March 18, 1969 T. W. SEGAR ET All- 3,433,584 PRODUCTION OF POTASSIUM NITRATE FROM CALCIUM NITRATE Filed March 7, 1966 7/wgs/WINVENTORS Go E- 77/Owas AZ-52-gaa af77%/yay 3,433,584 United States Patent Office Patented Mar. 18, 1969 2 We have discovered a simple economical process for 3,433,584 PRODUCTION OF POTASSUM NITRATE FROM producing KNOs from the reaction of potassium chloride CALCUMNTRATE and calcium nitrate in aqueous solution which results in Thomas W. Segar, Minneapolis, and Ting Sin Go, Rose effective yields as KNO of nearly 100% of theoretical mount, Minn., assignors to St. Paul Ammonia Products, without requiring the addition of reaction or solubility Inc., St. Paul, Minn., a corporation of Minnesota additives. By subjecting the calcium chloride brine result Filed Mar. 7, 1966, Ser. No. 532,169 ing from the reaction of the KCl and Ca(NO3)2 to liquid U.S. C. 23-102 7 Claims liquid extraction with a solvent for calcium nitrate we Int, C. C019/12 have found that nearly all of the unreacted nitrate and po 10 tassium values in the brine can be recovered to provide a procedure which results in practically quantitative yields ABSTRACT OF THE DISCLOSURE of potassium nitrate. Insofar as we are aware no one has A process is provided for producing potassium nitrate heretofore combined liquid-liquid extraction with the re from the reaction mixture of potassium chloride and cal action in aqueous medium of potassium chloride and cal cium nitrate in aqueous solution by subjecting the re 5 cium nitrate to increase the effective yield of potassium maining liquid following potassium nitrate precipitation nitrate. The advantages of this procedure are startlingly to liquid-liquid extraction with a solvent for calcium ni significant, transforming a heretofore uneconomical proc trate to recover the nitrate values for reuse while avoid ess into a readily practiced and economically practicable ing any problem of coprecipitation of potassium chloride method for producing potassium nitrate. with potassium nitrate, thereby greatly increasing the 20 In accordance with our invention potassium nitrate is effective yield of potassium nitrate in the process. produced by the reaction of potassium chloride with cal cium nitrate in aqueous solution by a procedure which -ammon eliminates significant loss of nitrate or potassium ions, The present invention relates to the production of po the process comprising precipitating potassium nitrate tassium nitrate and more particularly relates to a method from the calcium chloride brine resulting from the reac for economically producing potassium nitrate from the re tion, 2KCI--Ca(NO3)2 >2KNO--CaCl2, and recovering action of calcium nitrate and potassium chloride in aque the unreacted calcium nitrate from the brine by intimate ous medium. ly contacting said brine with an organic solvent which is Fertilizer grade potassium nitrate, i.e., potassium ni an extractant for calcium nitrate, which extractant is rela trate having a chlorine content of less than one (1%) 30 tively stable in the presence of the nitrate ion, of low percent, has until very recently been obtainable only volatility and relatively insoluble in calcium chloride from natural sources, e.g., from mining or the processing brine. Following extraction the rich solvent, or extractant, of animal wastes. The economical synthesis of potassium is made lean for reuse and the calcium nitrate recovered nitrate has long been sought through the reaction of for further reaction with potassium chloride by back ex calcium nitrate and potassium chloride in aqueous solu traction with water. Following calcium nitrate removal, tion. This route has many attractions because of its innate the unreacted potassium chloride remaining in the brine simplicity. The attractions are enhanced if the KNO3 is recoverable by precipitation upon concentrating the production is linked with the production of phosphoric now Ca(NO3)2 free brine in known manner. acid, or phosphatic fertilizers, by the nitric acid acidula In carrying out the process to obtain potassium nitrate tion of inorganic phosphate rock since the major by 40 of maximum purity the potassium chloride to calcium product of this acidulation reaction is calcium nitrate nitrate mol ratio, 2KCl/Ca (NO3)2, should be from about tetrahydrate Ca(NO3)2.4H2O). 