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Properties of complex ammonium nitrate-based fertilizers depending on the degree of phosphoric acid ammoniation

Properties of complex ammonium nitrate-based fertilizers depending on the degree of phosphoric... Int J Ind Chem (2017) 8:315–327 DOI 10.1007/s40090-017-0121-4 RESEARCH Properties of complex ammonium nitrate-based fertilizers depending on the degree of phosphoric acid ammoniation 1 2 1 1 • • • • Konstantin Gorbovskiy Anatoly Kazakov Andrey Norov Andrey Malyavin Anatoly Mikhaylichenko Received: 25 June 2016 / Accepted: 20 March 2017 / Published online: 3 April 2017 The Author(s) 2017. This article is an open access publication Abstract Complex ammonium nitrate-based NP and NPK Introduction fertilizers are multicomponent salt systems prone to high hygroscopicity, caking and explosive thermal decomposi- Ammonium nitrate (AN) is one of the most common tion. The slurries that used in the production of these fer- commercially available nitrogen fertilizers, the content of tilizers can also exhibit insufficient thermal stability. One nitrogen in which amounts up to 35% by mass. The main of the most important issues for such slurries is their vis- agrochemical advantage of AN compared to other simple cosity, which determines the energy costs for transportation nitrogen fertilizers is to present nitrogen both in ammonia and processing into the final product. Increasing the degree and nitrate forms. Herewith, the high content of this of phosphoric acid ammoniation helps to reduce the component enables to mix it with other types of fertilizers ammonium nitrate’s content in the product, but the main and obtain complex fertilizer with the high content of basic question remains about the properties of such fertilizers. nutrients—nitrogen, phosphorus and potassium. The main This article is devoted to studying properties of complex disadvantages of such types of fertilizers are their high NP and NPK ammonium nitrate-based fertilizers and their hygroscopicity, caking [1] and the increased requirements intermediates with increasing the degree of phosphoric acid for fire and explosion safety [2]. All the above-mentioned ammoniation. factors, and in particular the last, are the main disadvan- tages limiting the production of complex AN-based Keywords Ammonium nitrate-based fertilizer  fertilizers. Hygroscopicity  Caking  Microcalorimetry  Thermal Cases of explosion of AN and complex AN-based fer- decomposition  Slurry viscosity tilizers are well known: in 1921 in the warehouse in Oppau (Germany), in 1947 in the warehouse in the bay in Texas City (USA), in 2001 in the warehouse in Toulouse (France), in 2013 in the warehouse in West (USA). The largest explosion of technological installations was recor- ded in 1952 in Nagoya (Japan), in 1978—in Chirchik (Uzbekistan) in 1981—in Cherepovets (Russia), in 1994— in Port Neil (USA), in 2009—in Kirovo-Chepetsk (Russia). & Konstantin Gorbovskiy sulfur32@bk.ru Ammonium phosphates NH H PO and (NH ) HPO , 4 2 4 4 2 4 ammonium sulfate and potassium chloride are also used in The Research Institute for Fertilizers and Insecto-Fungicides the production of complex AN-based NPK fertilizers. Named after Professor Y. Samoilov, 162622 Cherepovets, Herewith, the following reactions take place: Vologda Region, Russia NH H PO þ KCl KH PO þ NH Cl; ð1Þ Institute of Problems of Chemical Physics of the Russian 4 2 4 2 4 4 Academy of Sciences, 142432 Chernogolovka, NH NO þ KCl KNO þ NH Cl; ð2Þ 4 3 3 4 Moscow Region, Russia ðNH Þ SO þ 2KCl K SO þ 2NH Cl: ð3Þ D. Mendeleev University of Chemical Technology of Russia, 4 4 2 4 4 125047 Moscow, Russia 123 316 Int J Ind Chem (2017) 8:315–327 production depending on the degree of phosphoric acid KH PO , KNO and K SO in combination with unre- 2 4 3 2 4 ammoniation. acted NH H PO ,NH NO and (NH ) SO (accordingly) 4 2 4 4 3 4 2 4 form solid solutions—compounds of isomorphic-substi- tuted type. Experimental section The composition of the solid solutions is determined by the extent of the conversion of the reactions (1–3). Preparation of the samples (NH ) HPO does not react with KCl. Moreover, AN can 4 2 4 form various double salts: NH NO 2KNO , (NH ) 4 3 3 4 2- To produce complex fertilizers, concentrated hemihydrate SO 2NH NO , (NH ) SO 3NH NO . Formation of NH 4 4 3 4 2 4 4 3 4- phosphoric acid, nitric acid, ammonium sulfate and NO 2KNO depends on the extent of the conversion of the 3 3 potassium chloride (mineral concentrate ‘‘Silvin’’) were reaction (2)[3]. The double salts (NH ) SO 2NH NO 4 2 4 4 3 used. Wet-process phosphoric acid was obtained from the and (NH ) SO 3NH NO in the presence of KCl can 4 2 4 4 3 Khibiny apatite concentrate (the Cola Peninsula, Russia) of decompose with the formation of solid solutions [4]. composition: P O —51.72, CaO—0.67, MgO—0.23, F— 2 5 Thus, complex AN-based fertilizers are complex salt 1.33, SO —4.53, Fe O —0.55, Al O —0.90, SiO — 3 2 3 2 3 2 systems, whose composition is defined by the ratio of ini- 0.43% by mass by sulfuric acid attack. Phosphoric and tial components. nitric acids were mixed in a certain ratio and ammoniated The presence of all the above-mentioned compounds in a reactor equipped with the agitator device, the reflux can variously affect the decomposition of complex AN- condenser and the water jacket, which allowed ammonia- based fertilizers and their propensity for detonation. The tion to be carried out under near-isothermal conditions at presence of NH H PO , (NH ) HPO and (NH ) SO 4 2 4 4 2 4 4 2 4 70 ± 2 C. reduces the rate of AN decomposition [5, 6], and chloride- The degree of ammoniation of phosphoric acid NH :- anions Cl , on the contrary, act as catalysts for AN H PO (M) was determined by pH value of the 1% by mass 3 4 decomposition [7–9]. aqueous solution of the slurry obtained and using the ref- Despite this, increasing demands of the agrochemical erence source [12]. Ammonium sulfate and potassium sector leads to the necessity to develop new grades of the chloride were introduced into the slurry in an amount fertilizers, the production of which is possible only when necessary to obtain the desired grade, mixed thoroughly using concentrated nitrogen fertilizers, especially ammo- and dried at 65 C. Then, the charge mixture was crushed nium nitrate and urea. However, considerable difficulties and put in a pan granulator with diameter of 300 mm and emerge in case of urea used, which consist in high length of 150 mm. Granules of 2–4 mm were finally dried hygroscopicity and caking, reduction of the amide nitrogen at 65 C to reach the required humidity. The product proportion in the product due to decomposition of urea at obtained was analyzed for content of basic elements. relatively low temperatures during granulation and drying, and complexity of the technological process because of X-ray diffraction analysis heavy clogging of equipment [10, 11]. One of the ways to improve the quality of complex AN- X-ray diffraction analysis of the investigated samples was based fertilizers and reduce the risk of explosion is to performed when used powder diffractometer «STADI-MP» increase the ammoniation degree of wet-process phospho- (STOE, Germany) with curved Ge (111) monochromator ric acid, which reduces the AN portion in the product. Such and radiation of CuK (k = 1.54056 A). The data acqui- way can improve the properties of the final product (de- sition was carried out in stepwise overlapping of scanning crease hygroscopicity and caking), increase its thermal area mode by means of position-sensitive linear detector, stability, decrease the amount of different compounds in the capture angle of which amounted 5 over 2h with exhaust gases (nitrous gases, chlorine and fluorine com- channel width of 0.02. The reliability and accuracy of pounds) during thermal decomposition, increase fire and compounds in X-ray patterns obtained were established by explosion safety, and also decrease viscosity of ammonium means of database of 2013 International Centre for phosphate–nitrate slurries produced during the production Diffraction Data. of fertilizer that can decrease energy cost for their trans- portation. However, information on influence of the degree Derivatographic analysis of phosphoric acid ammoniation on the above-mentioned properties of complex AN-based fertilizers and their Derivatographic analysis was carried out when used Pau- intermediates is absent in the literature. lik–Erdei derivatograph (MOM, Hungary) of Q-1500 series Thus, the purpose of this work is to study the properties while heating in the air at atmospheric pressure in open of complex AN-based fertilizers and intermediates in their quartz crucibles with heating rate of 2.5/min. Al O pre- 2 3 123 Int J Ind Chem (2017) 8:315–327 317 calcinated at 1000 C was used as a reference. The sample 2cm , a mass of each tested mixture sample was 1 g. The weight amounted 0.2 g. The thermocouple was Pt/Pt–Pd. free inner volume after putting each sample and sealing an The interpretations of the dependencies obtained were ampoule was in the range 0.7–1.2 cm per 1 g of the carried out in compliance with the literature data [13–16]. mixture tested. These ampoules were entirely put into the calorimeter and had no cold surfaces, and reaction products Hygroscopicity could not leave the boundaries of the reaction space. Hygroscopicity (K) of the samples obtained was deter- Gravimetric study of the thermal decomposition mined by means of climatic chamber BINDER KBF 115 (BINDER, Germany) with internal circulation. The value Studies of mass loss in the thermal decomposition were of K was determined by means of conditioning of granule conducted by maintaining granulated samples with mass of samples with the diameter of 3–4 mm with the mass of 20.00 ± 0.05 g in the electric oven without forced con- 3.500 ± 0.006 g in the chamber at 25 C and the relative vection at the given temperature for a given period of time. air humidity (u) of 80% for 1 h. Granules were uniformly The content of ammonium