Mannheim process

The Mannheim process is an industrial process for the production of hydrogen chloride and sodium sulfate.

History

Swedish chemist Carl Wilhelm Scheele discovered in 1772 that salt brine heated with litharge yielded small amounts of caustic soda. Over the following years, several others modified this approach. It was observed that mixing sodium sulfate (salt cake) with iron filings and coal produced sodium carbonate (known as soda ash). Another approach involved mixing salt or salt cake with calcium hydroxide (slaked lime). These methods produced small amounts of poor quality soda ash, unsuitable for large-scale output.^[1]

In the 1780s and 1790s, Nicolas Leblanc invented and perfected the Leblanc process to produce soda ash in an industrial scale, using the salt cake yielded by the Mannheim process as an intermediate. Factories using the Leblanc process generated heavy emissions of hydrogen chloride, damaging the local environment when it was vented to the atmosphere. The British Parliament passed the 1863 Alkali Act to regulate this kind of emissions, recognized as the first effective air pollution legislation.^[2]

In 1861, chemist and industrialist Ernest Solvay developed the Solvay process, a more direct method to obtain soda ash. This soon rendered Leblanc's invention obsolete for economic and environmental reasons.

Chemistry

The reactants in the chemical reaction are sulfuric acid (H₂SO₄) and sodium chloride (NaCl, table salt). The reaction yields sodium sulfate (Na₂SO₄) and gaseous hydrogen chloride (HCl).

2 NaCl + H₂SO₄ → Na₂SO₄ + 2 HCl ^[3]

References

1. ↑ Kiefer, David M. (January 2002). "It was all about alkali". Today's Chemist at Work. ACS Publications. 11: 45–46, 49. ISSN 1532-4494. Retrieved 2016-01-22. 
2. ↑ Benn, Doug. "Air Pollution: Solutions and Prospects". Retrieved 2016-01-22. 
3. ↑ Riegel, Emil Raymond (1974). Kent, James Albert, ed. Riegel's Handbook of Industrial Chemistry (7th ed.). New York: Van Nostrand Reinhold. p. 132. ISBN 9780442243470.