Question

Discuss the various reactions that occur in the Solvay process.

Answer 1

In Solvay process, also known as ammonia soda process, carbon dioxide is passed through a brine solution (containing about 28 % NaCl) which is saturated with ammonia to form sodium carbonate.
$2N{H}_3+H_{2}O+C{O}_2\to (N{H}_4{)}_{2}C{O}_3$
$(N{H}_4{)}_{2}C{O}_3+H_{2}O+C{O}_2\to 2N{H}_{4}HC{O}_3$
$N{H}_{4}HC{O}_3+NaCl\to NaHC{O}_3\downarrow +N{H}_{4}Cl$
The precipitate of sodium bicarbonate is filtered, dried and ignited to form sodium carbonate.
$2NaHC{O}_3\stackrel{heat}{\to }N{a}_{2}C{O}_3+C{O}_2+H_{2}O$
The carbon dioxide required for the reaction can be obtained by heating limestone (calcium carbonate) to 1300 K in a lime klin. Lime dissolves in water to form calcium hydroxide which is then transferred to the ammonia recovery tower.
$CaC{O}_3\stackrel{heat}{\to }CaO+C{O}_2$
$CaO+H_{2}O\to Ca(OH{)}_2$
Ammonia required for the process can be prepared by heating ammonium chloride with calcium hydroxide.
$2N{H}_{4}Cl+Ca(OH{)}_{2}2N{H}_3+CaC{l}_2+H_{2}O$
Hence, the only byproduct of the reaction is calcium chloride.