WO2001060765A1

WO2001060765A1 - Additive for preparing calcium ammonium nitrate (can) fertilizer and resulting can

Info

Publication number: WO2001060765A1
Application number: PCT/FR2001/000411
Authority: WO
Inventors: Jean-Claude Cheminaud; Dominique Imbert
Original assignee: Cfpi Nufarm
Priority date: 2000-02-15
Filing date: 2001-02-13
Publication date: 2001-08-23
Also published as: EP1212267A1; ZA200109115B; FR2804954A1; FR2804954B1; AU3566101A

Abstract

The invention concerns an additive for CAN fertilizer. Said additive consists of an aqueous solution comprising: at least a surfactant, selected among the group comprising organic sulphonates and organic sulphates; and at least a mineral agent selected among the group comprising ammonium sulphate, potassium sulphate, polyphosphates, alkali phosphates and borates, the concentrated forms in one or the other of said constituents being: for the surfactant, 2 to 20 wt. % of dry matter, preferably 5 to 15 %; for the mineral agent, 10 to 50 wt. % of dry matter, preferably 15 to 30 %.

Description

ADDITIVE AND PROCESS FOR THE PREPARATION OF CAN FERTILIZERS AND CAN CAN OBTAIN THEREOF

The subject of the invention is an additive for the preparation of CAN type fertilizers.

It also relates to a process for the preparation of said fertilizers with the use of the above additive, as well as the CAN thus obtained which constitutes a new industrial product. CAN type fertilizers consist of granules of ammonium nitrate diluted with inert fillers.

Pure ammonium nitrate, which is generally used as an explosive, contains 34.8% by weight of nitrogen. For the manufacture of CAN, pure ammonium nitrate is diluted with inert fillers chosen from the group comprising chalk, kaolin and dolomite, which is a mixture of calcium carbonate and magnesium carbonate; for this dilution, 200 to 250 kg of fillers are mixed with 800 to 750 kg of pure ammonium nitrate; the most common dilution rates are those which correspond to a nitrogen content of 26, 27 or 28% by weight of nitrogen.

The name CAN is an abbreviation, C denoting calcium, A denoting ammonium and N denoting nitrate.

In its use as a fertilizer, CAN is generally in the form of a particle size section of 1.4 to 4 millimeters, inside which the fraction of 1.4 to 2 mm represents around 10%, the fraction of 2 to 4 mm representing about 88%. This relatively large particle size dispersion and especially the presence of a high proportion of small granules, does not satisfy the farmer; in fact, with the generally used spreading devices, the treatment of crops is all the more homogeneous the higher the proportion of large granules. In addition, the increase in the proportion of small granules leads to an increase in the tendency to lump. However, conventional granulation methods do not make it possible to reduce the size of the fraction from 1.4 to 2 millimeters and even within the fraction from 2 to 4 mm the proportion of granules of size less than 3 mm remains important. To remedy this situation, it would obviously be possible to subject the granulate constituting the CAN to sieving leading to a cut of 1.4 to 4 mm in which the proportion of particles of size less than 2 mm would be lower and that of the particles larger than 3 mm in size.

However, if such a sieving operation is technically possible, it considerably increases the cost price of the final CAN since it leads to a non-negligible proportion of aggregate which is unsuitable and which must be reprocessed and recycled; by way of illustration, it is indicated in this regard that the cost price of 1000 kg of CAN corresponding to the desired particle size distribution would be approximately 30% higher than that of 1000 kg of conventional CAN. Another wish of the user is to have a product comprising granules having the highest possible hardness; in fact, the increase in hardness of the granules is accompanied by a greater solidity of these individual granules, in other words, of greater resistance to abrasion and, consequently, of a lower generation of dust.

The wish to have as hard as possible CAN granules is shared by the manufacturer himself, given that the generation of dust constitutes a hygiene problem for operators during the manufacture of the product.

The irritant nature of dust based on ammonium nitrate is indeed well known.

To meet these various desiderata, the CAN manufacturers first tried to vary the CAN production parameters to arrive at the preferred particle size distributions which have just been mentioned.

It turns out that these attempts were not successful.

Research has therefore been undertaken to find additives whose implementation in the manufacturing processes of CAN would lead to the desired improvements.

Thus, it has been proposed to use surfactants of the sulfonate type used at doses of 300 to 600 ppm; these attempts failed. In fact, the use of 300 to 600 ppm of the surfactant products in question has had a negative effect on the granulation yield and has led to a drastic increase, inside the section from 1.4 to 4 mm of the granule fraction corresponding to 1.4 to 3 mm.

