Method of formulating alkali earth salts

This application claims the benefit of U.S. Provisional Application No. 60/103,969, filed Oct. 13, 1998.

The present invention relates to a method of formulating alkali earth salts and more particularly, the present invention relates to a method of gene rating food grade sodium bicarbonate and fertilizer grade potassium sulfate.

A significant amount of prior art has been promulgated with respect to the formulation of alkali earth salts. Sodium bicarbonate, as an example, has been prepared in as many different ways as it has been known. Despite this fact, previous unit operations for bicarbonate synthesis have been hampered by inefficient energy use which results directly in increased synthesis costs. As a further limitation, known processes do not make efficient use of the unit operations involved in the preparation of salts. Typically, a single high quality product is formulated with concomitant byproduct formation of a quality inadequate for commercial purposes or that would require too substantial an investment to render them commercially viable.

Representative of the prior art is U.S. Pat. No. 3,429,657, issued Feb. 25, 1969, to D'Arcy. The reference discusses a method for recovering and producing potassium salts. In the reference, a potassium bearing brine is reacted with sodium perchlorate to precipitate potassium perchlorate. The potassium is removed by ion exchange with sodium and the free potassium is then combined with chloride, sulfate, nitrate inter alia.

One object of the present invention is to provide a method of formulating food grade sodium bicarbonate and potassium sulfate, comprising the steps of:

a) providing a source of liquid sodium sulfate;

b) providing a source of ammonium bicarbonate;

c) contacting the sodium sulfate and the ammonium bicarbonate;

d) precipitating sodium bicarbonate and forming a liquor;

e) precipitating sodium bicarbonate and forming a liquor by contacting the liquor from step d) with sodium sulfate;

f) saturating the liquor from step e) with sodium sulfate;

g) filtering solids from the liquor of step f);

h) contacting the liquor from step g) with sulfuric acid to precipitate carbonates;

i) cooling the liquor from step h) to 0° C. to form Glauber's salt precipitate;

j) heating the liquor from step i) to between 30° to 40° C.; and

k) precipitating potassium sulfate by contacting the liquor from step j) with potassium chloride.

A further object of the present invention is to provide a method of formulating food grade sodium bicarbonate and potassium sulfate, comprising the steps of:

a) providing a source of liquid sodium sulfate;

b) providing a source of ammonium bicarbonate;

c) contacting the sodium sulfate and the ammonium bicarbonate;

d) precipitating sodium bicarbonate and forming a liquor;

e) precipitating sodium bicarbonate and forming a liquor by contacting the liquor from step e) with sodium sulfate;

f) saturating the liquor from step e) with anhydrous sodium sulfate;

g) filtering solids from the liquor of step f);

h) contacting the liquor from step g) with at least one of ammonium bicarbonate, ammonia gas or carbon dioxide to precipitate sodium bicarbonate;

i) cooling the liquor from step h) to 0° C. to a precipitate of sodium bicarbonate and sodium sulfate; and

j) precipitating potassium sulfate by contacting the liquor from step i) with potassium chloride.

It has been found that following the sodium bicarbonate formulation, significant success in cooling the liquor to 0° C. is realized for removing sodium sulfate as Glauber's salt and sodium bicarbonate. Glauber's salt solubility in the system is contemplated by the ammonium sulfate-sodium sulfate phase diagram. By increasing the sodium sulfate in the bicarbonate circuit with increased Glauber's salt recycle, there is a tendency to decrease the bicarbonate solubility and increase the process efficiency.

Regarding the conversion of the starting reagents to potassium sulfate, particular success has been encountered by maintaining a mole ratio of five (5) or greater for the potassium and ammonium ions. This ratio ensures high conversion efficiency in the second stage of the process.

Having thus described the invention, reference will now be made to the accompanying drawings illustrating preferred embodiments.

FIG. 1 is a process flow diagram illustrating a first part of one process according to the present invention;

FIG. 1 a illustrates a second part of the process illustrated in FIG. 1;

FIG. 1 b illustrates a third part of the process illustrated in FIG. 1;

FIG. 2 is a is a process flow diagram illustrating a first part of a variation of the process according to the present invention;

FIG. 2 a illustrates a second part of the process illustrated in FIG. 2; and

FIG. 2 b illustrates a third part of the process illustrated in FIG. 2 .

Similar numerals in the figures denote similar elements.

Referring now to the drawings, FIGS. 1 through 1 b illustrate the process according to a first embodiment.

A source of liquid sodium sulfate 10 dissolved in fresh water and centrate water 12 discussed herein after. The solution is mixed in vessel 14 at 40° C. to a specific gravity of 1.30. The solution is filtered in filter 16 which, as an example, may comprise a 5 micron filter. The solids 18 are disposed of while the filtrate 20 is passed into a first sodium bicarbonate crystallization vessel 27 .

