SE311888

B10 and B11 are separated by an exchange reaction between the vapour of a boric ester and a solution of a metal borate in a liquidvapour contact column, the boric ester flowing countercurrent to the solution of metal borate. The preferred boric esters are ethyl and methyl borate and the preferred metal borate is an alkali metal or alkaline earth metal, e.g. potassium or calcium borate which may be dissolved in a water alcohol mixture. As shown, in Fig. 2, the exchange may be achieved by the countercurrent contact of the vapour and liquid in column 2, the vapours of boric ester emerging at the top of the column to be condensed in vessel 3. The condensate produced is continuously hydrolysed with an aqueous alcoholic solution of an alkali, e.g. NaOH supplied from vessel 6 via pump 9 and the product of hydrolysis returned to the column. If desired, part of the product may be withdrawn through tap 23. The alkali metal or alkaline earth metal borate in alcohol solution received in flask 1 at the base of the column, maintained under continuous reflux, is acidified from vessel 7 by a continuous supply of phosphoric acid which liberates the boric acid to form, almost immediately, a fresh supply of ester for the exchange process. Part of the contents of the flask 1 may be withdrawn, when desired, through cooler 21 into vessel 15 where agitation with magnetic stirrer 17 and decantation lead to the precipitation in vessel 16 of unwanted sodium phosphate 18. The supernatant liquor is returned by pump 19 through heaters 21 to the flask. Other methods of removing the sodium phosphate may be used. Any required product which is said to be methyl borate, may be withdrawn through tap 24. The raw feed liquor which may comprise natural boric acid in methyl alcohol is introduced through pipe 22 into the middle of the column.