A process for recovering tnt from decommissioned mixed explosive and catalytically hydrogenating to produce tat

Abstract

This invention provides a method for recovering TNT from decommissioned mixed explosives and catalytically hydrogenating it to prepare TAT, comprising: Step 1, raw material pretreatment: extracting the decommissioned mixed explosives with ethyl acetate, separating and purifying the TNT; Step 2, catalytic hydrogenation: adding the TNT obtained in Step 1, a modified aqueous palladium-on-carbon catalyst, and a composite reaction solution to a reactor, and carrying out a hydrogenation reaction in the presence of an inert atmosphere and hydrogen; the modification method of the modified aqueous palladium-on-carbon catalyst includes hydrophilic modification of the support, loading of the active components palladium and platinum, reduction, and stabilization treatment; the composite reaction solution contains water, ethyl acetate, a nonionic surfactant, and a weakly basic buffer; Step 3, post-treatment. The method of this invention forms a complete process chain from "impurity TNT pretreatment → preparation of a dedicated catalyst → efficient aqueous hydrogenation → product purification," providing a practical and feasible technical solution for the resource utilization of decommissioned energetic materials.

Description

Technical Field

[0001] This invention belongs to the field of energetic materials technology, and relates to the safe treatment and resource utilization of energetic materials. Specifically, it relates to a method for recovering TNT from decommissioned mixed explosives and preparing TAT by catalytic hydrogenation. Background Technology

[0002] Traditional methods for disposing of decommissioned TNT (2,4,6-trinitrotoluene) primarily involve incineration or detonation, which leads to resource waste and environmental pollution. Chemically converting it into TAT is a high-value utilization approach. However, the composition of actually recovered decommissioned TNT is extremely complex, typically originating from mixed explosives such as TNT / RDX and TNT / nitronaphthalene. Besides the main components, it generally contains various substances including RDX (cyclotrimethylenetrinitramine), octogen (HMX), nitronaphthalene, nitrate plasticizers, inorganic salts, and degradation products. Nitrogen-containing intermediates generated by RDX and HMX under hydrogenation conditions strongly adsorb and poison the active sites of catalysts, leading to rapid deactivation of conventional catalysts and significantly reducing the reaction rate and TAT (2,4,6-triaminotoluene) selectivity.

[0003] In existing technologies, most studies on the catalytic hydrogenation of TNT to TAT are based on high-purity TNT in organic solvent systems. For example, Chinese patent application CN113368887A discloses a "Pd / C catalyst for the hydrogenation of TNT to TAT and its preparation method," which uses methanol as a solvent and achieves high yields under mild conditions. However, this method explicitly states that it is applicable only to "pure TNT feedstock." The article "Continuous-Flow Hydrogenation of TNT to TAT Using a Pd / C Catalyst," published in the journal *Industrial & Engineering Chemistry Research* (2015, Vol. 54, No. 35, 8650-8658), systematically studied the process of hydrogenating TNT in a continuous flow reactor using a commercial Pd / C catalyst and methanol solvent, achieving TAT yields of over 95%. However, these studies cannot solve the problem of catalyst poisoning caused by complex impurities in decommissioned TNT feedstocks, and the use of organic solvents introduces safety and environmental burdens.

[0004] To advance green processes, research both domestically and internationally has shifted towards developing high-performance aqueous catalysts. Performance can be significantly improved through support design. For example, *Angewandte Chemie International Edition* (2013, 52, 1175–1179) reported that palladium supported on mesoporous nitrogen-doped carbon (MCN) exhibited high activity in the formic acid decomposition reaction, with an activity 8.6 times that of conventional palladium on carbon (Pd / C). Some studies have modified palladium catalysts by constructing hydrophobic nitrogen-doped carbon layers, effectively suppressing the competitive adsorption of water molecules to active sites and improving catalyst stability in water vapor environments. However, this type of fundamental research mainly focuses on model reactions and single substrates; the catalysts' resistance to poisoning in the presence of various real and complex impurities such as RDX, HMX, and nitronaphthalene contained in decommissioned TNT has not yet been verified.

