GB461641A - Improvements in or relating to the purification and granulation of pentaerythritol tetranitrate - Google Patents

Abstract

Pentaerythritol tetranitrate is precipitated in granular form from its concentrated solution in acetone or media rich in acetone by dilution of the solution at or near its boiling point with water, the concentration of acetone being at no time less than 25 per cent, and the final concentration preferably lying between 33 and 50 per cent by weight of the total solution. An acetone solution of the nitrate may be added slowly and simultaneously with water to a bath of aqueous acetone maintained at or near its boiling point. The distilled acetone may be re-used as a solvent. Precipitation as coarse granules is favoured by small difference between the solvent power of the two solutions, slow admixture, and high temperature. The solvent liquor may contain, e.g. up to 10 per cent of water when a precipitating bath of low solvent power is used. The crude water-washed nitrate may, alternatively, be stirred with acetone to remove most of the water and then treated in an extraction apparatus comprising boiler, reflux, and jacketed extraction vessel, constructed of chrome iron alloy or other resistant material if acid is present. The aqueous acetone washings, with the addition if necessary of dry acetone, are run into the steam-heated boiler so that acetone distils, condenses and extracts the nitrate in the extractor, the solution then flowing back to the boiler where precipitation occurs. Agitation of the boiler contents assists the granulation. The nitrate remaining in solution may be recovered by the introduction of live steam. In one example, the crude nitrate is stirred with acetone and placed in an extraction filter, the washings together with further acetone, including the washings from a previous batch, and the gummy by-product obtained by dilution of the refuse nitrating acid being run into the boiler. Sodium carbonate is added, and the boiler heated indirectly by hot water and directly by live steam. The condenser may be so run that cold acetone is used in the extraction until all residual moisture is removed, the extractor then being heated. The boiler contents are cooled and the granular nitrate filtered off.