Blow molding experts from Germany’s Kautex Maschinenbau have successfully produced a high-volume polyamide liner for hydrogen pressure tanks using extrusion blow molding. The liner is over two meters long (6.5 ft), with a diameter of approximately 500 mm (1.6 ft) and a volume of 320 liters (84.5 gal). This would be the first time a liner for a hydrogen tank has been produced in this size by blow molding.
Hydrogen presents considerable challenges with respect to the permeability of the coating material. Being the smallest molecule in the periodic table, hydrogen can diffuse through virtually any plastic. Special polyamides (PA) have the best barrier properties. However, due to their low melt stiffness and complexity, these PA variants have been difficult to process on this scale by blow molding. Newly developed PAs and a special extrusion technique made this possible.
“Producing a liner of this size in polyamide was a major challenge. The work we are doing here is truly pioneering,” said Abdellah El Bouchfrati, composites business development manager, where the new hydrogen coating was developed.
For some time, Kautex has been dedicated to the development of composite pressure vessels for various applications such as hydrogen, CNG and LPG tanks. Composite tanks are made of a thermoplastic liner; a boss part, to which the valve is connected; and a fiber wrap that adds mechanical strength.
Containers and pressure vessels (CPV) for hydrogen are generally designed for a working pressure of 700 bar and a burst pressure of 1750 bar. The liner is a central element – it is the inner skin of the tank, surrounding the contents and sealing it from the outside. The liner is subjected to high mechanical stress and temperatures ranging from –60° to 120°C (–140° to 248°F). The technology developed by Kautex in collaboration with a plastics processor enables hydrogen liners to be blown into sizes for industrial applications.
“The size of the liner we have now achieved is just the start. We are confident that in the future we will be able to use this method to produce significantly larger liners for hydrogen pressure tanks,” added El Bouchfrati.
The technology developed by Kautex Maschinenbau to produce high-volume liners for hydrogen containers means that a cost-effective solution for transport and infrastructure needs is now within reach. Hydrogen is now seen as an alternative to fossil fuels and battery-powered electric propulsion systems in many areas. China, Japan and South Korea are leading the way. However, Europe is also making great strides in promoting this technology. Experts have long considered that reliance on battery technologies alone will not achieve the long-term goal of carbon-neutral mobility.
While fuel cell technology in the passenger car sector does not yet seem economically viable due to production costs and lack of infrastructure, hydrogen drive and production technologies are already being successfully implemented. in other areas. This technology currently seems particularly interesting for the transport of heavy goods, local public transport, shipbuilding and the aeronautical industry. In these sectors, the main demand is for safe, light and leak-proof tank systems.
Hydrogen is also a prime energy storage medium, especially if it has been produced from renewable energy. Here, too, tank systems that can withstand the associated pressure while storing the extremely light gas safely are needed, Kautex said.