Life Cycle Aspects of Nanoproducts, Nanostructured Materials, and Nanomanufacturing: Problem Definitions, Data Gaps, and Research Needs
Chicago, Illinois: November 5-6, 2009
Nano Technology Assissment
Timothy G. Gutowski
Professor of Mechanical Engineering
M.I.T.
In terms of nano-materials applications, manufactures will seek large volume applications such as reinforcements and surface modifications for large applications, such as in the modification of wetting performance in heat transfer and/or skin friction. We will address these applications looking in particular at energy requirements for
manufacturing and the potential for recycling.
1. Thermodynamic Analysis of Nano-materials manufacturing
• We and others have measured and estimate manufacturing technologies especially for carbon nanomaterials. The trends appears to follow other new processing technologies (e.g. semi conductors, MEMS) with very high energy intensities (see figure below, carbon nano-products come in around 1 – 10 GJ(electricity)/kg [Gutowski 2009], with some higher values reported for SWNT, up to 300GJ/kg (electricity) [Healy 2008]. These do not include input materials.
• A lower bound estimate of the minimum work to produce carbon nanotubes from CO is about 10MJ/kg assuming 100% conversion. Potential for improvement appears good because of low yields, but, material purity and vapor phase processes will limit, this. Estimates with improved efficiency for high production come in around 1 - 2 GJ (electricity)/kg [Kushnir 2008]. These need to be confirmed. Currently estimates vary by almost 3 orders of magnitude.
2. End of Life Recycling of Nano-materials
‐ We review trends in both product (see below) and materials recycling [Ashby 2009]
‐ The high potential value of recycled nano-materials could encourage recycling,
‐ But evidence shows that complex material mixtures are rarely recycled, composite materials are, for all practical purposes, not recycled, polymers are not much better. See Ashby
‐ If complex (unrecycleable) materials are added to a product, they complicate the recycling process and devalue the recycled material value of the product. The product then moves down and to the right in the figure below. This reduces the chances of recycling.
‐ Some down cycling scenarios seem viable, but are unexplored.
‐ Hazards are unknown at this time
Figure from Dahmus 2007 shows the effect of material mixing (measured as the entropy of mixing – a measure of material complexity) on the recyclability of products. Circles around data points indicate recycling rates in the US (automobiles are at about 95%). Materially complex, low material value products are not recycled. However, technology and policy can move the boundary to include more of these produces.
References
Gutowski, Timothy G., Matthew S. Branham, Jeffrey B. Dahmus, Alissa J. Jones, Alexandre Thiriez and Dusan
Sekulic, Thermodynamic Analysis of Resources Used in Manufacturing Processes, Environmental Science and Technology, 2009, 43, pp 1584-90. January 29, 2009,
Dahmus, J. B., and T. G. Gutowski. "What Gets Recycled: An Information Theory Based Model of Product Recycling", Environmental Science and Technology, 2007, 41, 7543 – 7550,
Healy, M.L., Lindsay J. Dahlben and Jacqueline A. Isaacs, “Environmental Assessment of Single-Walled Carbon Nanotube Processes”, Journal of Industrial Ecology, Vol. 12, No. 3, pp. 376-393, June 2008.
Kushnir, D and Bjorn A. Sanden, “Energy Requirements of Carbon Nanoparticle Production”, Journal of Industrial Ecology, Vol. 12, No. 3, pp. 360 -375, June 2008.
Ashby, Michael F., Materials and the Environment – Eco-Informed Material Choice, Elsevier Inc., 2009.