Ammonium bicarbonate (also known as ammonium hydrogen carbonate) is a mildly basic inorganic compound with the formula (NH4)HCO3. It is a colourless, crystalline solid with the odour of ammonia. It is soluble in water, but insoluble in most organic solvents including ethanol, carbon disulphide and concentrated ammonia. It is volatile in solution and degrades readily into ammonia and carbon dioxide in an endothermic reaction. This property makes it useful as a leavening agent in baked products such as cakes and biscuits, and as a buffer in applications such as lyophilization and matrix assisted laser desorption. It is also a commonly used reagent in many industrial and research procedures. Ammonium bicarbonate is produced by passing carbon dioxide gas countercurrently through a descending stream of aqueous ammonia (ammonium hydroxide), usually in either a packed tower or an absorption column. Carbon dioxide gets absorbed into the liquid stream of ammonia and water, and reacts to form ammonium bicarbonate as below:CO2 + NH3 + H2O → (NH4)HCO3 .
Since the reaction is exothermic and ammonium bicarbonate is unstable, the system, especially the lower portion of the tower, is generally maintained at a lower temperature.Once the solution is sufficiently saturated, the ammonium bicarbonate crystallizes as a white solid. These crystals are separated from the solution by precipitation, followed by centrifugal separation and washing. The crystals are then dried using air at 50°C.Upon refining, the crystals are dissolved in water then recrystallized by adding ethanol.