In March 2018 Boeing applied for a patent to recover carbon fibers from composite waste. The patent was awarded in May 2019. The patent language is interesting: “A method for recovering carbon fibers from composite waste includes coating a water-soluble catalyst powder on a surface of composite waste having carbon fibers and a resin matrix and pyrolyzing the resin matrix of the coated composite waste.”
Intriguingly, the Boeing application claimed priority from Chinese Patent Application No. 201710213263.4 titled “A Method for Recycling Carbon Fibers from Composite Material Wastes by Catalytic Pyrolysis,” which was filed on Apr. 1, 2017.
Boeing has a big interest in dealing with composite waste – from current production to end of service. As Boeing pointed out: “Currently, carbon fiber-reinforced resin composites as solid waste are treated by way of milling into powder or particles and used as fillers for paving materials, etc., or even landfilled. Carbon fiber-reinforced resin composites contain high-value carbon fibers, and these treatment methods cause a tremendous waste of carbon fiber resources.”
Recovery of carbon fibers where solvents are used which may cause pollution to the environment. Using water is possible, but it needs to be “carried out under high temperature and high pressure reaction conditions, and has higher requirements on reaction equipment“.
Boeing’s patent is summarized as: “In one embodiment, a method for recovering carbon fibers from composite waste includes coating a water-soluble catalyst powder on a surface of composite waste having carbon fibers and a resin matrix, and pyrolyzing the resin matrix of the coated composite waste.
In another embodiment, a method for recovering carbon fibers from composite waste includes spraying a water-soluble catalyst powder on a surface of composite waste having carbon fibers and a resin matrix with an amount of 0.1-0.5 g/cm2, and putting the catalyst covered composite waste into a pyrolysis device and heating the catalyst covered composite waste to 250 to 450° C. for 10 to 30 minutes.
Other embodiments of the disclosed method for recovering carbon fibers will become apparent from the following detailed description, the accompanying drawings and the appended claims.”
Boeing claims that “The essence of the present description lies in reducing the temperature and time of the pyrolysis of the resin matrix in waste carbon fiber composites by catalyst addition. The catalyst forms a liquid film on the surface of the waste composites and permeates into the material, so that the temperature and time of the decomposition of the resin matrix are reduced.” Boeing also claims: “As compared to the prior art, the method in the present description has the following advantages: firstly, the equipment is simple, the technological process is facile, and the treatment cost is low.”