Patent GB-791768-A (GB)
Title: Process for preparing fluosilicates
IPC: C01B33/10
Filed: 1955-07-12
Abstract: A dry finely divided mixture of primary amine fluosilicate and silica is prepared by reacting silicon tetrafluoride at least 2/3 mol. of water vapour per mol. of SiF4 with a primary amine vapour at a temperature above the condensation point of water in the gaseous mixture.  Upper temperature limit is 300 DEG  C. and amines may be methylamine, ethylamine, isopropylamine, n-butylamine, aniline, benzylamine, cyclohexylamine, furfurylamine, ethylene diamine, phenylene diamine.  In carrying out the reaction, a tube is divided into two small compartments by glass wool plugs at the inlet end, and the remainder of the tube constitutes the reaction compartment. Three separate lines, ending in jets, pass through the inlet end stopper, and serve to introduce, respectively, air saturated with excess water vapour at 70 DEG  or 75 DEG  C. into the first compartment, silicon tetrafluoride into the second compartment, and air containing excess amine vapour into the reaction compartment. The powder formed may separate in the tube and be removed from the gases by a glass wool plug in the outlet end, or may be separated in a bag filter.  The reaction compartment may be kept at 100-250 DEG  C. for ammonia, or just above the boiling point for liquid amine, e.g. 100-140 DEG  C. for isopropylamine and 123-161 DEG  C. for n-butylamine.  The reaction may be effected without air dilution and with stoichiometric amounts of SiF4 and amine. The off-gases from phosphate rock acidulation containing 0.5-2 per cent SiF4 and sufficient water for the reaction may be used in the process.  The fluosilicate may be separated from the silica by leaching with water or other fluosilicate solvent.ALSO:A dry finely divided mixture of primary amine fluosilicate and silica, or ammonium fluosilicate and silica is prepared by reacting silicon tetrafluoride and at least two-thirds mole. of water vapour per mole. of SiF4 with a primary amine vapour of gaseous ammonia at a temperature above the condensation point of water in the gaseous mixture.  Upper temperature limit is 300 DEG  C. and amines may be methylamine, ethylamine, isopropylamine, n-butylamine, aniline, benzylamine, cyclohexylamine, furfurylamine, ethylene diamine, phenylene diamine. In carrying out the reaction, a tube is divided into two small compartments by glass wool plugs at the inlet end, and the remainder of the tube constitutes the reaction compartment.  Three separate lines, ending in jets, pass through the inlet end stopper, and serve to introduce, respectively, air saturated with excess water vapour at 70 DEG  or 75 DEG  C. into the first compartment, silicon tetrafluoride into the second compartment, and air containing excess amine vapour into the reaction compartment.  The powder formed may separate in the tube and be removed from the gases by a glass wool plug in the outlet end, or may be separated in a bag filter.  The reaction compartment may be kept at 100-250 DEG  C. for ammonia, or just above the boiling point for liquid amine, e.g. 100-140 DEG  C. for isopropylamine and 123-161 DEG  C. for n-butylamine.  The reaction may be effected without air dilution and with stoichiometric amounts of SiF4 and amine or ammonia.  The off-gases from phosphate rock acidulation containing 0.5-2 per cent SiF4 and sufficient water for the reaction may be used in the process.  The fluosilicate may be separated from the silica by leaching with water or other fluosilicate solvent.  The ammonium fluosilicate or the mixture with silica may be treated with conc. H2SO4 to yield pure SiF4.