ZSM-5 is a catalyst used for:

Converting alcohols into gasoline

The correct answer is option 2. Converting alcohols into gasoline.

ZSM-5 is a type of zeolite, a crystalline aluminosilicate mineral. Zeolites are known for their unique porous structures, which make them highly effective as catalysts in various chemical reactions. The structure of ZSM-5 consists of a three-dimensional framework of silicon, aluminum, and oxygen atoms, forming a network of channels and pores. These pores are of molecular dimensions, typically around 5-6 angstroms, which allow the selective passage and conversion of certain molecules.

The catalytic activity of ZSM-5 arises from its acidic sites (due to the presence of aluminum in the framework, which creates a negative charge balanced by protons). These acidic sites are crucial for facilitating various reactions, including the conversion of alcohols into hydrocarbons. The structure of ZSM-5 is highly stable and resistant to deactivation by coking (the formation of carbon deposits), which is a common problem in catalytic processes.

The Methanol-to-Gasoline (MTG) process is one of the most significant applications of ZSM-5. In this process, methanol (or other lower alcohols) is converted into hydrocarbons, including gasoline-range hydrocarbons, over a ZSM-5 catalyst.

Reaction Pathway:

Methanol Conversion: Methanol is first converted into dimethyl ether (DME) in the presence of an acid catalyst.

\(2 \text{CH}_3\text{OH} \rightarrow \text{CH}_3\text{OCH}_3 + \text{H}_2\text{O}\)

Oligomerization and Cyclization: The dimethyl ether and unreacted methanol then undergo a series of reactions, including oligomerization (combining smaller molecules into larger ones) and cyclization (forming rings), to produce a range of hydrocarbons.

Aromatization and Cracking: ZSM-5 catalyzes the aromatization (formation of aromatic compounds like benzene, toluene, and xylenes) and cracking (breaking down larger hydrocarbons into smaller ones) processes, leading to the production of a mixture of hydrocarbons that resemble gasoline.

Product Composition:

The product mixture typically includes a wide range of hydrocarbons, primarily:

Alkanes (paraffins): Saturated hydrocarbons (e.g., hexane, heptane).

Alkenes (olefins): Unsaturated hydrocarbons (e.g., ethylene, propylene).

Aromatics: Compounds with a benzene ring structure (e.g., benzene, toluene, xylene).

Significance of ZSM-5 in the MTG Process

Selectivity: ZSM-5 is highly selective for the production of gasoline-range hydrocarbons. Its pore structure allows it to favor the formation of molecules that are within the gasoline boiling range (C5-C10 hydrocarbons).

Efficiency: ZSM-5’s resistance to coking and its ability to regenerate make it an efficient catalyst for continuous industrial processes.

Economic Impact: The MTG process using ZSM-5 allows the conversion of methanol, which can be derived from coal, natural gas, or biomass, into liquid hydrocarbons. This is particularly valuable in regions where crude oil is scarce but other feedstocks (like natural gas) are abundant.

Why Other Options Are Incorrect:

Option 1: Converting Zinc into Aluminium: This is not related to ZSM-5. ZSM-5 is not involved in any metallurgical processes that convert one metal into another.

Option 3: Converting Zeolites into Zinc: ZSM-5 itself is a type of zeolite, and it does not participate in any process that converts zeolites into zinc.

Option 4: Converting Zinc to Zeolites: Similarly, ZSM-5 does not convert zinc into zeolites.

Summary:

ZSM-5 is a highly effective catalyst used in the Methanol-to-Gasoline (MTG) process, where it converts lower alcohols, particularly methanol, into a mixture of hydrocarbons that resemble gasoline. Its unique structure, acidity, and stability make it ideal for this application, allowing for the efficient production of gasoline-range hydrocarbons from methanol. The correct answer is therefore **2. Converting alcohols into gasoline**.