Process for refining picric acid for use in pyrotechnic compositions

Abstract

This invention discloses a method for refining picric acid for pyrotechnic agents, belonging to the field of pyrotechnic agent compound preparation technology. The method involves: adding an inorganic weak acid salt to a 6%–7% picric acid raw material aqueous solution under stirring and heating at (80±5)℃, reacting for approximately 0.5–1 hour to form a wine-red solution; collecting the filtrate; adding a strong acid solution to the filtrate under stirring and heating at (40±5)℃, reacting for 0.5–1 hour to form a yellow suspension; filtering the yellow suspension and washing it 6–8 times; filtering and drying to obtain refined yellow picric acid. This invention uses readily available inorganic weak acid salts and strong acid reagents, is simple to operate, has a short reaction time, low energy consumption, low pollution, and requires minimal equipment, thus improving work efficiency and reducing production costs. The high-purity picric acid prepared by this invention can be used directly as an explosive or for preparing derivatives containing metal ions, possessing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of pyrotechnic compound preparation technology, and more particularly to a method for purifying picric acid for pyrotechnic agents. Background Technology

[0002] Picric acid (2,4,6-trinitrophenol) can be used as an explosive. The pure form is a slightly yellow crystal at room temperature (also known as yellow explosive). It is a trinitro-substituted derivative of phenol and exhibits strong acidity due to the electron-withdrawing effect of the nitro group. Its metal ion-containing derivatives (Pb, Ag, K, etc.) are also heat-resistant explosives and high-performance delay and ignition charges.

[0003] However, most industrial picric acid is in the form of flaky crystals, and its purity is generally 80% to 88%. Because it contains 10% to 20% water, about 1% sulfate ions, as well as dinitrophenol, nitric acid, and other insoluble impurities, it seriously affects the performance of itself and picric acid derivatives. Therefore, the refining of picric acid is crucial to the development of pyrotechnic agents, because the crystal form of refined picric acid can be improved, and it can provide high-purity raw materials for the synthesis of picric acid derivatives.

[0004] Traditional methods for refining picric acid generally employ the "organic solvent recrystallization method." This method uses organic solvents, generates a large amount of waste liquid that is difficult to treat, and causes significant environmental pollution. Furthermore, the yield and purity cannot achieve the desired results. Therefore, developing a simple refining method has become an important part of the research and development and production of picric acid and its derivative compounds. Summary of the Invention

[0005] The purpose of this invention is to provide a method for refining picric acid for pyrotechnic agents, so as to solve the above-mentioned problems.

[0006] To achieve the above objectives, the technical solution adopted in this invention is the "recrystallization" method: crude picric acid is reacted with sodium salt of inorganic weak acid to generate a picric acid salt solution, which is then replaced with a strong acid to recrystallize and obtain picric acid and soluble salt. The soluble salt is then washed away to obtain refined picric acid.

[0007] For the preferred technical solution, please refer to the specific steps. Figure 1 ,for:

[0008] (1) Prepare an aqueous solution of 6% to 7% by mass of hydrated industrial picric acid with deionized water, heat it to 80±5℃, slowly add an inorganic weak acid salt of 35% to 45% by weight of hydrated picric acid, stop stirring after reacting for 0.5h to 1h, and then filter it while hot and keep the filtrate for later use.

[0009] (2) After the picric acid filtrate is cooled to 40±5℃ and kept at this temperature, a strong acid solution of 55% to 65% of the net weight of picric acid is slowly added. The reaction is carried out for 0.5h to 1h, and then filtered to obtain picric acid filter cake.

[0010] (3) Washing: Dilute the filter with deionized water at 400% to 600% of the mass of the picric acid filter cake and let it settle for 0.2 to 0.3 hours; discard the supernatant, add the discarded deionized water and stir, and soak for 0.2 to 0.3 hours; discard the supernatant, add more deionized water and stir, and soak for 0.2 to 0.3 hours; repeat this soaking, washing and water washing cycle until the water washing is qualified, then filter, and dry the filter material in a drying tray to obtain yellow refined picric acid.

[0011] This invention uses a "recrystallization" method to purify picric acid, washes the reagent by soaking, and detects the impurity content with a colorimetric reagent, effectively improving the purity and yield of picric acid.

