RU2542304C2 - Method of obtaining oxidiser of energetic condensed systems - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to field of energetic condensed systems, namely to oxidisers of solid fuel systems based on ammonium nitrate (AN). Method includes mixing salts of ammonium nitrate and potassium chloride, heating mixture in water medium to complete dissolution, reduction of temperature to crystal formation without mixing, after which mixture is intensively mixed until equilibrium is established, filtration of formed crystals and drying. Potassium chloride is dosed into initial mixture in amount making it possible to obtain its content in solid phase not less than 3%. In obtained oxidiser thermal decomposition of AN changes - explosive nature of exoeffect is observed, heat release increases sharply. Effect is achieved due to formation as a result of ion-exchange at nanolevel of equilibrium solid phase with complex composition, possessing novel physical-chemical properties.

EFFECT: method makes it possible to obtain AN-based oxidiser, which does not have phase conversions in the interval of temperatures from -50 to +100°C.

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Description

The present invention relates to the field of energy condensed systems (EX). The oxidizing agent obtained by this method can be used in solid fuel compositions of gas generating devices, for example, in automobile airbags, solid fuel fire extinguishers, lifeboats, rocket fuels, etc.

It is known that the problem of reducing emissions of unfavorable combustion products of EX-compounds: chlorine compounds (Cl ₂ , HCl, etc.), which have a harmful effect on the environment and human health, up to the occurrence of acid rain and the formation of ozone holes, can be solved by chlorine-free oxidizing agents, for example, cheap ammonium nitrate NH ₄ NO ₃ (HA) [Sinogina ES The study of ignition and combustion of high-energy materials based on chlorine-free oxidizing agents / abstract. diss. for the degree of candidate of technical sciences, 2006].

However, ECS based on ammonium nitrate (HA) have a number of disadvantages that limited their use: first of all, this is a low level of ballistic characteristics (low burning rate, high sensitivity of the burning rate to pressure), phase transformation in the crystal structure can be considered another significant drawback HA in the operational Temperature Range, since cyclic changes in temperature can be accompanied by an irreversible increase in the volume of oxidizing crystals and solid fuel gas generating compositions based on it, leading to cracking and destruction of their structure.

A known method (US patent No. 3018164 from 01/23/62), according to which phase-stabilized HA is obtained by introducing 10-15% potassium nitrate (NK) into the HA melt, cooling the melt, fractionating the obtained melt and adding a multiple portion of it to pure HA, to get the content of NK less than 8%, heating this mixture in a pipe placed in oil. This product has stability, expressed in the absence of the IV переходаIII modification transition in the temperature range from -45 to + 100 ° C.

This method has several disadvantages: during a cyclic test in the temperature range from -50 to + 50 ° C, the solid solution decomposes and phase transitions are restored, in addition, a significant drawback is the complex multi-stage technology in the industrial production of the oxidizing agent.

The second problem - the low burning rate of HA-based mixtures can be solved by the introduction of catalysts: effective catalysts are salts of tri- and hexavalent chromium, alkali and alkaline earth metal chlorides, copper, lead, iron compounds, potassium permanganate, vanadium pentoxide and some others [Rubtsov Yu .I., Kazakov A.I., Weiss N.G., Alekseev I.I., Strizhevsky I.I., Moshkovich E.B. An experimental study of the thermal decomposition of acidified ammonium nitrate // Journal of Applied Chemistry, 1988, vol. 61, issue 1, pp. 131-132. Arkhipov V.A., Gorbenko T.I., Savelyeva L.A., Sinogina E.S. Thermal decomposition and combustion of mixed compositions containing ammonium nitrate // News of Universities. Physics, 2005, v. 48, No. 11, pp. 11-14. Glazkova A.P. Catalysis of the combustion of explosives / A.P. Glazkova. - M .: Nauka, 1976, 264 p. Manelis G.B. Thermal decomposition and combustion of explosives and gunpowder / G.B. Manelis, G.M. Nazin, Yu.I. Rubtsov, V.A. Strunin. - M .: Nauka, 1996, 400 pp.].

