Patent GB-875899-A (GB)
Title: Recovery and purification of boron trichloride
Inventor: DANCE ELDRED LEROY
IPC: C01B35/06
Filed: 1959-04-24
Abstract: <PICT:0875899/III/1> Boron trichloride is recovered from a hot gaseous effluent containing it together with entrained solid particles and non-condensible gases resulting from reaction of an oxygenated boron compound with carbon and chlorine at a temperature above 600 DEG C. by contacting the effluent with an inert liquid having a boiling point of 70-200 DEG C. which is a solvent for boron trichloride, in an amount sufficient to vaporize substantially all of the inert liquid, cooling the resulting gaseous and vaporous effluent, to condense the major portion of the inert liquid which is separated and returned as reflux to be contacted with more hot gaseous effluent, contacting the uncondensed gaseous and vaporous effluent with an additional amount of cooled inert liquid to absorb and condense substantially all of the boron trichloride, separating the uncondensed gases from the resulting solution and separating boron trichloride from the inert liquid.  Boron trichloride-containing reaction gases produced by reaction of say boric oxide, carbon and chlorine at 800 DEG C. are introduced through line 10 into quench tower 1 where they are intimately contacted with an inert liquid, e.g. perchloroethylene, chlorobenzene, tin, titanium or carbon tetrachloride preferably having a boiling point of 100-120 DEG C., in sufficient quantity to vaporize substantially all of the inert liquid introduced, the remaining uncondensed portion being just sufficient to wash the entrained solids from the gases and to maintain them as a slurry in the bottom of the tower.  Periodically the slurry is removed through valve 13 and line 12 to screw still 11 where it is heated to remove the inert liquid, the vapour of which is passed off into line 21 the residual solids being removed through 17. The stream of gaseous and vaporous effluent leaving quench tower 1 is mixed with inert liquid vapour from line 21 and the admixture cooled in water condenser 22 the resultant condensate being separated in separator 26 and recycled to quench tower 1 through lines 29 and 30. Remaining uncondensed gases and vapours pass to cooler 27 through line 28 and are cooled further to about 10 DEG C. the condensate being removed in separator 31 and passed by line 36 to the inlet of pump 34.  Residual gases containing mainly boron p  trichloride pass through line 33 to the bottom of absorber 2 in which they are contacted with inert liquid cooled to below -15 DEG C., say -20 DEG C., which enters through line 38.  Boron trichloride-containing liquid is pumped by pump 34, through line 40 and heats exchanger 41 to stripping column 3 operated under pressure, e.g. 25 p.s.i.g., and connected to reboiler 46 with heater 47.  Boron trichloride is vaporized and passes through line 48, reflux 42, reflux accumulator 43 to pump 44 which delivers it half to line 52 and storage and half to line 51 for return to the column.  Inert liquid substantially free from boron trichloride is removed as bottoms from the column through line 56 and pump 54 and is returned through heat exchanger 41 to storage tank 57.  Inert liquid from tank 57 passes to absorption column 2 through line 61, pump 62 and coolers 64 and 65 and line 37 and through lines 63, 66 and 30 to quench tower 1.  Reference is made to a system as described above without cooler 27 and separator 31 and to the use of an absorption column modified to act also as a stripping column with a reboiler for use when the reaction gases contain a large proportion of volatile contaminants, e.g. chlorine.