[0005] For the treatment of multi-component energetic materials, cutting-edge research is beginning to explore novel reaction systems. A 2022 study in the Journal of Hazardous Materials reported a hydrogen-permeable membrane-based Pd nanocatalyst reactor (MCfR) for treating simulated wastewater containing TNT, RDX, and PETN (5 mg / L each). Operating at ambient temperature, the system achieved removal rates exceeding 96% for all three pollutants, with catalytic activity 20 to 90 times higher than other reported systems. This provides a novel approach to treating mixed pollutants. However, the technology is designed for the efficient "destruction" of trace pollutants in water, rather than "resource recovery." Its deep hydrogenation and even ring-opening reaction pathways are completely different from the requirements for highly selective, stepwise TAT preparation, and it is entirely unsuitable for treating high-concentration, solid-state decommissioned explosive raw materials.

[0006] There are significant gaps in existing technologies. On the one hand, mature and efficient TNT-to-TAT processes (such as the CN113368887A patent and continuous flow process research) strictly rely on pure raw materials and organic solvents, which are disconnected from actual decommissioned materials. On the other hand, cutting-edge technologies capable of handling multi-component systems or applicable to aqueous phases (such as MCN-supported Pd and membrane catalytic reactors) are either unproven in complex impurity environments or their technical objectives contradict the goal of "resource-based TAT preparation." Therefore, developing a highly efficient and stable catalyst and supporting integrated process that can directly withstand the interference of multiple impurities in decommissioned mixed explosives, is applicable to aqueous systems, and can selectively prepare TAT is a key technological bottleneck for achieving the green and high-value resource utilization of decommissioned TNT. Summary of the Invention

[0007] Existing research either uses pure products in an organic phase, which is disconnected from the actual raw materials; or it uses an aqueous phase and begins to process multiple components, but the purpose is only to harmlessly dispose of them. At present, there is a lack of a dedicated catalyst and integrated process that can directly target complex decommissioned mixed explosive recyclable materials, use water as the main reaction medium, and achieve high selectivity and high yield to prepare high value-added product TAT.

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a method for recovering TNT from decommissioned mixed explosives and catalytically hydrogenating it to prepare TAT, thereby solving the technical problem that existing methods cannot simultaneously address the three challenges of "raw material complexity," "greenness of the medium," and "high-value products."

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0010] A method for recovering TNT from decommissioned mixed explosives and catalytically hydrogenating it to prepare TAT, the method comprising the following steps.

[0011] Step 1: Raw material pretreatment.

[0012] TNT was obtained by extracting decommissioned mixed explosives with ethyl acetate, separating and purifying them.

[0013] Step two, catalytic hydrogenation.

[0014] The TNT, modified aqueous palladium-carbon catalyst, and composite reaction solution obtained in step one were added to the reactor, and a hydrogenation reaction was carried out in the presence of an inert atmosphere and hydrogen.

[0015] The modification method of the modified aqueous palladium-carbon catalyst includes hydrophilic modification of the support, loading of the active components palladium and platinum, reduction, and stabilization treatment.

[0016] The composite reaction solution contains water, ethyl acetate, a nonionic surfactant, and a weak alkaline buffer.

[0017] Step 3, post-processing.

[0018] After the catalytic hydrogenation reaction is completed, the modified aqueous palladium-on-carbon catalyst is separated and purified from the reaction solution to obtain the TAT product.

[0019] The present invention also has the following technical features.

[0020] Step two involves the following steps in preparing the modified aqueous palladium-carbon catalyst.

[0021] Step 201, hydrophilic modification of the carrier: The activated carbon carrier is impregnated with a polyvinyl alcohol aqueous solution and ultrasonically treated, and then heat-treated at 150-200℃ under an inert atmosphere to obtain the modified carrier.

[0022] Step 202, loading of active components: Disperse the modified support obtained in step 201 in deionized water, add palladium source and platinum source, and adjust the pH to 4-5 with acid.

