US3649173A

US3649173A - Stabilized ammonium nitrate

Info

Publication number: US3649173A
Application number: US5119A
Authority: US
Inventors: Rolf Falck-Muss; Daniel J Newman; Sydney Atkin
Original assignee: Chemical Construction Corp
Current assignee: Chemical Construction Corp
Priority date: 1970-01-22
Filing date: 1970-01-22
Publication date: 1972-03-14
Anticipated expiration: 1989-03-14
Also published as: FR2076915A5; BE761888A; GB1309612A; CA950638A; NL7100837A

Abstract

Solid ammonium nitrate particles are stabilized against thermal shock and cracking at phase transition temperatures by the inclusion of small but effective amounts of silicofluoride compound, a phosphate compound and a sulfate compound in combination, within the solid ammonium nitrate particles.

Description

United States Patent Falck-Muss et al.

STABILIZED AMMONIUM NITRATE Inventors: Rolf Falck-Muss, Arzew, Algeria; Daniel J. Newman, Jackson Heights, N.Y.; Sydney Atkin, Springfield, NJ.

Assignee: Chemical Construction Corporation, New

York, NY.

Filed: Jan. 22, 1970 Appl. No.: 5,119

U.S. Cl ..23/103, 71/35 Int. Cl ..C0lc l/18 Field of Search ..23/l03; 71/35; 252/385, 397

[ 51 Mar. 14, 1972 Primary ExaminerOscar R. Vertiz Assistant Examiner-G. O. Peters Attorney-J. L. Chaboty [5 7] ABSTRACT Solid ammonium nitrate particles are stabilized against thermal shock and cracking at phase transition temperatures by the inclusion of small but effective amounts of silicofluoride compound, a phosphate compound and a sulfate compound in combination, within the solid ammonium nitrate particles.

9 Claims, No Drawings STABILIZED AMMONIUM NITRATE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to the production of solid discrete particles of ammonium nitrate, and the prevention of thermal shock and cracking due to internal stress in the particles generated at phase transitions which occur due to temperature change.

2. Description of the Prior Art Numerous additive compounds have been suggested, either singly or in combination, for inclusion in solid ammonium nitrate particles, in order to prevent or alleviate the well known phenomenon of thermal shock and cracking of the particles which readily occurs in pure ammonium nitrate particles when the temperature of the particles is raised or lowered through the phase transition temperatures, of which the 32 C. transition point is most significant in practice. Among those compounds which have been suggested in the prior art are phosphates such as potassium metaphosphate, mono-and diammonium phosphate, sulfates such as ammonium sulfate, potassium chloride, magnesium salts, calcium salts, sodium silicate, clays, nitrates such as sodium nitrate, calcium nitrate and potassium nitrate, iron cyanides, copper oxides and boron compounds. These compounds and various combinations of compounds are proposed in US. Pat. Nos. 1,406,455; 1,698,793; 1,868,890; 1,932,434; 1,939,165; 1,947,601; 1,966,947; 2,124,332; 2,136,069; 2,657,977; 2,702,747; 2,879,133; 2,901,317; 2,943,928; 2,957,763; 3,007,773; 3,018,164; 3,021,207; 3,026,193; 3,030,179; 3,034,853;

3,034,858; 3,070,435; 3,116,108, 3,117,835; 3,148,945 and 3,317,276. The inhibition of calcium nitrate formation in the production of nitrochalk by silicofluoride addition is disclosed in U.S. Pat. No. 3,351,454.

