Improved Flow Synthesis

Abstract

The present invention relates to a method for synthesizing an organic explosive, the method comprising the steps of: i) providing a first solution A; ii) providing a second solution B, selected such that an admixture of solutions A and B reacts together upon formation of the admixture to provide the organic explosive; iii) mixing solutions A and B and passing them through a flow reactor to produce the admixture, the flow reactor comprising a pipe, the inner diameter of which is selected to be less than a critical diameter of the organic explosive, thereby preventing detonation of the formed organic explosive in said flow reactor.

Description

[Technical Field]

[0001] The following invention relates to a process for producing explosives by flow synthesis through the direct nitration of explosive precursors, and in particular to a process for producing RDX and HMX.

[0002] Before describing the invention in further detail, it is to be understood that this invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the scope of the present invention will be limited only by the claims and that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. Summary of the Invention

[0003] A first aspect of the present invention provides a method for synthesizing an organic explosive, the method comprising: i) providing a solution A containing a nitrating agent; ii) providing a solution B containing an explosive precursor reagent, the admixture of Solution A and Solution B is selected so that they react together upon forming the admixture to provide an organic explosive; iii) measuring the critical diameter of the organic explosive; iv) the flow reactor comprises a pipe, and the inner diameter of the pipe is selected so that the inner diameter is less than the critical diameter of the organic explosive, thereby preventing the formed organic explosive from detonating in said flow reactor; v) mixing solutions A and B and passing them through a flow reactor to form a mixture; Includes.

[0004] Solution A contains a nitrating agent such as nitric acid, nitrite, and combinations thereof.

[0005] Solution B contains explosive precursor reagents known in the art, which are often reagents of limited availability because they are easily nitrated with high concentrations of nitric acid, such as fuming nitric acid or 99% concentrated nitric acid.

[0006] Explosive precursors may be aromatic compounds, phenylamines, cycloamines, toluene, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (TAT), 1,3,5-triacetyl-1,3,5-triazacyclohexane (TRAT), 1,5-dinitroendomethylene-1,3,5,7-tetraazacyclooctane (DPT), triazoles, and hexamethylenetetramine. Although the formation of TAT, TRAT, and DPT may require several synthetic steps, they are not energetic materials and can therefore be safely produced by conventional batch techniques.

[0007] Solution A and / or B, or solution C that may be mixed in step ii), further contains a catalyst, a strong acid, a dehydrating agent, and an acid anhydride. The strong acid other than nitric acid may be sulfuric acid. The dehydrating agent may be P2O5. The acid anhydride may be acetic anhydride or trifluoroacetic anhydride.

[0008] The nitration reaction is typically exothermic and the flow reactor may be temperature controlled to ensure that the explosive material formed does not reach detonation.

[0009] The mixture may be passed through a flow reactor, to which Solution D is added and the reactants are post-treated to obtain a precipitate of the explosive material or a salt thereof. Solution D can quench the acid. Solution D may also contain cold water to cause the precipitation.

[0010] Batch synthesis of explosives is very strictly regulated due to the risk of explosion. However, in industrial batch synthesis, hundreds of kilograms of material are produced in the reactor. This necessitates a very large safety radius for the construction. Flow synthesis reduces the risk by allowing production in low kilogram quantities so that the explosive material can be collected away from stored solutions A, B, and / or C. Preferably, the separate collection location is behind a blast wall or in an explosives warehouse. Continuous production of small amounts of explosive material prevents hundreds of kilograms of batches from accumulating in one location.

[0011] The critical diameter of an explosive can be easily characterized by well-defined tests. Publicly available information indicates that the critical diameter is generally in the range of more than 1 mm, depending on the test.

[0012] The critical diameter of pure explosives is often altered by the use of desensitizing binders (IM explosives), and the critical diameter of compositions such as PBX (polymer-bonded explosives) may be different from the pure explosive material.

[0013] Flow synthesis allows for the selection of the inner diameter of the pipes used in synthesis, and the inner diameter of the flow reactor pipes must be less than the critical diameter of the explosive material being synthesized to mitigate subsequent detonations within the flow reactor. The critical diameter can be measured, and selecting a pipe diameter that avoids detonation improves the safety of the system. The parallel use of multiple flow reactors, each with a diameter selected to be less than the critical diameter of the explosive being produced, can increase the final output flow in parallel without compromising safety.

