FERTILIZER GRANULES CONTAINING AMMONIUM NITRATE

Abstract: Fertilizer granules containing ammonium nitrate and provided with a coating as protection against moisture uptake, in which the granules are coated with a petroleum wax which contains: alkanes with a carbon chain length between 18 and 40 with a linearity of the carbon chains higher than 40 %, the solidification range being between 50 and 15 DEG C, and in that the petroleum wax is a paraffin or hydrocarbon wax.

Description: Fertilizer granules containing ammonium nitrate It is generally known that fertilizer granules containing ammonium nitrate, especially ammonium nitrate (AN) and calcium ammonium nitrate (CAN), easily absorb water during storage and handling. Hence, the particles can dissolve partly, followed by recrystallisation. This phenomenon causes weakening of the fertiliser granules as well as hardening of the top layer. Consequently, further handling and distribution on the soil will be hampered dramatically. Addition of magnesium salts or aluminium compounds has led to an improvement of the hardness of nitrate containing granules. These type of fertilizers are nevertheless very sensitive towards moisture, so dissolution and recrystallisation of the nitrate salts can still occur. In EP-A-0 113 687 there is disclosed a treatment of the nitrate containing fertilizer with a mixture of mineral oil, mineral wax, alkylamine and a phosphate ester resulting into a protection against moisture of more than 60% compared to the blank. Later on, several improvements of water repellence have been published. Most of the processes have been based on addition of a mixture of active polar components with oil and petroleum wax blends. Well-known examples are fatty amines and fatty alcohol's (EP-A-0 574 306), carboxylic acid (or anhydride) and alcohol's or amines (EP-A-0 692 468), carboxylic acid (or corresponding metal salts) and fatty amide (EP-A-0 768 287), and mixtures of amine phosphate esters and amine sulphonates (EP-A-0 341 102). A number of patent publications describes the use of apolar components to reduce the moisture uptake by fertilizer salts. A remarkable performance of high molecular weight (30.000-5.000.000) viscoelastic elastomer has been disclosed in EP - A - 0 320 987 upon addition to a wax/oil blend to decrease the hygroscopicity of nitrate-containing fertilizer. Recently, it has been found that the water absorption of calcium salts can be lowered after treating the particle with a soluble nitrogen-containing material and a hydrophobic compound, preferably petrolatum having a melting point between 37.7 °C and 126.6 °C (WO-A-9817604). This overview illustrates that there is still a need for a chemical product which can be used as an additive to ammonium nitrate fertilizer granules in order to improve the water absorption tendency of the granules, which chemical product must be added in small quantity, have a low prize and a good efficiency. It is therefor an object of the invention to provide such a chemical product. The invention relates to fertilizer granules containing ammonium nitrate and provided with a coating as protection against moisture uptake characterized in that the granules are coated with a petroleum wax which contains : alkanes with a carbon chain length between 18 and 40, with a linearity of the carbon chains higher than 40 %, solidification range being between 50 and 15 ° C and in that the petroleum wax is a paraffin or a hydrocarbon wax. It has been found that paraffin and hydrocarbon waxes can improve the performance up to 60% compared to the blank, which is almost equal with blends from amines and phosphate esters. The paraffin waxes have to possess alkanes with a defined carbon chain length (C18-C40) as well as a specific linearity. A high amount (>55%) of normal alkanes is necessary to obtain a good performance. In addition, the solidification range of the paraffin mixture is of great importance: the best results have been obtained with blends, which have a solidification range between 50 and 15 °C. The efficiency of the coating can further be improved by adding a mixture of active polar organic compounds, preferably containing an alkylamine with a surface-active compound, more preferably containing a phosphate ester. The amount of active polar organic compounds added to the blend is preferably 0,01 - 15 % by weight of the total weight of the blend. Preferably the amount of the paraffin wax added is 0,01 - 0,30 % by weight, based upon the total weight of the fertilizer granules and the coating, more preferably 