Question

The catalyst used in the low-pressure Ziegler process for polyethylene manufacture _____________________

• A. Is Nickel
• B. Consists of aluminium triethyl combined with titanium tetrachloride
• C. Consists of aluminium chloride combine with titanium dioxide
• D. Is vanadium pentoxide

Hint:

Remember the names of the Nobel laureates, Karl Ziegler and Giulio Natta, who developed this groundbreaking catalytic system for polymer synthesis. Their work revolutionized the production of polymers like polyethylene and polypropylene.

Answer 1

The Correct Option is B

Step 1: Understand the Ziegler-Natta polymerization process.
The Ziegler-Natta polymerization process is a method used to produce high-density polyethylene (HDPE) and other polyolefins at relatively low pressures and temperatures compared to earlier radical polymerization methods. This process utilizes a special type of catalyst system known as the Ziegler-Natta catalyst.

Step 2: Identify the key components of a Ziegler-Natta catalyst.
A typical Ziegler–Natta catalyst system consists of two main components:

• A transition metal compound: This is usually a halide or oxyhalide of a transition metal from Group IV to VIII of the periodic table, such as titanium, vanadium, chromium, or zirconium. Common examples include titanium tetrachloride (\(\text{TiCl}_4\)), titanium trichloride (\(\text{TiCl}_3\)), and vanadium tetrachloride (\(\text{VCl}_4\)).
• An organometallic compound: This is typically an organoaluminum compound, such as triethylaluminum (\(\text{Al(C}_2\text{H}_5)_3\)), triisobutylaluminum (\(\text{Al(i-C}_4\text{H}_9)_3\)), or diethylaluminum chloride (\(\text{Al(C}_2\text{H}_5)_2\text{Cl}\)). These compounds act as cocatalysts.

The active catalytic species is formed through the interaction of these two components.

Step 3: Evaluate the given options based on the composition of Ziegler-Natta catalysts.
(1) Is Nickel: Nickel-based catalysts are used in some polymerization processes, but they are not the typical catalysts for the low-pressure Ziegler process for polyethylene manufacture.

(2) Consists of aluminium triethyl combined with titanium tetrachloride:

Aluminium triethyl \(\text{Al(C}_2\text{H}_5)_3\) is a common organoaluminum cocatalyst, and titanium tetrachloride \(\text{TiCl}_4\) is a widely used transition metal compound in Ziegler–Natta catalysts for polyethylene production. This option correctly describes a typical Ziegler–Natta catalyst.

(3) Consists of aluminium chloride combined with titanium dioxide:

Aluminium chloride \(\text{AlCl}_3\) and titanium dioxide \(\text{TiO}_2\) are not the standard components of a Ziegler–Natta catalyst system used for polyethylene production. The organoaluminum component usually has alkyl groups bonded to aluminum, and titanium is typically in a halide form.

(4) Is vanadium pentoxide:

Vanadium pentoxide \(\text{V}_2\text{O}_5\) can be used as a catalyst in some oxidation reactions, but it is not the primary catalyst for the low-pressure Ziegler process for polyethylene manufacture. Vanadium-based compounds (like \(\text{VCl}_4\)) are sometimes used in Ziegler–Natta catalysts, but they are usually paired with an organoaluminum cocatalyst.

Step 4: Conclude the correct composition of the Ziegler-Natta catalyst for polyethylene manufacture.
Based on the understanding of Ziegler-Natta catalysts, the combination of aluminium triethyl and titanium tetrachloride is the correct answer for the catalyst used in the low-pressure Ziegler process for polyethylene manufacture.