Patent GB-856987-A (GB)
Title: Improvements in or relating to the manufacture of boron trihalides other than boron trifluoride
IPC: C01B35/06
Filed: 1958-08-14
Abstract: <PICT:0856987/III/1> Boron trihalides other than boron trifluoride prepared by interaction, in a reaction zone, at elevated temperature, of a halogen and a mixture of boric oxide, boric acid or a borate of an alkali or alkaline earth metal with carbon, are removed from the reaction zone as a gaseous mixture comprising reaction products and volatilized boric oxide, and contacted with an inert solid in granular or powdered form or in a mixture of granular and powdered forms upon which the volatilized boric oxide is deposited, the pure boron trihalide being isolated from the residual gases.  A mixture of carbon and boric oxide or an alkali or alkaline earth metal borate containing a carbon to boric oxide molar ratio of from 1 to 10 and typically containing a 4-8 total excess of carbon over the stoichiometric amount required, is thoroughly mixed at 18 and preferably preheated to 700-1000 DEG C. to remove all traces of water and is then passed through 19 and lock 20 into reaction vessel 10 which comprises a vertical carbon tube mounted inside a ceramic tube 14 within steel shell 15.  The mixture is heated electrically by 34 to 600-1200 DEG C. depending upon the preparation. Halogen is supplied at 26 at a rate which ensures its complete consumption well within the reaction chamber and boron trihalide together with volatilized boric oxide is removed at 28.  In place of the finely divided boron compound/carbon charge the mixture of boron compound and carbon may take the form of pellets of 1/16 -\ba1/2 inch diameter prepared by treating the carbon and boron compound preferably at a temperature above the fusion temperature of the boron compound. Alternatively, pellets comprising either a core of a mixture of boron compound and carbon coated with a layer of carbon, or a carbon core coated with a layer of boron compound/carbon mixture may be employed. In the case of the pellets having carbon cores the overall weight ratio of carbon to boric oxide may be 3:1 to 10:1.  Charges comprising coated pellets together with added quantities of finely divided boron compound/carbon mixture in proportion insufficient to fill all the interstices between the pellets are also referred to. Reaction gases containing volatilized boric oxide pass through 28 which may be heated to prevent deposition of boric oxide, into chamber 50 provided with cooling means 52.  The gaseous mixture passes up through the chamber which is either packed with dehydrated carbon or with the carbon containing residue removed from reactor 10 which is conveyed to chamber 50 by delivery means 42 and 64.  The volatilized boric oxide deposits on the carbon packing and the purified gaseous mixture containing the boron trihalides and other gaseous reaction products e.g. CO and CO2 exits through 54 to a separating device 70 where the boron trihalide is isolated.  The entire preparation and isolation may be carried out in a batch process but preferably is continuous, the boron compound/carbon charge being caused to move down through reactor 10 against the rising stream of halogen the residual carbon containing packing being continuously removed and transported to chamber 50 where it is caused to move down through the chamber against a rising stream of gaseous mixture entering through 28. Carbon packing having boric oxide deposited thereon is removed from the bottom of the chamber and recycled to the start of the process for admixture with fresh boron compound/carbon charge either prior to the mixing and preheating in 18 by delivery means 70b or preferably direct to the reactor by means 70a.  As an alternative method of operation spent carbon from reactor 10 is recycled direct via 70a or 70b and part or all of the fresh charge is supplied either from 17 or 19 direct to chamber 50. Specification 855,024 is referred to.