Life Cycle Assessment of Mo, V, Ni, and Co Recovery from Spent Catalyst

MoCo/γ-Al₂O₃ catalysts used in petroleum refining are commonly recycled to recover Mo and V; however, the contained Ni and Co are not typically recovered as purified products. The goal of this study was to evaluate the environmental impacts of recycling a spent catalyst and recovering all of the valuable metals: Mo as MoO₃, V as V₂O₅, Ni as Ni(OH)₂, and Co as Co(OH)₂. Process simulation was used to study the inputs and outputs of the system, and the gathered process data inventory was used to perform life cycle assessment to determine the environmental impacts. The results show that when the content of Mo, V, Ni, and Co in the spent catalyst is high enough, the potential environmental impacts of the recycling system are lower than those of the primary production of equivalent products. For example, the global warming of the recycling systems decreases from 250% of the primary impacts (with 6 wt % metal content) to 53% (with 29 wt % metal content). The process hotspots in the recycling process were found to be mainly in the production of the chemicals and utilities consumed by the process. Particularly NH₃, electricity, HCl, NaOH, and H₂SO₄ increased the environmental impacts. In addition, in the recycling process direct gaseous emissions were generated, which contributed substantially to global warming and acidification.

The environmental impacts of MoCo/γ-Al₂O₃ catalyst recycling are evaluated using process simulation-based life cycle assessment with several uncertainty and sensitivity analysis methods to determine the influence of simulation parameter uncertainty.