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

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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. For convenience of opera bing procedures well known to the art or further dried tion, it is preferred to add the KCl as a solid. This initial 15 and recovered as anhydrous HCl. The resulting solu step is carried out at temperatures sufficiently high to tion may then be cooled as in a crystallizer at 35 to 50 form a solution of the potassium chloride with the po C. to precipitate the KHSO, product. The shurry is then tassium bisulfate and water. Once the solution is com removed to a separator such as a filter for removal of plete it is thereafter cooled, as for example in a crystal the solid potassium bisulfate. The filtrate, including any lizer, and the solid potassium sulfate will crystallize 20 wash water, is recovered from the separator and is from solution and can be easily recovered. A feature of suitable for recycle to the reaction with the sulfuric the invention is that the filtrate recovered after removal acid preferably after excess water removal. The solid of the solid potassium sulfate is then suitable for use in potassium bisulfate is then dissolved in the appropriate an initial reaction for preparation of the potassium amount of water to form a solution of about 10-50%, bisulfate starting material after removal of excess wa 25 for example, to be in a form suitable for reaction with ter. the potassium chloride in the preparation of the potas In the first step of the process of this invention, a sium sulfate in accordance with this invention. solution of potassium bisulfate in water is prepared, the The overall reaction scheme of the continuous pro solution containing a sufficient excess of water to pro cess is illustrated in FIG. 1 of the accompanying draw vide easy solubilization. Preferably, the KHSO, is dis 30 ing wherein it will be seen that in reactor 1, sulfuric solved in about 1 to 4 times its amount of water by acid from line 2 and potassium chloride from line 3 are weight. After this solution is prepared, the KCl is then reacted at a temperature of up to 120 C. with the added thereto. While the KCl may be added in aqueous evolution of hydrogen chloride through line 4. After solution, in preferred embodiments solid KCl is added the reaction is complete the resulting mixture is re slowly or in increments to the KHSO solution while the 35 moved by line 5 to crystallizer 6 which is maintained at latter is maintained at a temperature of about 65°-110 a temperature of about 45 C. to precipitate the C. In a continuous operation of course all reactant KHSO. The resulting slurry is removed by line 7 to additions are made continuously. Usually the heat of filter or other separator 8. From filter 8, the solid reaction will maintain the desired temperature. Alter KHSO is recovered by line 9. At this point the KHSO, natively, the KCl may be added and the mixture there 40 is in condition to be used in formation of the KSO. after heated to 65-1 10' C. to effect solubilization. In While any amount of the KSHO can be utilized in the any event complete solubilization is obtained. While KSO. reaction, in the continuous system of this pre the potassium chloride and potassium bisulfate may be ferred embodiment, it is preferred to separate the used in substantially equivalent molar amounts for KHSO, into two portions as the recycle requirements reaction, it is highly preferred that there be used a 45 are such that only a portion of the KHSO is reacted to slight molar excess, for example up to 15% and prefer form KSO, in the continuous operation. However, the ably up to 10%, of the potassium chloride in order to invention is inclusive of a system where all the KHSO enhance the yields and production of the potassium is utilized to react with KC in formation of the KSO. sulfate product. Accordingly, in the preferred continuous operation of After complete solution of the potassium chloride 50 FIG. 1, about 30-50 weight percent, preferably 35-40 has been obtained, the solution is then cooled for crys weight percent, of the KHSO, is removed by line 9' for tallization of the KSO. In a preferred aspect, the warm storage or other use while the remaining 50-70, prefer solution is fed to a vacuum crystallizer wherein temper ably 60-65, weight percent in line 9 is converted in the atures of 40-60C. are maintained. The solid potas potassium sulfate plant. The filtrate from filter 8 is sium sulfate will crystallize from solution and may be 55 removed by line 10 for evaporation of water therefrom recovered by use of a separator of the conventional and subsequent recycle to reactor 1. In the preferred type such as a filter or centrifuge. The recovered solid embodiment, the filtrate in line 10 is combined with the cake may be washed one or more times as desired in filtrate in line 21 coming from the KSO filter, with order to enhance purity. subsequent evaporation and recycle as explained here During the solubilization and crystallizing steps, the 60 inafter. evolution of HCl gas is almost undetectable and there The indicated portion of solid potassium bisulfate fore considered minimal. In fact, a maximum of about from line 9 is then dissolved in water. The water used 3% of the HCl present may be evolved. can be water recovered from evaporation 22 and re The filtrate recovered from the separation step com covered from line 23, which technique contributes to a prises a solution containing potassium, chloride, bisul 65 continuous procedure. The KHSO, from line 9 is dis fate, sulfate, and hydrogen ions and water and is suit solved in the water from line 12 in solution tank 11 and able for recycle to a reactor for use in the initial prepa then removed by line 13 to reactor 14 where, at a tem ration of the potassium bisulfate after excess water. perature of 65°-110°C., potassium chloride, preferably 3,998,935 S 6 in solid form, but if desired after dissolution in water, is ture of reaction affects the amounts of the various introduced by line 