Zeolite synthesis using recycled silicon and aluminum components from spent FCC catalysts

Abstract

Significant efforts have been made to partially reuse FCC catalysts, particularly rare earth elements (REE), but only comprehensive recycling strategies can effectively contribute to a sustainable chemical industry. This work presents a novel recycling process for spent FCC catalyst materials, involving pre-treatment, selective separation of silica and alumina species, and synthesis of zeolites or zeolite-like materials. The process exclusively utilizes silicon and aluminum recovered from the spent FCC catalyst to produce high-quality catalyst components and sorbents. Optional rare earth element (REE) leaching, acid treatment after reactivation with sodium hydroxide, precipitation, and filtration yield silicon species (silica). The acidic, aluminum-rich filtrate is processed further by converting it into an alkaline medium with sodium hydroxide, enabling the precipitation and removal of unwanted heavy metals and rare earth elements. Aluminum species are recovered through neutralization of the alkaline solution, followed by precipitation and filtration. Overall, up to 95 % of the silicic acid and aluminum oxide are recovered. Subsequent chemical syntheses yield high-crystalline zeolite Y and ZSM-5 as active zeolites for FCC catalysts, alongside AlPO₄ as an alternative binder. A techno-economic analysis reveals a manageable turnover on industrial scale next to a refinery, while the costs still surpass current market prices, as long they do not care about environmental remediation. Unlike recent studies, no additional silicon and aluminum sources are required, which promotes a more independent local recycling. Furthermore, zeolite A was synthesized as a sorbent using the filtrate solution obtained during the production of zeolite Y, thus nearly completing the recycling loop.