Preparation of Ammonium Sulphate : Popular Nitrogent Fertilizer



Ammonium Sulphate (NH4)2SO4

The nitrogen content in ammonium Sulphate is about 21%. Ammonium sulphate is obtained by the double displacement reaction of ammonium carbonate and calcium sulphate.

(NH4)2CO3 + CaSO4        →                                     (NH4)2SO4 + CaCO3

Calcium carbonate being insoluble, settles down and can be removed easily Calcium sulphate is used in the form of gypsum. Whereas ammonium carbonate is obtained by passing CO2 gas through NH40H solution.

CO2 + 2NH40H        →                       (NH4)2CO3 + H20

Carbon dioxide gas should be passed in calculated quantity because excess of carbon dioxide may result in the formation of ammonium bicarbonate.

NH4OH + CO2  →    NH4HCO3

This ammonium bicarbonate then reacts with calcium sulphate and forms calcium bicarbonate. Which being soluble in water, is also crystallized along with ammonium sulphate thus making it impure.

2NH4HCO3 + CaSO4  →   (NH4)2O4 + Ca(HCO3)2

PROCESS OF MANUFACTURE

The materials used for the manufacture of ammonium sulphate arc:

i)    Gypsum (CaSO4.2H2O)

ii)  Coal, which serves as a source of hydrogen and carbon.

iii) Air, which serves as a source of nitrogen.

iv) Iron free water.

The nitrogenous fraction obtained during the destructive distillation of :oal, is used along with nitrogen of the air, for the preparation of ammonia. This unmonia gas is then passed to the bottom of a tower from the top of which water s sprayed, to get ammonium hydroxide solution. Carbon dioxide gas obtained by tuning coke is passed through the ammonium hydroxide solution in calculated quantity to get ammonium carbonate. This solution of ammonium carbonate is hen reacted with calcium sulphate to form ammonium sulphate and calcium carbonate. The ammonium sulphate solution is then sent to a tank where crystals of  ammonium sulphate are formed by evaporation. These crystals are dried and packed in bags.

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