| 摘要 |
1463742 Phosphoric acid purification HOECHST AG 14 June 1974 [4 July 1973] 26472/74 Heading C1A Impure aqueous phosphoric acid is purified by mixing with an organic solvent in which it is soluble and which is immiscible or partially miscible with water, in a ratio by volume in the range 1 : 0À3 to 1 : 30; the solvent has a boiling point higher than that of water if no water/ solvent azeotrope is formed or if an azeotrope is formed higher than that of the resulting water/ solvent azeotrope and the phosphoric acid/ solvent mixture is heated to a temperature between the boiling point of water or of the azeotrope and that of the solvent to distil off the water present in the phosphoric acid/solvent solution followed by separation of the solid residue and the resulting anhydrous phosphoric acid/organic solvent mixture and recovery of the purified phosphoric acid in the form of the free acid or its salts. Preferably crude phosphoric acid from conduit 1 is admixed with scrubbed raffinate (recycled through conduit 17) and sulphuric acid (from conduit 2) is mixed with circulated solvent in a reactor A. A sodium compound, for example sulphate, hydroxide, phosphate or carbonate, is added through conduit 3 and a 20 wt. per cent solution of Na 2 S and active carbon are added from conduits 4 and 5 to effect precipitation of heavy metals and adsorb organic impurities. Pure water or azeotrope distils over at 10 and is cooled in condenser D or if an azeotrope separated into its components in a separator E. In the latter case the solvent is recycled through conduit 12 into the reactor A whereas the aqueous phase by way of conduits 13, 14 and 15 is used partially for scrubbing the organic solvent/phosphoric acid solution in B and partially for the reextraction of phosphoric acid in C by a multistage counter-flow scrubbing operation. The solvent by way of conduit 16, is recycled to the reactor A. Scrubbed raffinate, flowing through conduit 17 is recycled to A and extracted anew with solvent. Useful solvents include organic substances which are immiscible or partially miscible with water e.g. butanol, amyl alcohol, ethylhexanol, dibutylether, methylisobutyl ketone, butyl acetate or tributyl phosphate. |