SUMMARY OF THE INVENTION In the present invention, it has been determined that an improved solid ammonium nitrate composition may be produced in the form of discrete particles which resist thermal shock and cracking due to deformation at phase transition temperatures such as 32C., by the inclusion of a synergistic combination of compounds into the solid ammonium nitrate, preferably by the addition of small but effective amounts of these compounds to molten ammonium nitrate prior to solidification of the ammonium nitrate as discrete particles by prilling or the like. The molten ammonium nitrate is preferably initially in the form of a substantially anhydrous melt, however in some cases the melt may contain water in an amount up to about 5 percent by weight. The additive compounds employed in combination in the present invention are a silicofluoride compound, a phosphate compound and a sulfate compound. Numerous compounds within each of these categories may be effectively employed to stabilize ammonium nin'ate. Among the feasible silicofluoride compounds are ammonium silicofluoride, sodium silicofluoride, potassium silicofluoride, magnesium silicofluoride and zinc silicofluoride, or mixtures of these compounds. Usable phosphate compounds include monoammonium phosphate, diammonium phosphate, trisodium phosphate and mixed fertilizer compositions which include phosphatic fertilizer components. Among the many sulfate compounds which may be employed in the present invention are ammonium sulfate, sodium sulfate, potassium sulfate and calcium sulfate. A preferred method of adding a phosphate compound and a sulfate compound to the molten ammonium nitrate is by the addition of phosphoric acid and sulfuric acid to the molten ammonium nitrate, or to its precursor nitric acid, followed by in situ neutralization of the acids by addition of a suitable base or basic solution to the molten ammonium nitrate. Typical feasible basic materials for this purpose include ammonia, sodium hydroxide, sodium carbonate potassium hydroxide and potassium carbonate, and these bases may by added either in the anhydrous state or as aqueous solutions. The molten ammonium nitrate containing the additive compounds of the present invention in combination is preferably solidified in the form of discrete particles by a prilling procedure, in which the molten ammonium nitrate is sprayed into an airstream, so that the resulting ammonium nitrate droplets solidify in the airstream in the form of spherical solid prills. The resultant prills preferably contain up to about 0.5 percent by weight of each of the additive compounds, and in accordance with the present invention the resulting prills are highly resistant to thermal shock and cracking at the phase transition temperatures such as 32C. Alternative methods of solidifying the molten ammonium nitrate in the form of discrete particles after additives addition include granulation, crystallization, or by flowing the molten ammonium nitrate onto a chilled belt on which the molten material solidifies in the fonn of a thin sheet or film which is then broken up into small crystals or particles.

The principal advantage of the present invention is that the resulting solid ammonium nitrate composition is stabilized against thermal shock and cracking at phase transition temperatures, so that the product may be safely stored for extended periods of time without the development of a dusting or caking problem. Another advantage is that the production of fines or powdered material during the preparation of the discrete solid particles by prilling or the like is substantially reduced, so that the recycle of fines is reduced in the ammonium nitrate production facility, which reduces the capital and operating costs such as by decreasing stream consumption for concentration of remelt solutions. A further advantage is that the additive compounds of the present invention are relatively inexpensive, and in most cases these additives are readily available at fertilizer complexes or production sites, especially when phosphatic fertilizers are concomitantly produced from phosphate rock, phosphatic shales or the like. Silicofluorides are generally produced and recovered as byproducts in the processing of phosphatic raw materials to produce phosphate products, as for example in the production of phosphoric acid as described in US. Pat. No. 2,905,535. An additional advantage is that the additive compounds of the present invention can be disseminated and dissolved into the molten ammonium nitrate, and the provision of special or ancillary mixing equipment or apparatus is minimized.

It is an object of the present invention to provide an improved solid ammonium nitrate product.

Another object is to prevent thennal shock and cracking of solid ammonium nitrate particles at phase transition temperatures, by the addition of a synergistic combination of additive compounds to the ammonium nitrate.

A further object is to produce improved ammonium nitrate prills which are resistant to thermal shock and cracking at phase transition temperatures, and which may be safely stored for extended periods of time without dusting or caking.

An additional object is to reduce the amount of fines and powder which are formed when molten ammonium nitrate is converted to discrete solid particles by prilling or the like.

An object is to provide an improved method of stabilizing solid ammonium nitrate particles against thermal shock and cracking at phase transition temperatures, by employing a combination of additive compounds in the ammonium nitrate including a silicofluoride compound, a phosphate compound and a sulfate compound.

These and other objects and advantages of the present invention will become evident from the description which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS Ammonium nitrate crystals or prills without additives undergo volume expansion and contraction as they pass through the phase transition temperatures such as 32 and 83C., causing the prills to break down into fine particles or dust. The effect of various additives including the additives combination of the present invention was investigated on a laboratory scale, followed by further testing in a commercial facility,

which demonstrated the improved results obtained by the present invention.

In all cases, the prills were subjected to a number of temperature changes through a range which included a phase transition temperature, and the percentage of prills cracked from thermal shock at various numbers of transition was determined. Following are the results obtained in the laboratory scale and commercial plant facility tests.

EXAMPLE I. LABORATORY SCALE TESTS The ammonium nitrate prills produced in the laboratory were obtained by spraying a melt consisting of 99.5 percent ammonium nitrate plus additive from a gun containing 0.029 inch holes using about 10 p.s.i.g. nitrogen pressure. In order to obtain more failing height, the spray was arched from the top of a 27-feet-high platform toward the ceiling and allowed to fall to the floor. The prills produced in this manner contained considerable irregularly shaped prills and were weaker than prills produced in a commercial plant, but otherwise had characteristics similar to commercial prills.

TABLE I.