[0023] Step 203, Reduction: Add sodium borohydride aqueous solution for reduction.

[0024] Step 204, Stabilization treatment: Add a stabilizer solution containing polyvinylpyrrolidone and citrate and stir.

[0025] Step 205, Post-processing: After separation and washing, the modified aqueous palladium-on-carbon catalyst is obtained.

[0026] In step two, the volume percentage of ethyl acetate in the composite reaction solution is 15% to 30%, with the remainder being 0.5% to 2% (w / v) in volume; the volume concentration of the nonionic surfactant aqueous solution is 0.5% to 2% (w / v), and the volume concentration of the weak alkaline buffer aqueous solution is 0.1% to 0.5%.

[0027] In step two, preferably, the nonionic surfactant aqueous solution has a mass-volume concentration of 1.0% and the weak alkaline buffer aqueous solution has a mass-volume concentration of 0.3% in the composite reaction solution.

[0028] In step two, the nonionic surfactant is polyvinylpyrrolidone.

[0029] In step two, the weakly alkaline buffer is sodium bicarbonate or sodium carbonate.

[0030] In step two, the conditions for the hydrogenation reaction are: hydrogen pressure 0.8–1.2 MPa, reaction temperature 50–70 °C, and reaction time 1–3 hours.

[0031] In step two, the preferred conditions for the hydrogenation reaction are: hydrogen pressure 1.0 MPa, reaction temperature 60°C, and reaction time 2 hours.

[0032] Compared with the prior art, the present invention has the following technical effects.

[0033] (I) The method of the present invention can directly process decommissioned mixed explosives containing multiple impurities to recover TNT through a targeted ethyl acetate pretreatment step, thus overcoming the limitation of raw material purity on the hydrogenation process.

[0034] (II) The innovation of the modified aqueous palladium-carbon catalyst prepared by this invention lies in the following aspects.

[0035] Firstly, the hydrophilic-hydrophobic bifunctional carrier: PVA is used to hydrophilically modify activated carbon, and a hydrophilic layer is constructed on the surface of the activated carbon, which enables it to quickly disperse in water to form a stable suspension, thus solving the problems of easy sedimentation and poor mass transfer of traditional Pd / C in water.

[0036] Secondly, bimetallic synergy and surface modification: introducing trace amounts of Pt and Pd to form alloys or adjacent sites can modulate the electronic structure, thereby enhancing hydrogenation activity and anti-poisoning ability.

[0037] Thirdly, the subsequent PVP / sodium citrate treatment forms an "organic-inorganic" composite protective layer. While providing steric hindrance to prevent aggregation, its oxygen / nitrogen groups can compete with impurities for coordination, thereby protecting the active sites.

[0038] Fourthly, the modified aqueous palladium-carbon catalyst prepared by this invention has excellent aqueous dispersibility, high activity, and strong resistance to poisoning.

[0039] (III) The method of the present invention uses a special modified aqueous palladium-carbon catalyst to carry out catalytic hydrogenation under mild conditions to prepare TAT with high selectivity.

[0040] (IV) The method of this invention uses a water / ethyl acetate-based composite reaction solution, replacing a large amount of traditional organic solvents, making it safer and more environmentally friendly. The nonionic surfactant and weakly basic buffer in the composite reaction solution system have a synergistic effect, creating a microenvironment suitable for the selective hydrogenation of TNT, achieving a conversion rate of up to 99% and a TAT selectivity of over 95%.

[0041] (V) The method of the present invention forms a complete process chain from “impurity TNT pretreatment → preparation of special catalyst → high-efficiency aqueous phase hydrogenation → product purification”, providing a practical and feasible technical solution for the resource utilization of decommissioned energetic materials.

[0042] (VI) This invention realizes the efficient, green and high-value conversion of retired TNT containing impurities, and has significant economic and environmental benefits.

[0043] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0044] It should be noted that, unless otherwise specified, all raw materials and equipment used in this invention are those known in the art.

