An illustration of single-layer nanoporous graphene reinforced with a nanoporous carbon film for separating hydrogen from methane. Image: K. V. Agrawal/EPFL.Chemical engineers at the Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland have demonstrated for the first time that an atom-thick graphene membrane can separate gas mixtures with a high-efficiency. This ‘ultimate’ membrane, reported in a paper in Nature Communications, is scalable, making it a breakthrough for industrial gas separation.
Separating mixed gases, such as air, into their individual components is a process with multiple industrial applications, including production of biogas, air enrichment in metal working, removal of toxic gases from natural gas, and hydrogen recovery from ammonia plants and oil refineries.
Gas separation usually takes place through the use of synthetic membranes made from polymers such as cellulose or other materials. In recent years, research has turned to what many refer to as the ‘ultimate’ membrane: a layer of graphene, a single atom in thickness. This is the thinnest molecular barrier and hence the most efficient membrane, offering excellent permeance combined with robustness and scalability.
However, progress in developing graphene as a membrane has been hampered by two ‘bottlenecks’. First, a lack of methods for incorporating molecular-sized pores into the layer of graphene, and second, a lack of methods for actually manufacturing mechanically robust, crack- and tear-free, large-area membranes.
Now, in a breakthrough that solves both problems, the team of Kumar Varoon Agrawal at EPFL Valais Wallis has developed a large-area, single-layer graphene membrane that can separate hydrogen from methane with a high-efficiency (separation factor up to 25). It also has an unprecedented hydrogen permeance from a porosity that is only 0.025%.
The membrane contains nanopores to allow hydrogen to permeate through, for what is known as ‘gas-sieving’. The membrane was stable at industrial pressures and temperatures (at least up to 7 bar and 250°C). But, more importantly, the team was able to produce a surface area of 1mm2 – significantly larger than previous reports, where only a few square micrometers could be synthesized without cracks. Agrawal’s group is now working to incorporate a higher density of nanopores in graphene, so that it can realize its true potential.
“The novel technique to produce a crack-free graphene layer will go a long-way in realizing the ultimate performance of the atom-thick graphene membranes for a number of important chemical separations including carbon capture, hydrogen recovery and the purification of clean drinking water,” says Agrawal.
This story is adapted from material from EPFL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.