Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Reexamination Certificate
1999-06-14
2001-11-13
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
C423S357000, C423S430000, C423S518000, C423S544000, C423S552000
Reexamination Certificate
active
06315976
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of producing potassium sulfate and more particularly, the invention relates to a method of synthesizing pure potassium sulfate from brines of ammonium sulfate with up to 12% Na
2
SO
4
impurities.
BACKGROUND OF THE INVENTION
The prior art has established countless methods of preparing potassium sulfate. Typical of the known methods is exemplified by U.S. Pat. No. 4,588,573, issued May 13, 1986, to Worthington et al. In this reference, potassium chloride and sulfuric acid are reacted. Although meritorious, the method requires sulfuric acid which is generally expensive and requires special conditions for handling.
The co-production of potassium sulfate, sodium sulfate and sodium chloride is taught in U.S. Pat. No. 5,552,126, issued to Efraim et al., Sep. 3, 1996. Progressive precipitations with an evaporation step are requisite for the process. As is well known in chemical process design, costly energy consuming unit operations add to the overall operating expenses for the process which are translated to the profit margin. Accordingly, it is most desirable to avoid such operations in processes.
U.S. Pat. No. 5,549,876, issued Aug. 27, 1996, to Zisner et al., provides methodology for potassium sulfate production involving differential contacting. Potash, water and sodium sulfate are placed in a differential countercurrent contactor to produce the potassium sulfate.
Potassium chloride and sulfuric acid are reacted and the resulting mixture kneaded to produce potassium sulfate, as disclosed by Iwashita et al., in U.S. Pat. No. 4,342,737, issued Aug. 3, 1982.
Other methods of manufacture include fractional crystallization of sulfate ores or by the Hargreaves process.
It would be most desirable for potassium sulfate production to be achieved without the use of acids, high energy input or other such unit operations. The present invention provides for such a process.
SUMMARY OF THE INVENTION
One object of the present invention is to provide an improvement in potassium sulfate preparation.
Generally speaking, the process results in the formulation of useful products during the synthesis of the potassium sulfate with recovery of sulfate and potassium in excess of 95% completely in the absence of evaporation. This significant feature has particular importance in terms of energy efficiency and thus the costs of the process.
A further object of one embodiment of the present invention is to provide a method of producing potassium sulfate from a source containing ammonium sulfate, comprising the steps of:
contacting potassium chloride and ammonium sulfate in a mixer at a temperature of between 20° C. and 40° C.;
precipitating a first precipitate of double salt in a filtrate;
mixing, in a second mixing step, the filtrate with potassium chloride;
generating a second filtrate containing ammonium and potassium chloride and a second precipitate of double salt;
mixing the second double salt precipitate with the first precipitate in a solution of potassium chloride;
precipitating a third precipitate of potassium sulfate and a third filtrate;
recirculating the third filtrate into the second mixing step;
mixing the second filtrate in a mixing tank at a temperature of less than 70° C. in a solution of less than 10% by weight sodium chloride, calcium chloride and sodium sulfate; and
generating a syngenite precipitate and a fourth filtrate.
Another object of one embodiment of the present invention is to provide a method of producing potassium sulfate from a source containing ammonium sulfate, comprising the steps of:
contacting potassium chloride and ammonium sulfate in a mixer at a temperature of less than 30° C.;
precipitating a first precipitate of double salt in a filtrate;
mixing, in a second mixing step, said filtrate with potassium chloride;
generating a second filtrate containing ammonium and potassium chloride and a second precipitate of double salt;
mixing said second double salt precipitate with said first precipitate in a solution of potassium chloride;
precipitating a third precipitate of potassium sulfate and a third filtrate;
recirculating said third filtrate into said second mixing step;
mixing said second filtrate in a mixing tank at a temperature of less than 70° C. in a solution of less than 10% by weight sodium chloride, calcium chloride and sodium sulfate;
generating a syngenite precipitate and a fourth filtrate;
mixing, in a sealed mixing tank at a temperature of about 80° C., said fourth filtrate with less than about 18% by weight sodium chloride, about 23.6% ammonium chloride and lime or hydrated lime;
recovering ammonia from said fourth filtrate;
passing said fourth filtrate into an air scrubber and further removing ammonia from calcium chloride and sodium chloride;
passing said fourth filtrate into an ammonium scrubber to generate ammonium sulfate;
passing said syngenite precipitate into a mixing tank at a temperature of about 70° C. in the presence of ammonium bicarbonate;
generating a calcium carbonate precipitate and a fifth filtrate containing potassium sulfate and ammonium sulfate; and
recycling said fifth filtrate to at least one of the mixing steps.
Having thus described the invention, reference will now be made to the accompanying drawing illustrating a preferred embodiment.
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Database WPI, Section Ch, Week 9715, Derwent Publications Ltd., London, Great Britain, Class C04, AN 97-154962, XP002116365 and CN 1 091 112 A (Hunan Prov Chem Fertilizer Ind., Aug. 24, 1994, Abstract.
Aristos Capital Corporation
Griffin Steven P.
Vanoy Timothy C
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