Process for the production of hydrogen fluoride

Claim 1

THE PROCESS FOR THE PRODUCTION OF HYDROGEN FLUORIDE AND SILICA FROM SILICON TETRAFLUORIDE PREPARED FROM SILICONAND FLUORINE-CONTAINING MATERIAL IN WHICH THE SILICON CONTENT EXPRESSED AS SILICA IS GREATER THAN 3% WHICH COMPRISES THE STEPS OF REACTING THE SILICON TETRAFLUORIDE WITH WATER IN THE VAPOR PHASE TO FORM A GASEOUS SUSPENSION CONSISTING ESSENTIALLY OF HYDROGEN FLUORIDE, UNREACTED SILICON TETRAFLUORIDE AND SILICA, REMOVING THE SILICA FROM SUCH GASES TO OBTAIN A GASEOUS MIXTURE CONSISTING ESSENTIALLY OF HYDROGEN FLUORIDE AND UNREACTED SILICON TETRAFLUORIDE, REACTING THE HYDROGEN FLUORIDE AND SAID UNREACTUM BIFLUORIDE AND SODIUM FLUOSILICATE, HEATING THE SODIUM D SILICON TETRAFLUORIDE WITH SODIUM FLUORIDE TO FORM SODIBIFLUORIDE TO A TEMPERATURE TO DECOMPOSE IT WITHOUT SUBSTANTIAL DECOMPOSITION OF SODIUM FLUOSILICATE TO RECOVER A GAS HAVING A HIGHER CONCENTRATION OF HYDROGEN FLUORIDE THAN SAID GASEOUS MIXTURE, AND HEATING THE SODIUM FLUOSILICATE AT A TEMPERATURE IN EXCESS OF ABOUT 550* C. TO DECOMPOSE IT SELECTIVELY TO RECOVER A GAS HAVING A HIGHER CONCENTRATION OF SILICON TETRAFLUORIDE THAN SAID GASEOUS MIXTURE, AND RETURNING SAID LAST MENTIONED SILICON TETRAFLUORIDE TO SAID VAPOR PHASE WATER TREATING STEP.