Leblanc process

The Leblanc process is a historic process for the extraction of soda . It was developed by Nicolas Leblanc in 1791 .

Soda production according to Leblanc as a chemical step process ( Educts , Intermediate products , Products )

First of all, technical sodium chloride is treated with hot sulfuric acid , hydrogen chloride gas escapes and sodium sulphate remains as a "salt cake":

${\displaystyle \mathrm {2~NaCl+H_{2}SO_{4}\rightarrow Na_{2}SO_{4}+2~HCl} }$

Cylinder furnace for the large-scale implementation of the Leblanc process in the second half of the 19th century.

This reaction had already been discovered by Johann Rudolph Glauber around 1655 , whereas Leblanc's own contribution was the subsequent next step, in which the “salt cake” is burned mixed with lime and coal. The coal is oxidized to carbon dioxide and the sulfate is reduced to sulfide . The remaining “black ash” contains soda and calcium sulfide .

${\displaystyle {\begin{aligned}\mathrm {Na_{2}SO_{4}} +2\;\mathrm {C} &\rightarrow \mathrm {Na_{2}S} +2\;\mathrm {CO_{2}} \\\mathrm {Na_{2}S} +\mathrm {CaCO_{3}} &\rightarrow \mathrm {Na_{2}CO_{3}} +\mathrm {CaS} \\\hline \mathrm {Na_{2}SO_{4}} +\mathrm {CaCO_{3}} +2\;\mathrm {C} &\rightarrow \mathrm {Na_{2}CO_{3}} +\mathrm {CaS} +2\;\mathrm {CO_{2}} \end{aligned}}}$

In contrast to calcium sulphide, which, like the lime used, is insoluble in water, the water-soluble soda can easily be separated from the other components by washing and the water itself can also be removed again by boiling.

The Leblanc process was initially very harmful to the environment due to the escaping hydrogen chloride gas, and the calcium sulfide dumped on heaps also released toxic hydrogen sulfide when it was weathered .

${\displaystyle \mathrm {\ CaS+CO_{2}+H_{2}O\rightarrow CaCO_{3}+H_{2}S} }$

After the Solvay process for soda production had gained the upper hand over the Leblanc process, the initially released hydrogen chloride gas and the hydrochloric acid obtained from it became the main products of the Leblanc process. It was used to produce chlorine and chlorinated lime on a large scale before these products were also used in other ways, e.g. B. by chloralkali electrolysis began to win.

With today's technical possibilities, however, engineers see a new perspective in the Leblanc process in order to establish an inexpensive soda production that is more environmentally friendly than the Solvay process in countries with significant Na ₂ SO ₄ deposits. The process of carburization is the same, but the CO _{2 is} kept in solution under pressure and then precipitates as NaHCO ₃ (as in the Solvay process). The calcium sulfide is then separated off and oxidized to calcium sulfate ( gypsum ), which is a sought-after raw material in the affected (mostly developing) countries.

literature

• Christian Thieme: Sodium Carbonates . In: Ullmann's Encyclopedia of Industrial Chemistry . 6th edition. Wiley-VCH, Weinheim 2002, ISBN 978-3-527-30385-4 .

Individual evidence

1. ^ Hermann Ost : Textbook of Technical Chemistry , published by Robert Oppenheim, Berlin 1890.