(195b) Roadmap for Scale-up of Carbon Nanotube Production for Displacement of Difficult to Decarbonize Structural Materials with Free Hydrogen Co-Production

Manufacturing structural materials makes-up an enormous amount CO₂ emissions, with steel alone constituting ~8% of global CO₂ annually. Structural materials like metals and cement are required in large volumes to support our infrastructure, and the manufacturing process is CO₂ intensive and considered difficult-to-decarbonize because of stoichiometric emissions from high-temperature reduction steps. High-performance materials like carbon fiber seek to address these issues by requiring less material to meet the same strength requirements; however, half of the mass of fossil-based feedstock is lost converting to carbon fiber, so the process is too inefficient to achieve a cost and supply able to meet structural material demands, beyond niche applications in aerospace and recreation. Carbon nanotubes (CNT) and their macrostructures (e.g., fibers, yarns, woven mats, etc.) have much higher predicted strength and conductivity than carbon fiber but have a simpler manufacturing process that suggests a low floor for production cost and environmental footprint. Research on CNT to-date has largely focused on property improvement, but with reported tensile strength of CNT fibers already an order of magnitude higher than steel (on a mass basis) and demonstrated doubling of fiber properties every three years (Taylor et al. Improved Properties, Increased Production, and the Path to Broad Adoption of Carbon Nanotube Fibers, Carbon 171 (2021) 689-694) the question of scalability becomes interesting. Here, we propose a techno-economic model for the scale-up of CNT production with H₂ co-production using lab-scale reactor conditions like reaction conversion, selectivity, and temperature to create a roadmap for researchers to push the field towards scalable and high-performance CNT at low environmental costs as measured in CO₂ intensity, embodied energy, and process efficiency. Preliminary analysis of this roadmap suggests that CNT production has the potential to be a carbon sequestering process and can ultimately compete with steel given focused research and investment to push the material along its learning curve. Process simulation (Aspen Plus) confirms the tractable model, and work is ongoing to explore the implications of various hydrogen separation schemes on the techno-economics.