Screening of salt hydrates and cellulose nanocrystal composites for thermochemical energy storage using life cycle assessment

Abstract

Salt hydrate systems via thermochemical reactions can provide thermal storage for renewable-sourced alternatives to traditional heating systems like natural gas. In this study, we use life cycle analysis (LCA) along with the material prices to screen salts based on environmental impact and cost. Additionally, we performed LCA of producing a composite material of salt and cellulose nanocrystals (CNC) at a weight ratio of four to one. CNC is a stabilizing agent for salt. We assessed the salt-CNC composites based on a laboratory scale and scaled-up processing to identify low environmental impact formulations and to identify high environmental impact processes in the composite production. In general, lanthanum chloride, lithium hydroxide, and lithium chloride should be avoided due to high environmental impact or cost. For pure salts, our results showed magnesium sulfate, zinc sulfate, and calcium chloride are typically preferred with a close second tier of magnesium and strontium chlorides and strontium bromide. For the composite material, magnesium sulfate was preferred followed by zinc sulfate, sodium sulfide, and strontium chloride. CNC has a significant environmental impact, contributing over 50% of the environmental impact for these composites. Therefore, CNC production with lower environmental impacts needs to be pursued. In composite production, the environmental impact of mixing and sonication can be reduced by scaling production. However, drying remains a high-impact process. These results can help guide salt selection for other salt-based thermochemical materials and further development of the salt-CNC composite.