Title:
Method for separating ammonium sulfate from an aqueous solution of ammonium bisulfate and ammonium sulfate
United States Patent 3902859
Abstract:
A method is disclosed for separating ammonium sulfate from an aqueous solution of ammonium bisulfate and ammonium sulfate, and, in particular, where the aqueous solution additionally contains organics from a synthesis reaction. Separation is effected by the addition of an alcohol, preferably methanol, to the aqueous solution in an amount sufficient to precipitate substantially all of the ammonium sulfate and thereafter removing said precipitate from the solution.
Application Number:
05/456763
Publication Date:
09/02/1975
Assignee:
Koppers Company, Inc. (Pittsburgh, PA)
Other Classes:
23/300, 23/302A, 423/520, 423/545
International Classes:
C01C1/24; (IPC1-7): B01D9/02; C01C1/24
Field of Search:
23/296,299,300,302,32A 423
Other References:
Seidell, Solubility of Inorg. and Org. Cds., Vol. 1, 1919, pages 63 to 66..
Primary Examiner:
Yudkoff, Norman
Assistant Examiner:
Emery S. J.
Attorney, Agent or Firm:
Yeager, Robert D.
Parent Case Data:
This is a continuation, of
application Ser. No. 332,668, filed Feb. 15, 1973 now
abandoned.
Claims:
What is claimed is
1. A method for separating ammonium sulfate substantially free of ammonium bisulfate and organic impurities and obtaining a solution of ammonium bisulfate substantially free of any ammonium sulfate from an aqueous solution containing ammonium bisulfate and ammonium sulfate and dissolved organic impurities, said method consisting essentially of concentrating said solution to the maximum possible while maintaining the salts in solution, adding to said aqueous solution an alcohol selected from the group consisting of methanol, ethanol, propanol, butanol, and isopropanol in an amount of from about 400 to 500 percent by weight of the ammonium sulfate present in the solution and effective to precipitate substantially all of said ammonium sulfate without precipitating substantially any of the ammonium bisulfate and removing all of said precipitated ammonium sulfate from said solution to obtain a solution of ammonium bisulfate.
2. A method as set forth in claim 1 wherein said alcohol is methanol.
3. A method as set forth in claim 1 wherein said aqueous solution is maintained between about 15° and 30°C.
4. A method for obtaining an aqueous solution of ammonium bisulfate substantially free of ammonium sulfate and any dissolved, and ammonium sulfate substantially free of organic impurities from an aqueous solution containing ammonium bisulfate, ammonium sulfate, and dissolved organic impurities, said method consisting essentially of concentrating said solution to the maximum possible while maintaining the salts in solution, adding to said concentrated solution an alcohol selected from the group consisting of methanol, ethanol, propanol, butanol, and isopropanol, in an amount of from about 400 to 500 percent by weight of the ammonium sulfate present in the solution and effective to precipitate substantially all of said ammonium sulfate substantially free of ammonium bisulfate and organic impurities, removing said precipitated ammonium sulfate to form a remaining solution, and separating said alcohol from said remaining solution to obtain said aqueous solution of ammonium bisulfate.
Description:
FIELD OF THE INVENTION
The present invention relates to a method for separating ammonium sulfate from ammonium bisulfate, and, in particular, to a method of separating ammonium sulfate from an aqueous solution containing ammonium bisulfate and organic synthesis material.
BACKGROUND OF THE INVENTION
It has recently been found that certain organic synthesis can be carried out by utilizing ammonium bisulfate. In many of these reactions, ammonium sulfate. In many of these reactions, ammonium sulfate is formed as a byproduct that must either be disposed of or regenerated. Because the disposal problem is now becoming inherently more difficult to deal with, it is highly desirable to regenerate ammonium bisulfate therefrom. Not only does regeneration effectively avoid or eliminate the disposal problem, it also renders the organic synthesis more economical.
Also, in many of the synthesis reactions, excess quantities of ammonium bisulfate are preferred or required. In these reactions, not only is ammonium sulfate a byproduct, but it is usually found with the excess quantities of ammonium bisulfate and certain unreacted or partially reacted organics utilized in the synthesis reaction. Various methods of regeneration have recently been proposed. One such method first removes the organics found in the aqueous solution of ammonium bisulfate and ammonium sulfate to prevent undesirable foaming. Thereafter, a fused mixture of ammonium bisulfate and ammonium sulfate is prepared which is contacted with hot sweep gases to convert the ammonium sulfate to bisulfate.
While this method performs well and provides efficient regeneration of ammonium sulfate to bisulfate, it does require apparatus for handling large quantities of ammonium bisulfate that does not need to be regenerated. Accordingly, it is desirable to have a method which preferentially separates the ammonium sulfate and organics from the aqueous solution containing them as well as ammonium bisulfate.
