Patent GB-800164-A (GB)
Title: Method and apparatus for treating products resulting from the action of nitric acid and other nitric mixtures on organic substances
IPC: C01B17/94
Filed: 1956-07-10
Abstract: Mixtures obtained by the nitration or oxidation of organic substances by nitric acid, alone or together with sulphuric acid or phosphoric acid, are treated with a solvent, such as chloroform, which dissolves the organic compounds and some of the nitric acid but is only slightly miscible with water, sulphuric acid and phosphoric acid whereby two liquid phases are formed; these two phases are decanted and the solvent phase is distilled in order to separate nitric acid and solvent from the organic compounds, and the other phase is also distilled for recovery of nitric acid and sulphuric acid or phosphoric acid.  In an example, a mixture obtained by the oxidation of methyl stearate by <PICT:0800164/III/1> means of nitric acid in the presence of sulphuric acid, comprising nitric acid (153 parts by weight), sulphuric acid (15 parts), water (25 parts) and organic substances (21 parts), is passed through pipe 1 into extraction column 2, where it is mixed with a large excess of chloroform introduced through pipe 3.  The phase comprising water, sulphuric acid and nitric acid is withdrawn from column 2 through pipe 5; and the phase comprising chloroform, nitric acid and the organic products passes out through pipe 6 into reservoir 7.  This chloroform phase flows from the reservoir into the middle section of distilling column 9 which is heated at the base to a temperature of about 70 DEG  C., while the upper part of the column is maintained at a temperature of about 48 DEG  C.  The organic products, dissolved in a small quantity of chloroform, are withdrawn from column 9 through pipe 11. Chloroform vapour is withdrawn through pipe 12 and liquefied in a condenser (not shown); this chloroform is returned to reservoir 4. Vapours of the nitric acid-chloroform azeotrope leave the head of column 9, and are introduced through pipe 13 into washing-column 14. Sulphuric acid (containing a low concentration of HNO3) at a temperature greater than 60 DEG  C. is introduced into the upper part of column 14 through pipe 16.  The sulphuric acid dissolves the nitric acid out of the azeotrope-vapours, so that chloroform vapours leave the head of the column through pipe 17.  These chloroform vapours are condensed, and the resulting liquid is passed to reservoir 7.  The mixture of acids withdrawn from the base of column 14 is distilled in column 19 which may, if desired, be operated under reduced pressure.  Pure nitric acid is obtained at the head of column 19; and sulphuric acid together with a small amount of nitric acid is obtained at the base.  This sulphuric acid is returned to reservoir 15.  The aqueous phase withdrawn from extraction column 2 through pipe 5 is distilled for recovery of nitric acid in the form of its azeotrope with water. In a modification, the sulphuric acidnitric acid mixture withdrawn from the base of column 14 is distilled using two columns, the distillation in the first column being carried out in the presence of some of the vapours of chloroform and nitric acid taken off from pipe 13.  In this embodiment, the quantity of sulphuric acid required in column 14 is reduced.