems compared to the open systems is the possibility to select ad-hoc salt solutions to achieve high efficiencies. Therefore, the properties of the salt solutions are essential to assess the performance of the energy generation and solution regeneration processes. The aim of this study is to analyse the influence of thermodynamic properties of non-conventional salt solutions (i.e. other than NaCl-aqueous solutions) and their influence on the operation of the closed-loop RED. New data for caesium and potassium acetate salts, i.e. osmotic and activity coefficients in aqueous solutions, at temperature between 20 and 90°C are reported as a function of molality. The data are correlated using Pitzer's model, which is then used to assess the theoretical performance of the whole closed-loop RED system considering both single and multi-stage regeneration units. Results indicate that KAc, CsAc and LiCl are the most promising salts among those screened.

This work investigates the application of novel sorption materials to heat-powered desalination systems. Two ionic liquids 1-ethyl-3-methylimidazolium acetate (Emim-Ac) and 1ethyl-3-methylimidazolium methanesulfonate (Emim-Oms) ionic liquids were impregnated in two silica supports, namely Syloid AL-1FP and Syloid 72FP. Emim-Ac and Emim-Oms composite sorbents have been compared on morphology, water vapor sorption equilibrium and heat of sorption. Fourier-transform infrared spectroscopy shows the ionic liquid partly organises on the silica surface. When used in a sorption desalination process powered by low grade heat at 60°C, these composites have exceptionally high theoretical working capacities ranging from 1 to 1.7 gwater gsorbent-1. Experimental tests on a lab scale desalinator show that Emim-Ac/Syloid 72FP in real operating conditions can produce 25 kgwater kgsorbent-1 day-1. To date, this yield is 2.5 times higher than the best achieved with silica gel.

• Design and experimental results of the world's most compact adsorption desalinator for the first time • Achieving a Specific Daily Water Production of 7.7 kg w /(kg sg d) and Performance Ratio of 0.6 • The small scale is not detrimental to the performance as the system is on a par with the best performing system in the literature • A novel thermal response experiment informs about the partition of energy, the heat of adsorption, and water production

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Adsorption desalination and membrane distillation are the only thermally driven desalination technologies that can be undertaken at temperatures below 70 C. Adsorption desalination is based on an adsorber whose performance primarily depends on the properties of the water sorbent. Water sorption ionogel represents a novel class of materials offering a large working capacity for desalination. In this study, water-sorptive ionogels were prepared and their hydrothermal stability was assessed. The results show that Syloid 72FP silica-based ionogels are hydrothermally stable. The ionic liquid EMIM Ac can be tightly confined in silica at amounts of up to 50 wt% and still withstand high relative humidity and temperature swings. Water uptake of the synthesized ionogel can be up to 1.64 g water g ionogel-1 at 90% RH, which is ~3 times of that of Syloid 72FP silica and ~4 times of that of activated carbon. The EMIM Ac/Syloid 72FP ionogel thus exhibits features appropriate for adsorption desalination systems.

Industrial processes emit enormous amounts of waste heat below 40 °C into the environment as it is cannot be used in other processes. Adsorption desalination can be driven by low-grade heat but has never been proven at temperatures below 40 °C as current adsorption materials require heat sources of 50−150 °C. Here, we present the first experimental study on adsorption desalination using a novel class of ionogel adsorption materials, which can be regenerated at 25 °C or a driving temperature difference of 5 °C. This outstanding property contrasts with the benchmarking silica gel, which requires heat sources of at least 50 °C. Ionogels are solid-state ionic materials retaining the sorption properties of the constituent ionic liquid. Thermodynamic vapor−liquid equilibrium data of water sorption on commercial ionic liquids reveal 1-ethyl-3-methylimidazolium acetate as the best fluid for this specific application. A full experimental characterization of the material is performed from imaging at the nanoscale to testing on a real adsorption desalinator. At 25 °C, the material achieves a specific daily water production of 6.7 kg water /(kg ionogel d), increasing to 17.5 kg water /(kg ionogel d) at 45 °C, outperforming silica gel by a factor of 2.