In a stunning breakthrough with far-reaching implications for the future use of natural gas pipelines in the world, the Fraunhofer-Gesellschaft has developed a technology for the energy efficient separation of hydrogen from natural gas. This membrane technology enables two substances to be routed through the national natural gas grid together and then isolated from one another at their final destination. A major step forward in the transportation and distribution of hydrogen as an energy source.
How does a membrane work in principle? The gas mixture is surrendered to the input side of the membrane. The small hydrogen molecules pass through the membranes and the larger methane molecules are held back. And thus hydrogen is seen by Fraunhofer as a "beacon of hope" for establishing a CO2-free energy supply, or 'green' hydrogen.
Despite such progress Germany still lacks an extensive distribution network for green hydrogen. The HYPOS (Hydrogen Power Storage & Solutions East Germany) is working to solve this problem.
The HYPOS project partners are pursuing the idea, among other approaches, of transporting the hydrogen (H2) along with the natural gas (the principal component being methane, CH4). After all, Germany does have a 511,000 kilometer long gas grid and 33 gas storage locations. “The advantage of this infrastructure is that it allows hydrogen to be fed into the natural gas grid as well. The two substances can be transported together in one line. Once they arrive at the destination, we can separate them from one another again as needed,” explains Dr. Adrian Simon, Group Manager at Fraunhofer IKTS.
This is where carbon comes in. It forms an ultrathin layer on porous, ceramic substrates where it acts as a membrane, separating natural gas and hydrogen from one another. There are various processes involved in membrane production, starting with custom polymer synthesis. Polymers are substances consisting of branched macromolecules. These are then applied to the porous substrate. When the polymer is heated up and starved of oxygen at the same time, it forms a layer of carbon on its surface. The pores in the carbon are less than a nanometer in diameter, and this makes them effective for gas separation. Physical and chemical processes can be employed to adapt the membrane’s separation behavior even further. Fraunhofer IKTS has been collaborating with Leipzig-based DBI Gas- und Umwelttechnik GmbH to develop tubular carbon membranes.
According to Simon, during the separation process, hydrogen and natural gas are pushed through the tubular modules. The smaller hydrogen molecules are forced through the pores in the membrane and reach the outside in the form of gas, the larger methane molecules on the other hand are held back. This gives us hydrogen with an 80 percent degree of purity. We then filter the residual natural gas in a second separation step. The end result is a purity of over 90 percent.
The researchers at Fraunhofer IKTS are currently working on scaling the technology to an extent that will allow the separation of larger volumes of natural gas and hydrogen. The construction of prototypes is already in the pipeline.