15. The resulting solution is then compounds present in the system. However, K2SO4 in removed by line 16 to crystallizer 17 where it is cooled good yield is recovered at both temperatures. to a temperature of 45 C. for the precipitation of po As a result of the reaction of this invention there is tassium sulfate. The resulting slurry is removed by line provided a method for the production of potassium 18 to filter 19 and solid potassium sulfate is recovered sulfate under very moderate reaction conditions and by line 20. The filtrate from filter 19 is removed by line the formation of resultant reaction slurry containing 21 to evaporator 22, after combining with the KHSO the sulfate. In a continuous operation this provides a filtrate from filter 8, where excess water is removed by good recovery of high purity product. line 23. While the water removed by line 23 can be 10 The following examples are presented to illustrate used as desired, it is preferable to recycle at least a the invention but it is not to be considered as limited portion to solution tank 11 by line 12. The resulting thereto. In these examples and throughout the specifi mixture is then recycled via line 24 to reactor 1. Thus, cation parts are by weight unless otherwise indicated. it will be seen that a complete continuous process is provided in which moderate reaction conditions are 15 EXAMPLES I, II and III utilized in both systems with the recovery of potassium In these examples, continuous experiments were per sulfate as a final product. formed in which potassium bisulfate and potassium In an alternative embodiment, the continuous pro chloride were reacted in a three-stage continuous reac cess of the invention can be carried out by producing tor system to produce potassium sulfate. The potassium the desired 1:1 molar solution of KHSO and KCl nec 20 bisulfate starting material was diluted with the indi essary for the formation of KSO, directly in the first cated amount of water and fed into a mixing reactor reactor section by maintaining the KHSO/KCl solution using a metering pump. A screw feeder was used for the at its boiling point, e.g. about 115-120° C., to elimi introduction of the solid potassium chloride. nate excess HCl and then adding fresh feed comprising The first vessel was the mixing reactor for the two 2 moles of KCl and 1 mole of HSO, and cooling the 25 feeds. The slurry was maintained at 80° C. and was reaction solution to crystallize the KSO, and/or a mix rapidly stirred. All reactor vessles were under a slight ture of KHSO/KSO. This embodiment eliminates the vacuum to remove any hydrochloric acid produced and need to split the KHSO product into two portions prior to prevent steam or hydrogen chloride from wetting the to introduction into the KSO, plant and will utilize all sides of the potassium chloride entry port. After initial the KHSO, produced. 30 mixing the slurry flowed by gravity into the second In FIGS. 2 and 3 there are provided phase diagrams vessel which was the vessel for solubilization. In this which illustrate the theoretical amounts of potassium vessel the temperature was maintained at 100° C. and sulfate which may be obtained from this reaction when the slurry was rapidly stirred. The average retention carried out at 40 C. (FIG. 2) and 60° C. (FIG. 3), and time was 1 hour. The liquid produced from the solubili the various systems present therein. The phase dia 35 zation vessel was allowed to overflow into the third grams of FIGS. 2 and 3 are two-dimensional phase reactor which was a crystallizer maintained at a much diagrams and it will particularly be noted that a number lower indicated temperature to crystallize the potas of systems are present during the reaction including sium sulfate. After reaching steady state, liquid and potassium sulfate, potassium bisulfate, various double crystallized product which were equal to the weights of salts of each potassium sulfate as well as potassium 40 the feeds, were removed every hour and filtered. The chloride and sulfuric acid. These phase diagrams indi liquid was analyzed routinely and periodically, the un cate that the reaction should be operated under such washed cakes were dried at 110° C. and analyzed for conditions that the chloride content of the solution KO, SO hydrogen, chloride and by X-ray diffraction. does not exceed about 10 weight percent for pure solu In these runs the designation ratio of feed to water was tions and preferably is maintained below about 6-8% to 45 0.916 and the design mole ratio of potassium chloride prevent excessive crystallization of potassium chloride to KHSO was 1.11. Crystallization was carried out at within the solution. The phase diagrams also provide 40° C. The unwashed solid product was shown to be explanations of why the basic reaction of this invention about 85% KSO, and about 5% of a KSOKHSO salt leads to the formation and precipitation of the potas with a chloride content of about 2%. When this solid sium sulfate as the systems present, when maintained 50 was washed with saturated potassium sulfate the result under the reaction conditions stated, permit the K2SO4 ing solid contained 0.03% of chloride. In these runs the to precipitate within the system and thus upset the weight of unwashed dry solid per 100 parts of slurry equilibrium sufficiently to cause formation of addi was about 10. The amounts of reactants used and the tional potassium sulfate. As will be noted, the tempera results from these examples are set forth in the follow 55 ing Table I. TABLE I Actual Feed Ratio of Feed Grams Grams Example Grams/Hour Grams Filt- Product Number KC KO(1) SO KC KHSO HOH Rate Cake 229 140 268 60.3 100 175 1293 192 I 258 ... 138 264 60.3 100 175 743 97 II 264 138 264 60.3 100 175 1275 134

Filtrate Wt: Cake Wt: Crystallization Acid Product Acid Wt. Temperature C KO SO Cl Ton KO SO Cl- Ton Slurry 40 8.0 5.3 9.75 0.22 45.6 53.7 2.75 0.31 12.3 40 19.3 6. 9.31 0.23 46.1 56.1 2.09 0.32 1.3 3,998,935 7 8 TABLE I-continued 40 19.2 16.5 9.60 0.23 45.9 56.8 1.09 0.33 9.2 (1)KO in the Potassium Bisulfate only.

