Flow synthesis of RDX

Abstract

The present application relates to a method for producing RDX by flow synthesis, the method comprising the steps of preparing an input flow reagent A comprising hexamine dissolved in nitric acid at a concentration of less than 92%, preparing an input flow reagent B comprising nitric acid at a concentration of 99%, feeding the input flow reagents A and B to a flow reactor at flow rates such that the total concentration of nitric acid in the flow reactor is greater than 93%, cooling the reactor to less than 30°C, and quenching the output flow mixture.

Description

[Technical field]

[0001] This invention relates to a process for the production of explosives by direct nitration of hexamine in flow synthesis, in particular to a process for the production of RDX.

[0002] Before describing the present 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 process for the preparation of RDX by flow synthesis, the process comprising: i. preparing an input flow reagent A comprising hexamine dissolved in nitric acid at a concentration of less than 92%; ii. preparing an input flow reagent B comprising nitric acid at a concentration greater than 95%; iii. feeding input flow reagents A and B to the flow reactor at flow rates such that the total concentration of nitric acid in the flow reactor is greater than 93%; iv. cooling the reactor to below 30° C.; v. quenching the output flow mixture to precipitate RDX; Includes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0004] Flow synthesis provides a facile means of producing about 100 g of RDX at R&D scale in the laboratory, and production can be easily scaled up by adding additional flow reactors without the dangers associated with forming over 100 kg of RDX explosive in a single reaction vessel. It also avoids the use of hundreds of liters of highly concentrated acid in large reaction vessels in batch reactions. Flow synthesis allows for continuous removal and safe storage of the explosive end product RDX material from the flow reactor, avoiding the accumulation of large amounts of explosive material. This allows for the synthesis of explosive materials to produce large quantities of explosives in the explosive production building and / or reduce safety distances, since the explosive material can be transported to a safe area away from the flow reactor.

[0005] Hexamine may be added to the nitric acid of input flow reagent A in weight percent up to a nearly or completely saturated solution. The higher the concentration of hexamine in input flow reagent A, the more efficient the reaction will be. 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 chance of initiating a nitration reaction.

[0006] 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.

[0007] Preferably, input flow reagent A comprises only hexamine and nitric acid at a concentration of less than 92%.

[0008] 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%.

[0009] The use of a concentration of nitric acid below that which causes nitration allows the starting material hexamine to be dissolved without the nitration reaction starting. 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 concentration of nitric acid required for nitration to occur to be rapidly increased in the flow reactor. This avoids the problem of dilution of the nitric acid in the flow reactor, and therefore the input flow reagent B only needs to use a slightly higher concentration of nitric acid to ensure that the desired total concentration of sulfuric acid in the flow reactor is greater than 92%.

[0010] 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.

[0011] 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%.

[0012] 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%.

[0013] The flow rate of input flow reagent A can be selected from appropriate flow rates together 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.

[0014] The flow rate of input flow reagent B can be selected from appropriate flow rates together 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.

[0015] The flow ratio of input flow reagent A to input flow reagent B (A:B) may 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 is greater than 92%. The use of a high concentration of acid in input flow reagent B allows the volume / flow rate of input flow reagent B to be reduced, i.e., the ratio can be lowered, which may lead to a reduction in the amount of nitric acid used. This may occur, for example, by using other strong acids such as oleum.

[0016] The temperature in the flow reactor must be controlled to prevent highly exothermic reactions from occurring and is preferably below 30° C., preferably between 20° C. and 30° C., more preferably between 22° C. and 27° C., most preferably 24° C. The temperature is monitored by a water circulator. The flow reactor may be cooled by suitable means, for example a water circulator or an electrical cooler.

[0017] 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 bulk quench medium or may be mixed in a mixing tank.