In the work [Popok V.N., Khmelev V.N. The effect of metal oxides and chlorides on the energy release parameters in energy materials based on ammonium nitrate / Polzunovsky Vestnik, 2009, No. 3, p. 252-264], the simultaneous effect of metal chlorides on the rate of thermal decomposition of HA and combustion of a solid fuel composition is noted.

Closest to the proposed invention in technical essence and adopted as a prototype is the invention "Gas-generating compositions having a low self-ignition temperature, gas generation methods" [United States Patent 6,673,172 Wheatley et al. January 6, 2004], which consists in obtaining a low-melting oxidizing agent by mixing silver nitrate and potassium chloride, heating the mixture to form a low-melting eutectic and / or solid solution, and then obtaining granules with inclusions of compressed solid powders of gas-generating compositions.

The disadvantage of the prototype can be considered as the use of inorganic nitrate salts of silver nitrate in the amount of 25% wt. and about 10% wt. potassium chloride (HC). Such a content of metal salts will lead to the formation of a significant amount of a condensed phase and a decrease in the volume of gaseous products, which will lead to a decrease in the efficiency of the gas-generating composition. Only the replacement of silver nitrate with HA will eliminate the formation of a condensed phase, increase the volume of the resulting gas phase and reduce the cost of the final composition.

The problem solved by the invention is to develop a method for producing a cheap and environmentally friendly oxidizer EX with the required physico-chemical characteristics.

The technical result to which the present invention is directed is as follows: by a simple technological method, which is easy to implement on existing industrial equipment, an oxidizing agent for HA based EC is obtained, which is a joint oxidizing crystals with a catalyst for its thermal decomposition - potassium chloride, which have phase stability in the temperature range from -50 to + 100 ° C, exothermic decomposition of the system in one stage with a minimum content of additives.

A positive result achieved by the described method is ensured by the formation of an equilibrium complex system of solid solutions, double salt and eutectics in the final product of the interaction due to sequential operations and isothermal co-crystallization (IS).

The problem is solved by developing a method for producing an oxidizer of energy condensed systems, including mixing salts of ammonium nitrate and potassium chloride, heating the mixture to complete dissolution, and heating is carried out in an aqueous medium, then the temperature is reduced to form crystals without stirring, then the mixture is intensively mixed until equilibrium is established , the crystals formed are filtered off, dried, and potassium chloride is dosed into the initial mixture in an amount that allows to obtain its content in t at least 3%.

The achievement of the equilibrium state is monitored by the content of the K ⁺ ion - by flame photometric method.

A positive result is associated with the following regularities that occur during crystallization: as a result of ion exchange between HA and the additive, a complex system is formed (1),

consisting of salts of NH ₄ NO ₃ , KCl, KNO ₃ , NH ₄ Cl, between which interactions can occur with the formation of double salts, eutectics and solid solutions.

System (1) is a polythermal section of a triple reciprocal system, which includes the following binary systems:

NH ₄ NO ₃ -KNO ₃ (2), NH ₄ NO ₃ -NH ₄ Cl (3), KNO ₃ -KCl (4) and NH ₄ Cl-KCl (5) (Handbook on the fusibility of systems of anhydrous inorganic salts [Text ]. 2 vols., Vol. 2. Systems triple, triple mutual and more complex / Edited by NK Voskresenskaya et al. - M.-L.: Academy of Sciences of the USSR, 1961, 585 pp.). In system (2), solid solutions up to 40% KNO _{3 were} identified based on phase III of HA, eutectic and double salt 2NH ₄ NO ₃ · KNO ₃ (DS). In system (3), a eutectic with a melting point of 140 ° C with a content of 17.6% NH ₄ Cl was detected, in system (4), a eutectic was found at 5% KNO ₃ with a melting point of 320 ° C and a polymorphic conversion of KNO _{3 of} 128 ° C , the formation of solid solutions with a KCl content of up to 30% with a melting point of 520 ° C was confirmed in system (5). Such complex properties of binary systems that make up the main one determine the final physicochemical characteristics of the formed crystalline phase, which, in turn, depend on the degree of conversion of the additive and the homogenization of the final products.

