Chemical manufacturing procedures typically emphasize the need to maximize material performance and minimize production cost. Less attention is paid to mitigating the environmental impact of the production, and this has resulted in costly remediation efforts and redevelopment of technologies. Researchers at the Massachusetts Institute of Technology and the University of Michigan, Ann Arbor now report that side-products from the synthesis of carbon nanotubes, which include potent greenhouse gases and toxic chemical compounds, should be considered when designing the chemical processes1.

Using a custom-built chemical vapour deposition reactor, Desireé Plata and colleagues assessed the composition of effluent from the synthesis of multiwalled carbon nanotubes. Thermal pre-treatment of ethane and hydrogen reactant gases produced over 45 side-products including methane, benzene, various volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons. Increasing the temperature accelerated nanotube growth, but it also released more methane and benzene, which can be environmentally harmful. Depending on the size of the market and application requirements, the annual production of nanotubes for flat panel displays and thermal interface materials was estimated to represent between 0.34% and 0.002% of all anthropogenic sources of VOC emissions in the US, which includes industrial, residential and automotive sources.

As the carbon nanotube industry expands, it is suggested that suitable effluent treatment and recycling technologies are implemented when designing new chemical processes.