MXPA00011776A - Ammonium nitrate bodies and a process for their production - Google Patents

Abstract

A process for the production of ammonium nitrate bodies in particulate form wherein an ammonium nitrate/water liquid mixture containing at least 92%and preferably at most 97.5%by weight ammonium nitrate, optionally with a proportion of the ammonium nitrate substituted by alkali- and/or alkaline earth metal nitrate, and a small amount of poly-styrene sulphonate crystal-habit modifier is sprayed as droplets into an atmosphere in which cooling effects crystallisation of the ammonium nitrate and which the crystallised particles are dried to remove moisture, wherein the liquid mixture also contains ammonium sulphate, the concentration of poly-styrene sulphonate in the liquid mixture being at least 0.01%, preferably in the range 0.02 to 0.06%, by weight, and the concentration of ammonium sulphate in the liquid mixture being greater than that of the poly-styrene suphonate and at least 0.04%, preferably in the range 0.06 to 0.15%, by weight. Ammonium nitrate bodies, preferably prills, produced by the process may contain less than 0.1%by weight water and be able to absorb not less than 6%of their weight of fuel oil while remaining a pourable particulate material.

Description

BODIES OF AMMONIUM NITRATE AND A PROCESS FOR ITS PRODUCTION FIELD OF THE INVENTION This invention relates to ammonium nitrate bodies produced by spraying a liquid mixture of ammonium nitrate and water that is highly concentrated with ammonium nitrate (hereinafter "AN") in an atmosphere where the AN is rapidly crystallized and the water by evaporation. The bodies may be nuggets (ie, dense round particles resulting from the crystallization of droplets falling freely from the mixture) or agglomerates (ie, less dense associations of constitutive AN crystallites, of irregular shape and size) or granules (ie, generally rounded particles that grow upon spraying the mixture onto a drummed starting material such as small nuggets of AN, such that the layers of AN crystals are embedded on the initiator material). The invention relates particularly to ammonium nitrate bodies for use in explosive products, but is not restricted to such bodies. In particular, the invention can also be extended to such bodies for use in fertilizer products. -s.

DESCRIPTION OF THE PREVIOUS TECHNIQUE Descriptions of technologies for the production of AN nuggets and pangranulated bodies of AN are available in the patent literature and other literature. References that may be useful are EP-A-0320153 (formation of vibratory nuggets of acoustic frequency to produce a nugget substantially of a single size), U.S. Patent No. 5354520 (intensive process of nugget formation) and United States Patent No. 5395559 (pangranulation of small, single-size pips thickened). The preferred size for AN nuggets used in explosive products is approximately 2-3 mm; the preferred size of granular products is about 3-4 mm and for these, a 1 mm starter nugget may be suitable. A nug of AN designed for use as an oxidant in explosive products is required to have sufficient porosity to allow the absorption of 6 to 12% by weight of fuel oil and still be a free-flowing particulate product which can be poured or supplied by elicoidal screw in perforations. This product is called ANFO. Such a nugget is also a very satisfactory material to be combined with explosive emulsions. To obtain such porosity, an AN / water mixture must contain up to, and at most, Ba * »fe-t« * t. , * ..- "^. ... "..¿ ,,. "^. ,,.? T t ?. ^, ",,., AAU t; "M a ^ approximately 97.5% by weight of AN, the preferred range is 92-97.5% ', more preferably 94-96% by weight of AN. The water content of the AN / water mixture also affects the density and friability of the AN nugget. Thus, for example, an AN fertilizer grade nug which is produced from an AN / water mixture containing at least 98% by weight of AN is hard, dense and of slow porosity. Other characteristics of an AN nugget of explosive grade that affects friability and stability towards changes Atmospheric (for example, cycling of temperature and humidity) are the microcrystalline structure and the residual moisture content of the nugget. These characteristics are also important in other forms of AN bodies used as solid oxidants in explosive products, for example particles of pangranulated AN, although they do not have the hardness or low friability desired in a nugget of AN explosive grade. It is known to incorporate crystal habit modifiers in the AN / water mixtures used as feed in the described processes to encourage or cause AN to crystallize as small crystals of preferred conformation. As a general rule, smaller crystals of a smaller dimensional proportion are a characteristic of less reliable and more resistant AN bodies, especially nuggets. U.S. Patent No. 5597977 describes the use of sulfonate of ^ G »^ __ á_j _-_ 8 _? _ __? ___ ___ ___ ___ Polystyrene as an ingredient in the AN / water mixtures used to produce AN bodies. In addition to wastewater, minor impurities and minor amounts of deliberately added processing aids and enhancing products, AN bodies designed for use as explosive oxidants will preferably consist of AN. However, it is known to replace some of AN by alkali metal or alkaline earth metal nitrates, or both, in oxidants for explosives and references in the present AN should be considered as AN optionally with a proportion of the ammonium nitrate substituted by one or more additional nitrate oxidants. Therefore, references to proportions of AN in the feed mixes can be for practical purposes considered as proportions of the total nitrate oxidant.