[0012] As a further preferred technical solution, taking NaHCO3 as an example of inorganic weak acid salt and HNO3 as an example of strong acid, in step (3) of the technical solution, the method to determine whether the water washing is qualified is: take the upper clear liquid and test the nitrate with diphenylamine sulfuric acid reagent. If no blue substance is generated, the water washing is deemed qualified.

[0013] As a preferred technical solution: the inorganic weak acid salt in step (1) is sodium bicarbonate.

[0014] As a preferred technical solution: the strong acid in step (2) is nitric acid.

[0015] As a preferred technical solution, the mass concentration of the strong acid solution in step (2) is 60% to 70%.

[0016] Compared with the prior art, the advantages of the present invention are as follows: the picric acid refining method of the present invention can use readily available sodium bicarbonate and nitric acid reagents, is simple to operate, has a short reaction time, low energy consumption, and requires few equipment facilities, which improves work efficiency and reduces production costs. The high-purity picric acid prepared by the present invention can be used directly as explosives or used to prepare derivatives containing metal ions, and has broad application prospects.

[0017] Comparison of different refining methods for refining 1 kg of picric acid in a single batch

[0018] project The "recrystallization method" described in this invention Traditional "organic solvent recrystallization method" Refining time Approximately 3 hours Approximately 5 hours Energy consumption 3kW electricity + 20L water 5kW electricity + 15L organic solvent + 8L water cost Approximately 65 yuan Approximately 1500 yuan waste wastewater Organic solvents, wastewater Yield 96％～98％ 85％～90％ purity ≥99％ ≥98％ Attached Figure Description

[0019] Figure 1 The process flow diagram of the invention. Detailed Implementation

[0020] The invention will now be further described with reference to the accompanying drawings.

[0021] Example 1

[0022] A method for refining picric acid for pyrotechnic agents includes the following steps: 10g of picric acid (20% water content, 8g net weight of picric acid) is added to a stainless steel container, along with 140mL of deionized water. The mixture is stirred to dissolve the picric acid and obtain a yellow solution. When the temperature of the picric acid aqueous solution reaches 85℃, 4g of sodium carbonate is slowly added. The mixture is kept warm for 30 minutes. When less gas is produced, the reaction is nearing completion. The mixture is then filtered while hot, and the filtrate is collected for later use.

[0023] After the filtrate cooled to 40°C, 7 mL of 68 wt% hydrochloric acid solution was added under stirring. After the hydrochloric acid solution was added, the reaction was stirred for 30 min, then stirring was stopped. The solution was allowed to stand for 15 min, and the upper 1 / 4 of the solution was discarded. The solution was then filtered, and the filter cake was washed 4 times with deionized water. Five times the weight of the picric acid filter cake was added to a beaker to dissolve it, and the mixture was allowed to precipitate for 15 min. The upper clear liquid was then discarded, and the discarded deionized water was added and stirred. The mixture was soaked for 15 min, and the upper clear liquid was discarded again. The process continued until no white substance was generated when the upper clear liquid was tested with silver nitrate reagent. The mixture was then filtered, and the filter material was spread evenly on a drying tray and dried at 60°C to obtain yellow refined picric acid, weighing 7.74 g, with a yield of 96.8%.

[0024] The picric acid obtained by the above purification was tested and analyzed according to GB / T 25784-2010 and met the requirements of superior grade, with an HPLC purity of 99.4%. The ignition reliability test was carried out, and the surface properties were excellent, proving that the method of the present invention can also achieve good results even after large-scale production.

[0025] Example 1 Test Results

[0026] Testing items Test results Appearance Yellow granular crystals Crystallization point of dry product / ℃ ≥120 Moisture mass fraction / % 0.05 mass fraction of sulfate ions / % 0.13 Nitric acid content No color development Mass fraction of water-insoluble matter / % 0.09 Ash content (mass fraction) / % 0.12 ignition reliability 50 / 50 (50 test pieces all fired)

[0027] Example 2

[0028] A method for refining picric acid for pyrotechnic agents includes the following steps: 1000g of industrial picric acid (20% water content, 800g net weight of picric acid) is added to a beaker, along with 14L of deionized water. The mixture is stirred until the picric acid dissolves to obtain a yellow solution. The beaker is then heated until the temperature of the picric acid solution reaches 80℃. 400g of sodium bicarbonate is slowly added, and the mixture is kept at this temperature for 30 minutes. When less gas is produced, the reaction is nearing completion. The mixture is then filtered while hot, and the filtrate is collected for later use.