and nitrate nitrogen, chlorine, distributed in a cup with the diameter of 50 mm and height fluorine and sulfur was determined in products of the of 10 mm in a single layer. The value of K was determined thermal decomposition. The fraction of these elements that as the amount of water absorbed with a sample of unit mass have been released into the gas phase was calculated for 1 h. according to the formula: x ðAÞm  x ðAÞm 0 0 t t X = ; ð5Þ Caking where X is the fraction of A (A = N ,N , Cl, F) A amm nitr Determination of caking (r) of samples obtained was released into the gas phase per the unit mass of the initial conducted by means of climatic chamber with internal sample; x (A) is the mass fraction of A in the initial circulation BINDER KBF 115 (BINDER, Germany) at sample; m is the mass of the initial sample; x (A) is the 0 t temperature of 45 C, u = 40%, and special presses mass fraction of A in the sample after the decomposition equipped with calibrated spring. The spring load for each for time t; m is the mass of the sample after the decom- sample was 340 kPa. The samples detention time in the position for a time t. chamber was 6 h. Caking was determined as averaged maximum force required for breaking of formed cylindrical Dynamic viscosity pellet divided by its cross-section area (pellet size: diam- eter 33 mm, height 40 mm). The dynamic viscosity of slurries was determined by means of rotation viscometer HAAKE VT 74 Plus (Thermo Static strength Scientific, USA). In order to do that, the slurry obtained was placed in the cylindrical vessel provided with a ther- Determining the static strength, P was conducted by means mostatic jacket and connected to circulation bath in which of IPG-1M (Urals Scientific Research Institute of Chem- a polysilicon oil was circulated. After viscosity measure- istry with Experiment Plant, Russia) according to the ments, the slurry humidity was measured. formula: Processing experimental data obtained and the deter- F mination of confidence intervals for 95% confidence i¼1 P = ; ð4Þ pd probability were conducted with the mathematical statistics methods by means of software application of origin. where F is the mean force required for breaking of one granule, d is the mean diameter of one granule equal to 3.5 mm, and N is the number of measured granules. Results and discussion Microcalorimetry The composition of the fertilizer samples and X-ray diffraction analysis The microcalorimetric studies of the thermal decomposi- tion kinetics were conducted by measuring the heat release Table 1 shows the results of analyses of fertilizer samples. rate in the samples under study with differential automatic Figure 1 shows X-ray patterns for samples 1 and 2 calorimeter DAC-1-2 [17]. Tests were carried out in the (grade 26:13:0), 3 and 4 (grade 22:11:11), 5 and 6 (grade vacuum-sealed glass ampoules with inner volume of about 16:16:16). 123 318 Int J Ind Chem (2017) 8:315–327 Table 1 The composition of Sample no. Grade N N P O SK O M H O amm nitr 2 5 2 2 the fertilizer samples (%mass.) 1 26:13:0 18.5 7.8 13.8 8.4 – 1.68 0.55 2 15.8 10.1 13.3 4.2 – 1.06 0.42 3 22:11:11 14.9 7.6 11.4 5.6 11.4 1.71 0.59 4 13.6 10.8 11.7 4.0 11.4 1.04 0.55 5 16:16:16 13.8 2.2 15.9 8.2 16.5 1.65 0.52 6 12.3 4.0 16.5 4.0 16.4 1.07 0.48 7 20:10:10 16.0 3.9 9.9 11.0 10.3 1.70 0.53 8 14.9 5.2 10.5 10.1 10.5 1.03 0.52 9 19:9:19 12.6 6.6 9.3 8.0 20.0 1.67 0.44 10 11.6 8.2 9.3 2.8 20.3 1.03 0.51 11 27:6:6 16.4 10.9 6.4 2.6 6.5 1.66 0.49 12 15.8 11.9 6.3 2.6 6.4 1.06 0.50 Fig. 1 X-ray patterns of the fertilizer samples: a—1, b—2, c—3, d—4, e—5, f—6; 1 (NH ) HPO , 2 NH H PO , 3 4 2 4 4 2 4 NH NO , 4 (NH ) SO , 5 4 3 4 2 4 2NH NO (NH ) SO , 6 4 3 4 2 4 3NH NO (NH ) SO , 7 4 3 4 2 4 (NH ,K)H PO , 8 (NH ,K)NO , 4 2 4 4 3 9 (NH ,K) SO , 10 KCl, 11 4 2 4 NH Cl, 2h Bragg angle (degree) 123 Int J Ind Chem (2017) 8:315–327 319 X-ray patterns for the samples of grades 16:16:16 and 22:11:11 demonstrate the presence of solid solutions (NH ,K)NO , (NH ,K)H PO and (NH ,K) SO , as well as 4 3 4 2 4 4 2 4 of NH Cl and KCl. For samples 3 and 5, the presence of (NH ) HPO was established. 4 2 4 Comparing X-ray patterns for the samples 3 and 4 of grade 16:16:16 and 5 and 6 of grade 22:11:11 shows that the intensity of the main diffraction peak of NH Cl decreases with a higher degree of ammoniation. This is associated with a reduction of the original content of AN in the composition of samples that results in reducing the amount of NH Cl produced in reaction (2). Fig. 3 Curves of the differential thermal analysis (DTA) and of the differential thermogravimetric analysis (DTG) of sample 2: t time X-ray patterns for sample 1 of 26:13:0 grade demon- (min) strate the presence of (NH ) HPO ,NH H PO , (NH ) 4 2 4 4 2 4 4 2- SO , 2NH NO (NH ) SO and 3NH NO (NH ) SO and 4 4 3 4 2 4 4 3 4 2 4 for the sample 2 the presence of NH NO ,NH H PO , 4 3 4 2 4 2NH NO (NH ) SO and 3NH NO (NH ) SO . 4 3 4 2 4 4 3 4 2 4 Comparing X-ray patterns for samples 1 and 2 of grade 26:13:0 demonstrates that the composition of sample 2 has the unbound AN, which could not fully converted to 2NH NO (NH ) SO and 3NH NO (NH ) SO due to a 4 3 4 2 4 4 3 4 2 4 high content of AN and a low content of (NH ) SO in the 4 2 4 composition of the fertilizer. This may lead to significant deterioration of the properties of sample 2 compared with sample 1. All these compounds are typical for complex AN-based Fig. 4 Curves of the differential thermal analysis (DTA) and of the fertilizers that is noted in [1, 3, 4, 12]. differential thermogravimetric analysis (DTG) of sample 3: t time (min) Derivatographic analysis Figures 2, 3, 4 and 5 show the results of the derivato- graphic analysis for samples 1, 2, 3 and 4. Analysis of curves of the differential thermal analysis (DTA) and of the differential thermogravimetric analysis (DTG) confirms the data of X-ray diffraction analysis. Curves of the differential thermal analysis (DTA) for 22:11:11 samples are characterized by the following peaks: the reverse phase transition of (NH ,K)NO in 4 3 Fig. 5 Curves of the differential thermal analysis (DTA) and of the differential thermogravimetric analysis (DTG) of sample 4: t time (min) NH NO 2KNO (113.1 and 129.9 C, respectively) [15]; 4 3 3 melting (132.8 and 145.3 C) [15]; the exothermal decomposition of the product including the decomposition of NH NO [15], the polycondensation of (NH ,K)H PO 4 3 4 2 4 and the decomposition of (NH ) HPO for samples 3 and 4 4 2 4 (197.2 and 221.5 C[13]. Fig. 2 Curves of the differential thermal analysis (DTA) and of the It can be concluded by comparing the DTG and DTA differential thermogravimetric analysis (DTG) of sample 1: t time curves that sample 3 has the higher thermal stability as (min) 123 320 Int J Ind Chem (2017) 8:315–327 compared to sample 4, which may be related to a lower into a gas phase. However, sample 2 exhibits the higher content of AN and a higher content of (NH ) HPO .Itis thermo-stability than sample 1 when further heated. 4 2 4 also worth noting that there is no peak characteristic for the It should also be noted that the decomposition of sam- (NH ) HPO decomposition in the DTA and DTG curves ples 1 and 2 takes place endo-thermally as opposed to 4 2 4 of sample 3, which would be in the range of 120–200 C. It samples 3 and 4, whose decomposition proceeds with the may be assumed that its absence is due to the interaction release of the large amount of heat. This is due to the between (NH ) HPO and HNO , which is formed as the absence of chlorine compounds in the composition of 4 2 4 3 result of the partial dissociation of NH NO , according to samples 1 and 2, which are capable to accelerate the 4 3 the reaction: exothermal AN and complex AN-based fertilizers decom- position [7–9, 15]. ðNH Þ HPO þ HNO ! NH H PO þ NH NO : ð6Þ 4 4 3 4 2 4 4 3 The decomposition of (NH ) HPO is apparently to 4 2 4 Hygroscopicity, caking and static strength occur at higher temperatures due to the course of reaction (6). In the case of sample 3, this process takes place in the Table 2 presents the results of studying hygroscopicity, intensive exothermal decomposition of the product. caking and static strength of the fertilizer samples At heating sample 2, the peaks are observed on the DTA obtained. curve, which is related to the following phenomena: the The presented data show that for the same grade of the reverse phase transition of AN IV ? III (39.9 C) [13]; the fertilizer the increase of M reduces the hygroscopicity and reverse phase transition of AN III ? II (85.4 C) [13]; the caking; however, the static strength of granules decreases reverse phase transition of AN II ? I (116.3 C) [13]; also. The reduction of hygroscopicity can be associated melting and partial decomposition of adducts 2NH NO 4 3- with a reduced content of AN, which is highly hygroscopic. (NH ) SO and 3NH NO (NH ) SO (162.9 C) [16]; the 4 2 4 4 3 4 2 4 The reduction of caking can also be associated with a polycondensation of NH H PO (209.8 C) [13]; the AN 4 2 4 reduced ammonium chloride content with increasing M, decomposition (220.6 C) [13]. which is apparent from intensity of peaks for NH Cl in the There are no peaks, which are characteristic to AN in the presented X-ray patterns [1, 18]. The reduction of static DTA curve of sample 1. The thermal decomposition of this strength of granules can be the result of lower strength of sample is characterized by the following processes: the phase contacts between granules with increase of M in the decomposition of (NH ) HPO (138.6 C) [13]; the melt- 4 2 4 granulation process [19]. ing and partial decomposition of adducts 2NH NO 4 3- The maximum difference in hygroscopicity and caking (NH ) SO and 3NH NO (NH ) SO (152.2 C) [16]; the 4 2 4 4 3 4 2 4 is observed for 26:13:0 grade, which can be due to the polycondensation of NH H PO (210.8 C) [13]; the AN 4 2 4 presence of AN in sample 2, whereas in sample 1 AN is decomposition (219.5 C) [13]; the (NH ) SO decompo- 4 2 4 connected in double salts (NH ) SO 2NH NO and 4 2 4 4 3 