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From waste heat to ultrapure water: A new technology transforming renewable hydrogen

Hydrogen (H₂), produced using renewable energy, has emerged as a possible alternative to fossil fuel. This versatile molecule can serve as an energy carrier, an efficient storage solution, and a sustainable feedstock for transportation, chemical processing, and energy systems worldwide.

Unlike fossil fuels, hydrogen produces no harmful emissions when used. It can be generated using electrolyzers running on renewable energy and abundant water as feedstock. It then becomes a renewable and sustainable energy source, reducing reliance on depleting fossil fuel reserves, helping combat climate change. Consequently, hydrogen production has become a key priority on the political agenda of numerous countries.

However, the water used in electrolyzers must be ultrapure in order to protect the electrodes of electrolyzers from poisoning and avoid chloride oxidation to chlorine. Abundant seawater adds several challenges when directly fed to electrolyzer plants for hydrogen production, making highly pure water, specifically ultrapure water, an expensive necessity. Ultrapure water is produced in a series of steps, including pretreatment to remove suspended solids and desalination to eliminate salts, organics, and colloidal particles. Polishing techniques such as deionization, degasification, and ultraviolet treatment are then used to achieve the required quality. Among these processes, desalination is particularly critical for removing most impurities.

Reverse osmosis, especially seawater reverse osmosis, is a widely used desalination technology but has notable drawbacks, such as requiring high-pressure operation (high energy consumption), intensive pretreatment, and producing concentrated brine, which can harm marine ecosystems when discharged. Membrane distillation has gained attention as an alternative for producing high-quality water and supporting recovery applications. It operates at lower temperatures and has the ability to utilize waste heat.

Membrane distillation is a thermal separation process where a vapor pressure difference across a hydrophobic membrane causes liquid particles to phase change and pass through as gas. Operating at ambient pressure and utilizing low-temperature heat sources (<90 °C), membrane distillation offers significant advantages. However, research on membrane distillation as a viable alternative to reverse osmosis for ultrapure water production remains limited, particularly in areas such as module design and techno-economic analysis.

A group of researchers at the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg, Germany, has explored the potential of membrane distillation as a cost- and energy-efficient alternative to reverse osmosis for producing ultrapure water for proton exchange membrane (PEM) electrolyzers. The findings were recently published in the Desalination Journal. They introduced membrane distillation as a possible alternative to reverse osmosis for ultrapure water production. But here is the twist: the membrane distillation system ingeniously taps into waste heat from a 5 MW proton exchange membrane electrolyzer, transforming what would typically be an efficiency liability into an asset for sustainability. So far, their results are impressive—membrane distillation not only produces exceptional distillate (<3 μS/cm) but does so at a cost ranging from €2.33 to €2.85 per ton of distillate, compared to reverse osmosis’s €2.80 to €5.51. Using membrane distillation, seawater desalination could be 50% or more cheaper.

Economic analyses highlight that membrane distillation’s cost-effectiveness is driven by its low electrical energy requirements and optimized short-channel module design. Its impressive energy efficiency, enabled using low-grade thermal energy, establishes membrane distillation as a highly versatile and environmentally friendly solution that aligns seamlessly with the vision for renewable hydrogen production. This study positions membrane distillation as more than just an alternative to reverse osmosis: it is a smarter and greener approach to ultrapure water production.

Their findings have the potential to reshape the industrial approach to ultrapure water production. By demonstrating an efficient use of waste heat and providing a more economical solution, it offers industries a pathway to lower operational costs while advancing sustainability. This aligns particularly well with sectors striving for greener operations, such as renewable hydrogen production and other energy-intensive applications. Moreover, the adoption of membrane distillation could catalyze innovation in system design and integration, encouraging industries to optimize processes and reduce dependence on traditional, energy-intensive methods. This shift can contribute to broader sustainability goals and improve the economic feasibility of renewable energy initiatives.

At Frontis Energy, we are committed to advancing sustainable and green energy solutions by embracing innovative technologies like membrane distillation, bringing us closer to a sustainable future.

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Lead removal from water using shock electrodialysis

Lead was widely used in water pipes during the industrial revolution that triggered urbanization and exponential growth of the population in metropolitan centers. The reason for its popularity was the plasticity of the material used in service lines near the end user. The negative health effects have been known since the 1920s, but infrastructure modernization in industrialized countries remains an enormous economic challenge. Lead service lines therefore continue to circulate water in our supply systems. The city of Flint in the northwest of Detroit, for example, received much press attention due to its long struggle with lead poisoning (e.g. Flint Water Crisis). Dissolved lead is highly toxic in a very small concentration and accumulates in body tissues.