TYPICAL SCREEN ANALYSIS OF LABORATORY PRILLS Mesh Size By Weight .+6 mesh 0.0 6+8 mesh 9.! 8+l0 mesh 33.3 -l+ l4 mesh 43.3 l4 mesh 14.3

For the phase transition tests, only 8 0 mesh prills were used. Two different series of test were made to determine the resistance of ammonium nitrate prills produced without and with various additives, to thermal shock and cracking due to repeated passage through transition temperatures. In the first series of tests, prills were heated in an oven at 42C. for 2 hours and then allowed to cool to room temperature at 23C. for 2 hours. The temperature changes thus provided for a transit of the phase transition temperature of 32C. Alter each cycle, the percentage of unbroken prills was recorded. In the second series of tests, the prills were cycled between 91 and 42C. at 2 hour internals, to provide for a transit of the phase transition temperature of 83C. Following is data relative to the inclusion of additives in the prills.

TABLEII ADDITIVE INCLUSION IN PRILLS Run Nos. Additive (S) Added By Weight I and I4 none 0 2 and 15 ammonium sulfate 0.2 2 and 15 diammonium phosphate 0.2 2 and 15 sodium silicofluoride 0.2 3 and I6 diammoniurn phosphate 0.6 4 and 17 ammonium sulfate 0.6 5 and I8 ammonium sulfate 0.3 5 and I8 diammonium phosphate 0.3 6 and 19 sodium silicol'luoride 0.6 7 and 20 ammonium silicofluoride 0.6 8 and 2l potassium metaphosphate 0.6 9 and 22 potassium metaphosphate 0.3 9 and 22 sodium silicofluoride 0.3 10 and 23 boric acid 0.6 l l and 24 boric acid 0.3 II and 24 sodium silicofluoride 0.3 l2 and 25 aluminum phosphate 0.6 If! and 26 calcium carbonate 0.3 l3 and 26 ammonium sulfate 0.3

Number of transitions Percent prills cracked trom thermal shock (42 O.-23 0. cycle) TABLE IV.-EFFECT OF ADDITIVES ON PRILL BREAKA GE FROM THERMAL SHOCK AT 83 C. PHASE TRANSITION Number 0! transitions Percent prills cracked lrom thermal shock (91 C.42 0. cycle) From the results in Table IV, it is evident that the combination of additives of the present invention, as provided in Run No. 15, provided complete stabilization of the ammonium nitrate and attained the greatest improvement of all of the additives or additive combinations tested, as compared to Run No. 14 in which no additive was present in the ammonium nitrate.

EXAMPLE I]. COMMERCIAL PLANT TESTS Test were conducted at a commercial ammonium nitrate production facility to confirm the laboratory results of Example I. The facility was operated at a production rate of 300 tons/day of prilled ammonium nitrate. Initial prilled ammonium nitrate samples were taken without the addition of stabilizer, and further samples were taken after the stabilizer of the present invention was added to the molten ammonium nitrate prior to prilling the melt. Samples were taken at the prill cooler outlet, which discharged prills without stabilizer addition at a temperature of 50C. With the addition of stabilizer, prill cooler exit temperature was reduced to 38 or 29C. as indicated infra. The stabilizer was an aqueous solution made at the site and consisting (by weight) of 75.4 percent water and 8.2 percent each of sodium silicofluoride, ammonium sulfate and l8-460 fertilizer, the latter component consisting principally of diammonium phosphate. The fertilizer was dissolved in water, decanted and screened to remove sand and other insolubies. The stabilizer was constantly agitated and held at 66C. by steam coils.

After taking dry run samples without additive addition, the

prill breakage from thermal shock at the 32 C. transition point.

TABLE V ADDITIVE INCLUSION 1N PRILLS (BY ANALYSIS) Percent By Weight of Additive D' A m Run Nov Phosphate Sulfate Silicofluoride TABLE VI PLANT OPERATING CONDITION Prill Cooler Run No. Exit Temperature TABLE VIL-EFFECT 0F STABILIZER ON PRILL BREAK- I%IiIOROM THERMAL SHOCK AT 32 0. PHASE TRAN- N umber of transitions Percent prills cracked from thermal shock (42 C.23 0. cycle) The greatly improved results obtained in Run Nos. 2 and 3 due to stabilizer addition, as compared to Run No. l in which no stabilizer additives were provided, clearly indicate the commercial advantages of the invention in stabilizing ammonium nitrate against thermal shock at phase transitions. It should be noted that without the additive, prills cannot be cooled below 50C. without greatly excessive breakage.