Other additives, namely mineral agents consisting in particular of ammonium sulphate and of potassium sulphate have been proposed; these products are used at doses of 10,000 to 20,000 ppm.

Their use made it possible to obtain more favorable particle size distributions and better hardness of the final granules, but the disadvantages inherent in the use of relatively large quantities of these mineral additives practically canceled the advantages obtained from the point of view of particle size distribution. and hardness. Consequently, the problem which is to be able to manufacture with an acceptable cost price, a CAN of high hardness and of a particle size distribution corresponding to a high proportion of large granules inside the section of 1.4 at 4 mm has still not been resolved.

However, it is to the credit of the Applicant Company to have found, after extensive research, that it was possible to obtain, during the manufacture of CAN, a granulate whose constituent granules have an increased hardness d '' about 15 to 20% compared to that of the CAN that is commercially available and which corresponds to a particle size section of 1.4 to 4 mm inside which the particle size distribution is such that most of it granules have a size of 3 to 4 mm, using an aqueous additive comprising a very low content of surfactant and a mineral agent.

It follows that the additive according to the invention, for the manufacture of CAN, consists of an aqueous solution comprising - at least one surfactant, chosen from the group comprising organic sulfonates and more particularly C ₆ alkyl sulfonates a C _i2 , arylsulfonates, alkylarylsulfonates, alkylarylsulfonates polycondensed polycondensed aryl sulfonates, organic sulfates and particularly the alkyl sulfates, C ₆ -C _i2 alkali metal, ammonium, amine or lcanolamine and - at least one inorganic agent selected from the group comprising ammonium sulphate, potassium sulphate, polyphosphates, alkaline phosphates and borates, the concentrations of both of these constituents being: - as regards the surfactant, 2 to 20% by weight of dry product, preferably from 5 to 15%, with regard to the mineral agent, from 10 to 50% by weight of dry product, preferably from 15 to 30%.

Among the alkylarylsulfonates, mention is made of mono- or disulfonic mixtures in which the aromatic part, preferably benzene or naphthalene, is mono- or polyalkyl substituted; the degree of substitution is an average degree corresponding to the alkyl / aryl molar ratios used for the synthesis, it being understood that, for each of the degrees of substitution envisaged, namely from 1 to 4, it is possible to be in the presence of complex mixtures isomers; the total number of carbon atoms in the alkyl part does not exceed 16 in the mixtures in question; alkylarylsulfonates can also undergo a polycondensation reaction using formaldehyde, the formaldehyde / aryl molar ratio possibly ranging from 0.1 to 1 and more precisely from 0.5 to 1 and lead to another family of surfactants called polycondensed alkylarylsulfonates when in their neutralized form. The term polycondensed arylsulfonates denotes mono- or disulfonic compounds whose aromatic part, preferably naphthalene, has undergone a polycondensation using formaldehyde in the same molar ratios as those mentioned above.

In practice, the additive according to the invention is in the form of an aqueous solution with a concentration of 20 to 40% by weight, preferably 25 to

35% by weight; good results are obtained with solutions of a concentration of 30 to 35% by weight.

The above surfactant can be constituted in particular by one of those currently marketed under the trademark GALORYL.

Thanks to the use of the additive according to the invention, it becomes possible to obtain a CAN corresponding to a particle size cut of 1.4 to 4 mm with a particle size distribution such as the particle size fraction from to 3 to 4 mm represents at least 60% of the granules, the hardness of the granules being further improved by about 15 to 20% compared to that of the granules of the CAN currently marketed, this improved hardness corresponding to at least 4 kgf, preferably at least 4.2 kgf.

An additional advantage obtained thanks to the use of the additive according to the invention lies in the fact that the sphericity of the constituent granules of the

CAN is significantly improved, which contributes to increasing the resistance of the final product to caking.

The implementation of the additive according to the invention has the consequence of another extremely important advantage.

It is known that CAN, during its manufacture and during its storage, is the site of a reaction between ammonium nitrate which is the raw material and calcium and / or magnesium carbonate which are present in by the initial dilution of pure ammonium nitrate. This reaction between ammonium nitrate and carbonate leads to the formation of calcium nitrate and / or magnesium nitrate and to the release of NH3 and CO2. The formation of calcium and / or magnesium nitrate constitutes a drawback due to the hygroscopic nature of these products when they are mixed with ammonium nitrate.

The release of ammonia is annoying or even harmful for the installations and especially for the personnel.

Now, it turns out that the use of the additive in accordance with the invention makes it possible, unexpectedly, to significantly reduce the reaction between ammonium nitrate and carbonate and consequently the formation of troublesome products, namely calcium nitrate and NH3 gas.

As indicated above, the invention also relates to a process for manufacturing CAN.