[0029] After the filtrate cooled to 40°C, 700 mL of 68 wt% nitric acid solution was added under stirring. After the nitric acid solution was added, the reaction was stirred for another 30 minutes. Then, stirring was stopped, and the solution was allowed to stand for 15 minutes. The upper 1 / 4 of the solution was then discarded. The solution was filtered, and the filter cake was washed four times with deionized water. Five times the weight of the picric acid filter cake was added to a beaker to dissolve the picric acid and allow it to precipitate for 15 minutes. The upper clear liquid was then discarded, and the discarded deionized water was added back in and stirred. The mixture was soaked for 15 minutes, and the upper clear liquid was discarded. The process continued until the upper clear liquid was tested with diphenylamine sulfuric acid reagent and no blue substance was formed. The mixture was then filtered, and the filter material was spread evenly on a drying tray and dried at 60°C to obtain yellow refined picric acid, weighing 778 g, with a yield of 97.3%.

[0030] The picric acid obtained by the above purification was tested and analyzed according to GB / T 25784-2010, and met the requirements of superior grade, with an HPLC purity of 99.5%; the ignition reliability test results showed that the performance was excellent.

[0031] Example 2 Test Results

[0032] Testing items Test results Appearance Yellow granular crystals Crystallization point of dry product / ℃ ≥120 Moisture mass fraction / % 0.04 mass fraction of sulfate ions / % 0.11 Nitric acid content No color development Mass fraction of water-insoluble matter / % 0.06 Ash content (mass fraction) / % 0.10 ignition reliability 50 / 50 (50 test pieces all fired)

[0033] Example 3

[0034] This comparative example is based on Example 2, except that the amount of sodium bicarbonate added was changed to 360g and the concentration of nitric acid was changed to 65wt% and the amount added was changed to 810mL, while the other conditions remained the same. As a result, the weight of the purified picric acid obtained was 768.8g, and the yield was 96.1%. After packaging, the sample was analyzed, and the HPLC quality purity was 99.3%. The test results are shown in the table below, and all of them meet the requirements. This shows that different values ​​of raw material dosage within a given range can achieve the present invention.

[0035] Example 3 Test Results

[0036] Testing items Test results Appearance Yellow granular crystals Crystallization point of dry product / ℃ ≥120 Moisture mass fraction / % 0.05 mass fraction of sulfate ions / % 0.17 Nitric acid content No color development Mass fraction of water-insoluble matter / % 0.08 Ash content (mass fraction) / % 0.16 ignition reliability 50 / 50 (50 test pieces all fired)

[0037] Example 4

[0038] This comparative example is based on Example 2, except that the amount of sodium bicarbonate added is 440g and the concentration of nitric acid is 70% and the amount added is 640mL, while the other conditions are the same. As a result, the picric acid obtained weighed 781.6g, with a yield of 97.7%. After packaging, the sample was analyzed, and the HPLC purity was 99.6%. The test results are shown in the table below, and all meet the requirements. This shows that different values ​​of raw material dosage within a given range can achieve the present invention.

[0039] Example 4 Test Results

[0040] Testing items Test results Appearance Yellow granular crystals Crystallization point of dry product / ℃ ≥120 Moisture mass fraction / % 0.03 mass fraction of sulfate ions / % 0.08 Nitric acid content No color development Mass fraction of water-insoluble matter / % 0.06 Ash content (mass fraction) / % 0.09 ignition reliability 50 / 50 (50 test pieces all fired)

[0041] Comparative Example 1

[0042] A method for refining picric acid for pyrotechnic agents includes the following steps: 1000g of industrial picric acid (20% water content, 800g net weight of picric acid) is added to a beaker, along with 14L of deionized water. The mixture is stirred until the picric acid dissolves to obtain a yellow solution. The beaker is then heated until the temperature of the picric acid solution reaches 80℃. 300g of sodium bicarbonate is slowly added, and the mixture is kept at this temperature for 30 minutes. When less gas is produced, the reaction is nearing completion. The mixture is then filtered while hot, and the filtrate is collected for later use.