[0045] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0046] Example 1:

[0047] This embodiment provides a method for recovering TNT from decommissioned mixed explosives and catalytically hydrogenating it to prepare TAT. The method includes the following steps.

[0048] Step 1: Raw material pretreatment.

[0049] Take 100g of decommissioned mixed explosives, extract with 300mL of ethyl acetate at 60℃ for 2 hours with stirring, and then filter hot. Cool the filtrate to 0℃ to crystallize, and filter to obtain 65g of pale yellow TNT crystals.

[0050] In this embodiment, the decommissioned mixed explosive is a known decommissioned black explosive powder (containing 80 wt% TNT, 15 wt% RDX, and the remainder being impurities).

[0051] Step two, catalytic hydrogenation.

[0052] The 5g TNT, 40g modified aqueous palladium-carbon catalyst (10wt% solid content, 4g on a dry basis) and composite reaction solution obtained in step one were added to a 500mL reactor, and a hydrogenation reaction was carried out in the presence of inert nitrogen and hydrogen atmosphere.

[0053] In step two, the preparation method of the modified aqueous palladium-carbon catalyst includes the following steps.

[0054] Step 201, hydrophilic modification of the carrier: 10g of coconut shell activated carbon was impregnated with 100mL of 8wt% polyvinyl alcohol aqueous solution and ultrasonically treated for 1 hour. The modified carrier was then heat-treated at 180℃ for 2 hours under an inert nitrogen atmosphere to obtain the modified carrier.

[0055] In this embodiment, the polyvinyl alcohol aqueous solution used is the known PVA1788 polyvinyl alcohol aqueous solution, wherein the number average molecular weight of polyvinyl alcohol is 75000.

[0056] Step 202, loading of active components: Disperse the modified support obtained in step 201 in 200 mL of deionized water, add 0.5 g of PdCl2 palladium source and 0.05 g of H2PtCl6·6H2O platinum source, and adjust the pH to 4.5 with 6.3 wt% dilute acetic acid.

[0057] Step 203, Reduction: While stirring, slowly add 50 mL of an aqueous solution containing 0.8 g NaBH4. After the addition is complete, continue stirring for 30 minutes to carry out the reduction. FT-IR spectroscopy shows that PVA was successfully grafted onto the surface of activated carbon.

[0058] Step 204, Stabilization treatment: Add 50 mL of stabilizer solution containing 2 g polyvinylpyrrolidone and 0.5 g sodium citrate and stir for 1 hour. Transmission electron microscopy (TEM) shows that the metal nanoparticles treated with PVP / sodium citrate are uniformly dispersed and have no obvious agglomeration. X-ray photoelectron spectroscopy (XPS) shows that the introduction of Pt changes the electron binding energy of Pd.

[0059] In the preparation method of the modified aqueous palladium-carbon catalyst in this embodiment, the polyvinylpyrrolidone used is PVP K30 polyvinylpyrrolidone, which is known in the art and has a number-average molecular weight of 50,000.

[0060] Step 205, Post-processing: After filtration and washing with water, a modified aqueous palladium-carbon catalyst with a solid content of 10 wt% is prepared.

[0061] In step two, the composite reaction solution contains 50 mL of ethyl acetate, 200 mL of water, 2 g of nonionic surfactant polyvinylpyrrolidone, and 0.6 g of weak alkaline buffer sodium bicarbonate.

[0062] In the composite reaction solution of this embodiment, the polyvinylpyrrolidone used is PVP K30 polyvinylpyrrolidone, which is known in the art and has a number-average molecular weight of 50,000.

[0063] In step two, the hydrogenation reaction conditions are as follows: nitrogen and hydrogen are replaced three times each. Hydrogen is introduced to 1.0 MPa, the temperature is raised to 60°C, the stirring speed is 650 rpm, and the reaction is carried out for 2 hours.

[0064] Step 3, post-processing.