This product is conventionally manufactured in the following manner. In a first step, pure ammonium nitrate, previously brought to the molten state, that is to say at a temperature of at least 170 ° C., is mixed with a diluent chosen from the group comprising chalk, kaolin. and dolomite, so as to bring the nitrogen content of the final product to a value between 26 and 28%.

In practice, the order of 200 to 250 kg of calcium carbonate will be mixed with the quantity of molten pure ammonium nitrate necessary to make 1000 kg.

This mixing is carried out in a conventional mixing device, at the outlet of which the resulting product is introduced into a conventional granulation device leading to a product in the form of granules corresponding to a certain particle size cut. The process according to the invention for the manufacture of CAN and which comprises the actual mixing and granulation steps which have just been mentioned, is characterized in that at the time of the nitrate mixing step d molten pure ammonium, calcium carbonate and recycled granules, there is introduced in relation to the amount of nitrate used an amount of 50 ppm to 500 ppm, preferably from 150 ppm to 300 ppm of the additive in accordance with l The invention used in the form of an aqueous solution with a concentration of 25 to 35% by weight, ie 12.5 to 175 ppm, preferably 37.5 to 105 ppm of dry matter. Preferably the additive is incorporated into the molten nitrate before mixing with the other constituents.

It is possible, although not very advantageous, to make the above-mentioned mixture of molten pure ammonium nitrate, calcium carbonate and recycled granules include, not the additive according to the invention but the constituent elements of this additive in amounts such that the additive according to the invention is reconstituted in the mixture.

In practice the quantities in question are from 1 to

80, preferably from 10 to 50 ppm dry matter on the CAN for the surfactant and from 4 to 200, preferably from 12 to 120 ppm dry matter relative to the CAN for the mineral agent .

The new industrial product according to the invention consisting of the CAN obtained using the additive according to the invention is characterized in that the hardness of its constituent granules is greater than 4 kgf, that the particle size distribution inside the particle size section of which it is made, is such that the 3 to 4 mm granule fraction represents more than 60% of the total granules in the cut, that the constituent material of the granules contains from 1 to 80 ppm, preferably from 10 to 50 ppm dry on the CAN with regard to the surfactant and from 4 to 200 ppm preferably from 12 to 120 ppm in dry matter relative to the CAN with regard to the mineral agent constituting the additive according to the invention.

The invention can be understood even better with the aid of the nonlimiting examples which follow and which describe advantageous embodiments of the invention.

EXAMPLE 1 1 / A 800 kg of ammonium nitrate are brought to the molten state by heating to 170 ° C. inside a mixing device with 200 kg of calcium carbonate.

Beforehand, 250 g of aqueous additive solution according to the invention are added to the ammonium nitrate melt.

The additive according to the invention used is an aqueous solution at 35% by weight comprising 8% by weight of dry product of surfactant consisting of a mixture of isomers of mono-, di- and sodium triisopropyl sulfonate and 27% by weight of dry product of mineral agent consisting of monosodium phosphate.

There is practically no smell of ammonia at the level of the mixer during the entire period of introduction of the calcium carbonate. The mixture is vigorously stirred for a few seconds then transferred to a conventional granulation device known by the trade name of pugmill; the blenders designated by the terms of the blunger profession, paddle mixer or pugmixer could also be used.

After the granules formed in the granulator have dried and cooled, they are sieved so as to remove the fine and large particles which are recycled in the process.

The particle size analysis carried out on the product obtained gave the results collated in Table I.

TABLE I

The average, obtained over 100 measurements, of the hardness of the granules of the fraction 2 to 4 mm is 4.22 kgf.

1 / B Example 1 / A is repeated but without adding a granulation additive to the molten nitrate.

As soon as we begin to introduce the calcium carbonate into the molten nitrate, we notice the significant formation of foam as well as a very strong odor of ammonia; and this throughout the duration of introduction of the carbonate.

The particle size analysis carried out on the product obtained gives the results collated in Table II. TABLE II

The average hardness, obtained over 100 measurements, of the granules of the fraction 2 to 4 mm is 3.69 kgf, therefore almost 15% lower than that of the granules according to Example 1 / A.

Furthermore, the fractions 2 to 3, 15 mm and 3.15 to 4 mm represent 89% against 97.1% in Example 1 / A.

EXAMPLE 2

Example 1 / A is repeated, adding in the 800 kg of molten nitrate, instead of the additive according to the invention,

50 g of surfactant solution consisting of a mixture of isomers of 35% sodium mono-, di- and triisopropyl sulfonate, then 200 kg of calcium carbonate.