0,06-0,15 % by weight. These small amounts of coating blend have proven to give satisfactory results. The invention will now further be described based upon data collected by means of experiments. The experiments have shown that the active components mainly contribute to the quality of the top layer. Both the appearance and the hardness improve substantially, especially after addition of a mixture of amine and phosphate ester. The different data were measured in the following way, and the experiments were carried out based upon 5 materials and procedures as described below. The carbon chain distribution of the petroleum waxes has been analysed at SGS Laboratory Services, Dordrecht, The Netherlands. Only linear alkanes with less than 40 carbon atoms could be determined and calculated, using identical standard samples of normal alkanes. The amount of both branched and cyclic alkanes could be estimated from 10 the adjacent peak of the linear alkane. The solidification range has been determined by using DSC (DSC-12E, Mettler, 0 °C - 100 °C / 100 °C - 0 °C, rate 5 °C/min). 15 The fertilizers used, stabilised calcic ammonium nitrate (27 % nitrogen) or ammonium nitrate (33.5 % nitrogen), has been purchased from Hydro Sluiskil, The Netherlands. Before applying the coating (stored at 100 °C for 16 hours), the fertilizer (1.0 kilogram per sample) is stored in sealed plastic jars in an oven at 35 °C for 16 hours. The treatment occurs as follows. The fertilizer is placed in a rotating coating drum, which has a 20 temperature of approximately 35 °C. Then 200-1500 ppm of a coating is sprayed on the fertilizer, followed by rotating the drum for another 5 minutes. The treated fertilizer is transferred into a plastic jar. After sealing the jar, the compounds are allowed to stand at room temperature for 24 hours. 25 Two 200-ml plastic beakers are both filled with 160 grams of (blank or treated) fertilizer. The weight of both the plastic beaker and the fertilizer are measured on an analytical balance. The combined weight is registered. The beakers are placed into a climatic chamber under the following conditions: relative humidity 80%, temperature 20 °C. After 30 72 hours, the samples are removed from the climatic chamber, followed by weighing and by evaluating the physical appearance. The protection against water (MP) uptake is calculated by the equation: MP = (MUb - MVs) * 100 % in which : MP = Moisture Protection MUb = Average moisture uptake blank (g) MUs = Average moisture uptake sample (g) x 100 % The appearance has been classified as follows: 1. Considerable degranulation 2. Moderate degranulation 3. Slight degranulation 4. Slight surface degranulation 5. Surface not degraded The hardness of the top layer has been defined as follows : By placing the samples, which have been used for the multiple layer moisture uptake tests, into an oven of 30 °C for 48 hours, the hardness of the top layer has been inspected. The hardness can be determined by measuring the power (in Newton) necessary to penetrate the top layer. Description of the petroleum waxes explored * Classification according to Concawe dossier no. 99/110, Concawe Brussels, Belgium. The following specific tests have been performed : Example 1 Calcium ammonium nitrate (27 % N) has been treated with 1000 ppm of petroleum wax (1-10). After one day the coated samples have been used for a multiple layer moisture uptake test. After standing 72 hours in the climatic chamber (relative humidity 80%, temperature 20 °C), the following results have been obtained : This example demonstrates that petroleum waxes with a high amount of normal alkanes with a solidification range between 50 and 10 °C,wz. paraffin and hydrocarbon waxes 2-8, give the best performance with respect to moisture uptake. In addition, both the hardness and the appearance of the top layer have improved upon using paraffin waxes (2-8). Example 2 Subsequently, ammonium nitrate (33.5 % N) has been sprayed with 1000 ppm of paraffin (1-10). Following the same procedures as mentioned above, the performance of the individual petroleum waxes is: These experiments demonstrated the same trend as given in Example 1. Once again, linear alkanes with a carbon chain length between 18 and 40 were found to keep the fertiliser in the best condition after exposure to moisture. Especially paraffin waxes 3 and 4 showed a protection against moisture uptake, which can be compared with more advanced mixtures claimed by NSM (EP-A-0 113 687). In addition, the top layer appeared to be very soft after treating the ammonium