[0043] After the filtrate cooled to 40°C, 700 mL of 68 wt% nitric acid solution was added under stirring. After the nitric acid solution was added, the reaction was stirred for another 30 minutes. Then, stirring was stopped, and the solution was allowed to stand for 15 minutes. The upper 1 / 4 of the solution was then discarded, and the solution was filtered. After filtration, the filter cake was washed four times with deionized water. Five times the weight of the picric acid filter cake was added to a beaker to dissolve the picric acid and allow it to precipitate for 15 minutes. The upper clear liquid was then discarded, and the discarded deionized water was added back in and stirred. The mixture was soaked for 15 minutes, and the upper clear liquid was discarded again. The process continued until the upper clear liquid was tested with diphenylamine sulfuric acid reagent and no blue substance was formed. The mixture was then filtered, and the filter material was spread evenly on a drying tray and dried at 60°C to obtain yellow refined picric acid, weighing 702 g, with a yield of only 87.8%.

[0044] The picric acid obtained by the above purification was tested and analyzed according to GB / T 25784-2010, and met the requirements of superior grade, with an HPLC purity of 90.5%; the ignition reliability test was carried out, and the results showed that the performance was excellent.

[0045] Example 2 Test Results

[0046]

[0047]

[0048] Comparative Example 2

[0049] A method for refining picric acid for pyrotechnic agents includes the following steps: 1000g of industrial picric acid (20% water content, 800g net weight of picric acid) is added to a beaker, along with 14L of deionized water. The mixture is stirred until the picric acid dissolves to obtain a yellow solution. The beaker is then heated until the temperature of the picric acid solution reaches 80℃. 500g of sodium bicarbonate is slowly added, and the mixture is kept at this temperature for 30 minutes. When less gas is produced, the reaction is nearing completion. The mixture is then filtered while hot, and the filtrate is collected for later use.

[0050] After the filtrate cooled to 40°C, 700 mL of 68 wt% nitric acid solution was added under stirring. After the nitric acid solution was added, the reaction was stirred for another 30 minutes. Then, stirring was stopped, and the solution was allowed to stand for 15 minutes. The upper 1 / 4 of the solution was then discarded, and the solution was filtered. After filtration, the filter cake was washed four times with deionized water. Five times the weight of the picric acid filter cake was added to a beaker to dissolve the picric acid and allow it to precipitate for 15 minutes. The upper clear liquid was then discarded, and the discarded deionized water was added and stirred. The mixture was soaked for 15 minutes, and the upper clear liquid was discarded. The process continued until the upper clear liquid was tested with diphenylamine sulfuric acid reagent and no blue substance was generated. The mixture was then filtered, and the filter material was spread evenly on a drying tray and dried at 60°C to obtain yellow refined picric acid, weighing 734 g, with a yield of only 91.8%.

[0051] The picric acid obtained by the above purification was tested and analyzed according to GB / T 25784-2010, and met the requirements of superior grade, with an HPLC purity of 95.3%; the ignition reliability test results showed that the performance was excellent.

[0052] Example 2 Test Results

[0053]

[0054]

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for purifying picric acid for use in a pyrotechnic composition, characterized by, The crude picric acid is reacted with an inorganic weak acid salt to generate a picric acid salt, which is then replaced with a strong acid to obtain picric acid and a strong acid salt. The specific steps are as follows: (1) Prepare an aqueous solution of crude picric acid with deionized water with a mass fraction of 6% to 7%, heat it to 80±5℃, slowly add an inorganic weak acid salt of 35% to 45% of the mass of crude picric acid, stop stirring after reacting for 0.5h to 1h, filter while hot and take the filtrate for later use. The inorganic weak acid salt is sodium bicarbonate. (2) After the picric acid filtrate is cooled to 40±5℃ and kept at this temperature, a strong acid solution of 55% to 65% of the net weight of picric acid is slowly added. The reaction is carried out for 0.5h to 1h, and then filtered to obtain a picric acid filter cake. The strong acid is nitric acid, and the mass concentration of the strong acid solution is 60% to 70%. (3) Washing: Dilute the filtrate with deionized water at a mass of 400% to 600% of the picric acid filter cake mass and let it settle for 2 to 4 hours; pour off the clear liquid at the top, add the poured-off deionized water and stir, and soak for 2 to 4 hours; pour off the clear liquid at the top, add more deionized water and stir, and soak for 16 to 24 hours; repeat this soaking, washing and water washing cycle until the water washing is qualified and then filter. The filter material is dried in a drying tray to obtain yellow refined picric acid.

2. The method for refining picric acid for use in a pyrotechnic charge according to claim 1, characterized in that, In step (3), the method to determine whether the water washing is qualified is: take the supernatant and use a colorimetric reagent to test for soluble salts. If no reaction substance is generated, the water washing is qualified.

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