The Solvay Process: Process, Products & Environmental Issues Video

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  • 0:04 What is Sodium Carbonate?
  • 0:47 The Solvay Process
  • 5:02 Environmental Issues
  • 6:10 Lesson Summary
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Lesson Transcript
Instructor: Hemnath (Vikash) Seeboo

Taught Science (mainly Chemistry, Physics and Math) at high school level and has a Master's Degree in Education.

The Solvay process is used to make sodium carbonate. This lesson will help you understand the different reactions, conditions, products and the environmental issues that are involved in the manufacturing of sodium carbonate by the Solvay process.

What Is Sodium Carbonate?

Sarah's barbecue party is over and it's time to clean up! Sarah uses a product containing washing soda that effectively removes all the grease and oil that was on the barbecue grill and other utensils.

Washing soda (or soda ash or sodium carbonate), Na 2 CO 3 , is a key component to laundry soaps and many other household products. Sodium carbonate is also used in the paper and wool industries, but the major demand comes from the glass industry.

In fact, the world demand for sodium carbonate stands at over 50 million tons per year. How do we keep up with this huge demand? Well, it can be made in a variety of ways, but for economic reasons, most of it is now manufactured by an industrial process known as the Solvay process.

The Solvay Process

The Solvay process, also known as the ammonia-soda process, was developed in 1861 by the Belgian industrial chemist, Ernest Solvay.

Ernest Solvay

The materials used in the Solvay process are easily available and inexpensive. They include:

  1. Brine, or sodium chloride solution. It provides sodium ions in the making of the sodium carbonate. Brine can be easily sourced from both inland and the ocean.
  2. Limestone, or calcium carbonate. It provides carbonate ions in the production of the sodium carbonate. Limestone is readily available from mining.
  3. Ammonia is made industrially by the Haber's process. Ammonia is expensive, but as you will see, it's recycled in the process.

Making sodium carbonate by the Solvay process involve many reactions, but the main parts of the process include purification of the brine, formation of the sodium hydrogen carbonate and sodium carbonate, followed by ammonia recovery.

Let's go into the details of these main steps.

Stage 1: Brine Purification

First the brine is subjected to evaporation to increase the salt concentration and eventually form a saturated solution. Precipitation, for example using sodium hydroxide, is also carried out in order to remove any impurities like magnesium, iron, and calcium salts that may be present.

The saturated brine solution is then filtered and passed through an ammonia tower. The ammonia gas is absorbed in the concentrated brine to produce aqueous sodium chloride and aqueous ammonia. This ammoniation process is exothermic, so energy is released as heat. The ammonia tower eventually needs to be cooled.

Stage 2: Formation of Sodium Hydrogen Carbonate

Carbon dioxide is then bubbled through the ammoniated brine solution in a tower known as the carbonating or Solvay tower.

The carbon dioxide is produced in a lime kiln where limestone, CaCO 3 is calcinated or thermally decomposed at 900°C according to the equation:

CaCO3 ---> CO2 (g) + CaO(s)

The carbon dioxide dissolves in water to produce a carbonic acid, H2 CO3, which is a weak acid that dissociates to produce H+ ions.

CO2 (g) + H2 O(l) ---> H2 CO3 <------> HCO3 - (aq) + H+ (aq)

While the ammonia in the brine reacts with H+ to form ammonium ions (equation 1), the Na+ in the brine reacts with the HCO3 - to form sodium hydrogen carbonate (equation 2), which precipitates out.

  • Equation 1 : NH3 (aq) + H+ (aq) ----> NH4 + (aq)
  • Equation 2: HCO3 - (aq) + Na+ (aq) ---> NaHCO 3 (s)

The overall reaction in the carbonating tower that leads to the formation of sodium hydrogen carbonate is given by:

NH3 (aq) + CO2 (g) + NaCl(aq) + H2 O (l) ---> NaHCO3 (s) + NH4 Cl (aq)

Stage 3: Formation of Sodium Carbonate

Suspended sodium hydrogen carbonate is then removed from the carbonating tower and heated at 300o C to produce sodium carbonate.

2NaHCO3 (s) ---> Na2 CO3 (s) + CO2 (g) + H 2 O (g)

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