The authors were faced with the task of obtaining a thermodynamically stable crystalline composition by combining chemical (formation of a double salt, eutectic, solid solutions) and physical processes (formation of a crystalline phase).

Preliminary studies found that the double salt 2NH ₄ NO ₃ · KNO ₃ does not form at a temperature of 25 ° C, but forms only at temperatures above 80 ° C (Vorokhobin I.S. Physicochemical analysis of the NH ₄ NO ₃ -KNO _{3 system} -N ₂ O at 25 ° C / Vyazenova I.A., Taranushich V.A. // Engineering Bulletin of the Don: [electronic journal] - 2014, No. 1, - Access mode: archive / nly2014 / 2281), therefore To create conditions for the formation of DS and its isolation into the crystalline phase from the aqueous solution, supersaturation was created by heating the solution until it was completely dissolved (more than 80 ° C) with further cooling eat up to 25 ° C.

To assess the adsorbability of an additive, the Panet rule is considered to be the most reliable, according to which particles that give the least soluble compound with the main crystal as a result of ion exchange (Petrov TG Crystal growth from solutions [Text] / TG Petrov are firmly embedded in the crystal , E.B. Treyvus, Yu.O. Punin, A.P. Kasatkin; 2nd ed., Revised and additional - L .: Nedra, 1983, p. 53). We found that the solubility of DS in water is 38.04 at 25 ° C, and HA - 67.63 at 25 ° C, that is, DS, according to the Panet rule, will be built into the structure of HA.

If supersaturation increases beyond the limit, spontaneous or spontaneous crystallization occurs, and according to the Van Hoff rule of thumb, salts form supersaturated solutions the more easily, the greater the product of the valency of their constituent ions: HC with monovalent ions form solutions with low supersaturation, and substances that form several polymorphs can give highly supersaturated solutions (these include NK and NA, solutions of which can exist for a long time in a supersaturated state). The stability of supersaturated solutions also depends on the type of crystal lattice of the released salt [Matusevich L.N. Crystallization from solutions in the chemical industry [Text] / L.N. Matusevich. - M.: Chemistry, 1968, 304 p. 135, p. 68]: the most stable solutions of salts with crystals of low symmetry (monoclinic or triclinic), and substances with a cubic lattice crystallize more easily. That is, the introduction of the additive will facilitate the transition of the formed phase to higher symmetry (from IV to III), which will also lead to an increase in the rate of crystallization of the system.

The choice of the method of co-crystallization of the starting components was carried out on the basis of the analysis of known technologies (IV Melikhov, Sokristallizatsiya [Text] / IV Melikhov, MS Merkulova. - M .: Chemistry, 1975, 280 pp.): Diffusion annealing method requires a long time (up to 10 days); the method of spontaneous recrystallization is also associated with high costs for the time of the process, which is not economically profitable for large-capacity industries; methods of continuous and periodic forced recrystallization are complex, and the result is practically no different from other methods of co-crystallization, therefore, for further studies, the method of isothermal removal of supersaturation was chosen, the essence of which is as follows - after creating a supersaturation (which is easy for HA to create due to its high solubility in water) the solution with the additive is mixed vigorously for the time necessary to reach equilibrium. Under such conditions, crystals precipitate in the form of a highly dispersed phase, which is subject to shock recrystallization and ostwald ripening. Under the condition of initial high supersaturation and intensive mixing, the system quickly reaches equilibrium, and the formed crystals become as homogeneous and homogeneous as possible.

Only the use of the method of isothermal removal of supersaturation with vigorous stirring will allow us to establish the equilibrium distribution of the impurity, since equilibrium is established at a very slow crystallization rate with a small supersaturation of the solution at each instant of time, and since the concentration in the solution constantly changes, the composition of crystalline layers deposited on the faces of the crystal, and therefore the crystals grow heterogeneous in the composition of the isomorphic impurity. Proceeding from this, for the maximum degree of homogenization, it was necessary to simultaneously use factors of temperature reduction in order to form supersaturation in solution and intensive mixing, which will allow changing the crystallization rate.