nitrate with these particular paraffin waxes. Example 3 The best paraffin waxes from Examples 1 and 2 have been selected, wz. 3 and 4, and tested further on. First, emphasis has been laid on the minimum dosage of the paraffin to a fertilizer (AN or CAN) to maintain still some moisture repellence. The results have been as follows : Paraffin wax 3 on calcium ammonium nitrate Paraffin wax 3 on ammonium nitrate Paraffin wax 4 on calcium ammonium nitrate Paraffin wax 4 on ammonium nitrate The tests have shown that very low concentrations of both paraffin waxes 3 and 4 can give already some water repellence on nitrate fertilizer. Moreover, the appearance and the hardness of the top layer can be improved, especially by addition of 1000 ppm (or more) paraffin. In the next example the influence of active components in paraffin mixtures to the overall performance has been investigated. Example 4 As mentioned above, several active polar components have been claimed to decrease the hygroscopicity of nitrate containing fertilizers. Very often these formulations comprise fatty amines. We have selected the combination of alkylamine and alkyl phosphate ester, similar to the NSM patent EP-A-0 113 687. The contribution of active components towards the protection against moisture uptake has been studied by adding 0-8% (m/m) stearylamine and 0-8% (m/m) of 2-ethylhexyl phosphate ester to the paraffin wax 3. A dosage of 1000 ppm has been used for all formulations prepared. Paraffin wax 3 with active components on calcium ammonium nitrate Paraffin wax 3 with active components on ammonium nitrate The experiments in Example 4 have demonstrated that the addition of amine and/or phosphate ester towards paraffin 3 hardly affects the performance towards water repellence on ammonium nitrate containing fertilisers. However, the active components contribute strongly to the quality of the top layer: the appearance as well as the hardness improves substantially. The above mentioned tests have clearly demonstrated that paraffin waxes with a high amount of linear alkanes (>55%) and a solidification range between 50 and 10 °C are able to protect ammonium nitrate containing fertilisers from moisture very efficiently. The addition of active polar components, such as alkylamines and alkyl phosphate esters, to the paraffin waxes does not lead to a better protection against moisture uptake. However, its addition results in a remarkable improvement of the top layer, not only towards the hardness, but towards the appearance as well.

Claims: Claims 1. Fertilizer granules containing ammonium nitrate and provided with a coating as protection against moisture uptake, characterized in that the granules are coated with a petroleum wax which contains: alkanes with a carbon chain length between 18 and 40 with a linearity of the carbon chains higher than 40 %, the solidification range being between 50 and 15 °C, and in that the petroleum wax is a paraffin or hydrocarbon wax. 2. Fertilizer granules according to any one of the preceding claims, characterized in that the coating contains a mixture of active polar organic components. 3. Fertilizer granules according claim 2, characterized in that active organic polar components contain an alkylamine with a surface-active compound. 4. Fertilizer granules according to claim 2, characterized in that the coating contains a phosphate ester. 5. Fertilizer granules according to claim 3, characterized in that the amount of the alkylamine is 0.01-15% by weight of the total weight of the hydrocarbon wax. 6. Fertilizer granules according to claim 4, characterized in that the amount of the alkyl phosphate ester is 0.01-15% by weight of the total weight of the hydrocarbon wax. 7. Fertilizer granules according to anyone of the claims 1-6, characterized in that the coating is 0.01-0.30% by weight, based upon the total weight of the fertilizer granules and the coating. 8. Fertilizer granules according to anyone of the claims 1-6, characterized in that the coating is 0.06-0.15% by weight, based upon the total weight of the fertilizer granules and the coating.

Inventors: BIJPOST ERIK ALEXANDER, BRUINEKOOL ARJAN, VAN DE HOEVEN JOHN, VELZEL ARJEN WIM, BIJPOST, ERIK, ALEXANDER, BRUINEKOOL, ARJAN, VAN DE HOEVEN, JOHN, VELZEL, ARJEN, WIM
Applicants: BIJPOST ERIK ALEXANDER, BRUINEKOOL ARJAN, HOLLAND NOVOCHEM B V, VAN DE HOEVEN JOHN, VELZEL ARJEN WIM, BIJPOST, ERIK, ALEXANDER, BRUINEKOOL, ARJAN, HOLLAND NOVOCHEM B.V., VAN DE HOEVEN, JOHN, VELZEL, ARJEN, WIM
Application year: 2001
Main classification: C05C1
IPC codes: C05C1, C05G3