There is a significant formation of foam and a strong odor of ammonia throughout the duration of the introduction of the carbonate.

The quantity of ammonia released is greater than that noted in Example 1 / B, that is to say, without additive.

As soon as the addition of surfactant to the molten nitrate is stopped, the quantity of ammonia decreases until it reaches the value obtained in Example 1 / B (without additive).

The particle size analysis carried out on the product obtained gives the results collated in Table III. TABLE III

The average, determined over 100 measurements, of the hardness of the granules of fractions 2 to 4 mm is 4.05 kgf, therefore almost 4% lower than that of the granules according to Example 1 / A.

Furthermore, the fractions of 2 to 3.15 mm and 3.15 to 4 mm represent 95% against 97.1% in Example 1 / A.

In Table IV below, we have gathered for Examples 1 / A, 1 / B and 2, in relation to the particle size fractions 2 to 3.15 mm and 3.15 to 4 mm, the hardness values of the granules , the importance of the release of ammonia and the tendency to clumping, the content in% of the weight of the granules of calcium nitrate and the qualification of the sphericity.

TABLE IV

On examination of the information in Table IV, the following observations can be made.

The increase in the clumping tendency, for example 2 compared to example 1 / B (without additive) is due to a larger quantity of small granules (the fraction 2 to 3.15 is important), this which causes more contact between the granules.

The decrease in the clumping tendency for Example 1 / A compared to Example 1 / B (without additive) is due jointly to 2 factors, namely: the increase in the size of the granules (fraction 3, 15 to 4 mm is more important), improving the sphericity. These two factors in fact contribute to a reduction in the contact points between the granules, which leads to a reduction in the tendency to lump. On the graphs of FIGS. 1, 2 and 3, the importance of the particle size fractions of the three CANs corresponding to Examples 1 / A, 1 / B and 2 has been represented. respectively the fractions <4 mm, 1.4 to 2 mm, 2 to 3.15 mm, 3.15 to 4 mm and> 4 mm.

On the ordinate, the percentage that each fraction represents in relation to the whole is indicated. The comparison of the three figures clearly shows the superiority of example 1 / A.

Claims

1 - Additive for the manufacture of CAN characterized in that it consists of an aqueous solution comprising

at least one surfactant, chosen from the group comprising organic sulfonates and more particularly C ₆ to Cχ ₂ alkyl sulfonates, arylsulfonates, alkylarylsulfonates, polycondensed alkylarylsulfonates, polycondensed arylsulfonates, organic sulfates and more particularly d sulfates 'C ₁ to C ₁ alkyl of alkali metals, ammonium, amine or alkanolamine and - at least one mineral agent chosen from the group comprising ammonium sulphate, potassium sulphate, polyphosphates, phosphates alkali metals and borates, the concentrations of both of these constituents being: - as regards the surfactant, from 2 to 20% by weight of dry product, preferably from 5 to 15%, as regards the mineral agent, from 10 to 50% by weight of dry product, preferably from 15 to 30%.

2 - Additive according to claim 1 characterized in that the aqueous solution has a concentration of 20 to 40% by weight, preferably 25 to 35% by weight.

3 - Additive according to claim 1 characterized in that the aqueous solution has a concentration of 30 to 35% by weight. 4 - Process for the manufacture of CAN comprising a step of mixing molten ammonium nitrate and a diluent and a granulation step characterized in that at the time of the step of mixing molten pure ammonium nitrate , calcium carbonate and recycled granules, there is introduced in relation to the amount of nitrate used an amount of 50 ppm to 500 ppm, preferably from 150 ppm to 300 ppm of the additive according to claim 1 used under form of an aqueous solution with a concentration of 25 to 35% by weight, ie 12.5 to 175 ppm, preferably 37.5 to 105 ppm of dry matter.

5 - Process according to claim 4 characterized in that the additive is incorporated into the molten nitrate before mixing with the other constituents.

6 - Process for the manufacture of CAN according to claim 4 characterized in that it is understood that the mixture of molten pure ammonium nitrate, calcium carbonate and recycled granules the constituent elements of the additive according to one of claims 1 to 3 in amounts such that said additive is reconstituted in the mixture.

7 - CAN characterized by the fact that the hardness of its constituent granules is greater than 4 kgf, that the particle size distribution inside the particle size section of which it is made, is such that the fraction of granules of 3 to 4 mm represents more than 60% of the total granules of the cut, that the constituent material of the granules contains from 1 to 80 ppm, preferably from 10 to 50 ppm dry on the CAN as regards the surfactant and from 4 to 200 ppm preferably from 12 to 120 ppm as dry matter with respect to CAN as regards the mineral agent constituting the additive according to claim 1.