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United States Patent to (11) 3,998,935 Adams et al. 45 Dec. 21, 1976 54 MANUFACTURE OF POTASSIUM SULFATE 1,145,390 3/1969 United Kingdom ............... 4231482 75 Inventors: Ben E. Adams, Hanford, Calif.; John OTHER PUBLICATIONS B. Sardisco, Shreveport, La., Erhart Seidell, A., Solubilities of Inorganic and Metal Organic K. Drechsel, Houston, Tex. Compounds, American Chemical Society, Washington, 73) Assignee: Pennzoil Company, Shreveport, La. DC, 1965, 4th Edition, vol. II, pp. 1 16, 133-135, 297-299, 301,982–984. 22 Filed: Jan. 30, 1975 Handbook of Chemistry & Physics, Hodigins Editor, 43 (21) Appl. No. 545,554 edition, 1961, Chemical Rubber Publishing Company, 52 U.S. Cl. ............................. 4231552; 23/302 R; Cleveland, Ohio, pp. 626-627,636-637. 4231482 (51) Int. Cl.’....................... C01D 5/02; C01B 7/08 Primary Examiner-Oscar R. Vertiz (58) Field of Search .......... 423.1552, 481,482, 199, Assistant Examiner-Gary P. Straub " . 423/202; 23/296, 302 Attorney, Agent, or Firm-Lowe, King, Price & Markva (56) References Cited 57 ABSTRACT UNITED STATES PATENTS Potassium sulfate (KSO) is prepared by contacting 995,105 6/1911 Thompson ..................... 4231552 X potassium chloride with an aqueous solution containing 2,816,820 12/1957 Pernert .......................... 4231482 X potassium bisulfate at a temperature of about 65-10 2,902,341 9/1959 Baniel et al. .................. 423.1552 X C., cooling the solution and permitting the potassium 3,687,639 8/1972 Barlow et al. ................. 4231552 X sulfate to crystallize from solution. FOREIGN PATENTS OR APPLICATIONS 1,100,258 9/1955 France ............................... 423.1552 12 Claims, 3 Drawing Figures loss-to-coll" Il-1 || || || are U-1 || | | | | | | 1 \ | | | | | | 7 KH SO -7 t /I\ | | | | Z 52 5.I U.S. Patent Dec. 21, 1976 Sheet 1 of 3 3,998,935 3,998,935 1. 2 ous solution of KSO, by dissolving sufficient KCl in the MANUFACTURE OF POTASSIUM SULFATE solution to affect the solubility of the KSO, and cause it to crystallize. However, this is strictly a physical pro BACKGROUND OF THE INVENTION cedure as the KSO, is already formed. A similar refer 1. Field of the Invention 5 ence with respect to sodium sulfate recovery is U.S. This invention relates to the manufacture of potas Pat. No. 2,125,624. However, these patents are not sium sulfate and more particularly to a method for the concerned with the particular reaction of the present preparation of potassium sulfate by the reaction of invention. potassium chloride and potassium bisulfate contained To Applicants' knowledge, none of these prior meth in an aqueous solution under moderate reaction condi O ods have been entirely successful and there remains a tions. clear need in the art for methods by which potassium 2. Description of the Prior Art sulfate can be prepared under moderate reaction con Potassium sulfate is a well known inorganic com ditions and in high purity and yield. The present inven pound which has found great utility in many areas, for tion is believed to provide a solution to this problem. example, as a fertilizer and as an intermediate for the 15 production of useful products. Consequently, the prior SUMMARY OF THE INVENTION art has been aware of various methods for preparation It is accordingly one object of this invention to pro of potassium sulfate for many years. In one common vide a method for the preparation of potassium sulfate. procedure, potassium sulfate has been prepared by the A further object of the invention is to provide a reaction of potash (KCl) and sulfuric acid. Usually, 20 method for the preparation of potassium sulfate under however, it is necessary to carry out such reactions moderate reaction conditions and in high purity. under rather severe reaction conditions in order to A still further object of the invention is to provide a eliminate the hydrogen chloride evolved during the method for the production of potassium sulfate by reaction and shift the reaction toward production of contacting potassium chloride with potassium bisulfate the potassium sulfate. An inherent problem in carrying 25 in an aqueous solution. out this process is that it is a two step reaction involving A further object of the invention is to provide a an intermediate reaction in which the potash and sulfu method for the production of potassium sulfate under ric acid react to form potassium bisulfate (KHSO) moderate reaction conditions. with the elimination of one mole of hydrogen chloride. An even further object of the invention is to provide It has been difficult heretofore to carry the reaction to 30 a continuous method for the production of potassium completion and eliminate two moles of hydrogen chlor sulfate. ide in conducting this reaction in view of the thermody Other objects and advantages of the present inven namics involved in the reactions being carried out. For