Biomass-derived acrylonitrile (ACN) precursors for the manufacture of carbon fibre are the target of an ongoing research programme by the Renewable Carbon Fibre Consortium (RCFC), being led by the National Renewable Energy Laboratory (NREL), based in Golden, Colorado.
The RCFC is currently aiming to make 50 kg of ACN, convert it into carbon fibre and then conduct further testes.
ACN is commonly used to make acrylic fibres for garments and carpets, with over seven million tons produced annually. Current production, however, is an energy-intensive, petroleum-based process that produces hydrogen cyanide as a by-product. The DoE (US Department of Energy) is looking for a cheap and more environmentally friendly method for producing carbon fibre that would also negate the impact of variations in the price of petroleum.
In response, researchers at NREL led by Eric Karp came-up with six different ways to make biomass-based ACN. They have tested three of these methods, including a catalytic process they developed called nitrilation.
The nitrilation process produces a 98 % yield of ACN compared to the yield from the petroleum-based method range of 80-83 %. In addition, the only by-products of nitrilation are water and ethanol, the latter of which can be recycled. As a result, the NREL researchers say that the process cuts manufacturing costs by about two-thirds compared with the process used for the manufacture of conventional ACN.
A variety of feedstocks can be employed in nitrilation. During the first phase, NREL researchers used corn stover, which consists of the stalks and leaves left over after harvesting the crop. The sugars in this biomass are converted by a microorganism into 3-hydroxypropionic acid (3-HP), which in subsequent steps is transformed into ACN. RCFC member Cargill, headquartered in Minnetonka, Minnesota, now plans to produce larger volumes.
Non-profit research institute Matric of South Charleston, West Virginia, will convert Cargill’s 3-HP into CAN and Fisipe of Barreiro, Portugal, will use this ACN to produce carbon fibre that it will supply to Ford, which will manufacture composite parts and compare them with those reinforced with conventional carbon fibres. The results of these tests will determine the direction of future research.