Process for preparing alkali metal orthophosphates and ammonia

A process for preparing ammonia and a substantially ammonia-free solution of sodium orthophosphate comprising:

• a. introducing aqueous monoammonium phosphate into a substantially vertical first column provided with vapor-liquid contact means,
• b. introducing aqueous sodium carbonate into said first column at a level below that at which said monoammonium phosphate is introduced at a rate sufficient to maintain therein an Na/P molar ratio in the range of 0.5-1.5,
• c. permitting said monoammonium phosphate to flow downwardly in said column into continuous co-current contact and react with said sodium carbonate at a temperature of 125.degree.- 250.degree.F.,
• d. removing substantially ammonia-free carbon dioxide overhead and recovering a bottoms product comprising an aqueous solution of sodium ammonium phosphate having a reduced carbon dioxide content,
• e. introducing said bottoms product into a second column provided with vapor-liquid contact means,
• f. introducing aqueous sodium hydroxide into said second column at the same level or at a level above that at which the bottoms product of said first column is introduced at a rate sufficient to maintain in said second column a reaction mixture having a selected Na/P molar ratio of in the range of 1-2,
• g. permitting said sodium hydroxide to flow downwardly in continuous co-current contact with the bottoms product of said first column and to react with said sodium ammonium phosphate at elevated temperature and at a pressure in the range of 130-500 p.s.i.g.,
• h. recovering an overhead product comprising said ammonia and recovering from the bottom of said column a substantially ammonia-free solution of sodium orthophosphate having the selected Na/P molar ratio.

A process for preparing anhydrous ammonia and a substantially ammonia-free solution of sodium orthophosphate comprising:

• a. introducing aqueous monoammonium phosphate into a substantially vertical first column provided with vapor-liquid contact means,
• b. introducing aqueous sodium carbonate into said first column at a level below that at which said monoammonium phosphate is introduced at a rate sufficient to maintain in said column a reaction mixture having a selected Na/P molar ratio of 0.6-1.2,
• c. permitting said monoammonium phosphate to flow downwardly in said chamber in continuous co-current contact and react with said sodium carbonate at a temperature of 125.degree.-250.degree.F.,
• d. removing substantially ammonia-free carbon dioxide overhead and recovering a bottoms product comprising an aqueous solution of sodium ammonium phosphate having a reduced carbon dioxide content,
• e. introducing the solution of sodium ammonium phosphate from said first column into a second column provided with vapor-liquid contact means and stripping ammonia therefrom at elevated temperature and at a pressure in the range of 130-500 p.s.i.g while permitting said solution to flow downwardly in said second column,
• f. recovering an overhead product comprising said ammonia and separately recovering a bottoms producg comprising a substantially ammonia-free solution of sodium orthophosphate having an Na/P molar ratio in the range of 1-1.3.