The biggest challenge when removing lead from the water cycle is that it is usually dissolved in very low concentrations. Other compounds “mask” the dissolved lead, which makes its removal difficult. Sodium, for instance, is concentrated ten thousand times higher than lead. While nowadays lead can be removed from water by reverse osmosis or distillation, these processes are not selective and thus ineffective. They consume a lot of energy, which in turn is an environmental issue in itself. High energy consumption makes water treatment also very expensive. At the same time, other minerals dissolved ion water are beneficial and therefore desired ingredients that should not be removed.

MIT engineers have developed a much more energy-efficient method to selectively remove lead from water and published their results in the journal ACS EST Water. The new system can remove lead from water in private households or industrial plants and hence from the water cycle. Through its efficiency, it is economically attractive and offers its users the clear advantage of not being poisoned.

The method is the most recent of a number of development steps. The researchers started with desalination systems and later developed it into radioactive decontamination method. With lead the engineers have found an attractive market. It is the first system that is also suitable for private households. The new approach uses a process that was named shock electrodialysis by the MIT engineers. It is essentially very similar to electrodialysis as we know it, as charged ions migrate into an electric field through the electrolyte. As a result, ions are enriched on one side while being depleted on the other.

The difference of the new method is that the electric field moves as a sort of shock wave through the electrolyte and drags dissolved ions along. The shock wave traverses from one side to the other is the voltage increases. The process leads to a lead reduction of 95%. Today, similar methods are also used to clean up aquifers or soil contaminated by solvents. In principle, the shock wave makes the process much cheaper than existing processes because the electrical energy is targeted to remove specifically lead while leaving other minerals in the water. Hence, a lot less energy is consumed.

As usual for bench top prototypes, shock electrodialysis is still too ineffective to be economically viable. Its up-scaling will take time. But the strong interest of potential users will certainly accelerate its industrialization. For a household whose water supply is contaminated by lead, the system could be placed in the basement and slowly clean the water carried by the supply pipes because high rates occur only during peak hours. For this purpose, a water reservoir is necessary, keeping a stock of purified water. This can be a fast and cheap solution for communities such as Flint.

The process could also be adapted for some industrial purposes. The mining and oil industries produce much heavily contaminated wastewater. One imagine to reclaim dissolved metals and sell them to the market. This would create economic an incentives for wastewater treatment. However, a direct comparison with currently existing methods is difficult because the longevity of the developed system is yet to be demonstrated.

At Frontis Energy we are thrilled by the idea of ​​creating economic incentives to help implementing environmentally friendly processes and are already looking forward to a commercial product.

(Photo: Wikipedia)

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Highly efficient desalination using carbon nanotubes

Separating liquid compartments is not only important for generating energy in biological cells, respiration that is, but also for electrochemical cells and desalination through reverse osmosis and other processes. Therefore, scientists and engineers intensively research this field. We have already reported in several posts about promising attempts to make membranes cheaper and more effective. New nanomaterials have also been developed.

As a result of climatic changes caused by global warming, water scarcity is increasingly becoming a problem in many parts of the world. Settlements by the sea can secure their supply by desalinating water from seawater and brackish water sources. The process, however, is very energy intensive.

Now, researchers at California’s Lawrence Livermore National Laboratory (LLNL) have developed artificial pores made of carbon nanotubes that remove salt from water so efficiently that they are comparable to already available commercial desalination membranes. These tiny pores are only 0.8 nanometers in diameter. A human hair with a diameter of 60,000 nm. The researchers published the results in the journal Science Advances.

The predominant technology used to remove salt from water is reverse osmosis. A thin-film composite membrane (TCM) is used to separate water from ions. Hitherto the performance of these membranes has, however, been unsatisfactory. There is, for example, always a tradeoff between permeability and selectivity. In addition, exisiting membranes often show insufficient ion repulsion and are contaminated by traces of impurities. This requires additional cleaning stages, which again increase energy costs.

As is so often the case, the researchers got inspired by nature. Biological water channels, also known as aquaporins, are a great model for the structures that can improve performance. These aquaporins have extremely narrow internal pores that compress the water. This enables extremely high water permeability with transport rates of more than 1 billion water molecules per second per pore. Due to the low friction on the inner surfaces, carbon nanotubes represent one of the most promising approaches for artificial water channels.

The research group developed nanotube porins that insert themselves into artificial biomembranes. These engineered water channels simulate the functionality of aquaporin channels. The researchers measured the water and ion transport through their artificial porins. Computer simulations and experiments using the artificial porins in lipid membranes showed improved flux and strong ion repulsion in the channels of carbon nanotubes.

This measurement method can be used to determine the exact value of the water-salt permselectivity in such narrow carbon nanotubes. Atomic simulations provide a detailed molecular view of the novel channels. At Frontis Energy, we are excited about this promising approach and hope to see a commercial product soon.

(Image: Wikipedia)