3,728,086 United States Patent ice Patented Apr. 17, 1973 2 cipitating solution determines the particle size of the re 3,728,086 Sulting crystals. METHOD OF PREPARING AMMONUMPERCHLO The method described herein may be diagrammatically RATE CRYSTALS OF CONTROLLED SIZE illustrated as follows: Arnold Adicoff, China Lake, Calif., assignor to the United 5 States of America as represented by the Secretary of Percolated through Solvent saturated the Navy AP Solvent tra-rower-a- with AP No Drawing. Filed Apr. 17, 1969, Ser. No. 818,184 AP crystal bed Int, C. C01d 1/30 U.S. C. 23-302 5 Claims max-memorate- O

ABSTRACT OF THE DISCLOSURE Precipitation A method for preparing uniform well-defined ammoni Solvent for AP and um perchlorate crystals of controlled size which com non-solvent for prises dissolving ammonium perchlorate in an organic AP solvent and then precipitating in a mixture of an organic 5 Solvent and non-solvent for ammonium perchlorate. The ratio of solvent to non-solvent in the precipitating solu tion determines the size of the resulting crystals. aarasworworwoo-ray 20 Uniform AP GOVERNMENT INTEREST Crystals The invention described herein may be manufactured The ratio of solvent to non-solvent determines the size and used by or for the Government of the United States of the ammonium perchlorate crystals. of America for governmental purposes without the pay The crystals produced by this invention were prepared ment of any royalties thereon or therefor. 25 in a laboratory apparatus that has been used to circulate the solvent-non-solvent solution. A total of 2800 cc. BACKGROUND OF THE INVENTION tetrahydrofuran and Soltrol 180 (a high boiling hydro The invention relates to a method of producing am carbon) were placed in a large precipitation pot and some monium perchlorate crystals of controlled uniform size of the mixture was allowed to flow through a leveling tube and shape having well-defined crystalline structure. 30 into a distilling pot where it was heated. The volatile tet The customary method of preparing ammonium per rahydrofuran is distilled over to a condenser positioned chlorate crystals involves the aqueous recrystallization of above the ammonium perchlorate bed where it is con ammonium perchlorate from water and subsequent grind densed and allowed to trickle through the ammonium ing of the ammonium perchlorate by grinding procedures perchlorate crystals, then through a sintered glass filter into such as ball mills and grinding mills, often with an inert 35 the precipitation pot. The non-solvent, Soltrol 180, is solvent. The resulting product has a broad particle size returned to the precipitation pot permitting more of distribution of irregularly shaped particles having many the mixture of solvent-non-solvent to enter the distilling grain boundaries and containing inclusions of moisture. pot via the leveling tube. Particle size control by these methods is obtained by 40 The following are examples produced by the above grinding and sieving. The particles are sized by being described process: passed through one screen mesh and retained by a finer mesh screen. The present invention provides a method for Particle the continuous production of particles of ammonium per size chlorate of controlled particle size. The distribution of 45 Initial weight Final weight product particle size is narrow, the purity and moisture content Sample Fraction Fraction (micron) - 0.167 (THF) -- 0.123 (THF) --- i.20.38 can be controlled, and the crystals thus produced are 0.520 (THF). 3.37.9 well-defined rather than the irregular crushed crystals. 0.818 (THF). 61,510, 9 -- 0.365 (acetone) wn on as 53 It is a general object of this invention to produce am V------0.498 (acetone).------. 0.505 (acetone).----... 1.5 monium perchlorate crystals which are small, uniform VI------0.785 (acetone).------. 0.772 (acetone).------. 31.69 and well-defined with little or no occluded moisture for use as a composite propellant ingredient. Another object is to provide ammonium perchlorate crystals which can Some of the ammonium perchlorate crystals were selec be contaminated with selected burning rate modifiers for tively contaminated with the burning rate modifier, po use in propellant, explosive, and pyrotechnic composi 55 tassium permanganate, by allowing the ammonium per chlorate saturated solution to come into contact with tions. the permanganate and then precipitated in the mixed DESCRIPTION OF THE INVENTION solution. These modified crystals were then used in a In accordance with the present invention a predeter composite propellant composition which comprises an mined amount of organic solvent for ammonium per 60 oxidizer such as the ammonium perchlorate as herein chlorate (AP) such as tetrahydrofuran and acetone is prepared and a binder such as polyurethane, polybuta continuously percolated through a bed of ammonium diene and others. Controlled oxidizer crystal size enables perchlorate where it becomes saturated therewith. The those preparing propellants, explosives, and pyrotechnics Saturated solvent is then precipitated into a mixture com to improve the processibility. prising a predetermined amount of the solvent for am 65 The solvents for ammonium perchlorate used herein in monium perchlorate and a predetermined amount of cluded tetrahydrofuran and acetone. Other suitable or non-solvent for ammonium perchlorate such as hex ganic solvents may be used. The non-solvents used in ane. The resulting crystals are of uniform size. For cluded decane, and other high boiling point (180° C.) example 10 micron sized particles varied in size in the hydrocarbon liquids. High boiling point kerosene with order of only --3 microns, while with the larger crystals 70 low volatile content can also be used. Soltrol 180 is a of .28 mm. particle size a range of t. 13 mm, was ob trademark for an odorless mineral spirit having a boiling served. The ratio of solvent to non-solvent in the pre point of about 180° C. 3,728,086 3 4. In addition, it is possible to construct a system consist and acetone and a predetermined amount of non ing of volatile solvent and non-solvent, i.e., acetone and solvent for ammonium perchlorate selected from the hexane. To carry out a cyclical operation of this type group consisting of a high boiling mineral spirit, it would be desirable to construct a fractionating column kerosene, decane and hexane whereby uniform crys such that two distillation streams are obtained, one con tals are formed. taining only the non-solvent which would be returned 2. The method in accordance with claim 1 wherein to the precipitation pot, and the other containing the the organic solvent is tetrahydrofuran and the non-solvent solvent which would be dripped through the ammonium is a high boiling mineral spirit. perchlorate bed. The flow of both materials could be 3. The method in accordance with claim 1 wherein the monitored by a conductivity meter, refractometer, vapor 10 solvent is acetone and the non-solvent is hexane. chromatography or other monitoring device to maintain 4. The method in accordance with claim 1 wherein constant composition in the precipitation chamber. A flow the solvent is tetrahydrofuran and the non-solvent is chamber can be also inserted in the flow chain to remove decane. trace amounts of moisture that may be present in the 5. The method in accordance with claim wherein said original ammonium perchlorate. ammonium perchlorate is contaminated with potassium What is claimed is: permanganate prior to percolating through said organic 1. A method for the preparation of ammonium per solvent. chlorate crystals of substantially uniform size and shape References Cited having well-defined crystalline structure which comprises: UNITED STATES PATENTS (a) percolating an organic solvent for ammonium per 3, 160,535 12/1964 Wells ------149. .76 X chlorate selected from the group consisting of tetra 3,222,231 12/1965 Markels et al. 149-76 X hydrofuran and acetone through a bed of ammonium 3,259,531 7/1966 Lofberg ------149-76 perchlorate thereby forming a saturated solution of 3,383,180 5/1968 Kralik et al. ammonium perchlorate; (b) precipitating said saturated solution into a solu STEPHEN J. LECHERT, JR., Primary Examiner tion comprising a mixture of a predetermined amount of an organic solvent for ammonium perchlorate U.S. C. X.R. selected from the group consisting of tetrahydrofuran 423-476; 149-76