Feeds of water, ammonia and carbon dioxide all denoted by numeral 24 are reacted in vessel 22 in order to synthesize ammonium bicarbonate. Formulated ammonium bicarbonate is centrifuged in centrifuge 26 , with the solid product being passed into crystallization vessel 27 . A recycle loop 28 recirculates ammonium bicarbonate solids and liquor into reaction vessel 29 . The result of the combination in vessel 29 is the formulation of sodium bicarbonate. The mixture is filtered by filter 30 and centrifuged. The sodium bicarbonate is washed with water in vessel 32 , centrifuged in centrifuge 34 and the solid retained as food grade sodium bicarbonate. The wash water is returned to vessel 14 .

The liquor from filter 30 has a specific gravity of 1.25 with the contents including approximately 10.4% sodium sulfate, 17.1% ammonium sulfate, 8% sodium bicarbonate and excess ammonium bicarbonate for reaction with the Glauber's salt (discussed herein after). The liquor is reacted in a vessel 36 at 40° C. with Glauber's salt formulated in the cooling phase of the process, which will be discussed later, to produce sodium bicarbonate from the excess of ammonium bicarbonate from crystallization vessel 29 . Alternatively, the ammonium bicarbonate may be added to the second stage (vessel 36 ) as solid, slurry or solution.

To the liquor from vessel 36 is added to solid sodium sulfate from source 41 in vessel 40 to formulate a saturated liquor of sodium sulfate/ammonium sulfate. Sufficient ammonium bicarbonate may be present to complete the reaction is solution or some may be added to result in the liquor having a specific gravity of 1.285. The slurry from vessel 40 is filtered with filter 42 . The sodium bicarbonate solids 48 are passed to vessel 32 and the liquor 44 is further processed with additional separation of sodium bicarbonate, which is returned to vessel 32 . The liquor 44 , is then passed to vessel 46 (FIG. 1 A). Circuit volume from the sodium bicarbonate circuit can be controlled by evaporating the purified sodium sulfate in the feed to produce solid sodium sulfate to ensure circuit saturation.

Returning to FIG. 1A, vessel 46 contains sulfuric acid to precipitate carbonate compounds. The so treated liquor is cooled to 0° C. in chiller 48 to recover Glauber's salt and filtered in filter 50 . The recovered Glauber's salt is returned to the sodium bicarbonate crystallization vessel 36 .

The filtrate contains 25.25% by weight ammonium sulfate and up to 1% by weight sodium sulfate and is passed into a vessel 52 heated to between 30° C. and 40° C. and combined with solids 65 from filter 66 . This solution is passed into vessel 54 where solid potassium chloride is reacted therewith to formulate a 20% by weight solution of ammonium chloride also containing, by weight approximately, 20.2% ammonium chloride, 6.7% potassium chloride, 4.9% sodium chloride, 2.3% as (x) 2 SO 4 , where x=Na, K, and solid mixed crystals of potassium sulfate with 10%-20% ammonium sulfate.

The solution is filtered in filter 56 , with the solid fraction containing approximately by weight, 5% potassium chloride, 80%-85% potassium sulfate, 10%-15% ammonium sulfate. The solid fraction is combined in vessel 58 with water and potassium chloride brine from vessel 60 . The potassium sulfate solid is centrifuged and filtered in filter 62 and recrystallized with a solution of potassium chloride at 25° C. The remaining ammonium sulfate is converted to potassium sulfate. Grades of greater than 98% potassium sulfate are achievable.

In further unit operations, the liquor or filtrate from the potassium sulfate operations and specifically from filter 56 is processed in accordance with the unit operations set forth in FIG. 1 c . The liquor is evaporated in evaporator in order to concentrate the ammonium chloride liquor such that upon cooling the potassium chloride and residual sulphates are minimized in solution. The solution is filtered with filter 66 with the solid material 67 recycled to vessel 54 . The filtrate containing approximately 22% to 30% ammonium chloride is reacted with lime in reactor 68 with liberated ammonia recycled. The calcium chloride formed may be passed to a settler 70 or scrubber 72 depending on intended subsequent uses.

Having set forth the process according to this first embodiment, reference will now be made to an example of the process.

Feed—1 liter @ 1.3 S.G. 360 g/l Na 2 SO 4

1st STAGE

Production of NaHCO 3

Brine Exit at reaction termination:

2nd STAGE 0.95 l of brine will dissolve the following:

2nd STAGE Final Solution Composition

BASIS: One Tonne of Na 2 SO 4 Feed

Turning to FIGS. 2 through 2 b , an alternative processing scheme is schematically depicted. In this reaction scheme, prior to the production of sodium bicarbonate, the liquors are saturated with anhydrite.

