Reclaiming continuous fibers for hydrogen storage

The National Composites Centre (NCC) says that it has successfully reclaimed continuous carbon fibers from a whole pressure vessel and re-used them to manufacture a new pressure vessel.

This is the first time this process has been achieved in the UK, the organization said.  

Because hydrogen has low energy density, it needs to be compressed and stored at very high pressures, between 350 to 700 bar (5,076–10,152 psi). This makes high-strength, lower-weight carbon fiber the material of choice, especially for hydrogen pressure vessels in vehicles such as cars or aircraft, where power-to-weight is critical. However, demand for carbon fiber is expected to grow five-fold between 2025 and 2030, exceeding global manufacturing capacity.

Until recently, recycling processes for composite components such as aircraft wings and wind turbine blades has resulted in short fibers with lower mechanical properties than unrecycled fiber. While there are applications for this material, it is not suitable for re-use in high performing products, the NCC said.

The center partnered with UK-based B&M Longworth Ltd to reclaim the carbon fiber from end-of-life composite pressure tanks, using the company’s Deecom process.

According to Longworth, Deecom uses superheated steam, under compression, to penetrate microscopic fissures in the composite’s polymer, where it then condenses. On decompression, it boils and expands, cracking the polymer and carrying away broken particles. This pressure swing cycle is then repeated until all the material suspended in the polymer has been separated from the fiber, allowing the monomers to also be reclaimed for possible reprocessing. The process reportedly leaves the primary component material intact and undamaged, allowing for any length to be retained.

NCC engineers next worked with Cygnet Texkim, which makes fiber handling and conversion technology to use the reclaimed continuous carbon fiber to make a new pressure vessel using filament winding.

They also looked into refining composite pressure vessel designs in order to minimise waste and trial the tools and manufacturing processes. The engineers have also delivered composite design specification for cryogenic pressure vessels and are working on certifying the process for composite pressure pipes, including those to be used offshore.

The companies next plan to undertake fiber characterisation analysis of the reclaimed material and recycled vessel, with the aim of working with manufacturers to scale and industrialize the process.

"Achieving continuous fiber recovery is a significant step towards our goal of a fully recyclable certified tank – the critical technology barrier we need to address, if we are to embed hydrogen in our energy mix and meet net zero targets," said Marcus Walls-Bruck, chief engineer for hydrogen at the NCC.

"That commitment to fiber integrity is extremely significant because it allows us to reclaim and repurpose carbon fiber in a way that is reliable and sustainable, while creating end products of the highest quality and consistency," said Luke Vardy, CEO of Cygnet Texkimp.