sition (244.5 C) [14]. (NH ) SO 3NH NO . The minimum difference in hygro- 4 2 4 4 3 It can be concluded when compared the DTG and DTA scopicity and caking is observed for 27:6:6 grade, which curves that the presence of (NH ) HPO as a part of sample 4 2 4 can be explained by the high content of nitrate nitrogen in 1 leads to the fact that at temperatures over 100 C both samples and the small difference in its content (NH ) HPO decomposes to NH H PO to release NH 4 2 4 4 2 4 3 between them. Table 2 Hygroscopicity, -1 -1 -2 Sample no. Grade K, mmole g h r 9 10 , kPa P, MPa caking and static strength of granulated fertilizer samples 1 26:13:0 3.21 ± 0.13 3.00 ± 0.13 2.44 ± 0.14 2 5.30 ± 0.20 4.47 ± 0.18 3.70 ± 0.20 3 22:11:11 4.04 ± 0.19 3.54 ± 0.19 3.16 ± 0.19 4 5.00 ± 0.20 4,10 ± 0.30 4.40 ± 0.30 5 16:16:16 3.04 ± 0.12 1.76 ± 0.16 5.00 ± 0.30 6 3.51 ± 0.17 3.10 ± 0.30 5.10 ± 0.30 7 20:10:10 3.74 ± 0.17 2.97 ± 0.15 2.39 ± 0.15 8 4.06 ± 0.15 3.90 ± 0.20 3.80 ± 0.20 9 19:9:19 3.22 ± 0.15 2.59 ± 0.10 3.28 ± 0.19 10 3.96 ± 0.11 3.36 ± 0.16 4.40 ± 0.20 11 27:6:6 5.00 ± 0.10 3.90 ± 0.30 3.90 ± 0,20 12 5.16 ± 0.12 4.40 ± 0.30 4.90 ± 0.30 123 Int J Ind Chem (2017) 8:315–327 321 -1 Fig. 7 Dependence of the heat release rate dQ/dt (mW g ) on time t -1 Fig. 6 Dependence of the heat release rate dQ/dt (mW g ) on time (min) in the thermal decomposition of sample 4 t (min) in the thermal decomposition of sample 3 Cl accelerating action prevails over decreasing the AN It should also be noted that the highest increase of the - 2- decomposition rate in response to H PO , HPO and 2 4 4 caking was observed for 16:16:16 grade (r /r = 1.76), 6 5 2- SO anions and, therefore, the decomposition of this whereas for the other grades this ratio is much lower. This sample occurs with the self-acceleration. is possible due to the high ratio of the content of NH Cl in Sample 3 has a lower content of AN as compared to two samples of 16:16:16 grade and almost twofold increase sample 4, herewith in its composition a large portion of in the content of AN in sample 6 when M simultaneously - 2- 2- H PO is substituted with HPO . Anion of HPO is 2 4 4 4 reduced. The closest value to this one is r /r = 1.49 for 2 1 capable to a higher degree to reduce the concentration of 26:13:0 grade. The high ratio r /r for 26:13:0 grade is 2 1 undissociated nitric acid, and so to increase the thermal apparently due to the fact that in sample 2 the part of NA stability of sample 3. Besides, the content of (NH ) SO in 4 2 4 presents in the free form, while in sample 1 NA is fully sample 3 is also higher than in sample 4. All this con- bound in double salts. tributes to the fact that the accelerating action of Cl is not detected, and the decomposition occurs without self-ac- Microcalorimetry celeration. Thus, sample 3 has significantly higher thermal stability as compared to sample 4. Figures 6 and 7 show the curves of the heat release rate Besides the study of the fertilizer samples, the heat dependence on time in the thermal decomposition of samples release rate was also measured as a function of time in the 3 and 4 in the temperature range of 183.5–245.9 C. thermal decomposition of nitrate–phosphate–ammonium As indicated above, chloride-anions Cl contained in slurries at obtaining sample 3 with M = 1.0 (sample 3a) samples under study are catalysts of the AN decomposi- and M = 1.4 (sample 3b) with humidity of about 8% mass tion, and their catalytic effect increases with the increase of in the temperature range of 243.5–277.0 C (Figs. 8, 9). the content of nitric acid in the system and virtually does The study of the heat release rate for these samples not occur when its content is low. The accelerating action revealed their high thermal stability, while sample 3b was of Cl in the AN decomposition is related to accumulation more thermally stable than sample 3a, which can be of nitryl chloride NO Cl, nitrosyl chloride NOCl and explained by the higher content of (NH ) HPO in it. 4 2 4 chlorine Cl in the system, being more effective oxidizers Figure 10 shows the temperature dependencies of the of ammonium cation NH and ammonia as compared to initial heat release rates (dQ/dt) in the thermal decom- t=0 nitric acid. The presence of NH H PO ,(NH ) HPO and 4 2 4 4 2 4 position of samples 3, 4, 3a and 3b in Arrenius coordinates. - - (NH ) SO together with Cl reduces Cl catalytic effect 4 2 4 For comparison, Fig. 5 also illustrates the temperature in AN decomposition. dependence of the initial heat release rates in the AN The study of the heat release rate for sample 4 revealed thermal decomposition studied previously [20]. its low thermal stability. In the decomposition of sample 4 123 322 Int J Ind Chem (2017) 8:315–327 -1 3 -1 Fig. 10 Dependence of lg[dQ/dt (mW g )] on 10 /T (K ) for t=0 samples 3 (1), 4 (2), 3a (3), 3b (4) and ammonium nitrate (5) -1 Fig. 8 Dependence of the heat release rate dQ/dt (mW g ) versus dQ ð22:8  0:4Þ 10 time t (min) in the thermal decomposition of sample 3a 16:10:3 =10 exp  ; ð9Þ dt T t¼0 for sample 3b dQ ð12:7  0:9Þ 10 7:30:8 =10 exp  : ð10Þ dt T t¼0 The dependencies presented in Figs. 6, 7, 8, 9 and 10 show that the initial heat release rate of sample 4 is on average by 1–2 orders higher than that for sample 3. Herewith the initial heat release rate of sample 4 signifi- cantly exceeds that of AN, while for sample 3 the situation is inverse. Samples 3a and 3b have even higher thermal stability as compared to sample 3, which may be explained by lack of Cl in their composition and the high water content. In any real conditions of conducting the discussed reaction, the thermal explosion is only possible when the values of external parameters of the process exceed the critical ones for the thermal explosion, but calculation of -1 Fig. 9 Dependence of the heat release rate dQ/dt (mW g ) versus the critical conditions for a real complex production pro- time t (min) in the thermal decomposition of sample 3b cess is a very time-consuming task, and the adiabatic induction period of thermal explosion s is calculated ad The equations of the obtained dependence of (dQ/dt) t=0 simply. If the value s is much greater than the real time of -1 ad (mW g ) on temperature (K) are as follows: the production process at an appropriate temperature, then for sample 3 the thermal explosion will not occur, and in any real pro- dQ ð17:2  0:8Þ 10 cess conditions the induction period may only be greater 11:70:7 =10 exp  ; ð7Þ dt T than under adiabatic conditions. However, if the value s ad t¼0 and process real time are close enough or if s is even less, ad for sample 4 it is necessary to calculate the critical conditions of the thermal explosion (the critical temperature for the actual dQ ð22:3  0:9Þ 10 18:10:7 =10 exp  ; ð8Þ size of the unit and the conditions of heat transfer from it). dt T t¼0 Only these calculations can give final decision on possi- for sample 3a bility of the thermal explosion in the process considered. 123 Int J Ind Chem (2017) 8:315–327 323 Calculation of the adiabatic induction period is the most of a relative explosion risk of a substance. The adiabatic simple and available method to assess the possibility of the induction periods of the thermal explosion for samples 3, thermal explosion for any particular composition. In the 3a and 3b are greater than that for AN, and for sample 4 complete absence of heat removal (adiabatic conditions) they are almost by an order less, which reveals the potential and at a sufficiently high value of the process heat, the danger of thermal spontaneous ignition of the sample thermal explosion will always occur; besides, the degree of during production operations at high temperatures. conversion in the reaction discussed during induction per- iod will be very small, because all the heat is used for Gravimetric study of the thermal decomposition heating a substance. As far as there is no heat removal, the adiabatic induction period is independent of the sample The study of the mass loss in the thermal decomposition mass and heat removal conditions and it is considered as a was carried out for samples 3 and 4 at temperatures of 170, characteristic for a substance or mixture discussed. In the 180, 190 and 200 C. In addition to the study of the mass theory of thermal explosion because of the weak influence loss, the release of ammonium nitrogen, nitrate nitrogen, of the process acceleration, the exact quantitative equation chlorine and fluorine to the gas phase was also evaluated. for calculating the adiabatic induction period was obtained The research results are presented in Figs. 11, 12 and 13. only for zero-order reaction, and the reaction rate change in The decomposition intensity for sample 4 is much the subsequent stages is assumed to have a very small higher than that for sample 3. The release of chlorine, action on the adiabatic induction period [21]: fluorine, ammonium nitrogen, and nitrate nitrogen from sample 4 to the gas phase is also much more intensive than c RT E p c s =   exp ; ð11Þ that from sample 3. Ammonium nitrogen in the initial ad Q k E RT 0 0 0 decomposition stage is released from sample 3 in a greater where c is the heat capacity of the sample; Q is the total quantity than that from sample 4. It is related to the higher p 0 process heat; k and E are the pre-exponential factors and content of (NH ) HPO , which starts to decompose in NH 0 c 4 2 4 3 the activation energy of the decomposition rate constant; T and NH H PO at low temperatures. 