BRIEF DESCRIPTION OF THE INVENTION According to the present invention, there is provided a process for the production of ammonium nitrate bodies in particulate form, wherein the mixture of ammonium nitrate / liquid water contains at least 92% by weight of ammonium nitrate, optionally with a proportion of the ammonium nitrate substituted by alkali metal or alkaline earth metal nitrate, or both, and a small amount of a i **? ? t. , 1 polystyrene sulfonate crystal habit modifier which is sprayed as droplets within an atmosphere in which the cooling carries out the crystallization of the ammonium nitrate and in which the crystallized particles are dried to remove the moisture, characterized in that the liquid mixture also contains ammonium sulfate, the concentration of polystyrene sulfonate in the liquid mixture is at least 0.01% by weight, and the concentration of ammonium sulfate in the liquid mixture is higher than that of polystyrene sulfonate and is of at least 0.04% by weight. The present invention further provides a process for producing AN bodies by pilling, pangranulation or other means of producing AN particles composed of aggregates of AN crystals in which the AN / water mixture, as described immediately below Next, it is sprayed with cooling to carry out the crystallization of AN followed by drying a stream of gas, especially air to remove substantially all of the free moisture, preferably to a residual water content of at most 0.1% water by weight in the dry product. This type of process is preferably the formation of nuggets under conditions of formation of vibratory nuggets by acoustic frequency so that pips are produced substantially of a single size, with the drying carried out in one or a train of two or more rotary dryers under drying gas with current or countercurrent, for example, air, flow and the process preferably is in accordance with the immediately preceding paragraphs. The present invention also provides AN bodies, specifically AN nuggets, produced by a process as described in any of the two immediately preceding paragraphs. The invention also extends to the use of a cinergistic combination of polystyrene sulfonate and ammonium sulfate as crystal-field modifiers in the production of ammonium nitrate nuggets, especially nuggets of explosive-grade ammonium nitrate. Preferably, the AN / water mixture contains at most about 97.5%, more preferably 94-97%, even more preferably 95-97% AN. However, the AN / water mixture may contain more AN if the bodies of AN are to be used in fertilizer products. Preferably, the concentration of polystyrene sulfonate is at least 0.02% by weight of the mixture. The mixture further includes an amount of ammonium sulfate which is greater than the amount of polystyrene sulfonate present, preferably at a concentration in the mixture of, for example, 0.06 to 0.15% by weight, more preferably 0.08 to 0.13% in weigh. & amp; amp; amp; & amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; amp; ammonia salt preponderance, and the normal practice of pH adjustment to a value of about 5.5 by the addition of ammonia. The polystyrene sulfonate exists as a range of molecules, not only as a polymer but there will be a range of chain lengths determined by the polymerization process and any fractionation, but also because the degree of sulfonation of the polymer chains can vary widely. Therefore, at one end of the spectrum of possible molecules is poly (vinylbenzene sulfonate) and, descending from this best characterized species, is a range of sulfonated polystyrenes. Preferably, these may be sulfonated at a level of at least 50% relative to the poly (vinylbenzene sulfonate), more preferably at least 75%, and much more desirable at least 90%. We have produced sulphonated polystyrenes with more than 90% degree of sulfonation from a range of polystyrenes whose average molecular weight is from 40,000 to 200,000; and all are effective additives. The higher molecular weight materials are more viscous and this makes production and handling more difficult. Low molecular weight material has been produced by polymerization of styrene followed immediately by sulfonation without any intermediate step of separation or purification. These materials have molecular weights that range from approximately 10,000 to 20,000, and again they are found to be effective. Actually, after sulfonation, the reaction product can be neutralized with ammonia and the result then is a mixture of sulfonated polymer and ammonium sulfate which can be used in the process of the invention to produce the ammonium nitrate bodies. . Typically, the ratio of polymer to ammonium sulfate, the weight, may be in the range of about 1: 5 to about 1:10, and this range is also very suitable for mixtures made by separately mixing the components obtained. The ability to use raw mixtures of sulfonated polystyrene and ammonium sulfate (from the neutralization of mother liquor with ammonia) is important in economic terms because polystyrene sulfonates are not readily available in commerce and to the extent When these become available, they are expected to be specific materials made with very different end uses in mind. The effect observed using polystyrene sulfonate only in minor amounts as a crystal habit modifier (ie, at a concentration in weight in the mixture of AN / water fed to the spray head of * í -? ^ ¡^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^ Jí * * J ^ &^^^^^^^ 0.06%) is that it allows the production of AN bodies that have a lower water content at rest compared to that which can be obtained using similar regimes of a thermal moisture gradient using ammonium sulfate or other crystal habit modifiers known alone. Therefore, while a residual water content of, at best, 0.1% by weight will typically be observed for product nuggets made using other crystal habit modifiers, the use of polystyrene sulfonate allows the nugget AN is coated with a water content as low as 0.05% or even 0.03% by weight. We believe that the reasons for this effect is that the polymeric sulfonate facilitates the transport of free water to the surface of the exposed AN particle so that the removal of moisture is faster in the drying stage or steps and acts to "expand" the proportion of water contained which is more tenaciously retained by ammonium nitrate and thus releases it for transport and evaporation. Surprisingly, we have prepared in batches raw batches of sulfonated polystyrene synthesized in the laboratory even in mixture with substantial amounts of ammonium sulfate (which results from the