[0018] Preferably, the output flow mixture containing RDX dissolved in nitric acid is mixed with a quenching medium via a SOR mixer at the end of the flow reactor. The quenching medium may be pH 7 or less and may be selected from an acidic aqueous solution or water. The quenching agent may be cooled, preferably to less than 20°C, preferably 10°C or less, to induce crystallization.

[0019] 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.

[0020] A further aspect of the invention provides the use of flow synthesis to provide explosives from hexamine.

[0021] A further aspect of the invention provides an apparatus for carrying out the method according to any one of claims 1 to 11, the apparatus being adapted to accommodate explosions.

[0022] A further aspect of the present invention provides a process for the preparation of RDX by flow synthesis, the process comprising: i. preparing an input flow reagent A comprising hexamine dissolved in nitric acid at a concentration of less than 92%; ii. preparing an input flow reagent B comprising a nitrating reagent; iii. feeding input flow reagents A and B to the flow reactor at flow rates such as to nitrate RDX in the flow reactor; iv. cooling the reactor to below 30° C.; v. quenching the output flow mixture and contacting it with an aqueous solution to allow precipitation of RDX; Includes.

[0023] The nitration reagent can be selected from those with a concentration of at least 70% nitric acid and NaNO2, or those with a concentration of 99% nitric acid alone. EXAMPLES

[0024] Experimental Reagents 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 from Sigma-Aldrich in 250g quantities, catalog number 797979-250G, lot number MKCJ7669. Oleum was purchased in 500 mL quantities from Fisher, catalog number S / 9440 / PB08, lot number 1689177. Flow reactor used: 3222 Labtrix.

[0025] experiment [ka]

[0026] 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 NaNO2. Input flow reagent A and input flow reagent B react in a flow reactor to give the product RDX.

[0027] The synthesis of RDX using a flow reactor poses more difficult design challenges than simply pumping a solution through a well-known and quantified batch reaction, primarily because the starting material, hexamine, is a solid and 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, which can lead to blockage of the flow reactor, which can lead to a catastrophic event.

[0028] 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 that was passed through the reactor to fully prime the system.

[0029] Experiment 1 Syringe A: 0.100 g hexamine in 5 mL 99% HNO3 Syringe B: 0.1079 g NaNO2 in 10 mL 70% HNO3

[0030] [ka]

[0031] Initial experiments focused on directly converting the batch synthesis to a flow reactor and involved the preparation of a premixed solution of hexamine and 99% HNO3 (solution A) and NaNO2 in 70% HNO3 (solution B).

[0032] The first hexamine stock solution, 1 The results were analyzed by H NMR. It was clear that the majority of the reaction had already gone to completion in solution before the initial hexamine HNO3 solution passed through the reactor. Therefore, the experimental methodology was modified so that the reaction occurred in the flow reactor rather than in the initial hexamine stock solution.

[0033] Experiment 2: Experiment with saturated hexamine Syringe A: Saturated hexamine in 70% HNO3 (approximately 1 g in 5 mL) Syringe B: 99% HNO3

[0034] It is preferable to use nitric acid as the sole nitrating agent, rather than using another reagent such as NaNO2. Experiment 1 was repeated without NaNO2, but using nitric acid at 99% concentration in syringe B to act as the sole nitrating agent.

[0035] When the solution from the reactor was withdrawn in water, no precipitate was obtained. It can be concluded that the acid concentration throughout the reaction was too low to produce sufficient amounts of RDX, and therefore, the acid concentration throughout the reaction was the focus of attention.

[0036] Experiment 3: High acid concentration experiment Syringe A: Saturated hexamine in 90% HNO3 (approximately 1 g in 5 mL) Syringe B: 99% HNO3

[0037] The concentration of nitric acid in syringe A was increased. The flow rate was set at 1:3 (A:B), but limited product was obtained. The flow rate of syringe B, i.e., the supply of 99% HNO3, was increased so that the flow ratio of A:B was 1:9. When a sample was collected in water, the solution became opaque, indicating that RDX had been obtained.