0 4 2 4 is the absolute temperature of the decomposition; It is also worth mentioning that the maximum amount of -1 -1 R = 8.314 J mole K is the universal gas constant. fluorine released into the gas phase for both samples is dQ E almost the same. It is related to the fact that fluorine in both When = Q k exp  Eq. (11) takes the 0 0 RT dt 0 t¼0 samples according to [22] is present in the form of com- following form: pounds (NH ) SiF ,NH F, NH NO (NH ) SiF ,KNO 4 2 6 4 4 3 4 2 6 3- RT c K SiF ,(NH ) SiF NH F, etc., the decomposition of p 2 6 4 2 6 4 s =  : ð12Þ ad dQ which depends only on the process temperature. The higher dt t¼0 fluorine release rate for sample 4 is related to the more intense exothermal decomposition of this sample. The results from paper [12] were used to determine the For chlorine, the release into the gas phase depends on heat capacity of samples under study, provided that in a the content of AN, so for sample 4 a significantly greater first approximation the heat capacities of samples 3, 4 and amount of chlorine is released into the gas phase than for 3a, 3b are equal in pairs. The value of the AN heat capacity sample 3. was taken according to the data in [2]. The s values ad The release of chlorine, fluorine, nitrous gases and obtained are given in Table 3. The s values for the same ad ammonium compounds into the gas phase leads to the initial temperature may be considered as the characteristics essential complication and more expensive purification of Table 3 Adiabatic induction T,K s , h ad period of the thermal explosion s of samples 3, 4, 3a and 3b ad Sample 3 Sample 4 Sample 3a Sample 3b Ammonium nitrate and AN depending on temperature T 473 94.64 1.50 226.83 232.00 11.38 478 68.04 0.97 146.60 180.92 7.00 483 49.29 0.63 95.69 142.00 4.35 488 35.97 0.42 63.05 112.02 2.73 493 26.45 0.28 41.94 88.90 1.73 498 15.58 0.19 28.14 70.94 1.11 503 14.59 0.13 19.05 56.90 0.72 508 10.94 0.09 13.01 45.88 0.47 123 324 Int J Ind Chem (2017) 8:315–327 -1 Fig. 13 Release of fluorine into the gas phase X (g kg ) in the thermal decomposition of samples 3 (curve 1) and 4 (curve 2)at temperature 180 C versus time t (min) Fig. 11 Dependence of thermal decomposition degree b = (m - m )/m 100 (%) versus time t (min) for samples 3 and 4 0 0 at constant temperature; sample 3: 1 170 C, 2 180 C, 3 190 C, 4 200 C; sample 4: 5 180 C Fig. 14 The dependence of dynamic viscosity g (mPa s) of ammo- nium–phosphate–nitrate slurry on M at temperature 110 C and for different values of humidity: 1 5% mass., 2 6% mass., 3 7% mass., 4 8% mass., 5 10% mass Fig. 12 Release of chlorine X , ammonium X and nitrate Cl Namm -1 nitrogen X (g kg ) into the gas phase in the thermal decompo- Nnitr Figure 14 shows the dependence of dynamic viscosity sition of samples 3 and 4 at temperature of 180 C versus time of such slurry on M for different values of humidity at t (min); sample 3: curve 1 Cl, 2 N , 3 N ; sample 4: curve 4 Cl, 5 am nit 110 C. The slurry viscosity is apparent to reach the min- N , 6 N am nit imum value at M = 1.45 for all the values of humidity. It should be mentioned that the same behavior of vis- exhaust gases from them, as well as to the more intense cosity was observed for phosphate ammonia slurries corrosion of equipment. obtained from various types of a phosphate raw [3, 23]. The presence of minimum in the viscosity curve is prob- Dynamic viscosity ably due to the high solubility of ammonium phosphates at M = 1.4–1.5. The presence in the slurry of impurities of The study of dynamic viscosity was performed for iron, aluminum, magnesium, fluorine, silicon, etc. leads to ammonium–phosphate–nitrate slurries obtained at produc- increasing viscosity due to the formation of poorly soluble tion of 22:11:11 grade when M = 1.7. To obtain such compounds [3, 24, 25]. slurries, phosphoric and nitric acids were mixed in the ratio Figures 15 and 16 show the dependences of the slurry P O :HNO = 0.36:1 (by mass.) and ammoniated up to the 2 5 3 dynamic viscosity (for M = 1.05 and M = 1.45) on specified value of M. humidity at different temperatures. The figures show that 123 Int J Ind Chem (2017) 8:315–327 325 g ¼A ; ð13Þ exp RT where A is the pre-exponential factor and E is the acti- vation energy for viscous flow. Table 4 presents the equations of dynamic viscosity dependence on temperature at the different values of humidity for slurries studied. As can be seen from the equations presented, the activation energy of a viscous flow, the values of pre-exponential factor and the value of dynamic viscosity of the slurry for M = 1.45 are substan- tially less than for M = 1.05. Using the slurries having higher mobility and flowability during their processing in the granular product can signif- Fig. 15 Dependence of dynamic viscosity g (mPa s) of ammonium– icantly reduce the energy costs for the removal of moisture phosphate–nitrate slurry for M = 1.05 on humidity (%mass.) for from the granules and reduce the amount of the recirculated different values of temperature: 1 100 C, 2 105 C, 3 110 C, 4 115 C, 5 120 C product obtainable by a recycle method. Conclusions On the basis of the studies performed, it has been found that increasing the degree of phosphoric acid ammoniation with M = 1.0–1.1 to M = 1.6–1.7 influences on the properties of the complex AN-based NP and NPK fertilizers. It has been shown by X-ray diffraction and derivato- graphic analysis that the composition of NPK fertilizer (16:16:16 and 22:11:11) contains (NH ,K)H PO , (NH ,- 4 2 4 4 K) SO , (NH ,K)NO , KCl and NH Cl. When 2 4 4 3 4 M = 1.6–1.7, (NH ) HPO presents also additionally. The 4 2 4 Fig. 16 Dependence of dynamic viscosity g (mPa s) of ammonium– composition of NP fertilizer (26:13:0) contains NH H PO , 4 2 4 phosphate–nitrate slurry for M = 1.45 on humidity (%mass.) for 2NH NO (NH ) SO and 3NH NO (NH ) SO . When 4 3 4 2 4 4 3 4 2 4 different values of temperature: 1 100 C, 2 105 C, 3 110 C, 4 M = 1.0–1.1, NH NO presents additionally in the system, 4 3 115 C, 5 120 C when M = 1.6–1.7, (NH ) HPO and (NH ) SO present 4 2 4 4 2 4 additionally. the slurry viscosity increases with decreasing humidity. It is found that the decomposition of NPK fertilizers Herewith for the slurries at M = 1.05, a more rapid occurs with the strong exothermal effect and NP fertilizers increase of viscosity with decreasing humidity is observed. decomposition occurs with the endothermal effect. The Temperature influence on dynamic viscosity of the strong exothermal effect of the thermal NPK fertilizer slurries obeys the law of Arrhenius–Andrade [26]: Table 4 Equations of dynamic W M = 1.05 M = 1.45 viscosity (mPas) dependence for ammonium phosphate 3 3 ð14:70:6Þ10 ð9:00:4Þ10 5 13:60:6 8:50:4 g =10 exp g =10 exp nitrate slurries for M = 1.05 T T and M = 1.45 for the various 3 3 10 11:70:6 ð11:90:6Þ10 5:10:2 ð5:70:3Þ10 g =10 exp g =10 exp humidity values W (% mass.) T T 3 3 ð10:50:4Þ10 ð3:70:1Þ10 15 10:60:5 3:030:13 g =10 exp g =10 exp T T 3 3 ð9:60:3Þ10 ð2:40:1Þ10 20 9:80:3 1:590:02 g =10 exp g =10 exp T T 3 3 9:20:3 ð9:00:3Þ10 0:470:01 ð1:300:05Þ10 g =10 exp g =10 exp T T 123 326 Int J Ind Chem (2017) 8:315–327 8. Rubtsov YI, Strizhevsky II, Kazakov AI, Moshkovich EB, decomposition is associated with the presence of chlorine- Andrienko LP (1989) Kinetic mechanism of influence of Cl on contained compounds. thermal decomposition of ammonium nitrate. J Appl Chem- It has been shown that hygroscopicity and caking for USSR 62:2417–2422 26:13:0, 22:11:11, 16:16:16, 20:10:10, 19:9:19 and 27:6:6 9. Rubtsov YI, Kazakov AI, Nedelko VV, Shastin AV, Larikova TS, Sorokina TV, Korsounskii BL (2008) Thermolysis of ammonium grades decrease by increasing M from 1.0–1.1 to 1.6–1.7. nitrate/potential donor of active chlorine compositions. J Therm The study of the thermal decomposition by the example Anal Calorim 93:301–309. doi:10.1007/s10973-007-8868-z of 22:11:11 grade has demonstrated that increasing the 10. Chatterjee SK (1990) Experience with production of urea-based degree of ammonization up to the specified values increa- high-grade NPK fertilizers, urea-based NPK plant design and operating alternative: workshop proceedings. International ses the thermal stability and reduces the intensity of the Development Centre, Muscle Shoals, pp 14–20 release of compounds of chlorine, fluorine and nitrous 11. Ranadurai S (1990) Operation experiences with NP-NPK gran- gases into the gas phase. ulation of coromandel fertilizers. Urea-based NPK plant design The study of thermal and rheological properties of and operating alternative: workshop proceedings. International Development Centre, Muscle Shoals, pp 21–26 ammonium–phosphate–nitrate slurries has allowed to set 12. Borisov VM, Azhikina YV, Galtsov AV (1983) Physics and their high thermal stability, which increases with the chemistry of phosphoric fertilizers production. Reference book, increase of the phosphoric acid ammoniation degree. The Khimiya viscosity of the slurries changes extremely having the 13. Zaitsev PM, Tavrovskaya AY, Podlesskaya AV, Portnova NL (1982) Thermal stability of mineral fertilizer components. Report minimum value at M = 1.4–1.5 and the maximum value at 1. Nitrates, chlorides, fluorides, fluorine silicates, ammonium, M = 1.0. The viscosity of the slurries increases with potassium, calcium, aluminum and iron phosphates. Trudy decreasing moisture content and decreases with increasing NIUIFa 240:154–167 temperature according to the law of Arrhenius–Andrade. 