[0065] After the catalytic hydrogenation reaction was completed, the mixture was cooled and filtered under nitrogen protection to recover the modified aqueous palladium-on-carbon catalyst. Ethyl acetate was recovered from the filtrate by rotary evaporation. The remaining aqueous phase was adjusted to weakly acidic pH with hydrochloric acid, cooled to crystallize, filtered, and dried to obtain 3.8 g of white TAT solid. HPLC analysis showed a TNT conversion of 99.5% and a TAT selectivity of 96%.

[0066] Example 2: This embodiment provides a method for recovering TNT from decommissioned mixed explosives and preparing TAT by catalytic hydrogenation. The method is basically the same as that in Example 1, except that in step two of this embodiment, the composite reaction solution contains 37.5 mL of ethyl acetate, 212.5 mL of water, 1.0625 g of nonionic surfactant polyvinylpyrrolidone, and 0.6375 g of weak alkaline buffer sodium bicarbonate.

[0067] The product obtained in this embodiment was analyzed by HPLC, and the TNT conversion rate was 98.2% and the TAT selectivity was 92.1%.

[0068] Example 3: This embodiment provides a method for recovering TNT from decommissioned mixed explosives and preparing TAT by catalytic hydrogenation. The method is basically the same as that in Example 1, except that in step two of this embodiment, the composite reaction solution contains 75 mL of ethyl acetate, 175 mL of water, 1.75 g of nonionic surfactant polyvinylpyrrolidone, and 0.525 g of weak alkaline buffer sodium bicarbonate.

[0069] The product obtained in this embodiment was analyzed by HPLC, and the TNT conversion rate was 99.5% and the TAT selectivity was 94.5%.

[0070] Comparative Example 1: This comparative example provides a method for recovering TNT from decommissioned mixed explosives and catalytically hydrogenating it to prepare TAT. This method is essentially the same as in Example 1, except that in step two of this example, an equal amount of ordinary commercial Pd / C catalyst is used instead of the modified aqueous palladium-carbon catalyst in Example 1. Specifically, 5g of TNT obtained in step one, 4g of ordinary commercial Pd / C catalyst (with an active component percentage of 5wt%), and the composite reaction solution are added to a 500mL reactor, and a hydrogenation reaction is carried out in the presence of an inert atmosphere of nitrogen and hydrogen.

[0071] The product obtained in this comparative example was analyzed by HPLC. After 4 hours, the TNT content was less than 60%, the product was complex, the TAT selectivity was less than 70%, and black gelatinous substances were obviously adsorbed on the catalyst surface, indicating a severe decrease in activity.

[0072] As can be seen from the comparison between Example 1 and Comparative Example 1, the method of the present invention uses a special modified aqueous palladium-carbon catalyst to carry out catalytic hydrogenation under mild conditions, and prepares TAT ​​with high selectivity.

[0073] Comparative Example 2: This embodiment provides a method for recovering TNT from decommissioned mixed explosives and preparing TAT by catalytic hydrogenation. The method is basically the same as that in Example 1, except that in step two of this embodiment, the nonionic surfactant polyvinylpyrrolidone is not added to the composite reaction solution. That is, in step two, the composite reaction solution contains 50 mL of ethyl acetate, 200 mL of water, and 0.6 g of sodium bicarbonate, a weak alkaline buffer.

[0074] The product obtained in this comparative example was analyzed by HPLC, and the TNT conversion rate was 95%, and the TAT selectivity was 88.3%.

[0075] Comparative Example 3: This embodiment provides a method for recovering TNT from decommissioned mixed explosives and preparing TAT by catalytic hydrogenation. The method is basically the same as that in Example 1, except that in step two of this embodiment, the weak alkaline buffer sodium bicarbonate is not added to the composite reaction solution. That is, in step two, the composite reaction solution contains 50 mL of ethyl acetate, 200 mL of water, and 2 g of nonionic surfactant polyvinylpyrrolidone.

[0076] The product obtained in this comparative example was analyzed by HPLC, and the TNT conversion rate was 98.8%, and the TAT selectivity was 90.5%.

