1. Introduction
First synthesized by Mobil Oil Company in the 1970s, ZSM-5 zeolite belongs to the MFI topological structure family, with a unique dual-pore three-dimensional network system composed of straight 10-membered ring channels (0.56 nm × 0.53 nm) and sinusoidal cross channels (0.51 nm × 0.55 nm) . Different from one-dimensional pore zeolites, the intersecting pore structure of ZSM-5 provides efficient mass transfer channels for reactant and product molecules, while its moderate pore size endows it with precise molecular shape selectivity for hydrocarbon molecules. In addition, ZSM-5 exhibits a wide tunable range of silica-alumina ratios (from low silicon to ultra-high silicon), which enables flexible regulation of Brønsted and Lewis acid site density and strength . Its excellent thermal stability (calcination resistance above 800 °C) and hydrothermal stability allow it to adapt to harsh high-temperature and high-pressure industrial reaction conditions.
Owing to the above unique structural and physicochemical properties, ZSM-5 zeolite has irreplaceable application value in traditional petrochemical industry, emerging coal chemical industry, fine chemical synthesis and environmental governance fields. It has become a core catalytic material for upgrading petroleum products, converting coal-based chemicals and treating industrial pollutants. This paper comprehensively expounds the typical industrial applications and research progress of ZSM-5 zeolite in various fields, and analyzes the internal correlation between its structural characteristics and application performance.
2. Applications in Petroleum Refining Industry
The petroleum refining industry is the most mature and largest application field of ZSM-5 zeolite. Relying on its shape-selective cracking, isomerization and aromatization performance, ZSM-5 is widely used in fluid catalytic cracking (FCC), diesel hydrodewaxing, alkane isomerization and other key processes, significantly improving the quality and yield of petroleum products .
2.1 Fluid Catalytic Cracking (FCC) Auxiliary Catalyst
ZSM-5 is the most commonly used high-efficiency auxiliary catalyst in industrial FCC units. Traditional FCC catalysts mainly rely on Y-type zeolites for macromolecular cracking, but they have poor selectivity for light olefins and high yield of heavy by-products. After adding a small amount of ZSM-5 into the FCC catalyst system, the unique 10-membered ring shape-selective pores can selectively crack straight-chain alkanes and low-branched hydrocarbons in gasoline and diesel fractions. This process effectively increases the octane number of gasoline, reduces the content of heavy aromatic impurities, and significantly boosts the yield of high-value light olefins such as propylene and butylene . In industrial production, ZSM-5 modified FCC catalysts can increase the propylene output by 2%–5% while maintaining stable gasoline yield, which greatly improves the economic benefits of refineries.
2.2 Diesel Hydrodewaxing
Straight-chain paraffins in diesel oil will increase the freezing point and viscosity of fuel, reducing the low-temperature fluidity of diesel. ZSM-5 zeolite, with moderate pore size and appropriate acid strength, is an ideal catalyst for diesel hydrodewaxing. Its shape-selective effect allows straight-chain alkanes to enter the pore channels for selective cracking and isomerization, while retaining branched alkanes and cyclic hydrocarbons with high combustion calorific value . This technology can efficiently reduce the freezing point of diesel without causing excessive loss of diesel yield, and is widely used in the production of low-temperature resistant clean diesel in industrial refineries.
2.3 Alkane Isomerization and Aromatization
ZSM-5 can catalyze the isomerization of low-carbon straight-chain alkanes to branched alkanes, effectively improving the antiknock performance of gasoline. Meanwhile, its moderate strong acid sites and confined pore environment can promote the cyclization and aromatization of light alkanes, converting low-value C4–C6 alkanes into high-value benzene, toluene and xylene (BTX) aromatic products. Compared with other zeolite catalysts, ZSM-5-based aromatization catalysts have higher BTX selectivity and lower coking rate, showing excellent industrial application stability.
3. Applications in Coal Chemical Industry
With the development of clean coal chemical technology, ZSM-5 zeolite has become a core catalytic material for coal-based resource conversion. It is mainly applied in methanol-to-hydrocarbons (MTH), methanol-to-aromatics (MTA) and bioethanol conversion reactions, realizing the efficient conversion of coal-based methanol to high-value chemical products .
3.1 Methanol-to-Aromatics (MTA) Reaction
MTA is a key technology for coal-to-aromatic production, and ZSM-5 is the most suitable catalyst for this reaction. The MFI pore structure of ZSM-5 can accurately screen intermediate hydrocarbon molecules, and its matched acid distribution can promote the dehydration, oligomerization and cyclization of methanol, finally generating high-purity BTX aromatics . Ultra-high silicon ZSM-5 with modified acidity can effectively inhibit the generation of heavy polycyclic aromatics, reduce catalyst coking deactivation, and significantly improve the single-pass service life and aromatic selectivity of the catalyst. At present, ZSM-5-based MTA catalysts have been successfully applied in large-scale coal chemical industrial plants.
3.2 Methanol-to-Olefins (MTO) and Alkane Dehydrogenation
By regulating the acid density of ZSM-5 (reducing strong acid sites and increasing weak-medium acid sites), it can be used for methanol-to-light-olefins reaction, efficiently producing ethylene and propylene. In addition, modified ZSM-5 catalysts loaded with metal active components show excellent catalytic performance in butane dehydrogenation reaction, which can convert low-carbon alkanes into high-value olefin monomers and has broad application prospects in the field of low-carbon olefin production .
3.3 Bioethanol Conversion to Ethylene
As a renewable green chemical raw material, bioethanol can be efficiently converted to ethylene via ZSM-5 catalytic dehydration. ZSM-5 with appropriate surface acidity can reduce the reaction activation energy of ethanol dehydration, realize high-efficiency and high-selectivity ethylene production at moderate temperature, and inhibit side reactions such as ethanol polymerization and carbon deposition . This green catalytic process provides a new path for sustainable ethylene production and has become a research hotspot in green coal chemical industry.
