Assessing the environmental impact and payback of carbon nanotube supported CO2 capture technologies using LCA methodology

Climate change caused by excessive CO2 emissions in the atmosphere has attracted widespread public concern in recent years. Current industrial methods generally utilize monoethanolamine for CO2 capture; however, the CO2 regeneration requires a high temperature and energy demand during every adsorption/desorption process, along with material losses. Many solid amines with high capture capacity and stability are developed as adsorbents to overcome the limitations. However, the environmental impacts caused by adsorbents themselves are not holistically considered and discussed; meanwhile, material syntheses and consumptions are also associated with CO2 emission. To determine the environmental impacts and identify hotspots of novel CO2 capture adsorbents, two carbon nanotube supported polyethyleneimine, physically adsorbed and covalently bonded, were compared with traditional monoethanolamine method using life cycle assessment. The carbon payback periods were also analyzed to gain understanding on whether the currently evaluated novel materials are suitable for industrial application. Results suggest that, material usage, especially carbon nanotubes, contributes the majority of the overall environmental impacts for both types of carbon nanotube supported polyethyleneimine. Meanwhile, their carbon payback periods are over 40 times longer than monoethanolamine during the synthesis phase. However, the energy consumption of physically adsorbed polyethyleneimine saves up to 60% compared to monoethanolamine in every adsorption/desorption cycle due to its lower heat capacity. In addition, the rate of cumulative CO2 remission for carbon nanotube supported polyethyleneimine is twice higher than monoethanolamine, indicating the potential application for industrial CO2 capture. Overall, our study indicates that current status of solid amine has a potential in CO2 capture, but requires much improvements. Future research should pay attention on decreasing the initial material synthesis and increasing the product life time due to their high environmental tradeoffs. Meanwhile, our study highlights that unilateral emphasis of the CO2 capture efficiency by novel materials may not be adequate, comprehensive considerations should be focused on the comparison throughout material life cycles including use and preparation phases. [Display omitted] •Life cycle environmental impacts of carbon capture techniques were assessed.•Carbon nanotube supported amine generates higher environmen