14. Tavrovskaya AY, Podlesskaya AV, Portnova NL (1982) Thermal stability of mineral fertilizer components. Report 2. Ammonium, Compliance with ethical standards potassium, calcium, aluminum and iron phosphates. Magnesium compounds. Trudy NIUIFa 240:168–185 15. Tavrovskaya AY, Portnova NL, Abashkina TF (1976) Thermo- Conflict of interest The authors declare no competing financial graphic study of ammonium nitrate phosphate fertilizer. Byul- interest. leten Techniko-Ekonomicheskoi Informacii NIITEKHIMa 7:10–14 Open Access This article is distributed under the terms of the 16. Babkina TS, Golovina NB, Bogachev AG, Olenev AV, She- Creative Commons Attribution 4.0 International License (http://crea velkov AV, Uspenskaya IA (2012) Crystal structures and tivecommons.org/licenses/by/4.0/), which permits unrestricted use, physicochemical properties of mixed salts of ammonium nitrate distribution, and reproduction in any medium, provided you give and sulfate. Russ Chem B 61:3339. doi:10.1007/s11172-012- appropriate credit to the original author(s) and the source, provide a 0005-x link to the Creative Commons license, and indicate if changes were 17. Galperin LN, Kolesov YR, Mashkinov LB, Terner YE (1973) made. Differential automatic calorimeters (DAC) of different purpose. Book of reports from VI USSR conference on calorimetry. Inorganic Chemistry and Electrochemistry Institute of GSSR References Academy of Sciences, Tbilisi, pp 539–543 18. Walker GM, Magee TRA, Holland CR, Ahmad MN, Fox JN, Moffat NA, Kells AG (1998) Caking process in granular NPK 1. Kuvshinnikov IM (1987) Mineral fertilizers and salts: properties fertilizer. Ind Eng Chem Res 37:435–438. doi:10.1021/ie970387n and methods of their improvement. Khimiya, Moscow 19. Shchukin ED, Amelina EA (2003) Surface modification and 2. Olevskiy VM (1978) Ammonium nitrate technology. Khimiya, contact interaction of particles. J Dispers Sci Technol Moscow 3. Kononov AV, Sterlin VN, Evdokimova LI (1988) Principles of 24:377–395. doi:10.1081/DIS-120021796 technology of complex fertilizers. Khimiya, Moscow 20. Rubtsov YI, Kazakov AI, Morozkin SY, Andrienko LP (1984) 4. Shmulyan EK, Portnova NL, Doroshina TV, Abashkina TF, Kinetics of heat release at thermal decomposition of commercial Vinnik MM (1975) Determination of ammonium nitrate phos- ammonium nitrate. J Appl Chem-USSR 57:1926–1929 phate fertilizers and intermediate products composition in the 21. Frank-Kamenetskiy DA (1987) Diffusion and heat exchange in process of nitric-sulfuric decomposition of Karatau rock phos- chemical kinetics. Nauka, Moscow phates. Byulleten Techniko-Ekonomicheskoi Informacii NIITE- 22. Tavrovskaya AY, Portnova NL, Abashkina TF, Zaitsev PM KHIMa 8:18–23 (1977) Thermographic study of fluorine silicate compounds 5. Rubtsov YI, Strizhevsky II, Kazakov AI, Andrienko LP, Mosh- contained in ammonium nitrate phosphate fertilizer. Trudy kovich EB (1989) Possibility of reduction of thermal decompo- NIUIFa 231:184–194 sition rate for ammonium nitrate. J Appl Chem-USSR 23. Akiyama T, Ando J (1972) Constituents and properties of ammoniated slurry from wet-process phosphoric acid. B Chem 62:2169–2174 Soc Jpn 45:2915–2920. doi:10.1246/bcsj.45.2915 6. Kazakov AI, Ivanova OG, Kurochkina LS, Plishkin NA (2011) 24. Zhong B, Li J, Xiang Zhang Y, Liang B (1999) Principle and Kinetics and mechanism of thermal decomposition of ammonium technology of ammonium phosphate production from middle- nitrate and sulfate mixtures. Russ J Appl Chem 84:1516–1523. quality phosphate ore by a slurry concentration process. Ind Eng doi:10.1134/S1070427211090102 Chem Res 38:4504–4506. doi:10.1021/ie980419m 7. Keenan AG, Dimitriades B (1962) Mechanism for the chloride- 25. Campbell GR, Leong YK, Berndt CC, Liow JL (2006) Ammo- catalyzed thermal decomposition of ammonium nitrate. J Chem nium phosphate slurry rheology and particle properties—the Phys 37:1583–1586. doi:10.1063/1.1733343 123 Int J Ind Chem (2017) 8:315–327 327 influence of Fe(III) and Al(III) impurities, solid concentration and 26. Barnes HA (2000) Handbook of elementary rheology. University degree of neutralization. Chem Eng Sci 61:5856–5866. doi:10. of Wales Institute of Non-Newtonian Fluid Mechanicsm, 1016/j.ces.2006.05.010 Aberystwyth http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Industrial Chemistry Springer Journals

Properties of complex ammonium nitrate-based fertilizers depending on the degree of phosphoric acid ammoniation

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Int J Ind Chem (2017) 8:315–327 DOI 10.1007/s40090-017-0121-4 RESEARCH Properties of complex ammonium nitrate-based fertilizers depending on the degree of phosphoric acid ammoniation 1 2 1 1 • • • • Konstantin Gorbovskiy Anatoly Kazakov Andrey Norov Andrey Malyavin Anatoly Mikhaylichenko Received: 25 June 2016 / Accepted: 20 March 2017 / Published online: 3 April 2017 The Author(s) 2017. This article is an open access publication Abstract Complex ammonium nitrate-based NP and NPK Introduction fertilizers are multicomponent salt systems prone to high hygroscopicity, caking and explosive thermal decomposi- Ammonium nitrate (AN) is one of the most common tion. The slurries that used in the production of these fer- commercially available nitrogen fertilizers, the content of tilizers can also exhibit insufficient thermal stability. One nitrogen in which amounts up to 35% by mass. The main of the most important issues for such slurries is their vis- agrochemical advantage of AN compared to other simple cosity, which determines the energy costs for transportation nitrogen fertilizers is to present nitrogen both in ammonia and processing into the final product. Increasing the degree and nitrate forms. Herewith, the high content of this of phosphoric acid ammoniation helps to reduce the component enables to mix it with other types of fertilizers ammonium nitrate’s content in the product, but the main and obtain complex fertilizer with the high content of basic question remains about the properties of such fertilizers. nutrients—nitrogen, phosphorus and potassium. The main This article is devoted to studying properties of complex disadvantages of such types of fertilizers are their high NP and NPK ammonium nitrate-based fertilizers and their hygroscopicity, caking [1] and the increased requirements intermediates with increasing the degree of phosphoric acid for fire and explosion safety [2]. All the above-mentioned ammoniation. factors, and in particular the last, are the main disadvan- tages limiting the production of complex AN-based Keywords Ammonium nitrate-based fertilizer  fertilizers. Hygroscopicity  Caking  Microcalorimetry  Thermal Cases of explosion of AN and complex AN-based fer- decomposition  Slurry viscosity tilizers are well known: in 1921 in the warehouse in Oppau (Germany), in 1947 in the warehouse in the bay in Texas City (USA), in 2001 in the warehouse in Toulouse (France), in 2013 in the warehouse in West (USA). The largest explosion of technological installations was recor- ded in 1952 in Nagoya (Japan), in 1978—in Chirchik (Uzbekistan) in 1981—in Cherepovets (Russia), in 1994— in Port Neil (USA), in 2009—in Kirovo-Chepetsk (Russia). & Konstantin Gorbovskiy sulfur32@bk.ru Ammonium phosphates NH H PO and (NH ) HPO , 4 2 4 4 2 4 ammonium sulfate and potassium chloride are also used in The Research Institute for Fertilizers and Insecto-Fungicides the production of complex AN-based NPK fertilizers. Named after Professor Y. Samoilov, 162622 Cherepovets, Herewith, the following reactions take place: Vologda Region, Russia NH H PO þ KCl KH PO þ NH Cl; ð1Þ Institute of Problems of Chemical Physics of the Russian 4 2 4 2 4 4 Academy of Sciences, 142432 Chernogolovka, NH NO þ KCl KNO þ NH Cl; ð2Þ 4 3 3 4 Moscow Region, Russia ðNH Þ SO þ 2KCl K SO þ 2NH Cl: ð3Þ D. Mendeleev University of Chemical Technology of Russia, 4 4 2 4 4 125047 Moscow, Russia 123 316 Int J Ind Chem (2017) 8:315–327 production depending on the degree of phosphoric acid KH PO , KNO and K SO in combination with unre- 2 4 3 2 4 ammoniation. acted NH H PO ,NH NO and (NH ) SO (accordingly) 4 2 4 4 3 4 2 4 form solid solutions—compounds of isomorphic-substi- tuted type. Experimental section The composition of the solid solutions is determined by the extent of the conversion of the reactions (1–3). Preparation of the samples (NH ) HPO does not react with KCl. Moreover, AN can 4 2 4 form various double salts: NH NO 2KNO , (NH ) 4 3 3 4 2- To produce complex fertilizers, concentrated hemihydrate SO 2NH NO , (NH ) SO 3NH NO . Formation of NH 4 4 3 4 2 4 4 3 4- phosphoric acid, nitric acid, ammonium sulfate and NO 2KNO depends on the extent of the conversion of the 3 3 potassium chloride (mineral concentrate ‘‘Silvin’’) were reaction (2)[3]. The double salts (NH ) SO 2NH NO 4 2 4 4 3 used. Wet-process phosphoric acid was obtained from the and (NH ) SO 3NH NO in the presence of KCl can 4 2 4 4 3 Khibiny apatite concentrate (the Cola Peninsula, Russia) of decompose with the formation of solid solutions [4]. composition: P O —51.72, CaO—0.67, MgO—0.23, F— 2 5 Thus, complex AN-based fertilizers are complex salt 1.33, SO —4.53, Fe O —0.55, Al O —0.90, SiO — 3 2 3 2 3 2 systems, whose composition is defined by the ratio of ini- 0.43% by mass by sulfuric acid attack. Phosphoric and tial components. nitric acids were mixed in a certain ratio and ammoniated The presence of all the above-mentioned compounds in a reactor equipped with the agitator device, the reflux can variously affect the decomposition of complex AN- condenser and the water jacket, which allowed ammonia- based fertilizers and their propensity for detonation. The tion to be carried out under near-isothermal conditions at presence of NH H PO , (NH ) HPO and (NH ) SO 4 2 4 4 2 4 4 2 4 70 ± 2 C. reduces the rate of AN decomposition [5, 6], and chloride- The degree of ammoniation of phosphoric acid NH :- anions Cl , on the contrary, act as catalysts for AN H PO (M) was determined by pH value of the 1% by mass 3 4 decomposition [7–9]. aqueous solution of the slurry obtained and using the ref- Despite this, increasing demands of the agrochemical erence source [12]. Ammonium sulfate and potassium sector leads to the necessity to develop new grades of the chloride were introduced into the slurry in an amount fertilizers, the production of which is possible only when necessary to obtain the desired grade, mixed thoroughly using concentrated nitrogen fertilizers, especially ammo- and dried at 65 C. Then, the charge mixture was crushed nium nitrate and urea. However, considerable difficulties and put in a pan granulator with diameter of 300 mm and emerge in case of urea used, which consist in high length of 150 mm. Granules of 2–4 mm were finally dried hygroscopicity and caking, reduction of the amide nitrogen at 65 C to reach the required humidity. The product proportion in the product due to decomposition of urea at obtained was analyzed for content of basic elements. relatively low temperatures during granulation and drying, and complexity of the technological process because of X-ray diffraction analysis heavy clogging