0.7 to 1.0. Preferably the mol ratio is less than stoichio Heretofore, the production of potassium nitrate by the metric, being from about 0.8 to about 0.9. If less than 0.7, the maximum amount of potassium nitrate is not reaction in aqueous solution of precipitated and if the mol ratio is greater than about 1, then the potassium chloride tends to precipitate. has not been successful, either because the potassium ni The weight ratio of water to reactants trate yield has been too low or the procedures proposed to raise the yield have been too expensive. The yield of KNO is ordinarily only about 65% since beyond this point KCl coprecipitates. It has heretofore been proposed in the initial aqueous solution should be maintained at to increase the yield by the addition of an alcohol to about 0.7 to about 1.1. The preferred weight ratio is aqueous Ca(NO3)-KCl solution, thereby reducing the from about 0.8 to about 1; this results in a potassium solubility of the potassium nitrate in the solution and nitrate yield of about 65% of theoretical. The less water increasing the yield, e.g. (German Patent No. 606,385, 5 5 used the higher the yield of KNO3 in this initial reaction, November 1934). It has also been proposed to add am but potassium chloride also tends to precipitate. Of monia gas to the residual liquor following potassium course, the more water used the lower the yield of potas nitrate precipitation therefrom (e.g., U.S. Patent No. sium nitrate. 1,835,704, issued Dec. 8, 1931). More recently ion ex Following precipitation of potassium nitrate, a calcium change through a sulfonated styrene resin (e.g. U.S. 60 chloride brine remains containing in weight percent, in Patent No. 2,751,280, issued Feb. 19, 1956), has been addition to water, about 65% calcium chloride (CaCl2), proposed. While all of these procedures are effective, they about 17% potassium chloride (KCl) and about 17% raise other problems. Thus, the addition of alcohol to calcium nitrate Ca(NO3)2, the latter two compounds rep increase crystallization of KNO3 from calcium chloride resenting unreacted portions. brine while increasing KNO3 crystallization to about 65 Temperature also effects the potassium nitrate yield and 85%, also requires redistillation of the alcohol for reuse, while the highest crystallization of KNO (about 68%) which becomes economically unattractive. The addition occurs at about -23 C., at temperatures of about -15 of NH3 in water results in undesirable nitrogen losses. C. KCl also precipitates; thus, a practical low temperature With ion exchange, the sulfonated styrene used is initially 70 range of KNO crystallization is from about 5 C. to expensive and an intricate alternating flow pattern neces about -10° C. At room temperature, e.g., 25 C., to sitating a large number of exchange columns is required. about 30% of the potassium nitrate precipitates and the 3,433,584 3 4 remaining 35% of the approximately 65% precipitated is augmented with suitable piping, heat exchangers, centri takes place at temperatures down around -10° C. fuges, evaporators and other auxiliary components to After precipitation of the KNO by crystallization, the make the process. unreacted calcium nitrate and potassium chloride in the Lines 11, 13, and 15 feed into the main line 17 conduct brine can be readily recovered for reuse, the unreacted ing calcium nitrate tetrahydrate to the reacting vessel 12. calcium nitrate by the liquid-liquid extraction procedure Line 11 carries calcium hydroxide as a neutralizing agent of this invention and the potassium chloride by known to neutralize any free acids which may still remain in concentration procedures. the calcium nitrate tetrahydrate, presuming that the calci To recover the unreacted calcium nitrate by liquid um nitrate tetrahydrate by-product of a nitric-phosphate liquid extraction, an organic liquid solvent must be chosen process is used as the nitrate source. Line 13 is the potas as an extractant in which calcium nitrate is soluble, which 10 sium chloride feed and line 15 is a recycling line returning is stable in the presence of the nitrate ion, which is of potassium chloride and calcium nitrate for recycling low volatility, and of insignificant solubility in the calcium through the reactor 12. Steam is provided to heat the re chloride brine. We have discovered that tributyl phosphate actor 12 to a temperature of approximately 70° C. to satisfies all of these requirements and is an excellent ex assure dissolution of the reactants and completion of the tractant for calcium nitrate which, even when calcium ni reaction. The principal reactions are: trate rich, is quite stable and readily handled under ordi nary conditions. It is practically insoluble in calcium chlo ride brine and is readily made lean for reuse for further ex traction by the simple expedient of back extracting with 20 The resulting reaction liquor is then fed through line Water. 19 through a heat exchanger 20 wherein it is cooled by Liquid-liquid extraction is ideally suited for continuous heat exchange with calcium chloride brine from which potassium nitrate production, the calcium chloride brine the potassium nitrate crystals have been removed which being contacted by counter-current flow with the ex brine is brought from the crystallizer 14 through line 21 tractant in a solvent (extractant) to feed (brine) ratio in through the heat exchanger 20 and out therefrom through parts by weight of about 3:1 to 6:1.