Comments on Energy Use in Manufacturing and the Recycling Potential of Carbon Nanotubes Timothy G. Gutowski Massachusetts Institute of Technology Chicago, IL Nov 5, 2009

Outline Toxicity Energy Recycling Brian Wardle, MIT Kripa Varanasi MIT

Energy to make SWNT “HiPco” Process 2CO  CO 2 + C Nikolaev et al 1999

HiPco Process Estimates Gutowski & Liow 2010 IEEE

Ref: Gutowski & Liow 2010 IEEE Theoretical minimum Electricity (Exergy) Estimates for Synthesis only. Does not include losses at process, nor other steps in the process, nor infrastructure requirements, nor losses at the utilities. Does not include energy cost of raw materials. Healy et al Estimates of actual Theoretical Minimum Electricity Requirements

Ashby 2009 Estimate of embodied energy for SWNT = Synthesis + purification + infrastructure + utilities + input materials ≈ TJ/kg

Electrical energy requirements for five materials in MJ/kg.

The Energy Paradox One of the most energy intensive materials known to humankind Less than 1% of the mfg cost (Healy, Isaacs, 2008)

Gutowski 2009 Compared to other processes 5 kW 50 kW

Gutowski & Liow 2010 IEEE CNF energy estimates Why so much variation? Many products Many processes All changing

Gutowski & Liow 2010 IEEE 1 kW 5 kW, 50 kW

Carbon source: CH 4, C 2 H 4, CO Metal catalyst: Ni Mo/Co Fe Growth substrate AJHart T= o C Synthesizing CNTs: Catalytic chemical vapor deposition (CVD) Work by Desiree Plata Mt Holyoke College and MIT

Resistively heated platform for VA-MWCNT growth Cold-wall reactor tube Pre-heater: TURNED OFF T gas Direct delivery of potential precursors Desiree Plata 09

Deliver at equal partial pressures: 0.01 atm (1% v/v) Desiree Plata 09

Deliver at equal partial pressures: 0.01 atm (1% v/v) * vinyl acetylene at atm (0.3% v/v) * Rapid CNT formation without thermal pre-treatment of feedstock gases: Potential 55% energetic savings Desiree Plata 09

Recycling and Separation The Science of Separation Phase separation boundary Nanotubes in solvents, Plata 2009 Separation of Hexane from Polybutadiene Gutowski 1981 Flory 1953

Practical Recycling Issues Value Quantity Toxicity Easy of isolation Quality after isolation Down cycle

Dahmus & Gutowski 2007 Potential for Recycling

Dahmus PhD ‘07

Trends in Product Design Dahmus & Gutowski 07

Composite materials are not recycled Ashby 2009

End of Life for CNTs?

From an environmental protection point of view… Toxicity - Is what we are interested in Energy - Is very large and incomplete Recycling - Lots of Science, but…