neutralization of spent acid ammonia) and we have observed, first of all, that there is no interference with the sulfonate performance although ammonium sulfate is a crystal habit modifier. Experience shows the opposite. Then we investigated the effect of reducing the proportion of the raw mixture used in the preparation of AN pips with a liquor with 94-96% of AN. We are amazed to discover that sulphonate concentrations less than 0.02% by weight of mother liquor are acceptable in pilot operations (at 60 kg / h of mother liquors of AN) and even 0.01% by weight is functional at feed rates of formation of nuggets on commercial scale (superior to 10 te / h). The sulfonate used alone would not be as effective at such low levels. Nor would the use of ammonium sulfate alone have provided the observed results. Clearly a cinergia is observed. The same result is obtained by using mixtures of sulphonate and sulphate in similar ratios, for example, from 1: 5 to 1:10 of sulfonate to sulfate, by weight. Therefore, we have discovered that the advantages obtained from the use of polystyrene sulfonate only at an effective level in the mother liquors of AN fed in the process described for the production of AN bodies in terms of removal rate of humidity, final water content (when desired), particle integrity and oil absorption, can be obtained by using a cynergistic combination of polystyrene sulfonate and ammonium sulfate so that the sulfonate concentration in the mother liquor feed of AN is 0.01 to, for example 0.06% by weight, and the dt.aSS 'l t, i? t fasta- »c.Áni? .nJ». _, *. *** A? ~ -, Íin. iS.?.Aa. ii &? ?. *. *. juk jH. The concentration of ammonium sulfate is 0.04 to 0.15%, for example. The optional upper values in these established concentration ranges only reflect economic preference. At sulfonate levels greater than 0.06%, the advantage of cinergy can not be enjoyed, but the advantage of being susceptible to using neutralized sulphonate raw batches containing substantial amounts of ammonium sulfate is still real. Similarly, when the cinergist effect is going to be used, there is no use for ammonium sulfate levels higher than 0.15% by weight in the mother liquors of AN, although technically it is acceptable. Our experience has established that optimization of the polystyrene sulphonation process does not result in relative levels of spent acid (sulfuric acid) so that after neutralization by ammonia there is a large excess of ammonium sulfate in the product mixture. This is the case whenever the preselected polystyrene is sulfonated or the styrene is first polymerized and then sulfonated in a continuous process without isolation of the polystyrene. Reference has been made to the level of residual water in the AN bodies produced. This is especially important in our experience when AN bodies are nuggets. The crystals of ammonium nitrate are thermodynamically stable in different crystal structures within different temperature bands. The eÁ? iíTTi i mt, .. •• Í -? . - > • i t * > í * -. . t ^ * l, "?. t. «A. "i, t. I.". i- ¿¿^ ': • &.;. j. &. '. < & * transition from the so-called phase IV to phase III occurs at approximately 32 degrees Celsius.The presence of moisture seems to encourage the transition so that the usual nuggets of familiar ANs to the explosives producers of a The sequence of storage of a hot day / cold night often leads to fracture of the pips, increased friability and consequent creation of fines (pulverized AN) The handling, storage, transport and production of explosives of the product are adversely affected. TO levels of low residual water in the pip, that is, less than 0.1% by weight, there seems to be a significant kinetic impediment to the problematic transition. The initial pip hardness afforded by the use of polystyrene sulfonate as a crystal habit modifier does not seem by itself being a sufficient reason for stability under repeated thermal cycling in the observed degree. An incidental and commercially important advantage of using less polystyrene sulfonate in the production of AN bodies is that when the bodies are used for To make mother liquors of AN for the production of emulsion of explosives there is less opportunity for emulsion stability which is adversely affected by interference of the polymeric sulfonate (a surfactant) with the emulsifier. xtsrí. ßtjpt? 0 k £ .a, 1 A- .: DETAILED DESCRIPTION OF THE PREFERRED AND OPTIONAL MODALITIES METHODS OF SYNTHESIS OF POLYSTYRENE SULPHONATE 5 The desired molecular weight polystyrene is dispersed as a fine powder in sulfuric acid with a force of 98% containing silver sulphate catalyst at a temperature in the range of 98 to 120 degrees Celsius. He powdered polystyrene is added with intensive agitation to ensure dissolution. The reaction proceeds in the course of this addition and subsequent subsequent for a period sufficient to obtain the desired or maximum degree of sulfonation. The product of the reactor is neutralized with ammonia. Alternatively, styrene is first polymerized by low temperature cationic polymerization (15 to 20 degrees Celsius) in a 96% strength sulfuric acid (90 parts by weight) and fortified phosphoric acid mixture. with phosphorus pentoxide (10 parts by weight). A small amount of surfactant (dipropylene glycol diphosphoric acid) is included. After the polymerization has advanced sufficiently, the temperature is increased to carry out the sulfonation as described above. The product of The reactor is neutralized with ammonia. i '' - ». • -" * • -tti & L *. & *. - >., - .. ..- «.,.,. .¿. -ia .. * .--, The following process effects according to the invention are provided for the purpose of illustration only and are not to be construed as limiting the scope of the invention 5 EXAMPLE 1 Three equal weight samples of ammonium nitrate / water mixtures containing 90% by weight of AN. To a sample (sample 1) an amount of poly (sodium vinylbenzene sulfonate) was added. Its concentration in the mother liquors was 0.06% by weight. To another sample (sample 2) was added a mixture of 1 part by weight of the same sulfonate and 4 parts by weight of ammonium sulfate. The The concentration of sulfonate and mother liquor is 0.02% by weight. The third sample (sample 3) was used as such, without any additive. The samples were placed at a temperature of 130 degrees Celsius in petri dishes of identical weight and allowed them to cool to room temperature to 21 degrees celsius. The containers are weighed periodically to measure the loss of water. Table 1 below shows the percentage of water loss in the elapsed time.