SUMMARY OF THE INVENTION
The present invention provides a method for separating ammonium sulfate from an aqueous solution containing same and ammonium bisulfate. The method of the present invention also provides for removing organics present in the aqueous solution of ammonium bisulfate.
Generally, the method of the present invention comprises adding to an aqueous solution of ammonium bisulfate, ammonium sulfate, and residual organics, if any, an alcohol, preferably methanol. The addition of alcohol preferentially causes the precipitation of all of the ammonium sulfate from the aqueous solution. Preferably, the ammonium sulfate is thereafter filtered and the filtered solids washed with an alcohol, preferably methanol, to clean any of the organics present thereon. The organics dissolved by the alcohol can be recovered after recovering the alcohol by distillation and recycled, if desired, back to the synthesis reaction together with the aqueous ammonium bisulfate solution. Because the method of the present invention provides for the precipitation of substantially pure crystalline ammonium sulfate, the sulfate can be used substantially in precipitated or preferably washed form after drying of methanol as a fertilizer or may be regenerated to ammonium bisulfate by known methods for use in the organic synthesis.
DESCRIPTION OF THE INVENTION
Solutions of ammonium bisulfate, ammonium sulfate and, optionally water, from organic synthesis reactions are treated with alcohol, preferably methanol, after the synthesized product has been removed therefrom. Suitable alcohols in addition to methanol include ethanol, butanol, isopropanol, and the like. However, because of the relative cheapness of methanol, it is preferred. The alcohol is added to the aqueous solution preferably in amounts from about 400 to 500% by weight of the amount of ammonium sulfate theoretically present. The temperature at which separation is effective to remove all of the ammonium sulfate present is from preferably 15° to 30°C.
It may be desirable to concentrate the aqueous solution prior to the sulfate removable, since less alcohol would be required to effectuate precipitation. For instance, in Example 1 below, it was found advantageous to concentrate the raffinate by evaporation of 40% of the water present therein. This provided a more concentrated solution of ammonium sulfate and ammonium bisulfate. With that particular concentration, for example, substantially all of the ammonium sulfate present was removed by precipitation. That concentration of salt before precipitation is about the minimum concentration possible while maintaining the salt in solution at room temperature.
The following generalized examples more clearly set forth the advantages of the present invention:
EXAMPLE 1
1 mole of an aromatic amine was reacted with 7.5 moles of ammonium bisulfate in 100 moles water and 0.7 moles of ammonium sulfate were charged into a glass lined shaker autoclave. After 3 hours at 240°C., a yield of 83% synthesized material was extracted from the solution. The raffinate was concentrated to remove 40% of the water present. After cooling, 400 ml of methanol were added. The precipitate was centrifuged and washed twice with 100 ml portions of methanol giving 82.0 g. of salt which analyzed as 99% (NH4)2 SO4 which was 92% of the theoretical amount present.
EXAMPLE 2
Example 1 was repeated using methanol for the selective precipitation and recovery of ammonium sulfate from the concentrated raffinate after extraction of the synthesized material. The raffinate was thereafter fortified with ammonium bisulfate in water, an aromatic amine equal in amount to those consumed and recycled. The results of these runs are set forth in the following table:
TABLE __________________________________________________________________________ Recovery of Ammonium Sulfate From Aqueous Mixtures With Ammonium Bisulfate Resulting From Synthetic Reactions Employing Amines Products Crude Reactor Charge, g. Product Synthesized Salt Analysis1) Aromatic Time, Temp., Recovered % of Theory % % Cycle Amine NH4 HSO4 (NH4)2 SO4 hrs. °C. g. % Yield Salt, g. as (NH4)2 SO4.sup .4) (NH4)2 SO4 NH4 HSO4 __________________________________________________________________________ 1 32.4 258.7 27.7 3 240 27.8 84.2 99.5 96.0 98.0 2.0 2 27.3 69.0 none 3 236 25.0 90.0 51.5 63.5 97.7 2.3 3 28.7 61.2 27.7 2 236 21.4 73.0 85.7 91.1 98.3 1.7 4 24.5 57.2 27.7 3 240 22.8 91.2 72.4 82.0 99.6 0.4 52) none none none 2 240 2.1 8.4 -- -- Totals 112.9 446.1 83.1 13 99.1 86.13) 83.2 5) __________________________________________________________________________ 1) (HN4)2 SO4 obtained by difference after titration of NH4 HSO4. 2) Concentrated to give 73 moles of water per theoretical mole of amine. 3) Crude was analyzed to be 96.1% product, giving an 82.6% corrected yield. 4) Assuming 1 m. amine charged gives 2 m. (NH4)2 SO4. 5) Avg. recovery over four cycles.