[0038] Experiment 4 Addition of fuming sulfuric acid Syringe A: 0.5 g hexamine dissolved in 2.5 mL 90% HNO3. The solution was cooled during addition of hexamine. Syringe B: 0.95mL 99% HNO3 + 0.05mL oleum

[0039] A series of experiments were carried out aimed at monitoring the effect of oleum on the formation of RDX, which showed that an opaque solution was obtained when collected in water, 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.

[0040] Experiment 5: 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 addition of hexamine. Syringe B: 0.9mL 99% HNO3 + 0.1mL oleum

[0041] Increasing the amount of oleum by 100% led to the formation of an RDX precipitate when collected on ice. 6 -When collected in DMSO, 1 1 H NMR spectrum indicated the formation of RDX.

[0042] The use of another acid, such as oleum, helps to keep the concentration of acid in the reactor high and may facilitate the dehydration of the reaction. The use of a nitrating species, such as NaNO2, allows the total concentration of nitric acid to be lower.

[0043] It has been found that low acidity in the reactor will cause the RDX to precipitate out of solution. It is essential to monitor the flow reactor pathway for solidified product. Additionally, it is desirable to increase the acidity of the nitric acid, which will dissolve the hexamine, but if the concentration is too high, the product will begin to form before mixing begins, and again the RDX product may clog the flow reactor. Preferably, the hexamine is dissolved in nitric acid before use and is not stored for long periods as a stock solution.

Claims

1. 1. A process for producing RDX by flow synthesis, the process comprising: i. preparing an input flow reagent A comprising hexamine dissolved in nitric acid at a concentration of less than 92%; ii. preparing an input flow reagent B containing nitric acid at a concentration of more than 95%; iii. feeding the input flow reagents A and B to the flow reactor at a flow rate such that the total concentration of nitric acid in the flow reactor is greater than 93%; iv. cooling the reactor to below 30° C.; v. Quenching the output flow mixture to precipitate RDX. A method comprising:

2. 2. The method of claim 1, wherein in step i, the hexamine is dissolved in nitric acid having a concentration of 88% to 90%.

3. 3. The method of claim 1 or 2, wherein in step i, the hexamine is dissolved in nitric acid to form a saturated solution.

4. 4. The method according to claim 1, wherein in step ii, the input flow reagent B is nitric acid at a concentration of 99%.

5. The method according to any one of claims 1 to 4, wherein in step iii, the total concentration of nitric acid in the flow reactor is 90 to 99%.

6. The method according to any one of claims 1 to 5, wherein the flow ratio of input flow reagent A:input flow reagent B (A:B) is higher than 1:3 (A:B).

7. The process according to any one of claims 1 to 6, wherein the temperature in the reactor is between 20°C and 27°C.

8. In step ii, the nitric acid in the input flow reagent B is replaced with oleum or NaNO ２ The method of any one of claims 1 to 7, further comprising:

9. 9. The method of any one of claims 1 to 8, wherein in step v, the quenching occurs by mixing the output flow mixture and a quenching agent.

10. 10. The method of claim 9, wherein the quenching agent is an aqueous solution, such as for precipitating RDX.

11. 11. The method of claim 9 or 10, wherein the quenching agent is cooled to less than 10°C.

12. 1. A process for producing RDX by flow synthesis, the process comprising: vi. preparing an input flow reagent A comprising hexamine dissolved in nitric acid at a concentration of less than 92%; vii. preparing an input flow reagent B comprising a nitrating reagent; viii. feeding said input flow reagents A and B to said flow reactor at flow rates such as to nitrate RDX in said flow reactor; ix. cooling the reactor to below 30° C.; x. Quenching the output flow mixture and contacting it with an aqueous solution to allow precipitation of RDX. A method comprising:

13. The nitrating reagent is a mixture of nitric acid and NaNO ２ 13. The method according to claim 12, wherein the nitric acid is selected from the group consisting of 99% nitric acid alone.

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