We claim:

1. A method of stabilizing solid ammonium nitrate particles against thermal shock at phase transition temperatures which comprises adding a small but effective amount of a silicofluoride compound, a phosphate compound and a sulfate compound to molten ammonium nitrate, whereby said compounds are distributed in said molten ammonium nitrate, and solidifying said molten ammonium nitrate in the form of dis crete particles, said solid ammonium nitrate particles containing said compounds in sufficient proportion to render said particles resistant to cracking from thermal shock at phase transition temperatures.

2. The method of claim 1, in which said molten ammonium nitrate contains water in an amount up to about 5 percent by weight.

3. The method of claim 1, in which said silicofluoride compound is selected from the group consisting of ammonium silicofluoride, sodium silicofluoride, potassium silicofluoride, magnesium silicofluoride and zinc silicofluoride.

4. The method of claim 1, in which said phosphate compound is selected from the group consisting of monoammonium phosphate, diammonium phosphate and trisodium phosphate.

5. The method of claim 1, in which said sulfate compound is selected from the group consisting of ammonium sulfate, sodium sulfate, potassium sulfate and calcium sulfate.

6. The method of claim 1, in which said phosphate compound and said sulfate compound are added to said molten ammonium nitrate by adding phosphoric acid and sulfuric acid to said molten ammonium nitrate during production of the ammonium nitrate, and neutralizing said acids within said molten ammonium nitrate by the addition of a base selected from the group consisting of ammonia, sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate.

7. The method of claim 1, in which said molten ammonium nitrate containing said compounds is solidified in the form of discrete particles by spraying said molten ammonium nitrate into an air stream, whereby said molten ammonium nitrate flows downwards through said air stream as discrete droplets which solidify in the form of prills.

8. The method of claim 1, in which each of said compounds is added to said molten ammonium nitrate in a proportion up to about 0.5 percent by weight of said molten ammonium nitrate.

9. A solid ammonium nitrate composition stabilized against thermal shock at phase transition temperatures which comprises ammonium nitrate containing small but effective amounts of a silicofluoride compound, a phosphate compound and a sulfate compound.

Patent No 3649173 Dated March 14, 1972 Inventor(s) R. Falck-Muus, D. J. Newman, S. Atkin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 2 line 28, read "steam" instead of "stream". Also line 71, read "32C" instead of "32".

Col. 3 line- 6, read "transitions" instead of "transition". Also line 46, read "91C" instead of "91". Also line 47, read "intervals" instead of "internals".

Claim 1 line 3 (col. 6 line 7) after "adding", delete "a" and read "the combination of". Also read "amounts" instead of "amount", Also read "at least about 0.12% by weight of" after "of",

Claim 9 line 4 (col, 6 line 52) read "at least about 0.12% by weight of" after "of" Signed and sealed this 29th day of August 1972.

(SEAL) Attest:

EDWARD MJLETGHER,JR. ROBERT GOTTSCHALK Attosting Officer Commissioner of Patents ORM FO-lOSO (10-69) USCOMM-DC 60376-7 69 u 5. GOVERNMENT PRINTING OFFICE: I969 0366-334

Claims

2. The method of claim 1, in which said molten ammonium nitrate contains water in an amount up to about 5 percent by weight.
3. The method of claim 1, in which said silicofluoride compound is selected from the group consisting of ammonium silicofluoride, sodium silicofluoride, potassium silicofluoride, magnesium silicofluoride and zinc silicofluoride.
4. The method of claim 1, in which said phosphate compound is selected from the group consisting of monoammonium phosphate, diammonium phosphate and trisodium phosphate.
5. The method of claim 1, in which said sulfate compound is selected from the group consisting of ammonium sulfate, sodium sulfate, potassium sulfate and calcium sulfate.
6. The method of claim 1, in which said phosphate compound and said sulfate compound are added to said molten ammonium nitrate by adding phosphoric acid and sulfuric acid to said molten ammonium nitrate during production of the ammonium nitrate, and neutralizing said acids within said molten ammonium nitrate by the addition of a base selected from the group consisting of ammonia, sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate.
7. The method of claim 1, in which said molten ammonium nitrate containing said compounds is solidified in the form of discrete particles by spraying said molten ammonium nitrate into an air stream, whereby said molten ammonium nitrate flows downwards through said air stream as discrete droplets which solidify in the form of prills.
8. The method of claim 1, in which each of said compounds is added to said molten ammonium nitrate in a proportion up to about 0.5 percent by weight of said molten ammonium nitrate.
9. A solid ammonium nitrate composition stabilized against thermal shock at phase transition temperatures which comprises ammonium nitrate containing small but effective amounts of a silicofluoride compound, a phosphate compound and a sulfate compound.