Application Note: USY for FCC
USY zeolite is the primary cracking component in modern FCC catalysts.
Unit Cell Size: The Key QC Parameter
| UCS (Å) | Framework SAR | Activity | Gasoline Selectivity | Best For |
|---|---|---|---|---|
| 24.24–24.30 | 40–80 | Moderate | High | Maximum stability, low coke |
| 24.30–24.38 | 20–40 | Balanced | Good | General-purpose FCC |
| 24.40–24.50 | 10–20 | High | Moderate | Maximum conversion |
| 24.50–24.58 | 5–10 | Very high | Lower | High-activity matrix |
Each 0.01 Å reduction in UCS corresponds to measurable framework dealumination. Lower UCS produces higher gasoline selectivity; higher UCS provides more total acidity.
Rare-Earth Exchange
RE-USY (RE₂O₃ 1–5 wt%) increases hydrogen transfer activity, favoring gasoline yield. RE-free USY reduces hydrogen transfer, increasing propylene. For maximum propylene FCC, combine RE-free USY with ZSM-5 additive.
Mesoporosity
Mesopore volume (0.10–0.35 cm³/g) from dealumination improves heavy feed accessibility and metals tolerance. Resid FCC operations should specify mesopore-enhanced grades.
See USY for FCC and the USY TDS.
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