Views: 0 Author: QT Publish Time: 2025-09-23 Origin: QT
In the refining and petrochemical industries, the choice of zeolite catalyst can determine the efficiency, selectivity, and profitability of entire production lines. Among the many zeolite frameworks, two have stood out for decades: ZSM-5 (MFI structure) and ZSM-22 (TON structure).
Both are medium-pore zeolites with unique advantages, but they differ in pore architecture, selectivity, and industrial applications. The question facing process engineers today is:
When should you choose ZSM-22 over ZSM-5, and vice versa?
This article provides a deep technical comparison, supported by academic research and industrial applications, to guide decision-makers.
Pore System: 3D, intersecting 10-membered ring channels.
Channel Dimensions: ~0.55 × 0.55 nm (straight) and 0.51 × 0.55 nm (zig-zag).
Strength: Large network → versatility in aromatization, cracking, and methanol-to-hydrocarbons.
Weakness: Intersections can trap intermediates → higher coke formation.
Pore System: 1D, straight 10-membered ring channels.
Channel Dimensions: ~0.45 × 0.55 nm.
Strength: Straight, narrow pores → excellent shape selectivity for linear n-paraffins.
Weakness: Diffusion limitations for bulky molecules; less versatile than MFI.
Reference: Kokotailo, G. T. et al., Nature, 1982; Corma, A., Journal of Catalysis, 1994.
| Property | ZSM-5 (MFI) | ZSM-22 (TON) |
|---|---|---|
| Acid Site Density | Moderate–High (tunable via Si/Al) | Moderate–High (tunable) |
| Selectivity | Broad (aromatics, cracking, isomerization) | Narrow (linear paraffin isomerization) |
| Coke Formation | Higher (due to channel intersections) | Lower (straight channels, fewer traps) |
| Diffusion Characteristics | Multidirectional | One-dimensional |
| Thermal Stability | Excellent | Excellent |
Fluid Catalytic Cracking (FCC): Improves gasoline octane via aromatics formation.
Methanol-to-Olefins (MTO): Converts methanol into light olefins (ethylene, propylene).
Aromatization: Widely used for toluene disproportionation and xylene isomerization.
Drawback: High coke formation → shorter regeneration cycles.
n-Paraffin Isomerization: Produces monobranched isomers → better cold-flow for diesel and jet fuels.
Lubricant Base Oils: Enhances viscosity index without excessive cracking.
Low-Coke Processes: Preferred in hydroisomerization units requiring long catalyst life.
Drawback: Limited versatility compared to ZSM-5.
Reference: Corma, A. & Martínez, A., Applied Catalysis A, 1993; Raeissi et al., Applied Catalysis A, 2008.
ZSM-5: High, due to channel intersections.
ZSM-22: Lower, thanks to straight channels.
If you need long operational cycles → ZSM-22 is preferred.
ZSM-5: Produces aromatics, good for octane but not ideal for cold-flow improvement.
ZSM-22: Produces monobranched isomers → better pour points in diesel.
For cold-climate fuels → ZSM-22 is the winner.
ZSM-5: Used across FCC, MTO, aromatization, gasoline upgrading.
ZSM-22: More niche, focused on isomerization.
If multipurpose use is needed → ZSM-5 dominates.
ZSM-5: Good for gasoline octane but less relevant for ultra-low sulfur diesel cold-flow standards.
ZSM-22: Aligned with diesel/jet regulations requiring low-pour-point fuels.
Future fuel compliance → ZSM-22 has an edge.
Shell & ExxonMobil patents (2000s): Adoption of ZSM-22 in hydroisomerization for diesel cold-flow improvement.
Corma et al., Journal of Catalysis (1994): Demonstrated that ZSM-22 showed higher selectivity for monobranched isomers vs. ZSM-5.
Raeissi et al., Applied Catalysis A (2008): ZSM-22 maintained activity longer than ZSM-5 due to reduced coke formation.
| Refinery Goal | Best Choice | Why? |
|---|---|---|
| Improve gasoline octane | ZSM-5 | Produces aromatics. |
| Cold-flow diesel improvement | ZSM-22 | Selective to monobranched isomers. |
| Methanol-to-olefins | ZSM-5 | High olefin yield. |
| Long catalyst lifetime (low coke) | ZSM-22 | Coke-resistant. |
| Multipurpose petrochemical production | ZSM-5 | Versatility. |
| Lubricant base oil upgrading | ZSM-22 | High viscosity index improvement. |
As refining faces tighter environmental regulations and demand for clean fuels, ZSM-22 is expected to grow in significance. Meanwhile, ZSM-5 will remain a cornerstone of petrochemicals due to its flexibility.
Our company will soon introduce new ZSM-22 catalysts designed specifically for n-paraffin isomerization, alongside our existing ZSM-5 product line, allowing refiners to select the best-fit catalyst for their unique processes.
ZSM-5 and ZSM-22 are not competitors, but complementary tools in the refinery toolbox.
Choose ZSM-5 for versatility, aromatization, and gasoline octane upgrading.
Choose ZSM-22 for selective n-paraffin isomerization, long catalyst life, and cold-flow improvement.
By understanding these strengths, refiners can make informed decisions that optimize yield, efficiency, and sustainability.
Q1: Can ZSM-22 completely replace ZSM-5 in refineries?
Not entirely. ZSM-22 excels in paraffin isomerization, but ZSM-5 remains superior in aromatization and olefin production.
Q2: Which zeolite has a longer lifetime?
ZSM-22 generally shows longer cycle times due to reduced coke formation.
Q3: Is ZSM-22 more expensive than ZSM-5?
ZSM-22 synthesis is more specialized, but the extended lifetime and fuel compliance benefits often outweigh cost differences.
Q4: Can ZSM-22 be used in FCC units?
Not typically. ZSM-22 is better suited for hydroisomerization units rather than FCC cracking.
Q5: What’s the Si/Al ratio effect in ZSM-22 vs ZSM-5?
Higher Si/Al ratios reduce acidity and coke formation. ZSM-22 with controlled Si/Al ratios shows excellent stability in isomerization.
Q6: Will your company supply ZSM-22 soon?
Yes — we will introduce ZSM-22 catalysts optimized for paraffin isomerization, complementing our current ZSM-5 solutions.