EXAMPLE IV -continued In the following example, a complete three phase Recycle filtrate 8.3 g/min continuous experiment was carried out for the produc- 10 Water removed 4.2 g/min tion of KSO. In the initial phase, KHSO, is prepared byKSO, the reactionis produced of KCl from and KCl HSO; and in25% the of second the KHSO phase c this tigii, Ga t inted gd produced from the initial phase; and in the third phase, E. lo. 2 at d e E. 1 the KHSO4 is produced by mixing the filtrate recovered 15 e reaction was carried out ". or step from the second phase with the recycle filtrate. Water to provide product at the rate of filtrate 7. g/min. wet was removed from the combined filtrates and the KCL cake, 6.3 g/min. and dry cake 6.1 g/min. The product and HSO, feed rates were reduced to compensate for cake was washed with a saturated KSO. aqueous solu the KO, Cand SO, contents in the filtrate from the tion. The products analyzed as follows: second phase. 20 In the initial phase, KHSO was prepared by contact ing H2SO4 at a E. rate of 3.5 g/min. and ki at a feed Component Filtrate Washed Cake rate of 2.6 g/min. in a series of two reactors. Reactor s: E; No. 1 was maintained at 80 C. and reactor No. 2 at 119 0.12 100° C. The contact time was 2 hours and the crystal- 25 9. & lizer for formation of the solid was maintained at a HOH 59.4 --- temperature of 45 C. - The products recovered from the reaction consisted of 4.8 g/min. of wet cake, 1.3 g/min. of HCl evolved The invention has been described herein with refer and 7.9 g/min. of filtrate. The washed wet cake ana- 30 ence to certain preferred embodiments. However, as lyzed as 36.5% K2O, 64.2% SO4 and 0.10% Cl. The obvious variations thereon will appear to those skilled X-ray diffraction pattern of the cake indicated the in the art the invention is not to be considered as lim presence of 90% of KHSO, and 10% KH(SO). The ited thereto. filtrate analyzed as 5.0 wt.% K2O, 19.0 wt.% SO 14 What is claimed is: wt.% Cl, 1.0 wt.% Na, 0.6 wt.% hydrogen ion and 35 1. A method for the production of potassium sulfate 61.2 wt.% water. substantially free from double salts thereof which com In the second step or phase, 25 weight percent of the prises: KHSO solid was contacted in a solubilizer at a rate of 1. forming an aqueous solution containing potassium 6.7 g/min. with KCl at a rate of 4.2 g/min. and water at bisulfate; a rate of 11.7 g/min. The solubilizer was maintained at 40 2. heating said aqueous solution to a temperature of a temperature of 100° C. until complete solution was about 65°-1 10° C.; obtained. The solution was continuously removed to a 3. adding potassium chloride to said aqueous solution crystallizer maintained at a temperature of 40 C. for to react with said potassium bisulfate, the amount product precipitation with recovery by filtration. The of potassium chloride being added ranging from a product dry cake (not washed) was recovered at a rate 45 substantially molar equivalent amount up to about of 3.3 g/min. and product filtrate was recovered at a a 15% molar excess, but wherein the maximum rate of 17.0 g/min. The recovered cake after washing chloride content of the resulting solution is main with a saturated KSO, aqueous solution, analyzed as tained below about 6-8 wt.%; 51.7% KO, 46.9% SO, and 0.03% Cl. X-ray diffraction 4. continuing the reaction at a temperature of about indicated the cake product contained 96% K2SO and 50 65-1 10° C. until complete solution is achieved; 4% of the double salt KSO.KHSO4. The recovered 5. cooling the resulting solution to a temperature of filtrate analyzed as 19.0% K2O, 16.0% SO, 9.6% Cl, about 40°-60° C.; 58.3% HO and 0.23% hydrogen ion. 6. permitting the resulting said potassium sulfate to In the third phase, the filtrate from the KSO, plant is crystallize from solution; and recycled to the KHSO4 plant by initially mixing the 55 7. recovering the solid potassium sulfate, filtrate from the KHSO plant with the filtrate from the wherein crystallization and initial precipitation of the KSO, plant and removing an equivalent amount of potassium sulfate on cooling upsets the equilibrium water from the resulting mixed stream. The resulting