The key difference between Leblanc and Solvay process is that the starting materials in the Solvay process are more cost-effective than the starting materials in the Leblanc process.
Leblanc process and Solvay process are important in chemical synthesis of sodium carbonate. Sodium carbonate is an inorganic compound having the chemical formula Na2CO3. The starting materials for the Leblanc process are sodium chloride, sulfuric acid, coal, and calcium carbonate. The starting materials for the Solvay process are salt brine and limestone.
CONTENTS
1. Overview and Key Difference
2. What is Leblanc Process
3. What is Solvay Process
4. Side by Side Comparison – Leblanc vs Solvay Process in Tabular Form
5. Summary
What is Leblanc Process?
Leblanc process is an industrial process that is important in producing sodium carbonate using sodium chloride, sulfuric acid, coal, and calcium carbonate. This process comes under the sector of Chlor-alkali industry. Nicolas Leblanc invented this process in 1791. Thereafter, some other scientists including William Losh, James Muspratt, and Charles Tennant further developed this process.
Figure 01: Leblanc Process
There are two steps of the Leblanc process: the production of sodium sulfate from sodium chloride and the reaction of sodium sulfate with coal and calcium carbonate producing sodium carbonate. However, this process gradually became obsolete after the introduction of the Solvay process.
The first step of the Leblanc process is the reaction between sodium chloride and sulfuric acid, which produces sodium sulfate and hydrogen chloride. The second step involves the reaction between a mixture of the salt cake and crushed limestone that is reduced by heating with coal. This second step occurs in two stages; first is the carbothermic reaction in which the coal reduces sulfate to sulfide while the second stage is the reaction that produces sodium carbonate and calcium sulfide. The product mixture that comes from the second stage is named black ash. We can extract soda ash or sodium carbonate from this black ash in the presence of water. This extraction is named lixiviation; here, the water and calcium sulfide is evaporated, yielding sodium carbonate in solid state.
What is Solvay Process?
Solvay process is an industrial process that is important in the production of sodium carbonate using salt brine and limestone. It is the major industrial process used for the production of sodium carbonate. This method is also known as the ammonia-soda process. It was developed by Ernest Solvay in 1860. The starting materials for this process are readily available and cheap as well. Due to this reason, the Solvay process dominates over the Leblanc process.
Figure 02: Solvay Process
Brine is a source of sodium chloride and limestone is a source of calcium carbonate. There are four basic reactions that take place during the Solvay process: the first step includes the passing of carbon dioxide through a concentrated aqueous solution of sodium chloride (brine) and ammonia. Here, sodium bicarbonate precipitates out of the solution. Secondly, sodium bicarbonate is filtered out from the solution and the solution is then treated with quicklime making a strongly basic solution. As the third step, the sodium bicarbonate is then converted into the final product via calcination. Finally, carbon dioxide produced from the third step is recovered for reuse.
What is the Difference Between Leblanc and Solvay Process?
Leblanc process and Solvay process are important in producing sodium carbonate. Leblanc process involves producing sodium carbonate using sodium chloride, sulfuric acid, coal, and calcium carbonate while Solvay process involves the production of sodium carbonate using salt brine and limestone. The key difference between Leblanc and Solvay process is that the starting materials in the Solvay process are more cost-effective than the starting materials in the Leblanc process.
Below infographic shows more details of the difference between Leblanc and Solvay process.
Summary – Leblanc vs Solvay Process
Leblanc process and Solvay process are important in producing sodium carbonate. The key difference between Leblanc and Solvay process is that the starting materials in the Solvay process are more cost-effective than the starting materials in the Leblanc process.
Image Courtesy:
1. “Leblanc process reaction scheme” By Sponk (talk) (Vectorization and coloring) – Own work, based on the raster graphic Soda nach Leblanc.png created by Qniemiec (CC BY-SA 3.0) via Commons Wikimedia
2. “Solvay Process” By Eric A. Schiff, 2006. (CC BY-SA 2.5) via Commons Wikimedia