Question

Write equations for all steps in the manufacture of acetylene starting from limestone and coal.

Short answer

The manufacture of acetylene from limestone and coal involves four main steps with their corresponding chemical equations: 1. \(CaCO_3(s) \rightarrow CaO(s) + CO_2(g)\) (calcination of limestone) 2. \(C_{coal}(s) \rightarrow C_{coke}(s) + volatiles(g)\) (production of coke from coal) 3. \(CaO(s) + 3 C_{coke}(s) \rightarrow CaC_2(s) + CO(g)\) (production of calcium carbide) 4. \(CaC_2(s) + 2H_2O(l) \rightarrow C_2H_2(g) + Ca(OH)_2(aq)\) (hydrolysis of calcium carbide to produce acetylene)

Step-by-step solution

Production of calcium oxide (CaO) and carbon dioxide (CO2) from limestone

Limestone, which is mainly composed of calcium carbonate (CaCO3), is heated in a process called calcination. This process results in the formation of calcium oxide (CaO) and carbon dioxide (CO2) as byproducts. The chemical equation for this reaction is: \(CaCO_3(s) \rightarrow CaO(s) + CO_2(g)\)

Production of coke (a form of carbon) from coal

Coke is produced by heating coal in the absence of air. The impurities in coal are removed, and a more carbon-rich and pure substance called coke is obtained. The chemical equation for this reaction is: \(C_{coal}(s) \rightarrow C_{coke}(s) + volatiles(g)\)

Production of calcium carbide (CaC2) from calcium oxide and coke

Calcium oxide (CaO) from the first step is mixed with coke from the second step and heated to high temperatures. This leads to the formation of calcium carbide (CaC2) and carbon monoxide (CO) as products. The chemical equation for this reaction is: \(CaO(s) + 3 C_{coke}(s) \rightarrow CaC_2(s) + CO(g)\)

Hydrolysis of calcium carbide to produce acetylene and calcium hydroxide

To produce acetylene gas from calcium carbide, water must be added to the reaction. This process is known as hydrolysis. The chemical equation for the hydrolysis of calcium carbide is: \(CaC_2(s) + 2H_2O(l) \rightarrow C_2H_2(g) + Ca(OH)_2(aq)\) In conclusion, the manufacture of acetylene from limestone and coal involves four main steps, and their corresponding chemical equations are: 1. \(CaCO_3(s) \rightarrow CaO(s) + CO_2(g)\) 2. \(C_{coal}(s) \rightarrow C_{coke}(s) + volatiles(g)\) 3. \(CaO(s) + 3 C_{coke}(s) \rightarrow CaC_2(s) + CO(g)\) 4. \(CaC_2(s) + 2H_2O(l) \rightarrow C_2H_2(g) + Ca(OH)_2(aq)\)

Key concepts

Calcination

Calcination is a crucial process in the production of acetylene. This process involves heating limestone, which is primarily made up of calcium carbonate (\(CaCO_3\)), at high temperatures. When heated, the limestone decomposes to form calcium oxide (\(CaO\)) and carbon dioxide (\(CO_2\)) as illustrated in the equation:
\[CaCO_3(s) \rightarrow CaO(s) + CO_2(g)\]

• Importance: Produces calcium oxide, a key component for the next steps in acetylene production.
• Conditions: Calcination usually occurs at temperatures above 825°C.

The gases released during calcination are collected and managed to reduce emissions into the atmosphere.

Coke Production

Coke production from coal is an essential step in this process. Coke is a carbon-rich material obtained by heating coal in the absence of air, allowing impurities to be removed and volatile components to be released. This is represented by:
\[C_{coal}(s) \rightarrow C_{coke}(s) + volatiles(g)\]

• Purity: Coke has a higher carbon content compared to raw coal.
• Usage: It is used as a reducing agent in the next step to produce calcium carbide.

Coke provides the necessary carbon needed to convert calcium oxide into calcium carbide.

Calcium Carbide

The production of calcium carbide involves reacting calcium oxide with coke. This chemical reaction requires high temperatures and results in the formation of calcium carbide (\(CaC_2\)) and carbon monoxide as a byproduct:
\[CaO(s) + 3 C_{coke}(s) \rightarrow CaC_2(s) + CO(g)\]

• Significance: Calcium carbide is the key precursor for acetylene gas.
• Process: Typically carried out in an electric arc furnace to achieve the necessary temperature.

The carbon monoxide produced in this reaction can be redirected for other industrial uses, reducing waste.

Hydrolysis

The final step in acetylene production is hydrolysis, where water is added to calcium carbide to produce acetylene gas (\(C_2H_2\)) and calcium hydroxide (\(Ca(OH)_2\)):
\[CaC_2(s) + 2H_2O(l) \rightarrow C_2H_2(g) + Ca(OH)_2(aq)\]

• Outcome: This reaction is exothermic, releasing heat while generating acetylene.
• Applications: Acetylene is widely used for welding and as a chemical feedstock.

Proper handling is essential as acetylene is highly flammable, requiring careful control during production.