(342f) Challenges to Tackle with Membrane Science for a More Sustainable Future

We are facing environmental challenges of concerning dimensions. Furthermore, in times of political uncertainty, the reasons for an independency from fossil fuels becomes evident. More energy-efficient processes are needed. The history tells us that times of crisis have seeded disrupting technological advances. Separation processes consume a large portion of energy worldwide, since they are mostly thermally driven. Membrane technology has a unique opportunity to catalyze the transition to more sustainable separations and to fully sustainable energy, enabling also holistic approaches of rarifying material resources recovery. Important is to invest in processes that would be realistically profitable in terms of the overall energy impact. We are in an exciting situation compared to decades ago concerning the versatility of materials available for membrane preparation. The solutions must be scalable and the materials for the membrane fabrication must be easily processable. Critical analysis of the results and strategic feasibility is required. Considering sustainability goals, my group has dedicated in the past more than a decade to hydrogen technology, mainly to the development of fuel cell polymeric membranes and to the separation of CO₂ and other gases in coal plants. Fuel cell and electrolyzers (also operating with ion-exchange polymeric membranes, like fuel cells) shall have an important role in our sustainable future, by enabling energy conversion with green hydrogen. However, CO₂ separation should be a transitory solution, hopefully to a time in which coal and oil will not be the main energy resource. CO₂ capture technologies should be carefully evaluated, since in many cases their operation might require a substantial energy consumption to succeed, compromising part of its benefit. At least as relevant for our future is the opportunity of applying membranes to enable process intensification and integration with lower carbon footprint and the opportunity to enable more efficient purifications, fractionation and material resources in the chemical, petrochemical, and pharmaceutical industry. By making a separation efficient, the number of steps for achieving a satisfactory level of purity can be reduced with consequent energy reduction. By considering all these aspects, the main research focuses of my group are currently the development of the following topics (relevant for different sectors):

• High-performance polymeric membranes for nanofiltration and pervaporation application in organic solvent medium and at high temperatures (100-500^oC) (chemical, petrochemical separations)
• Highly selective nanofiltration membranes for precise ions (mining) and for chiral separations (pharmaceutical separations)
• Membranes with high permeance for dehumidification (energy-efficient air condition) and natural gas dehydration (petrochemical separations)
• Sustainable membrane fabrication (green solvents, natural polymers, recycling, and circular chemistry)

The choice of materials is essential to fulfil the requirements to provide the needed progress in the different sectors. A deep understanding of the polymeric material chemistry, the mechanism of membrane formation, considerations on processability and scalability are relevant. A variety of materials have been considered in the last decade for the membrane fabrication as flat-sheet and hollow fibers, including high-performance functionalized polymers, like polytriazole and polyoxadiazole, submitted to different chemical and thermal crosslinking strategies, self-assembled block copolymers, stimuli responsive covalent-organic networks, macrocycles, organic cages and different 2D fillers. Each of them is more suitable for a different manufacturing method, such as phase inversion, dip-coating or interfacial polymerization. By the incorporation of building blocks with intrinsic selectivity, it is essential to avoid diluting their contribution to the membrane properties. Common issues are lack of filler-matrix adhesion, lack of percolation, undesired aggregation, and polymer filler permeability mismatch, which have affected the success of approaches like mixed-matrix membranes which are being proposed for decades without a real breakthrough. More effective approaches to secure the benefit of advanced porous selective building blocks are therefore important and are topic of research in our group keeping in mind the possibility of preparation in continuous machines and integration in modules with the necessary mechanical stability.

While we see challenges, we see also daring initiatives in previously unexpected parts of the world. An example is the announcement of a series of strategies to diversify the economy of Gulf countries from oil and gas to renewables. There is now the awareness that oil should be rather considered to produce more valuable chemicals in a sustainable way, there is a consideration that desalination should not only provide water but should be seen as an opportunity for potentially harvesting ions for holistic industrial processes. The completely renewable city NEOM shall integrate technologies that only now are becoming reality. The market for pharmaceutical and biotech industries is fast growing in this part of the world. The chances to extend the use of membrane technology might be larger than in long established industrial economies. It would be more beneficial to build a sustainable industry with newly available technology and easier to do it than to substitute long operating analogous systems in other countries. New great chances for membrane technology development and industrial implementation are there to be explore. It is the responsibility of membrane scientist community to invest in the right challenges and propose the most competitive solutions.