In the forced convection mode (intensive mixing), with an increase in the flow rate of the solution and a decrease in the thickness of the diffusion layer, the diffusion rate increases even more, and the supersaturation gradients along the face decrease, which makes it possible to quickly grow large homogeneous crystals, which are difficult to obtain under other conditions (Petrov T.G. Crystal growth from solutions [Text] / TG Petrov, E.B. Treivus, Yu.O. Punin, AP Kasatkin; 2nd ed., Revised and additional - L .: Nedra, 1983, p. 26).

The influence of solution mixing - the “mechanical" factor is of great importance in the processes of mass crystallization, not only because in industrial crystallization the process proceeds with the movement of the solution, but also because it is one of the few factors by which you can change the quality of the finished product (Matusevich LN Crystallization from solutions in the chemical industry [Text] / LN Matusevich. - M.: Chemistry, 1968, p. 75).

The studied system consists of isomorphic components and their entry into the crystal depends on the physicochemical properties of the starting materials, the degree of their interaction, the composition of the solution, and crystallization conditions: temperature, crystallization rate, mixing intensity.

An increase in the mixing rate leads to a uniform distribution of impurities in the crystal due to the fact that:

- crystals do not coalesce among themselves (do not form drusen);

- crystals become homogeneous (impurity is distributed evenly);

- reduces the possibility of capture of the mother liquor due to repeated recrystallization;

- the diffusion rate changes, which helps to equalize the concentration of the additive near the crystal surface and in solution.

Matusevich L.N. emphasizes "sometimes only by selecting hydraulic conditions a homogeneous product can be obtained" (Matusevich LN Crystallization from solutions in the chemical industry [Text] / LN Matusevich. - M .: - Chemistry,).

As a result of using the proposed technology, an equilibrium homogeneous solid phase is formed, consisting of a complex system of solid solutions, a double salt and eutectics and possessing new physicochemical properties: phase stability in the temperature range from -50 to + 100 ° C, intense exothermic decomposition of the system into one stage with a minimum content of additives.

The authors first established that the combination of the above technological operations allows us to solve the technical problem due to the formation of an equilibrium solid phase of a complex composition with new physicochemical properties as a result of ion exchange at the nanoscale. The totality of the formed solid phases made it possible to achieve the technical result claimed in the patent.

In FIG. Figure 1 shows the differential thermal analysis curves. In FIG. 2 presents X-ray diffraction patterns of samples. In FIG. Figure 3 shows the curves of IR spectroscopic analysis. In FIG. 4 electronic photographers and samples.

Example 1

The process is carried out according to US patent No. 6673172: HA brand "chda" in the amount of 4.85 g and HC brand "h" in the amount of 0.15 g after mixing is loaded into a heat-resistant glass vessel with controlled heating and the mixture is heated until complete dissolution of the solid phase ( carry out co-crystallization from a melt of components - CP). After completion of the process, the mixture is cooled, crushed, fractionated if necessary and examined by methods of physicochemical analysis: FIG. 1 (curve 3), FIG. 2 (curve 4), FIG. 3 (curve 3). A sample was obtained with a Ch content of 3%.

Example 2 (mechanical mixing)

For the “chda” grade in the amount of 4.85 g and the “h” grade HC in the amount of 0.15 g after mixing and mechanical abrasion in a porcelain mortar, the DTA method is used: FIG. 1 (curve 2). A sample was obtained with a Ch content of 3%.