of the system sufficiently to cause formation and combined concentrate was analyzed and found to con- precipitation of additional potassium sulfate prod tain 19.6% K2O, 28.8% SO, 10.5% CI, 0.43% hydrogen 60 uct. ion, 1.0% Na and 42.9% HO. In order to reduce the 2. A method according to claim 1 wherein about one equivalent amount of KCl and HSO, from the feed to mole of potassium chloride is added to an aqueous the KHSO4 plant requirements, the feed rates were as solution containing about one mole of potassium bisul follows: fate. 65 3. A method according to claim 1 wherein a molar excess of up to about 15% of potassium chloride is So, (97%) 28 E. added to an aqueous solution containing about one Filtrate from KSO, plant 8.3 g/min mole of potassium bisulfate. 3,998,935 10 4. A method according to claim 1 wherein the chlor 10. evaporating excess water from the solution to ide content of the solution in step (3) is maintained in provide a mother liquor concentrate; and the range of about 1 to about 4 wt.%. 11. recycling the mother liquor concentrate to step 5. A method according to claim 1 wherein reaction of (1) as reaction medium for potassium bisulfate the solution of potassium chloride and potassium bisul- 5 fate is carried out at a temperature of about 100° C. formation; and the resulting solution is cooled to a temperature of wherein crystallization and initial precipitation of the about 40 C. to crystallize the potassium sulfate. potassium sulfate on cooling upsets the equilibrium 6. A continuous method for the formation of potas of the system sufficiently to cause formation and sium sulfate substantially free from double salts 10 precipitation of additional potassium sulfate prod thereof, which comprises: uct. 1. reacting potassium chloride and sulfuric acid with 7. A method according to claim 6 wherein the potas evolution of hydrogen chloride to produce a slurry sium bisulfate formation reaction is carried out at a of potassium bisulfate; temperature of about 80°-120° C. 2. recovering the solid potassium bisulfate; 15 8. A method according to claim 7 wherein the potas 3. dissolving at least a portion of the potassium bisul sium chloride and sulfuric acid are mixed in substan fate in an excess of water to form an aqueous solu tially equimolar amounts. tion containing potassium bisulfate; 9. A method according to claim 8 wherein the hydro 4. heating said aqueous solution to a temperature of gen chloride evolved from the potassium bisulfate reac about 65°-1 10 C.; tion is recovered by water scrubbing or as anhydrous 5. adding potassium chloride to said aqueous solution HC. to react with said potassium bisulfate, the amount 10. A method according to claim 6 wherein solid of potassium chloride being added ranging from a potassium chloride is added to the potassium bisulfate substantially molar equivalent amount up to about solution. 15% molar excess, but wherein the maximum 25 chloride content of the resulting solution is main 11. A method according to claim 6 wherein about tained below about 6-8 wt.%; 50-70 weight percent of the potassium bisulfate recov 6. continuing the reaction at a temperature of about ered from step (2) is dissolved in an excess of water, 65°-1 10°C. until complete solution is achieved; heated to a temperature of 65°-1 10°C., and about one 7. cooling the resulting solution to a temperature of 30 molar equivalent of solid potassium chloride added about 40-60C.; thereto. 8. permitting the resulting said potassium sulfate to 12. A method according to claim 11 wherein solid crystallize from solution; potassium chloride is added to the aqueous solution of 9. recovering the solid potassium sulfate from the potassium bisulfate at a temperature of about 100 C. solution; 35 k is

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65 Disclaimer 3,998,935.-Ben E. Adams, Hanford, Calif.; John B. Sardisco, Shreveport, La.; and Erhart K. Drechsel, Houston, Tex. MANUFACTURE OF POTAS SIUM SULFATE. Patent dated Dec. 21, 1976. Disclaimer filed Nov. 24, 1982, by the assignee, Pennzoil Co. Hereby enters this disclaimer to claims 1, 2, 3, 4, 5 and 6 of said patent. Official Gazette January 11, 1983.)