tion will become apparent as the description thereof these reasons, it has been necessary for the art to utilize proceeds. rather extreme reaction conditions, e.g. temperatures 35 In satisfaction of the foregoing objects and advan of above 100° C. and higher in order to obtain an eco tages, there is provided by this invention a method for nomically attractive yield of potassium sulfate of rea the production of potassium sulfate which comprises sonable purity from the reaction. These extreme reac reacting potassium chloride with potassium bisulfate in tion conditions however merely cause additional prob an aqueous solution at a temperature of about 65-1 10 lems as the strong sulfuric acid and chlorine present at 40 C., permitting the solid potassium sulfate to crystallize high temperatures cause severe corrosion problems. from the solution by cooling to a temperature to about Therefore, a clear need remains in the art for methods 40°-60° C. and recovering the solid potassium sulfate by which potassium sulfate can be produced under formed. The present invention also provides a method moderate reaction conditions utilizing readily available by which this reaction can be carried out in the sub starting materials. 45 stantial absence of hydrogen chloride evolution and In most of the prior art procedures, the key to a wherein after removal of the solid potassium sulfate, successful process resides in complete elimination of there is provided a filtrate solution which after excess the HCl gas. A large body of art is available which water removal, is suitable for recycle to a plant which discloses such reactions involving the production of provides for preparation of the potassium bisulfate KSO, or NaSO. A typical art reference of this type is 50 starting material. Further, the invention provides a U.S. Pat. No. 2,762,689 which involved the reaction of combination procedure for the preparation of the po NaCl and HSO, attempertures of 200 to 250°C. Also tassium bisulfate starting material and its use in the in U.S. Pat. No. 2,275,825 NaSO, and hydrochloric preparation of potassium sulfate. acid are prepared by the reaction of a slurry comprising BRIEF DESCRIPTION OF THE DRAWINGs water, NaCl, NaHSO and HSO, with steam in a coun 55 tercurrent reaction zone at temperatures of 120 to Reference is now made to the drawings accompany 160° C. With respect to prior art of this type, it should ing this application wherein there is shown in FIG. 1 a be noted that the aqueous sulfuric acid systems of Na2 schematic diagram showing the process steps of a con SO, and KSO, are not generally considered to be tinuous method of the present invention; and equivalent in the recovery of desired products as they 60 FIGS. 2 and 3 show phase diagrams which illustrate behave differently. Thus, KSO forms mixed acid salts the concepts under which the reaction of the present on solution/crystallization whereas Na2SO4 forms hy invention is carried out when conducted at different drates of either NaSO, or NaHSO; "Solubilities of temperatures. Inorganic and Metal Organic Compounds", Seidell 4th Ed., Vol. 2, pps. 1126–27. 65 DESCRIPTION OF PREFERRED EMBODIMENTS A patent of somewhat more pertinence to the present As indicated above, the present invention is con invention is U.S. Pat. No. 3,687,639 which discloses a cerned with a unique method for the preparation of process of precipitating KSO, crystals from an aque potassium sulfate (KSO4), by the reaction of potas 3 3,998,935 4 sium chloride and potassium bisulfate (KHSO) in removal. Thus, the potassium sulfate process when aqueous solution. It has been found that the simple combined with a potassium bisulfate plant as disclosed procedures provided by this invention will operate to herein, lends itself economically and conveniently to a provide a relatively pure solid potassium sulfate to continuous method. gether with a filtrate which is suitable for recycle to a The method for preparation of the potassium bisul plant which provides the starting potassium bisulfate fate utilizes the reaction of sulfuric acid and potassium It has been found according to this invention that chloride on substantially a molar basis with the evolu solid potassium sulfate can be prepared from potassium tion of hydrogen chloride. In this reaction potassium chloride/potassium bisulfate?water solutions by a chloride and sulfuric acid are added to a reactor and unique series of steps. In general, this process com 10 maintained at a temperature of about 80 to 120°C. or prises initial formation of a solution of potassium bisul up to the boiling point of the solution. As the reaction fate in water at any desired temperature and thereafter proceeds, hydrogen chloride gas is evolved and may be adding the potassium chloride thereto either as a solid removed and recovered by conventional water scrub or as an aqueous solution.

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