Example 3 (the claimed method)

On the “chda” grade in the amount of 32.03 g, HC in the amount of 3.96 g and 15 g of distilled water are loaded into a glass co-crystallization unit with controlled heating (thermostat) and the temperature is raised to 80 ± 2 ° C until the solid phase is completely dissolved . After the formation of a homogeneous solution, stirring is stopped and the temperature is lowered to 25 ° C, the solution is stirred vigorously and kept until it reaches equilibrium for at least 1.5 hours (equilibrium isothermal co-crystallization at 25 ° C - IP). The crystals formed are separated from the filtrate on a Schott filter and dried in a vacuum oven at 90 ° C for 2 hours. The content of HC additives in the solid phase is 2.62%: FIG. 1 (curve 6).

Example 4 (the claimed method)

On the “chda” grade in the amount of 32.03 g, HC in the amount of 5.08 g and 15 g of distilled water are loaded into a glass co-crystallization unit with controlled heating and heated until the solid phase is completely dissolved at a temperature of 80 ± 2 ° C. After the formation of a homogeneous solution, the temperature is reduced to 25 ° C and intensive mixing is turned on until equilibrium is reached (at least 1.5 hours). The crystals formed are separated from the filtrate on a Schott filter and dried in a vacuum oven at 90 ° C for 2 hours. The content of HC additives in the solid phase is 3.11%: FIG. 1 (curve 5).

Example 5 (co-crystallization from water at 90 ° C)

On the “chda” grade in the amount of 4.85 g, HC in the amount of 0.15 g and 15 g of distilled water are loaded into the evaporator, the process of co-crystallization is carried out at a constant temperature of 90 ± 2 ° C and intensive stirring until the moisture is completely removed (co-crystallization method from an aqueous solution at 90 ° C - CBP). After completion of the process, the mixture is cooled, crushed, fractionated if necessary and dried in a vacuum oven at a temperature of 90 ° C for 2 hours. Sample with a CK content of 3%: FIG. 1 (curve 4), FIG. 2 (curve 3), FIG. 3 (curve 4).

In FIG. Figure 1 shows the differential thermal analysis (DTA) curves of the samples (curves 2-6) and ammonium nitrate (curve 1). According to the DTA results, it can be concluded that only the isothermal co-crystallization (IS) method developed by the authors allows one to obtain an HA-based oxidizer with a CC content of 3.11%, which does not have phase transformations in the temperature range from -50 to + 100 ° C (curve 5). At the same time, the nature of the thermal decomposition of this sample changes - an explosive form of the exo effect is observed, and heat release sharply increases. In the sample with a CK content of 2.62% (curve 6) obtained by the present method, a polymorphic transition at a temperature of -20 ° C is observed, in the temperature range from -50 to + 100 ° C, i.e. This sample does not have phase stability in a given temperature range, which indicates the need to introduce HC in an amount of at least 3%.

In FIG. Figure 2 presents the results of X-ray phase analysis (XRD) of samples of HA without additives III phase (curve 1), HA with 3.11% HC obtained IS (curve 2), HA with 3% HC obtained SVR (curve 3), HA with 3 % HC obtained CP (curve 4). The XRD data showed that the sample obtained by the present method crystallizes in phase III of HA (curve 2).

In FIG. 3 presents the results of IR spectroscopic analysis: HA without additives (curve 1), HA with 3% HC according to example 1 (curve 3), HA with 3% HC according to example 2 (curve 2), HA with 3% HC according to example 5 (curve 4), ON with 3.11% HC according to example 4 (curve 5). The results of IR spectroscopy confirmed the individuality and high crystallinity of the phase formed when using the proposed method of IP - curve 5.

In FIG. 4 shows electronic photographs of samples of HA with the addition of HC obtained according to example 1, 5 and 3. As can be seen from the above results of the study, a uniform distribution of the additive is observed only in the sample obtained by the claimed method.

Claims (1)

A method of producing an oxidizing agent of energy condensed systems, comprising mixing salts of ammonium nitrate and potassium chloride, heating the mixture to complete dissolution, characterized in that the heating is carried out in an aqueous medium, then the temperature is reduced to form crystals without stirring, then the mixture is intensively mixed until equilibrium is established, the crystals formed are filtered off, dried, and potassium chloride is dosed into the initial mixture in an amount that makes it possible to obtain its content in the solid phase of at least 3%.

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