TABLE 1 Qualitatively, this example shows that the drying rate is improved by the additives and that, the ammonium sulfate is present, the concentration of polystyrene sulfonate can be substantially reduced without loss of drying speed.

EXAMPLE 2 A pilot pip formation plant was used to produce samples of AN nuggets. The plant is a scaled-down version of a commercial pip formation plant. The interior of the pip formation column measures 0.6m x 9m, through which it passes to the environment. At the base of the column the solidified nuggets are directed to a first and second rotating drums for moisture removal at cocurrent or countercurrent airflow (0.7m / s). The temperature in the first dryer is in the range of 50 to 70 degrees Celsius and the temperature in the second is at 50 degrees Celsius. The drums rotate at 8 rpm and are provided with several sample collection points along the same so that the speed and degree of moisture removal can be monitored. The nugget formation head vibrates laterally at a selected acoustic frequency and the nuggets produced are substantially of a single size of approximately 1.7mm in diameter. The mother liquors of AN fed are 94% or 96% strength of AN. They are included in the mother liquors of AN polystyrene sulfonate or ammonium sulfate, or both. The speed and feeding of the mother liquors of AN is 60 kg / h and the drying times are usually between 30 and 60 minutes. Table 2 presents results of a test sequence. The term "% by weight of additive in the feed" provides the proportion of polystyrene sulfonate or ammonium sulfate, or both, in the feed, with the proportion of ammonium sulfate determined by subtracting "% by weight of poly-SS " * l «d * S? 4., Í t TABLE 2 fifteen twenty In the table, poly-SS is established for polystyrene sulfonate; in tests 1-3 is poly (vinylbenzene sulfonate) of average average molecular weight; in the tests Atüt uás¡ &S &? *. 4-7 is the product is sulfonation of medium molecular weight polystyrene by the method described above, followed by neutralization with ammonia, in test 11 is the material of test 1 mixed with reactive grade ammonium sulfate. 5 The relative friability quantities indicate a measure of the production of fines after sending the nuggets of product to a particular compression regime, - it is the trend of the values displayed as which is important.