of equipment [10, 11]. One of the ways to improve the quality of complex AN- X-ray diffraction analysis of the investigated samples was based fertilizers and reduce the risk of explosion is to performed when used powder diffractometer «STADI-MP» increase the ammoniation degree of wet-process phospho- (STOE, Germany) with curved Ge (111) monochromator ric acid, which reduces the AN portion in the product. Such and radiation of CuK (k = 1.54056 A). The data acqui- way can improve the properties of the final product (de- sition was carried out in stepwise overlapping of scanning crease hygroscopicity and caking), increase its thermal area mode by means of position-sensitive linear detector, stability, decrease the amount of different compounds in the capture angle of which amounted 5 over 2h with exhaust gases (nitrous gases, chlorine and fluorine com- channel width of 0.02. The reliability and accuracy of pounds) during thermal decomposition, increase fire and compounds in X-ray patterns obtained were established by explosion safety, and also decrease viscosity of ammonium means of database of 2013 International Centre for phosphate–nitrate slurries produced during the production Diffraction Data. of fertilizer that can decrease energy cost for their trans- portation. However, information on influence of the degree Derivatographic analysis of phosphoric acid ammoniation on the above-mentioned properties of complex AN-based fertilizers and their Derivatographic analysis was carried out when used Pau- intermediates is absent in the literature. lik–Erdei derivatograph (MOM, Hungary) of Q-1500 series Thus, the purpose of this work is to study the properties while heating in the air at atmospheric pressure in open of complex AN-based fertilizers and intermediates in their quartz crucibles with heating rate of 2.5/min. Al O pre- 2 3 123 Int J Ind Chem (2017) 8:315–327 317 calcinated at 1000 C was used as a reference. The sample 2cm , a mass of each tested mixture sample was 1 g. The weight amounted 0.2 g. The thermocouple was Pt/Pt–Pd. free inner volume after putting each sample and sealing an The interpretations of the dependencies obtained were ampoule was in the range 0.7–1.2 cm per 1 g of the carried out in compliance with the literature data [13–16]. mixture tested. These ampoules were entirely put into the calorimeter and had no cold surfaces, and reaction products Hygroscopicity could not leave the boundaries of the reaction space. Hygroscopicity (K) of the samples obtained was deter- Gravimetric study of the thermal decomposition mined by means of climatic chamber BINDER KBF 115 (BINDER, Germany) with internal circulation. The value Studies of mass loss in the thermal decomposition were of K was determined by means of conditioning of granule conducted by maintaining granulated samples with mass of samples with the diameter of 3–4 mm with the mass of 20.00 ± 0.05 g in the electric oven without forced con- 3.500 ± 0.006 g in the chamber at 25 C and the relative vection at the given temperature for a given period of time. air humidity (u) of 80% for 1 h. Granules were uniformly The content of ammonium and nitrate nitrogen, chlorine, distributed in a cup with the diameter of 50 mm and height fluorine and sulfur was determined in products of the of 10 mm in a single layer. The value of K was determined thermal decomposition. The fraction of these elements that as the amount of water absorbed with a sample of unit mass have been released into the gas phase was calculated for 1 h. according to the formula: x ðAÞm  x ðAÞm 0 0 t t X = ; ð5Þ Caking where X is the fraction of A (A = N ,N , Cl, F) A amm nitr Determination of caking (r) of samples obtained was released into the gas phase per the unit mass of the initial conducted by means of climatic chamber with internal sample; x (A) is the mass fraction of A in the initial circulation BINDER KBF 115 (BINDER, Germany) at sample; m is the mass of the initial sample; x (A) is the 0 t temperature of 45 C, u = 40%, and special presses mass fraction of A in the sample after the decomposition equipped with calibrated spring. The spring load for each for time t; m is the mass of the sample after the decom- sample was 340 kPa. The samples detention time in the position for a time t. chamber was 6 h. Caking was determined as averaged maximum force required for breaking of formed cylindrical Dynamic viscosity pellet divided by its cross-section area (pellet size: diam- eter 33 mm, height 40 mm). The dynamic viscosity of slurries was determined by means of rotation viscometer HAAKE VT 74 Plus (Thermo Static strength Scientific, USA). In order to do that, the slurry obtained was placed in the cylindrical vessel provided with a ther- Determining the static strength, P was conducted by means mostatic jacket and connected to circulation bath in which of IPG-1M (Urals Scientific Research Institute of Chem- a polysilicon oil was circulated. After viscosity measure- istry with Experiment Plant, Russia) according to the ments, the slurry humidity was measured. formula: Processing experimental data obtained and the deter- F mination of confidence intervals for 95% confidence i¼1 P = ; ð4Þ pd probability were conducted with the mathematical statistics methods by means of software application of origin. where F is the mean force required for breaking of one granule, d is the mean diameter of one granule equal to 3.5 mm, and N is the number of measured granules. Results and discussion Microcalorimetry The composition of the fertilizer samples and X-ray diffraction analysis The microcalorimetric studies of the thermal decomposi- tion kinetics were conducted by measuring the heat release Table 1 shows the results of analyses of fertilizer samples. rate in the samples under study with differential automatic Figure 1 shows X-ray patterns for samples 1 and 2 calorimeter DAC-1-2 [17]. Tests were carried out in the (grade 26:13:0), 3 and 4 (grade 22:11:11), 5 and 6 (grade vacuum-sealed glass ampoules with inner volume of about 16:16:16). 123 318 Int J Ind Chem (2017) 8:315–327 Table 1 The composition of Sample no. Grade N N P O SK O M H O amm nitr 2 5 2 2 the fertilizer samples (%mass.) 1 26:13:0 18.5 7.8 13.8 8.4 – 1.68 0.55 2 15.8 10.1 13.3 4.2 – 1.06 0.42 3 22:11:11 14.9 7.6 11.4 5.6 11.4 1.71 0.59 4 13.6 10.8 11.7 4.0 11.4 1.04 0.55 5 16:16:16 13.8 2.2 15.9 8.2 16.5 1.65 0.52 6 12.3 4.0 16.5 4.0 16.4 1.07 0.48 7 20:10:10 16.0 3.9 9.9 11.0 10.3 1.70 0.53 8 14.9 5.2 10.5 10.1 10.5 1.03 0.52 9 19:9:19 12.6 6.6 9.3 8.0 20.0 1.67 0.44 10 11.6 8.2 9.3 2.8 20.3 1.03 0.51 11 27:6:6 16.4 10.9 6.4 2.6 6.5 1.66 0.49 12 15.8 11.9 6.3 2.6 6.4 1.06 0.50 Fig. 1 X-ray patterns of the fertilizer samples: a—1, b—2, c—3, d—4, e—5, f—6; 1 (NH ) HPO , 2 NH H PO , 3 4 2 4 4 2 4 NH NO , 4 (NH ) SO , 5 4 3 4 2 4 2NH NO (NH ) SO , 6 4 3 4 2 4 3NH NO (NH ) SO , 7 4 3 4 2 4 (NH ,K)H PO , 8 (NH ,K)NO , 4 2 4 4 3 9 (NH ,K) SO , 10 KCl, 11 4 2 4 NH Cl, 2h Bragg angle (degree) 123 Int J Ind Chem (2017) 8:315–327 319 X-ray patterns for the samples of grades 16:16:16 and 22:11:11 demonstrate the presence of solid solutions (NH ,K)NO , (NH ,K)H PO and (NH ,K) SO , as well as 4 3 4 2 4 4 2 4 of NH Cl and KCl. For samples 3 and 5, the presence of (NH ) HPO was established. 4 2 4 Comparing X-ray patterns for the samples 3 and 4 of grade 16:16:16 and 5 and 6 of grade 22:11:11 shows that the intensity of the main diffraction peak of NH Cl decreases with a higher degree of ammoniation. This is associated with a reduction of the original content of AN in the composition of samples that results in reducing the amount of NH Cl produced in reaction (2). Fig. 3 Curves of the differential thermal analysis (DTA) and of the differential thermogravimetric analysis (DTG) of sample 2: t time X-ray patterns for sample 1 of 26:13:0 grade demon- (min) strate the presence of (NH ) HPO ,NH H PO , (NH ) 4 2 4 4 2 4 4 2- SO , 2NH NO (NH ) SO and 3NH NO (NH ) SO and 4 4 3 4 2 4 4 3 4 2 4 for the sample 2 the presence of NH NO ,NH H PO , 4 3 4 2 4 2NH NO (NH ) SO and 3NH NO (NH ) SO . 4 3 4 2 4 4 3 4 2 4 Comparing X-ray patterns for samples 1 and 2 of grade 26:13:0 demonstrates that the composition of sample 2 has the unbound AN, which could not fully converted to 2NH NO (NH ) SO and 3NH NO (NH ) SO due to a 4 3 4 2 4 4 3 4 2 4 high content of AN and a low content of (NH ) SO in the 4 2 4 composition of the fertilizer. This may lead to significant deterioration of the properties of sample 2 compared with sample 1. All these compounds are typical for complex AN-based Fig. 4 Curves of the differential thermal analysis (DTA) and of the fertilizers that is noted in [1, 3, 4, 12]. differential thermogravimetric analysis (DTG) of sample 3: t time (min) Derivatographic analysis Figures 2, 3, 4 and 5 show the results of the derivato- graphic analysis for samples 1, 2, 3 and 4. Analysis of curves of the differential thermal analysis (DTA) and of the differential thermogravimetric analysis (DTG) confirms the data of X-ray diffraction analysis. Curves of the differential thermal analysis (DTA) for 22:11:11 samples are characterized by the following peaks: the reverse phase transition of (NH ,K)NO in 4 3 Fig. 5 Curves of the differential thermal analysis (DTA) and of the differential thermogravimetric analysis (DTG) of sample 4: t time (min) NH NO 2KNO (113.1 and 129.9 C, respectively) [15]; 4 3 3 melting (132.8 and 145.3 C) [15]; the exothermal decomposition of the product including the decomposition of NH NO [15], the polycondensation of (NH ,K)H PO 4 3 4 2 4 and the decomposition of (NH ) HPO for samples 3 and 4 4 2 4 (197.2 and 221.5 C[13]. Fig. 2 Curves of the differential thermal analysis (DTA) and of the It can be concluded by comparing the DTG and DTA differential thermogravimetric analysis (DTG) of sample 1: t time curves that sample 3 has the higher thermal stability as (min) 123 320 Int J Ind Chem (2017) 8:315–327 compared to sample 4, which may be related to a lower into a gas phase. However, sample 2 exhibits the higher content of AN and a higher content of (NH ) HPO .Itis thermo-stability than sample 1 when further heated. 