Process of producing hydrogen fluoride in a two-stage procedure and effecting a rapid evolution and an effective recovery of the hydrogen fluoride by sweeping the second stage with a condensible inert gas

Claim 1

IN A PROCESS OF PRODUCING HYDROGEN FLUORIDE AS A VAPOR FROM FLUOSILICIC ACID-CONTAINING SOLUTIONS WITH A TWO-STAGE PROCEDURE, THE IMPROVEMENT WHICH COMPRISES SUBJECTING A FLUOSILICIC ACID-CONTAINING SOLUTION SUBSTANTIALLY FREE FROM SILICA TO THE ACTION OF HEATED CONCENTRATED SULFURIC ACID IN QUANTITY SUFFICIENT TO CONTROL THE TERMINAL CONCENTRATION BELOW ABOUT 78% H2SO4 IN A CLOSED REACTOR IN THE FIRST STAGE UNDER CONDITIONS OF TEMPERATURE AND RETENTION TIME SO THAT SUBSTANTIALLY ALL OF THE SILICON TETRAFLUORIDE IS EVOLVED IN THE FIRST STAGE AS A SUBSTANTIALLY DRY VAPOR WHILE MOST OF THE HYDROGEN FLUORIDE IS RETAINED IN THE REMAINING DILUTED WEAKER SULFURIC ACID SOLUTION, WITHDRAWING SAID VAPOR CONTAINING SILICON TETRAFLUORIDE FROM SAID CLOSED REACTOR IN SAID FIRST STAGE, REMOVING SAID DILUTED WEAKER SULFURIC ACID SOLUTION CONTAINING HYDROGEN FLUORIDE FROM SAID CLOSED REACTOR IN