ZSM-5 for FCC Additives

ZSM-5 is the most effective FCC additive for simultaneously increasing propylene yield and gasoline octane without raising reactor severity. Unlike USY and Y zeolites that form the base cracking catalyst, ZSM-5 is used as a separate additive particle at 2-10 wt% of the total FCC catalyst inventory.

How ZSM-5 Works in FCC

ZSM-5’s 10-membered ring channels (5.1-5.6 Å) selectively admit low-octane linear and mono-methyl-branched C₇-C₁₂ olefins in the gasoline boiling range while excluding higher-octane branched, cyclic, and aromatic molecules. Inside the channels, these gasoline-range olefins are cracked to lighter C₃-C₅ olefins — primarily propylene.

This shape-selective mechanism has two effects that both benefit the refiner. First, it increases propylene yield by 2-6 percentage points, depending on ZSM-5 loading and base catalyst activity. Second, it increases gasoline research octane by 1-3 numbers because the low-octane linear olefins that were cracked were also the molecules depressing the gasoline octane pool.

Recommended ZSM-5 Grades

Phosphorus-stabilised ZSM-5 is available for units operating under severe hydrothermal conditions. Phosphorus reduces further dealumination of the ZSM-5 framework in the regenerator, extending additive life.

Key Operating Parameters

ZSM-5 additive is typically introduced at 2-5 wt% for moderate propylene enhancement and 5-10 wt% for maximum propylene mode. The propylene yield increase is roughly linear with ZSM-5 loading up to ~8 wt%, after which incremental benefit diminishes. ZSM-5 addition does not significantly affect conversion or coke yield at typical loadings.

When requesting a sample, specify your target Si/Al ratio, preferred crystal size, and whether you need H-form powder, phosphorus-stabilised grade, or NH₄-form precursor.