COMMENTARY ON PILOT PROOFS Tests 1 and 2 show the results obtained using poly-SS only at a concentration of 0.06% by weight in the mother liquors of AN; Test 3 shows that a The reduction in the amount of poly-SS to 0.02% by weight provides poor results as the product is wet. Test 4 compared to test 3 shows the benefit of a copresence of ammonium sulfate at 0.13% by weight in the mother liquors of AN. Test 8 shows 20 that ammonium sulfate alone at that level is not effective. Test 5 shows that at this scale of operation a low concentration of both additives is not effective. However, as shown in tests 6 and 7, increasing the concentration of ammonium sulfate restored the quality of the product. The test does not show the effect of a high concentration of ammonium sulfate alone. Tests 10 and 11 show results when using more aqueous NA feedwater. In test 10 there is no additive; in test 11 the additive is a mixture very rich in ammonium sulfate and the product nuggets show good oil absorbency and good friability for a low density material. Commercial scale tests at feed rates of mother liquors of AN, at or above 10 t / h have confirmed the trends of the pilot scale tests but have shown significantly that the amounts of additives below the levels of effectiveness shown in the pilot tests are an option, but not in the preferred operating regime. Therefore, the commercial scale results indicate a lower polystyrene sulfonate threshold of 0.01% by weight of the AN feed mother liquor and a lower threshold for ammonium sulfate of 0.04% by weight, but preferably a concentration is present of at least 0.06% by weight, and more preferably up to 0.15% or more. We believe that those skilled in the art of producing AN bodies by the processes described can, without undue difficulty or extensive testing, establish adequate levels of mixed additives for their operations and the specifications of their products.

