Industrial chemistry: Bulk Inorganic Chemicals

Production

Table 1 depicts a selection of the main inorganic chemicals which are produced in annual quantities of several millions of tonnes. Substances that are made in comparable amounts which are not listed include fuels and organic chemicals created from petroleum, and construction metals like iron. In several cases the basic chemical reactions employed to generate the compounds in Table 1 are simple, even though catalysts are frequently needed.  The design of processes to create the most economical use of raw materials and energy, and to minimize polluting wastes, is, though, not simple. The raw materials required involve air (for N₂ and O₂), sulfur (mined like native S or acquires from processing sulfide minerals), natural gas and oil (is a source of energy and H₂), NaCl, and the calcium carbonate and phosphate. It is interesting to refer some facts of the chlor-alkali industry, one of the very old sectors of the chemical industry that links the manufacture of Cl₂, NaOH and Na₂CO₃. The source material, NaCl, is employed in greater amounts than any other raw material in the complete inorganic chemical industry.

Cl₂ is produced through electrolysis of NaCl. A molten NaCl-CaCl₂ mixture provides metallic Na and Ca at another electrode; these metals are employed industrially; for instance, like reducing agents for production of other electropositive metals like Ti. Very much greater quantities of NaCl are electrolyzed within aqueous solution to provide NaOH, with H₂ like a byproduct. Cells along with a mercury electrode provide Na-Hg amalgam like the initial product that is then reacted with water; modern diaphragm cells providing aqueous NaOH directly are cheaper to run and prevent the use of toxic mercury.

For economic basis the amount of NaOH produced relies on the demand for Cl₂. Though, NaOH and Na₂CO₃ are interchangeable in several uses (example. glass and paper manufacture), and so any short-fall in NaOH production could be made up through the carbonate. A few Na₂CO₃ is obtained from natural deposits but it is also prepared synthetically through the ammonia-soda or Solvay process. The entire reaction, 

2NACL + CaCO3 → CaCI2 + Na2CO3

is thermodynamically not favourable but can be achieved in various steps:

1.      NaCI + NH₃ + H₂O + CO₂ → NH⁺₄ (aq) + CI^- (aq) + NaHCO₃(s)

2.      2NaHCO₃(s)→Na₂CO₃(S)+ CO₂(g)+H₂O(g)

3.      CaCO₃(s)→CaO(s) + CO₂(g)

4.      CaO(s)+2NH₄⁺ (aq) + 2CI^-(aq)→ Ca²⁺(aq) +2CI^-(aq) + 2NH₃(g)+H₂O

NH₃ and CO₂ are recycled. The equilibrium is shifted in favor of the results through providing heat in the endothermic stages (ii) and (iii). The complete energy that is needed comes from burning coke, mixed with CaCO₃ in stage (iii), and a few heat is also recycled from the exothermic steps (i) and (iv).