4 2 4 also worth noting that there is no peak characteristic for the It should also be noted that the decomposition of sam- (NH ) HPO decomposition in the DTA and DTG curves ples 1 and 2 takes place endo-thermally as opposed to 4 2 4 of sample 3, which would be in the range of 120–200 C. It samples 3 and 4, whose decomposition proceeds with the may be assumed that its absence is due to the interaction release of the large amount of heat. This is due to the between (NH ) HPO and HNO , which is formed as the absence of chlorine compounds in the composition of 4 2 4 3 result of the partial dissociation of NH NO , according to samples 1 and 2, which are capable to accelerate the 4 3 the reaction: exothermal AN and complex AN-based fertilizers decom- position [7–9, 15]. ðNH Þ HPO þ HNO ! NH H PO þ NH NO : ð6Þ 4 4 3 4 2 4 4 3 The decomposition of (NH ) HPO is apparently to 4 2 4 Hygroscopicity, caking and static strength occur at higher temperatures due to the course of reaction (6). In the case of sample 3, this process takes place in the Table 2 presents the results of studying hygroscopicity, intensive exothermal decomposition of the product. caking and static strength of the fertilizer samples At heating sample 2, the peaks are observed on the DTA obtained. curve, which is related to the following phenomena: the The presented data show that for the same grade of the reverse phase transition of AN IV ? III (39.9 C) [13]; the fertilizer the increase of M reduces the hygroscopicity and reverse phase transition of AN III ? II (85.4 C) [13]; the caking; however, the static strength of granules decreases reverse phase transition of AN II ? I (116.3 C) [13]; also. The reduction of hygroscopicity can be associated melting and partial decomposition of adducts 2NH NO 4 3- with a reduced content of AN, which is highly hygroscopic. (NH ) SO and 3NH NO (NH ) SO (162.9 C) [16]; the 4 2 4 4 3 4 2 4 The reduction of caking can also be associated with a polycondensation of NH H PO (209.8 C) [13]; the AN 4 2 4 reduced ammonium chloride content with increasing M, decomposition (220.6 C) [13]. which is apparent from intensity of peaks for NH Cl in the There are no peaks, which are characteristic to AN in the presented X-ray patterns [1, 18]. The reduction of static DTA curve of sample 1. The thermal decomposition of this strength of granules can be the result of lower strength of sample is characterized by the following processes: the phase contacts between granules with increase of M in the decomposition of (NH ) HPO (138.6 C) [13]; the melt- 4 2 4 granulation process [19]. ing and partial decomposition of adducts 2NH NO 4 3- The maximum difference in hygroscopicity and caking (NH ) SO and 3NH NO (NH ) SO (152.2 C) [16]; the 4 2 4 4 3 4 2 4 is observed for 26:13:0 grade, which can be due to the polycondensation of NH H PO (210.8 C) [13]; the AN 4 2 4 presence of AN in sample 2, whereas in sample 1 AN is decomposition (219.5 C) [13]; the (NH ) SO decompo- 4 2 4 connected in double salts (NH ) SO 2NH NO and 4 2 4 4 3 sition (244.5 C) [14]. (NH ) SO 3NH NO . The minimum difference in hygro- 4 2 4 4 3 It can be concluded when compared the DTG and DTA scopicity and caking is observed for 27:6:6 grade, which curves that the presence of (NH ) HPO as a part of sample 4 2 4 can be explained by the high content of nitrate nitrogen in 1 leads to the fact that at temperatures over 100 C both samples and the small difference in its content (NH ) HPO decomposes to NH H PO to release NH 4 2 4 4 2 4 3 between them. Table 2 Hygroscopicity, -1 -1 -2 Sample no. Grade K, mmole g h r 9 10 , kPa P, MPa caking and static strength of granulated fertilizer samples 1 26:13:0 3.21 ± 0.13 3.00 ± 0.13 2.44 ± 0.14 2 5.30 ± 0.20 4.47 ± 0.18 3.70 ± 0.20 3 22:11:11 4.04 ± 0.19 3.54 ± 0.19 3.16 ± 0.19 4 5.00 ± 0.20 4,10 ± 0.30 4.40 ± 0.30 5 16:16:16 3.04 ± 0.12 1.76 ± 0.16 5.00 ± 0.30 6 3.51 ± 0.17 3.10 ± 0.30 5.10 ± 0.30 7 20:10:10 3.74 ± 0.17 2.97 ± 0.15 2.39 ± 0.15 8 4.06 ± 0.15 3.90 ± 0.20 3.80 ± 0.20 9 19:9:19 3.22 ± 0.15 2.59 ± 0.10 3.28 ± 0.19 10 3.96 ± 0.11 3.36 ± 0.16 4.40 ± 0.20 11 27:6:6 5.00 ± 0.10 3.90 ± 0.30 3.90 ± 0,20 12 5.16 ± 0.12 4.40 ± 0.30 4.90 ± 0.30 123 Int J Ind Chem (2017) 8:315–327 321 -1 Fig. 7 Dependence of the heat release rate dQ/dt (mW g ) on time t -1 Fig. 6 Dependence of the heat release rate dQ/dt (mW g ) on time (min) in the thermal decomposition of sample 4 t (min) in the thermal decomposition of sample 3 Cl accelerating action prevails over decreasing the AN It should also be noted that the highest increase of the - 2- decomposition rate in response to H PO , HPO and 2 4 4 caking was observed for 16:16:16 grade (r /r = 1.76), 6 5 2- SO anions and, therefore, the decomposition of this whereas for the other grades this ratio is much lower. This sample occurs with the self-acceleration. is possible due to the high ratio of the content of NH Cl in Sample 3 has a lower content of AN as compared to two samples of 16:16:16 grade and almost twofold increase sample 4, herewith in its composition a large portion of in the content of AN in sample 6 when M simultaneously - 2- 2- H PO is substituted with HPO . Anion of HPO is 2 4 4 4 reduced. The closest value to this one is r /r = 1.49 for 2 1 capable to a higher degree to reduce the concentration of 26:13:0 grade. The high ratio r /r for 26:13:0 grade is 2 1 undissociated nitric acid, and so to increase the thermal apparently due to the fact that in sample 2 the part of NA stability of sample 3. Besides, the content of (NH ) SO in 4 2 4 presents in the free form, while in sample 1 NA is fully sample 3 is also higher than in sample 4. All this con- bound in double salts. tributes to the fact that the accelerating action of Cl is not detected, and the decomposition occurs without self-ac- Microcalorimetry celeration. Thus, sample 3 has significantly higher thermal stability as compared to sample 4. Figures 6 and 7 show the curves of the heat release rate Besides the study of the fertilizer samples, the heat dependence on time in the thermal decomposition of samples release rate was also measured as a function of time in the 3 and 4 in the temperature range of 183.5–245.9 C. thermal decomposition of nitrate–phosphate–ammonium As indicated above, chloride-anions Cl contained in slurries at obtaining sample 3 with M = 1.0 (sample 3a) samples under study are catalysts of the AN decomposi- and M = 1.4 (sample 3b) with humidity of about 8% mass tion, and their catalytic effect increases with the increase of in the temperature range of 243.5–277.0 C (Figs. 8, 9). the content of nitric acid in the system and virtually does The study of the heat release rate for these samples not occur when its content is low. The accelerating action revealed their high thermal stability, while sample 3b was of Cl in the AN decomposition is related to accumulation more thermally stable than sample 3a, which can be of nitryl chloride NO Cl, nitrosyl chloride NOCl and explained by the higher content of (NH ) HPO in it. 4 2 4 chlorine Cl in the system, being more effective oxidizers Figure 10 shows the temperature dependencies of the of ammonium cation NH and ammonia as compared to initial heat release rates (dQ/dt) in the thermal decom- t=0 nitric acid. The presence of NH H PO ,(NH ) HPO and 4 2 4 4 2 4 position of samples 3, 4, 3a and 3b in Arrenius coordinates. - - (NH ) SO together with Cl reduces Cl catalytic effect 4 2 4 For comparison, Fig. 5 also illustrates the temperature in AN decomposition. dependence of the initial heat release rates in the AN The study of the heat release rate for sample 4 revealed thermal decomposition studied previously [20]. its low thermal stability. In the decomposition of sample 4 123 322 Int J Ind Chem (2017) 8:315–327 -1 3 -1 Fig. 10 Dependence of lg[dQ/dt (mW g )] on 10 /T (K ) for t=0 samples 3 (1), 4 (2), 3a (3), 3b (4) and ammonium nitrate (5) -1 Fig. 8 Dependence of the heat release rate dQ/dt (mW g ) versus dQ ð22:8  0:4Þ 10 time t (min) in the thermal decomposition of sample 3a 16:10:3 =10 exp  ; ð9Þ dt T t¼0 for sample 3b dQ ð12:7  0:9Þ 10 7:30:8 =10 exp  : ð10Þ dt T t¼0 The dependencies presented in Figs. 6, 7, 8, 9 and 10 show that the initial heat release rate of sample 4 is on average by 1–2 orders higher than that for sample 3. Herewith the initial heat release rate of sample 4 signifi- cantly exceeds that of AN, while for sample 3 the situation is inverse. Samples 3a and 3b have even higher thermal stability as compared to sample 3, which may be explained by lack of Cl in their composition and the high water content. In any real conditions of conducting the discussed reaction, the thermal explosion is only possible when the values of external parameters of the process exceed the critical ones for the thermal explosion, but calculation of -1 Fig. 9 Dependence of the heat release rate dQ/dt (mW g ) versus the critical conditions for a real complex production pro- time t (min) in the thermal decomposition of sample 3b cess is a very time-consuming task, and the adiabatic induction period of thermal explosion s is calculated ad The equations of the obtained dependence of (dQ/dt) t=0 simply. If the value s is much greater than the real time of -1 ad (mW g ) on temperature (K) are as follows: the production process at an appropriate temperature, then for sample 3 the thermal explosion will not occur, and in any real pro- dQ ð17:2  0:8Þ 10 cess conditions the induction period may only be greater 11:70:7 =10 exp  ; ð7Þ dt T than under adiabatic conditions. However, if the value s ad t¼0 and process real time are close enough or if s is even less, ad for sample 4 it is necessary to calculate the critical conditions of the thermal explosion (the critical temperature for the actual dQ ð22:3  0:9Þ 10 18:10:7 =10 exp  ; ð8Þ size of the unit and the conditions of heat transfer from it). dt T t¼0 Only these calculations can give final decision on possi- for sample 3a bility of the thermal explosion in the process considered. 