Question

What is the disadvantage of Solvay process?

• A. Higher salt consumption
• B. No co-products to dispose
• C. Use of low-grade brine
• D. Less electric power

Hint:

The Solvay process requires significant salt (NaCl) input, leading to higher salt consumption as a key disadvantage, along with calcium chloride byproduct disposal challenges.

Answer 1

The Correct Option is A

Step 1: Understand the Solvay process.

The Solvay process is a method for producing sodium carbonate (soda ash, Na₂CO₃) from salt (NaCl), ammonia (NH₃), carbon dioxide (CO₂), and limestone (CaCO₃). The key reactions are:

\[ \text{NH}_3 + \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{NH}_4\text{HCO}_3, \] \[ \text{NaCl} + \text{NH}_4\text{HCO}_3 \rightarrow \text{NaHCO}_3 + \text{NH}_4\text{Cl}, \] \[ 2\text{NaHCO}_3 \xrightarrow{\text{heat}} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2. \]

The byproduct calcium chloride (CaCl₂) is produced when ammonia is recovered:

\[ 2\text{NH}_4\text{Cl} + \text{Ca(OH)}_2 \rightarrow 2\text{NH}_3 + \text{CaCl}_2 + 2\text{H}_2\text{O}. \]

Step 2: Analyze the disadvantages of the Solvay process.

Salt consumption: The process requires a large amount of salt (NaCl) as a raw material. For every ton of soda ash produced, approximately 1.5 tons of salt are consumed, which is relatively high compared to alternative processes.

Co-products: The process produces calcium chloride (CaCl₂) as a byproduct, which can be difficult to dispose of or sell, especially in large quantities, creating a waste management challenge.

Brine quality: The Solvay process can use low-grade brine (impure NaCl solution), which is an advantage, not a disadvantage.

Electric power: The Solvay process is not particularly energy-intensive in terms of electricity, as it relies more on chemical reactions and heat (e.g., for calcining limestone). So, “less electric power” is a disadvantage. The primary disadvantage is the higher salt consumption, increasing raw material costs and resource demand.

Step 3: Evaluate the options.

• (1) Higher salt consumption: Correct, as the Solvay process consumes a large amount of salt (NaCl), making it a notable disadvantage in terms of resource usage.
• (2) No co-products to dispose: Incorrect, as the process does produce co-products like calcium chloride (CaCl₂), which can be a disposal challenge.
• (3) Use of low-grade brine: Incorrect, as the ability to use low-grade brine is an advantage, not a disadvantage.
• (4) Less electric power: Incorrect, as the Solvay process is not disadvantaged by low electric power usage; it is more heat-intensive than electricity-intensive.

Step 4: Select the correct answer.

The disadvantage of the Solvay process is higher salt consumption, matching option (1).