[0014] Typical large-diameter tubular reactors used in industrial chemical synthesis have pipes with an internal diameter of at least 3-4 mm. This diameter allows for the use of a very large number of reagents, but also allows explosive material to accumulate at diameters greater than its critical diameter if it precipitates and / or becomes blocked within the pipe. This diameter can pose a significant hazard because the precipitated explosive material can sustain a detonation.

[0015] The industrial synthesis of explosive materials may be a flow synthesis, preferably with an internal diameter of the pipe less than 1 mm, more preferably less than 500 microns, preferably between 100 and 500 microns, preferably between 250 and 350 microns.

[0016] A further aspect of the present invention provides an apparatus for carrying out the method of the present invention, comprising a plurality of flow reactors in parallel, each flow reactor comprising a pipe, the inner diameter of the pipe being selected to be less than the critical diameter of the organic explosive.

[0017] A further aspect of the present invention provides a method for synthesizing an organic explosive, the method comprising: i) providing at least one solution comprising a nitrating agent and an explosive precursor; ii) mixing the solution and passing it through a flow reactor, the flow reactor comprises a pipe, the inner diameter of the pipe being selected to be less than a critical diameter of the energetic material being formed, thereby preventing detonation of the energetic material within said flow reactor; Includes. DETAILED DESCRIPTION OF THE INVENTION

[0018] Flow synthesis provides a facile means for producing approximately 100 g of RDX, HMX, etc. at the R&D scale in the laboratory, and production can be easily scaled up by adding additional flow reactors without the risks associated with forming over 100 kg of RDX explosive in a single reactor. Furthermore, it avoids the use of hundreds of liters of highly concentrated acid in large reactors in batch reactions. Flow synthesis allows for the continuous removal and safe storage of explosive end-product materials from the flow reactor, avoiding the accumulation of large amounts of explosive material. This allows for the synthesis of explosive materials to be transported to a safe area away from the flow reactor, thereby enabling the production of large quantities of explosives in the explosive production building and / or reducing safety distances.

[0019] Synthesis of RDX Hexamine was added to the nitric acid of input flow reagent A in weight percent amounts until a fully and nearly saturated solution was achieved. The higher the concentration of hexamine in input flow reagent A, the more efficient the reaction. It is highly preferred to dissolve the hexamine in the nitric acid as quickly as possible before feeding it to the reactor to reduce the possibility of initiating the nitration reaction.

[0020] Hexamine may be dissolved in nitric acid at a concentration of 70% to 92%, more preferably 88% to 92%, and other solvents may be added to aid in dissolving the hexamine.

[0021] Preferably, input flow reagent A comprises only hexamine and nitric acid at a concentration of less than 92%.

[0022] Input flow reagent B may contain nitric acid at a concentration of 99% to ensure that the total concentration of nitric acid in the flow reactor is at least 92%, and more preferably, input flow reagent B has only nitric acid at a concentration of 99%.

[0023] The use of a concentration of nitric acid below that which would cause nitration allows the starting hexamine to dissolve without initiating the nitration reaction. This prevents the product from precipitating before entering the flow reactor and prevents blockage of the flow reactor and associated mixing vessel. Furthermore, the use of a high concentration of hexamine as a dissolving agent allows the total nitric acid concentration in the flow reactor to be rapidly increased to the level required for nitration to occur. This avoids the problem of dilution of the nitric acid in the flow reactor, and therefore, input flow reagent B only requires a slightly higher concentration of nitric acid to ensure the desired total sulfuric acid concentration in the flow reactor exceeds 92%.

[0024] To facilitate achieving the desired concentration of nitric acid to initiate the nitration of hexamine, the input flow reagents A and B may be premixed in a mixing tank before being fed to the flow reactor after step ii.

[0025] It has been found that in step iii) the total concentration of nitric acid in said flow reactor may be between 90 and 99%, more preferably between 93 and 95%.

[0026] If input flow reagent A and input flow reagent B have only nitric acid as the acid and only nitrating agent, the total concentration of nitric acid must be sufficient for nitration to occur, for example, greater than 92%.

[0027] The flow rate of input flow reagent A can be selected from appropriate flow rates, along with the flow rate of input flow reagent B, to provide a total concentration of nitric acid capable of nitrating hexamine (e.g., greater than 92%). The actual flow rate of input flow reagent A can be in the range of microliters to milliliters to liters, depending on the volume of the flow cell.