[0077] As can be seen from the comparison of Example 1, Comparative Example 2 and Comparative Example 3, the nonionic surfactant and weak alkaline buffer in the composite reaction liquid system of the present invention have a synergistic effect, creating a microenvironment suitable for the selective hydrogenation of TNT, achieving a conversion rate of up to 99% and a TAT selectivity of over 95%.

Claims

1. A method for recovering TNT from decommissioned mixed explosives and catalytically hydrogenating it to prepare TAT, characterized in that, The method includes the following steps: Step 1, Raw material pretreatment: TNT was obtained by extracting decommissioned mixed explosives with ethyl acetate, followed by separation and purification. Step 2, catalytic hydrogenation: The TNT, modified aqueous palladium-carbon catalyst and composite reaction solution obtained in step one are added to the reaction vessel, and a hydrogenation reaction is carried out in the presence of an inert atmosphere and hydrogen. The modification method for the modified aqueous palladium-carbon catalyst includes hydrophilic modification of the support, loading of the active components palladium and platinum, reduction, and stabilization treatment. The composite reaction solution contains water, ethyl acetate, a nonionic surfactant, and a weakly basic buffer. Step 3, Post-processing: After the catalytic hydrogenation reaction is completed, the modified aqueous palladium-on-carbon catalyst is separated and purified from the reaction solution to obtain the TAT product.

2. The method for recovering TNT from decommissioned mixed explosives and preparing TAT by catalytic hydrogenation as described in claim 1, characterized in that, Step two, the preparation method of the modified aqueous palladium-carbon catalyst includes the following steps: Step 201, hydrophilic modification of the carrier: The activated carbon carrier is impregnated with a polyvinyl alcohol aqueous solution and ultrasonically treated, and then heat-treated at 150-200℃ under an inert atmosphere to obtain the modified carrier. Step 202, loading of active components: Disperse the modified support obtained in step 201 in deionized water, add palladium source and platinum source, and adjust the pH to 4-5 with acid; Step 203, Reduction: Add sodium borohydride aqueous solution for reduction; Step 204, Stabilization treatment: Add a stabilizer solution containing polyvinylpyrrolidone and citrate and stir; Step 205, Post-processing: After separation and washing, the modified aqueous palladium-on-carbon catalyst is obtained.

3. The method for recovering TNT from decommissioned mixed explosives and preparing TAT by catalytic hydrogenation as described in claim 1, characterized in that, In step two, the volume percentage of ethyl acetate in the composite reaction solution is 15% to 30%, and the remaining volume percentage is water; the mass-volume concentration of the nonionic surfactant aqueous solution is 0.5% to 2%, and the mass-volume concentration of the weak alkaline buffer aqueous solution is 0.1% to 0.5%.

4. The method for recovering TNT from decommissioned mixed explosives and preparing TAT by catalytic hydrogenation as described in claim 3, characterized in that, In step two, the nonionic surfactant aqueous solution in the composite reaction solution has a mass-volume concentration of 1.0% and the weak alkaline buffer aqueous solution has a mass-volume concentration of 0.3%.

5. The method for recovering TNT from decommissioned mixed explosives and preparing TAT by catalytic hydrogenation as described in claim 1, characterized in that, In step two, the nonionic surfactant is polyvinylpyrrolidone.

6. The method for recovering TNT from decommissioned mixed explosives and catalytically hydrogenating it to prepare TAT as described in claim 1, characterized in that, In step two, the weakly alkaline buffer is sodium bicarbonate or sodium carbonate.

7. The method for recovering TNT from decommissioned mixed explosives and catalytically hydrogenating it to prepare TAT as described in claim 1, characterized in that, In step two, the conditions for the hydrogenation reaction are: hydrogen pressure 0.8–1.2 MPa, reaction temperature 50–70 °C, and reaction time 1–3 hours.

8. The method for recovering TNT from decommissioned mixed explosives and catalytically hydrogenating it to prepare TAT as described in claim 7, characterized in that, In step two, the conditions for the hydrogenation reaction are: hydrogen pressure 1.0 MPa, reaction temperature 60°C, and reaction time 2 hours.