Manufacture of sodium tripolyphosphate

Claim 1

THE CONTINUOUS METHOD OF MAKING ALKALI METAL TRIPOLYPHOSPHATES OF SUBSTANTIALLY PURE FORM II WHICH CONSISTS OF MIXING A SOLUTION OF MONO- AND DI-ALKALI METAL ORTHOPHOSPHATE WITH PREVIOUSLY FORMED TRIPOLYPHOSPHATE, PASSING THE MIXTURES AS A STREAM THROUGH A CALCINING ZONE HAVING A CALCINING TEMPERATURE BETWEEN ABOUT 300 AND 450*C. AND A DISCHARGE TEMPERATURE NOT SUBSTANTIALLY ABOVE 140*C., WETTING THE STREAM WITH AN AQUEOUS LIQUID FROM THE CLASS CONSISTING OF WATER AND ORTHOPHOSPHATE SOLUTION AS IT PASSES TO THE CALCINING ZONE, ENDING THE WETTING WHILE THE MIXTURE HAS A CONSISTENCY PERMITTING IT TO TRAVEL READILY IN THE CALCINING ZONE, RECYCLING THE STREAM THROUGH THE WETTING AND CALCINING ZONES UNTIL IT ISSUES FROM THE CALCINING ZONE AS ABOUT 97-98% TRIPOLYPHOSPHATE OF SUBSTANTIALLY PURE FORM II, AND CONTINUOUSLY EXTRACTING A MINOR PROPORTION OF THE FINISHED PRODUCT FROM THE CYCLING STREAM AND REPLACING IT WITH AN EQUIVALENT AMOUNT OF ORTHOPHOSPHATE, THE ORTHOPHOSPHATE BEING ADDED TO THE STREAM AT A PLACE AHEAD OF THE WETTING STEP.