[0028] The flow rate of input flow reagent B can be selected from appropriate flow rates, along with the flow rate of input flow reagent A, to provide a total concentration of nitric acid capable of nitrating hexamine (e.g., greater than 92%). The actual flow rate of input flow reagent A can be in the range of microliters to milliliters to liters, depending on the volume of the flow cell.

[0029] The flow ratio of input flow reagent A to input flow reagent B (A:B) can be B>A, preferably greater than 1:3 (A:B), more preferably 1:4 to 1:10, to ensure that the total concentration of nitric acid in the flow reactor exceeds 92%. The use of a high concentration of acid in input flow reagent B allows for a reduction in the volume / flow rate of input flow reagent B, i.e., a lower ratio, which may lead to a reduction in the amount of nitric acid used. This may occur, for example, with the use of other strong acids, such as oleum.

[0030] The temperature in the flow reactor must be controlled to prevent a highly exothermic reaction from occurring and is preferably below 30°C, preferably between 20°C and 30°C, more preferably between 22°C and 27°C, and most preferably 24°C. The temperature is monitored by a water circulator. The flow reactor may be cooled by suitable means, for example by a water circulator or an electrical cooler.

[0031] In the reaction in step v, the output flow mixture is quenched to stop the reaction and precipitate the RDX product. The output flow may be transferred to a larger volume of quenching medium or may be mixed in a mixing vessel.

[0032] Preferably, the output flow mixture containing RDX dissolved in nitric acid is mixed with a quenching medium via an SOR mixer at the end of the flow reactor. The quenching medium may have a pH of 7 or less and may be selected from an aqueous acid solution or water. The quenching agent may be cooled, preferably to less than 20°C, preferably 10°C or less, to induce crystallization.

[0033] The RDX precipitate is filtered, collected, and then washed in an aqueous solution, preferably the quenching solution may have a pH of 7 or less, and is preferably water.

[0034] The nitrating reagent can be selected from nitric acid and NaNO2 at a concentration of at least 70% or nitric acid alone at a concentration of 99%.

[0035] A further aspect of the present invention provides a method for synthesizing an organic explosive, the method comprising: i) providing a first solution A; ii) providing a second solution B, the admixture of Solution A and Solution B is selected so that they react together upon forming the admixture to provide an organic explosive; iii) mixing solutions A and B and passing them through a flow reactor to form a blend; the flow reactor comprises a pipe, the inner diameter of the pipe being selected to be less than the critical diameter of the organic explosive, thereby preventing detonation of the formed organic explosive within said flow reactor; Includes. [Example]

[0036] Experimental Reagents for RDX / HMX 99% HNO3 was purchased in 500mL quantities from Honeywell, catalog number 84392-500ML, lot number I345S. 70% HNO3 was purchased in 2.5L quantities from Fisher Scientific, code number: N / 2300 / PB17, lot number: 1716505. Hexamine was purchased in 250g quantities from Sigma-Aldrich, catalog number 797979-250G, lot number MKCJ7669. Oleum was purchased in 500 mL quantities from Fisher, catalog number S / 9440 / PB08, lot number 1689177.

[0037] experiment [ka]

[0038] A general reaction is shown above, where input flow reagent A contains hexamine dissolved in nitric acid, and input flow reagent B contains a nitrating agent, which may be a higher concentration of nitric acid (than input flow reagent A) and / or another nitrating agent, such as a metal nitrite, such as NaNO. Input flow reagent A and input flow reagent B react in a flow reactor to give the product RDX.

[0039] Synthesis of RDX using a flow reactor presents more challenging design challenges than simply pumping a solution through a well-known, quantified batch reaction. This is primarily due to the fact that the starting material, hexamine, is a solid and that RDX can precipitate during the reaction. As the acid concentration decreases and the water content increases, precipitation of RDX can occur during passage through the flow reactor, causing blockage of the flow reactor, which can lead to a catastrophic event.

[0040] Before starting the experiment, the reactor was prepared by flushing the system with methanol followed by water. The two input systems were then filled with 70% HNO3, which was passed through the reactor, to fully prime the system.