The steps, features, compositions and compounds described herein or referred to herein or indicated in the specification and / or the claims of this application, individually or collectively, and any combination thereof. of two or more of these stages or characteristics.

Claims (14)

1. A process for the production of ammonium nitrate bodies in particulate form wherein a liquid mixture of ammonium nitrate / water contains at least 92% by weight of ammonium nitrate, optionally with a proportion of the ammonium nitrate substituted by nitrate of ammonium nitrate. alkali metal or alkaline earth metal, or both, and a small amount of polystyrene sulfonate crystal habit modifier which is sprayed as droplets in an atmosphere in which the cooling produces the crystallization of the ammonium nitrate and in which the crystallized particles are dry to remove moisture, characterized in that the liquid mixture also contains ammonium sulfonate, the concentration of polystyrene sulfate in the liquid mixture is at least 0.01% by weight, and the concentration of ammonium sulfate in the liquid mixture is higher that of polystyrene sulfonate and is at least 0.04% by weight

2. The process as described in claim 1, wherein the The process is a pip formation process.

3. A process as described in claim 1 or claim 2, wherein the liquid mixture contains at most about 97.5% by weight of ammonium nitrate, more preferably between i-, «?» U Mg ^ < ^^ about 94% and about 97% by weight of ammonium nitrate, even more preferably between about 95% and about 97% by weight of ammonium nitrate.

4. The process as described in any of the preceding claims, wherein the concentration of polystyrene sulfonate is at least 0.02% by weight.

A process as described in any of the preceding claims, wherein the concentration of polystyrene sulfonate is at most about 0.06% by weight, more preferably at most about 0.05% by weight, even more preferably as maximum approximately 0.04% by weight.

The process as described in any of the preceding claims, wherein the concentration of ammonium sulfate is in the range of from about 0.06 to about 0.15%, more preferably from about 0.07% to about 0.13% by weight.

The process as described in any of the preceding claims, wherein the ratio of polystyrene sulfonate to ammonium sulfate is in the range of about 1: 5 to about 1:10.

The process as described in any of the preceding claims, wherein the polystyrene sulfonate is a poly (vinylbenzene sulfonate).

9. The process as described in any of claims 1 to 7, wherein the polystyrene sulfonate is a post-sulfonated polystyrene in which the degree of sulfonation, relative to the poly (vinylbenzene sulfonate) is at least 50%, preferably at least 75%, and more preferably superior if 90%.

The process as described in claim 9, wherein the polystyrene sulfonate is produced by a sulfonation process in which the sulfonate is formed in a sulfuric acid medium and the residual sulfuric acid is neutralized with ammonia so that the sulfonate is mixed with ammonium sulfate and this mixture is used in the production of the ammonium nitrate bodies.

The process as described in claim 10, wherein the polystyrene is made by polymerization of styrene and the polystyrene is then sulfonated without first isolating it.

12. Ammonium nitrate bodies, especially nuggets, produced by a process as described in any of the preceding claims.

13. Ammonium nitrate bodies, as described in claim 12, which contain less than 0.1% by weight of water and are capable of absorbing not less than 6% of their weight of fuel oil while remaining as a particulate material that is can pour.

14. The use of a synergistic combination of polystyrene sulfonate and ammonium sulfate as a crystal habit modifier in the production of ammonium nitrate nuggets, especially explosive-grade ammonium nitrate nuggets.