Process of producing hydrogen fluoride in a two-stage procedure and effecting evolution of the hydrogen fluoride in the second stage by the conjoint action of the addition of hot concentrated sulfuric acid and the application of vacuum

Claim 1

IN A PROCESS OF PRODUCING HYDROGEN FLUORIDE AS DRY VAPOR FROM FLUOSILICIC ACID-CONTAINING SOLUTIONS IN A TWOSTAGE PROCEDURE, THE IMPROVEMENT WHICH COMPRISES SUBJECTING A FLUOSILICIC ACID-CONTAINING SOLUTION SUBSTANTIALLY DEVOID OF FREE SILICA TO THE ACTION OF HEATED CONCENTRATED SULFURIC ACID IN A CLOSED REACTOR IN THE FIRST STAGE UNDER CONDITIONS OF CONCENTRATION OF SULFURIC ACID, TEMPERATURE, AND RETENTION TIME SO THAT SUBSTANTIALLY ALL OF THE SILICON TETRAFLUORIDE IS EVOLVED IN THE FIRST STAGE AS SUBSTANTIALLY DRY VAPOR WHILE MOST OF THE HYDROGEN FLUORIDE IS RETAINED IN THE RESULTANT DILUTED WEAKER SULFURIC ACID SOLUTION, WITHDRAWING SAID VAPOR CONTAINING SILICON TETRAFLUORIDE FROM SAID CLOSED REACTOR IN SAID FIRST STAGE, REMOVING SAID RESULTANT DILUTED WEAKER SULFURIC ACID SOLUTION CONTAINING HYDROGEN FLUORIDE FROM SAID CLOSED REACTOR IN THE FIRST STAGE, CONDUCTING SAID REMOVED SOLUTION TO A CLOSED SECOND REACTOR HAVING A GAS SPACE ABOVE THE TOP OF THE SOLUTION IN A SECOND STAGE, INTRODUCING INTO SAID CLOSED REACTOR HOT CONCENTRATED SULFURIC ACID OF SUFFICIENTLY HIGH STRENGTH TO MAINTAIN A TERMINAL CONCENTRATION EFFECTIVE TO CAUSE LIBERATION OF HYDROGEN FLUORIDE AS SUBSTANTIALLY DRY VAPOR MAINTAINING THE TOP OF SAID SECOND REACTOR IN THE SECOND STAGE UNDER THE CONSTANT ACTION OF A VACUUM TO EFFECT LIBERATION OF SUBSTANTIALLY ALL OF THE HYDROGEN FLUORIDE FROM SAID SOLUTION, AND CONDENSING SAID LIBERATED HYDROGEN FLUORIDE WITHDRAWN FROM SAID SECOND REACTOR IN SAID SECOND STAGE BY MEANS OF SAID VACUUM.