[0041] Experiment 1 Syringe A: saturated hexamine in 90% HNO3 (approximately 1 g in 5 mL) Syringe B: 99% HNO3 Flow reactor used: 3222 Labtrix

[0042] [ka]

[0043] The concentration of nitric acid in syringe A was 90%. The flow rate was set at 1:3 (A:B), but the product obtained was limited. The flow rate of syringe B, i.e., the amount of 99% HNO3 supplied, was increased so that the A:B flow rate ratio was 1:9. When the sample was collected in water, the solution became opaque, indicating that RDX had been obtained.

[0044] Experiment 2 Addition of fuming sulfuric acid Syringe A: 0.5 g hexamine dissolved in 2.5 mL 90% HNO3. The solution was cooled during the addition of hexamine. Syringe B: 0.95 mL of 99% HNO3 + 0.05 mL of oleum

[0045] A series of experiments were conducted to monitor the effect of oleum on RDX formation, which, when recovered in water, gave an opaque solution indicating that RDX was obtained. 1 1 H NMR spectra showed that RDX was present in solution prior to precipitation using water as the quenching agent.

[0046] Experiment 3: Increasing the amount of fuming sulfuric acid added Syringe A: 0.5 g hexamine dissolved in 2.5 mL 90% HNO3. The solution was cooled during the addition of hexamine. Syringe B: 0.9 mL of 99% HNO3 + 0.1 mL of oleum

[0047] Increasing the amount of oleum by 100% led to the formation of an RDX precipitate when collected on ice. 6 -When recovered in DMSO, 1 1 H NMR spectrum indicated the formation of RDX.

[0048] The use of another acid, such as oleum, helps to maintain a high acid concentration in the reactor and may facilitate dehydration of the reaction. The use of a nitrating species, such as NaNO2, allows for a lower total concentration of nitric acid.

[0049] Low acidity in the reactor has been found to cause RDX to precipitate from solution. Monitoring the flow reactor pathway for solidified product is essential. Additionally, increasing the acidity of the nitric acid is desirable to dissolve the hexamine, but if the concentration is too high, product may begin to form before mixing begins, potentially causing the RDX product to clog the flow reactor. Preferably, hexamine is dissolved in nitric acid prior to use and not stored as a stock solution for extended periods.

[0050] Example of HMX TAT can be easily synthesized from hexamine via DAPT as an intermediate. The main advantage of this route is the formation of an eight-membered ring, thus eliminating the possibility of RDX formation as a by-product. Nitration in a flow synthesizer allows direct conversion of TAT to HMX via controlled explosive material production rates.

[0051] [ka]

[0052] Experiment 1 Line A - A solution of 100 mg of TAT, 1000 mg of P2O5, and 2 mL of 99% HNO3 was premixed into a single solution and placed in a Labtrix reactor. The preferred reaction time of 120 seconds in the flow synthesis reactor was sufficient for nitration to occur. Flow synthesis was performed above room temperature, and a temperature of 75°C was found to be high enough to allow the reaction to proceed, but not so high as to cause an undesirable explosive event. HMX was isolated without any RDX contamination.

[0053] Experiment 2: Scaled-up Protrix reactor Line A: 2.0061 g of TAT and 20.0357 g of P2O5 were dissolved in 40 mL of 99% HNO3. Line B was used as an emergency flush and was primed with 70% HNO3.

[0054] Line A and Protrix were primed first with 70% HNO3, followed by 99% HNO3. The reaction mixture was prepared in stages. First, P2O5 was slowly dissolved in a stirred solution of 99% HNO3. This solution was kept in an ice bath. This resulted in an opaque yellow solution. Addition of TAT to this solution reduced the opacity of the solution, but the reaction mixture remained opaque.

[0055] Line A was then primed with the reaction mixture.

[0056] [Table 1]