In this embodiment, sodium bicarbonate is produced in crystallization unit 22 and undergoes generally similar steps as set forth for FIGS. 1 through 1B. The brine or filtrate is saturated with anhydrous sodium sulfate in vessel 36 and filtered with filter 38 to remove insolubles which are discarded. The filtrate from this operation is reacted with ammonium bicarbonate in vessel 80 . As an alternative, the filtrate could be reacted with ammonia or carbon dioxide to precipitate the sodium bicarbonate. The solution is filtered with filter 82 and the sodium bicarbonate remains. The latter is combined with the sodium bicarbonate from filter 30 and then washed, centrifuged and dried. These steps are not shown.

The filtrate remaining has a composition of approximately, on a by weight basis, 10% sodium sulfate, 24% ammonium sulfate and 8% sodium bicarbonate. The solution has a specific gravity of 1.285 at 40° C.

From this stage, the filtrate solution is cooled in a chiller 84 to approximately 0° C. in order to produce a filtrate containing approximately, on a by weight basis 5% sodium sulfate, 28% ammonium sulfate and 6% sodium bicarbonate. The solution is filtered with filter 86 and precipitated sodium bicarbonate and sodium sulfate are recycled back to the bicarbonate crystallization vessel 32 , while the filtrate is reacted with potassium chloride in vessel 88 to synthesize first stage potassium sulfate in a purity range of about 75% to 90%. The solid potassium sulfate is repulped with potassium chloride brine from vessel 92 in vessel 94 . This results in high quality, high grade potassium sulfate. The product is washed with water in a conventional washing stage 96 with recycle to vessel 94 .

The solution from filter 90 is evaporated in evaporator 98 (FIG. 2A) to concentrate ammonium chloride liquor whereby upon cooling the potassium chloride and sulfates are minimized. The solution is filtered using filter 100 with the precipitated potassium chloride and (x)SO 4 , where x=K, Na, recycled to vessel 88 .

The filtrate from filter 100 containing ammonium chloride, potassium chloride and potassium sulfate is passed into evaporator 102 . The sodium bicarbonate backs the reaction and as a result, ammonia and carbon dioxide are released. These gases are then scrubbed/handled using suitable techniques. The calcium chloride generated is then discarded or sold.

Feed—1 liter @ 1.3 S.G. 360 g/l Na 2 SO 4

1 st STAGE

Production of NaHCO 3

Brine Exit at reaction termination:

Resaturation with Na 2 SO 4 : brine will hold 150 g Na 2 SO 4 . This brine is then filtered and fed to the second stage NaHCO 3 crystallizer.

The exit brine is then cooled to 0° C.

Brine composition is: 5.0% Na 2 SO 4 which mean 60 g Na 2 SO 4 precipitates as 136 g of Na 2 SO 4 10H 2 O precipitate and remove 76 g of H 2 O.

Therefore: 907−76=831 g H 2 O

Brine composition @ 0° C. and 1.26 S.G.

70 g Na 2 SO 4

353 g (NH 4 ) 2 SO 4

100 g NaHCO 3

831g H 2 O

1354g TOTAL

About 1 liter brine K 2  SO 4 a )     70     g     Na 2  SO 4 142 × 174 = 85.8 b )     353     g     ( NH 4 ) 2  SO 4 132 × 174 = 465.3     g

Boil up to 33.0% NH 4 Cl.

Release of NH 3 and CO 2 from evaporator but NH 4 Cl salts out KCl and not the NaCl. KCl is recovered same as in Example 1.

BASIS: One Tonne Na 2 SO 4 Feed

This brine is then heated to 25° C. where KCl solid is added to produce K 2 SO 4 . The exit brine from the K 2 SO 4 circuit has the following composition:

This brine is than heated and reacted with lime to recover the ammonia and bypass the evaporator. The KCl reports to the CaCl 2 brine rather than being recovered in the evaporator. This represents a 15 to 20% loss of K to the CaCl 2 brine. The KCl in the CaCl 2 brine can be reduced to as low as 1.0% by adding solid Na 2 SO 4 to CaCl 2 /KCl brine. The potassium is effectively collected as apprecipitated of syngenite (CaSO 4 .K 2 SO 4 .xH 2 O) at 0 to 100° C. with preferred temperatures of 20 to 30° C. so that SO 4 solubility is kept to minimum and the reaction occurs at a reasonable rate.

CaCl 2 Brine composition

The exit brine can be deep well disposed of and cake can be blended into the K 2 SO 4 product as binder or further processed to remove the CaSO 4 .

The cake can be reacted with (NH 4 ) 2 HCO 3 from the NaHCO 3 process feed and the CaSO 4 reacts quickly to produce a brine of (NH 4 ) 2 SO 4 and K 2 SO 4 and a filter CaCl 3 precipitate which is disposed of. The (NHa) 2 SO 4 /K 2 SO 4 brine is recycled to K 2 SO 4 first stage crystallizer.

Although embodiments of the invention have been described above, it is not limited thereto and it will be apparent to those skilled in the art that numerous modifications form part of the present invention insofar as they do not depart from the spirit, nature and scope of the claimed and described invention.