123 Int J Ind Chem (2017) 8:315–327 323 Calculation of the adiabatic induction period is the most of a relative explosion risk of a substance. The adiabatic simple and available method to assess the possibility of the induction periods of the thermal explosion for samples 3, thermal explosion for any particular composition. In the 3a and 3b are greater than that for AN, and for sample 4 complete absence of heat removal (adiabatic conditions) they are almost by an order less, which reveals the potential and at a sufficiently high value of the process heat, the danger of thermal spontaneous ignition of the sample thermal explosion will always occur; besides, the degree of during production operations at high temperatures. conversion in the reaction discussed during induction per- iod will be very small, because all the heat is used for Gravimetric study of the thermal decomposition heating a substance. As far as there is no heat removal, the adiabatic induction period is independent of the sample The study of the mass loss in the thermal decomposition mass and heat removal conditions and it is considered as a was carried out for samples 3 and 4 at temperatures of 170, characteristic for a substance or mixture discussed. In the 180, 190 and 200 C. In addition to the study of the mass theory of thermal explosion because of the weak influence loss, the release of ammonium nitrogen, nitrate nitrogen, of the process acceleration, the exact quantitative equation chlorine and fluorine to the gas phase was also evaluated. for calculating the adiabatic induction period was obtained The research results are presented in Figs. 11, 12 and 13. only for zero-order reaction, and the reaction rate change in The decomposition intensity for sample 4 is much the subsequent stages is assumed to have a very small higher than that for sample 3. The release of chlorine, action on the adiabatic induction period [21]: fluorine, ammonium nitrogen, and nitrate nitrogen from sample 4 to the gas phase is also much more intensive than c RT E p c s =   exp ; ð11Þ that from sample 3. Ammonium nitrogen in the initial ad Q k E RT 0 0 0 decomposition stage is released from sample 3 in a greater where c is the heat capacity of the sample; Q is the total quantity than that from sample 4. It is related to the higher p 0 process heat; k and E are the pre-exponential factors and content of (NH ) HPO , which starts to decompose in NH 0 c 4 2 4 3 the activation energy of the decomposition rate constant; T and NH H PO at low temperatures. 0 4 2 4 is the absolute temperature of the decomposition; It is also worth mentioning that the maximum amount of -1 -1 R = 8.314 J mole K is the universal gas constant. fluorine released into the gas phase for both samples is dQ E almost the same. It is related to the fact that fluorine in both When = Q k exp  Eq. (11) takes the 0 0 RT dt 0 t¼0 samples according to [22] is present in the form of com- following form: pounds (NH ) SiF ,NH F, NH NO (NH ) SiF ,KNO 4 2 6 4 4 3 4 2 6 3- RT c K SiF ,(NH ) SiF NH F, etc., the decomposition of p 2 6 4 2 6 4 s =  : ð12Þ ad dQ which depends only on the process temperature. The higher dt t¼0 fluorine release rate for sample 4 is related to the more intense exothermal decomposition of this sample. The results from paper [12] were used to determine the For chlorine, the release into the gas phase depends on heat capacity of samples under study, provided that in a the content of AN, so for sample 4 a significantly greater first approximation the heat capacities of samples 3, 4 and amount of chlorine is released into the gas phase than for 3a, 3b are equal in pairs. The value of the AN heat capacity sample 3. was taken according to the data in [2]. The s values ad The release of chlorine, fluorine, nitrous gases and obtained are given in Table 3. The s values for the same ad ammonium compounds into the gas phase leads to the initial temperature may be considered as the characteristics essential complication and more expensive purification of Table 3 Adiabatic induction T,K s , h ad period of the thermal explosion s of samples 3, 4, 3a and 3b ad Sample 3 Sample 4 Sample 3a Sample 3b Ammonium nitrate and AN depending on temperature T 473 94.64 1.50 226.83 232.00 11.38 478 68.04 0.97 146.60 180.92 7.00 483 49.29 0.63 95.69 142.00 4.35 488 35.97 0.42 63.05 112.02 2.73 493 26.45 0.28 41.94 88.90 1.73 498 15.58 0.19 28.14 70.94 1.11 503 14.59 0.13 19.05 56.90 0.72 508 10.94 0.09 13.01 45.88 0.47 123 324 Int J Ind Chem (2017) 8:315–327 -1 Fig. 13 Release of fluorine into the gas phase X (g kg ) in the thermal decomposition of samples 3 (curve 1) and 4 (curve 2)at temperature 180 C versus time t (min) Fig. 11 Dependence of thermal decomposition degree b = (m - m )/m 100 (%) versus time t (min) for samples 3 and 4 0 0 at constant temperature; sample 3: 1 170 C, 2 180 C, 3 190 C, 4 200 C; sample 4: 5 180 C Fig. 14 The dependence of dynamic viscosity g (mPa s) of ammo- nium–phosphate–nitrate slurry on M at temperature 110 C and for different values of humidity: 1 5% mass., 2 6% mass., 3 7% mass., 4 8% mass., 5 10% mass Fig. 12 Release of chlorine X , ammonium X and nitrate Cl Namm -1 nitrogen X (g kg ) into the gas phase in the thermal decompo- Nnitr Figure 14 shows the dependence of dynamic viscosity sition of samples 3 and 4 at temperature of 180 C versus time of such slurry on M for different values of humidity at t (min); sample 3: curve 1 Cl, 2 N , 3 N ; sample 4: curve 4 Cl, 5 am nit 110 C. The slurry viscosity is apparent to reach the min- N , 6 N am nit imum value at M = 1.45 for all the values of humidity. It should be mentioned that the same behavior of vis- exhaust gases from them, as well as to the more intense cosity was observed for phosphate ammonia slurries corrosion of equipment. obtained from various types of a phosphate raw [3, 23]. The presence of minimum in the viscosity curve is prob- Dynamic viscosity ably due to the high solubility of ammonium phosphates at M = 1.4–1.5. The presence in the slurry of impurities of The study of dynamic viscosity was performed for iron, aluminum, magnesium, fluorine, silicon, etc. leads to ammonium–phosphate–nitrate slurries obtained at produc- increasing viscosity due to the formation of poorly soluble tion of 22:11:11 grade when M = 1.7. To obtain such compounds [3, 24, 25]. slurries, phosphoric and nitric acids were mixed in the ratio Figures 15 and 16 show the dependences of the slurry P O :HNO = 0.36:1 (by mass.) and ammoniated up to the 2 5 3 dynamic viscosity (for M = 1.05 and M = 1.45) on specified value of M. humidity at different temperatures. The figures show that 123 Int J Ind Chem (2017) 8:315–327 325 g ¼A ; ð13Þ exp RT where A is the pre-exponential factor and E is the acti- vation energy for viscous flow. Table 4 presents the equations of dynamic viscosity dependence on temperature at the different values of humidity for slurries studied. As can be seen from the equations presented, the activation energy of a viscous flow, the values of pre-exponential factor and the value of dynamic viscosity of the slurry for M = 1.45 are substan- tially less than for M = 1.05. Using the slurries having higher mobility and flowability during their processing in the granular product can signif- Fig. 15 Dependence of dynamic viscosity g (mPa s) of ammonium– icantly reduce the energy costs for the removal of moisture phosphate–nitrate slurry for M = 1.05 on humidity (%mass.) for from the granules and reduce the amount of the recirculated different values of temperature: 1 100 C, 2 105 C, 3 110 C, 4 115 C, 5 120 C product obtainable by a recycle method. Conclusions On the basis of the studies performed, it has been found that increasing the degree of phosphoric acid ammoniation with M = 1.0–1.1 to M = 1.6–1.7 influences on the properties of the complex AN-based NP and NPK fertilizers. It has been shown by X-ray diffraction and derivato- graphic analysis that the composition of NPK fertilizer (16:16:16 and 22:11:11) contains (NH ,K)H PO , (NH ,- 4 2 4 4 K) SO , (NH ,K)NO , KCl and NH Cl. When 2 4 4 3 4 M = 1.6–1.7, (NH ) HPO presents also additionally. The 4 2 4 Fig. 16 Dependence of dynamic viscosity g (mPa s) of ammonium– composition of NP fertilizer (26:13:0) contains NH H PO , 4 2 4 phosphate–nitrate slurry for M = 1.45 on humidity (%mass.) for 2NH NO (NH ) SO and 3NH NO (NH ) SO . When 4 3 4 2 4 4 3 4 2 4 different values of temperature: 1 100 C, 2 105 C, 3 110 C, 4 M = 1.0–1.1, NH NO presents additionally in the system, 4 3 115 C, 5 120 C when M = 1.6–1.7, (NH ) HPO and (NH ) SO present 4 2 4 4 2 4 additionally. the slurry viscosity increases with decreasing humidity. It is found that the decomposition of NPK fertilizers Herewith for the slurries at M = 1.05, a more rapid occurs with the strong exothermal effect and NP fertilizers increase of viscosity with decreasing humidity is observed. decomposition occurs with the endothermal effect. The Temperature influence on dynamic viscosity of the strong exothermal effect of the thermal NPK fertilizer slurries obeys the law of Arrhenius–Andrade [26]: Table 4 Equations of dynamic W M = 1.05 M = 1.45 viscosity (mPas) dependence for ammonium phosphate 3 3 ð14:70:6Þ10 ð9:00:4Þ10 5 13:60:6 8:50:4 g =10 exp g =10 exp nitrate slurries for M = 1.05 T T and M = 1.45 for the various 3 3 10 11:70:6 ð11:90:6Þ10 5:10:2 ð5:70:3Þ10 g =10 exp g =10 exp humidity values W (% mass.) T T 3 3 ð10:50:4Þ10 ð3:70:1Þ10 15 10:60:5 3:030:13 g =10 exp g =10 exp T T 3 3 ð9:60:3Þ10 ð2:40:1Þ10 20 9:80:3 1:590:02 g =10 exp g =10 exp T T 3 3 9:20:3 ð9:00:3Þ10 0:470:01 ð1:300:05Þ10 g =10 exp g =10 exp T T 123 326 Int J Ind Chem (2017) 8:315–327 8. Rubtsov YI, Strizhevsky II, Kazakov AI, Moshkovich EB, decomposition is associated with the presence of chlorine- Andrienko LP (1989) Kinetic mechanism of influence of Cl on contained compounds. thermal decomposition of ammonium nitrate. 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