[0057] The solution from Protrix was allowed to stand overnight, resulting in the formation of crystals, which were isolated, washed with water, then with acetone, and analyzed by nuclear magnetic resonance spectroscopy. 1 The H NMR spectrum shows that multiple species are present in the sample. Some of these peaks correspond to unreacted TAT and partially nitrated TAT. These impurities are also observed in the industrial batch synthesis of HMX from TAT and can be removed by boiling the material in acetone followed by recrystallization. 1 In the 1 H NMR spectrum, the peak at 6.02 ppm is characteristic of HMX. The inventions described in the claims of the original application are as follows: [1] A method for synthesizing an organic explosive in a flow reactor, the method comprising: i) providing a solution A containing a nitrating agent; ii) providing a solution B containing an explosive precursor reagent, the admixture of Solution A and Solution B is selected so that they react together upon forming the admixture to provide the organic explosive; iii) measuring the critical diameter of the organic explosive; iv) the flow reactor comprises a pipe, and the inner diameter of the pipe is selected so that the inner diameter is less than the critical diameter of the organic explosive, thereby preventing the formed organic explosive from detonating in the flow reactor; v) mixing said solutions A and B and passing them through said flow reactor to form said admixture and provide said organic explosive. A method comprising: [2] The method according to [1], wherein the nitrating agent comprises nitric acid or nitrite. [3] The method according to [1] or [2], wherein the organic explosive is nitramine. [4] The method according to [3], wherein the nitramine is RDX or HMX. [5] The method according to any one of [1] to [4], wherein the explosive precursor is a cycloamine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (TAT), 1,3,5-triacetyl-1,3,5-triazacyclohexane (TRAT), 1,5-dinitroendomethylene-1,3,5,7-tetraazacyclooctane (DPT), and hexamethylenetetramine. [6] The method according to any one of [1] to [5], wherein the solution A and / or B, or the solution C mixed in step v), further contains a catalyst, a strong acid, a dehydrating agent, and an acid anhydride. [7] The method according to any one of [1] to [6], wherein the flow reactor is temperature controlled. [8] The method according to any one of [1] to [7], wherein after the mixture has passed through the flow reactor, Solution D is added and the reacted mixture is post-treated to obtain a precipitate of the explosive material or a salt thereof. [9] The method according to [8], wherein solution D may contain cold water.

[10] The method according to any one of [1] to [9], wherein the inner diameter of the pipe is less than 500 microns.

[11] The method according to any one of [1] to

[10] , wherein the explosive material is collected away from the stored solutions A, B and / or C, for example to reduce the risk of an event.

[12] The method of

[10] , wherein the remotely collected is behind a blast wall or in an explosives depot.

[13] An apparatus for carrying out the method according to any one of [1] to

[12] , comprising a plurality of flow reactors arranged in parallel, each of the flow reactors comprising a pipe, the inner diameter of the pipe being selected to be less than the critical diameter of the organic explosive.

Claims

1. 1. A method for synthesizing an organic explosive in a flow reactor, the method comprising: i) providing a solution A containing a nitrating agent; ii) providing a solution B comprising an explosive precursor reagent, the admixture of Solution A and Solution B is selected so that they react together upon forming the admixture to provide the organic explosive; iii) measuring the critical diameter of said organic explosive; iv) the flow reactor comprises a pipe, and the inner diameter of the pipe is selected so as to be less than the critical diameter of the organic explosive, thereby preventing the formed organic explosive from detonating in the flow reactor; v) mixing said solutions A and B and passing them through said flow reactor to form said admixture and provide said organic explosive. Including, The method wherein said organic explosive is a nitramine.

2. The method of claim 1 , wherein the nitrating agent comprises nitric acid, nitrite.

3. 2. The method of claim 1, wherein the nitramine is RDX or HMX.

4. 10. The method of claim 1, wherein the explosive precursors are cycloamines, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (TAT), 1,3,5-triacetyl-1,3,5-triazacyclohexane (TRAT), 1,5-dinitroendomethylene-1,3,5,7-tetraazacyclooctane (DPT), and hexamethylenetetramine.

5. The method according to claim 1, wherein the solution A and / or B, or the solution C mixed in step v), further comprises a catalyst, a strong acid, a dehydrating agent, and an acid anhydride.

6. The method of claim 1 , wherein the flow reactor is temperature controlled.

7. 10. The method of claim 1, wherein after the admixture passes through the flow reactor, Solution D is added and the reacted admixture is post-treated to obtain a precipitate of the organic explosive or salt thereof, wherein Solution D quenches the acid.

8. 8. The method of claim 7, wherein solution D may comprise cold water.

9. The method of claim 1 , wherein the inner diameter of the pipe is less than 500 microns.

10. 10. The method of claim 1, wherein the organic explosive is collected away from the stored solutions A, B and / or C, e.g., to reduce the risk of an event.

11. The method of claim 10, wherein the remotely collected is behind a blast wall or in an explosives depot.

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