Life Cycle Assessment of Cobalt Catalyst Production and Recycling

Catalysts with an active phase of cobalt are crucial for Fischer–Tropsch synthesis (FTS), yet the environmental impacts of the catalyst production and the recycling of the spent catalyst remain largely unknown. The goal of this study was to evaluate the impacts of both catalyst production as well as the recycling of spent catalyst as cobalt hydroxide, cobalt sulfate, or cobalt carbonate. Life cycle assessment (LCA) was used to quantify the environmental impacts of the studied processes. The life cycle inventory (LCI) was gathered based on the mass and energy balances of process simulations built on information available in the literature. The results show that compared to primary production of equivalent products, all studied recycling processes for spent catalyst decrease the environmental impacts by more than 50% in all investigated impact categories. For example, the global warming potential (GWP) of cobalt recovery from spent FTS catalyst as cobalt sulfate was 1.7 kg CO₂-eq./kg CoSO₄whereas the corresponding GWP for primary production was 4 kg CO₂-eq./kg CoSO₄. The process hotspots of recycling were found to be the production of the chemicals consumed, particularly sodium hydroxide and sulfuric acid, which together contributed between 64 and 95% of the total environmental impacts. LCAs on FTS have included the consumption of cobalt catalyst in the LCI using various approximations. The impacts calculated for the production of cobalt catalyst in this study were found to be markedly higher. The largest contributors included the production of materials for the precursor and support, as well as NO_x emissions and consumption of nitric acid.

Graphical Abstract