A direct granulation anti-agglomeration method for energetic aqueous waste HTPB propellant

Abstract

This invention provides a direct granulation method for preventing agglomeration of energetic, water-containing waste HTPB propellant, comprising: Step 1, microsphere suspension preparation: dissolving polylactic acid, polylactic acid-glycolic acid copolymer, and amphiphilic modified polymer mPEG-PLAA in a safe organic solvent, and preparing a microsphere suspension using a microfluidic emulsion method. The amphiphilic modified polymer mPEG-PLAA modifies the microspheres, forming a porous structure on the surface of the microspheres. Step 2, mixing and coating: directly mixing energetic, water-containing waste HTPB propellant with a water content of 55%–70% with the microsphere suspension obtained in Step 1, and using shear force or slight vibration to uniformly coat the energetic, water-containing waste HTPB propellant particles with a microsphere network, forming a microsphere coating layer. Step 3, granulation. The method of this invention is simplified and efficient: it does not require complete dehydration, operates directly in a water-containing state, shortens the granulation cycle to 2–12 hours, and reduces energy consumption per ton of propellant to 10–20 kWh.

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 to a direct granulation method for preventing agglomeration of energetic and water-containing waste HTPB propellant. Background Technology

[0002] When solid rocket engines reach the end of their service life or undergo maintenance, their metal casings are often recyclable, requiring the separation of the internal HTPB (hydroxyl-terminated polybutadiene) propellant from the casing. Currently, the mainstream separation technology in the industry is high-pressure water jet technology: using a high-pressure water jet (typically 100–300 MPa) to impact the propellant, causing it to peel off from the casing surface and pulverize into micron-sized particles. This technology has advantages such as no open flame, high safety, and minimal damage to the casing, but it has a core drawback—the pulverized propellant particles contain the HTPB polymer matrix (which has strong adhesive properties), and the separated particles have a high water content of 55%–70%, making them highly susceptible to re-agglomeration during collection, transportation, and temporary storage.

[0003] Agglomerated lumps / clumps (often exceeding 1 mm in diameter) can cause the following problems: First, subsequent sorting (e.g., separating metallic impurities), chemical treatment (e.g., degrading and recovering polymer components), or resource utilization (e.g., as fuel additives) processes are hindered, and equipment is prone to clogging. Second, agglomerated particles easily accumulate moisture, which may lead to localized mold growth or component deterioration during long-term storage, increasing safety risks.

[0004] Existing processing technologies require the particle moisture content to be reduced to below 10% through hot air drying (temperature 50-60℃) or vacuum drying (vacuum degree 10-20Pa) to inhibit agglomeration. However, the drying process is energy-intensive (approximately 50-80 kWh per ton of propellant) and inefficient (drying cycle 8-12 hours). Furthermore, high temperatures may cause a decrease in the stability of energetic components in the propellant (such as ammonium perchlorate), making it difficult to meet the safe disposal requirements for large-scale (ten thousand tons / year) waste propellant. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a direct granulation method for preventing agglomeration of energetic and water-containing waste HTPB propellants, thereby solving the technical problem that existing anti-agglomeration methods, while ensuring the effectiveness of anti-agglomeration, require further improvement in efficiency.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0007] A direct granulation method for preventing agglomeration of energetic and water-containing waste HTPB propellant, comprising the following steps.

[0008] Step 1: Preparation of microsphere suspension.

[0009] Polylactic acid (PLA), polylactic acid-glycolic acid copolymer (PLGA), and amphiphilic modified polymer mPEG-PLAA were dissolved in a safe organic solvent, and a microsphere suspension was prepared by microfluidic emulsion method. Through modification of the amphiphilic modified polymer mPEG-PLAA, a porous structure was formed on the surface of the microspheres.

[0010] Step 2: Mix and coat.

[0011] Energetic, water-containing waste HTPB propellant with a water content of 55%–70% is directly mixed with the microsphere suspension obtained in step one. Through shear force or slight vibration, the energetic, water-containing waste HTPB propellant particles are uniformly coated by the microsphere network to form a microsphere coating layer.

[0012] Step 3: Granulation.

[0013] The propellant particles are granulated, and the resulting propellant particles are monodisperse microparticles. The monodisperse microparticles are prevented from agglomerating during processing and storage by the steric hindrance and physical barrier effect of the microsphere coating layer.

[0014] The present invention also has the following technical features.

[0015] In step one, the microspheres have a particle size of 5–15 μm, the pore diameter of the pore structure is 2–5 nm, and the porosity of the pore structure is 10%–20%.

[0016] In step one, the amount of the amphiphilic modified polymer mPEG-PLAA added is 5% to 15% of the mass of the polylactic acid (PLA).

[0017] In step one, based on the subsequent degradation rate requirements, the mass ratio of polylactic acid (PLA) to polylactic acid-glycolic acid copolymer (PLGA) is 1:(0.5~2).

[0018] Preferably, in step one, the mass ratio of polylactic acid (PLA) to polylactic acid-glycolic acid copolymer (PLGA) is 1:1.

[0019] In step one, the safe organic solvent is ethyl acetate, and the total mass concentration of polylactic acid (PLA) and polylactic acid-glycolic acid copolymer (PLGA) dissolved in ethyl acetate is 10% to 20%.

[0020] In step two, the shearing rotation speed of the shearing force is 500-1000 r / min, and the shearing time is 10-20 min; the frequency of the slight vibration is 50-100 Hz, and the vibration time is 15-25 min.

[0021] In step three, the particle size distribution range of the monodisperse microparticles is 100–500 μm.

[0022] Preferably, in step three, the particle size distribution range of the monodisperse microparticles is 120–450 μm.

[0023] In step three, the granulation includes freeze-drying granulation or centrifugal granulation; the freeze-drying process conditions for freeze-drying granulation are: pre-freezing at -35℃ for 3 hours, and sublimation drying at 1Pa vacuum for 10 hours; the inlet air temperature of the spray granulator for spray granulation is 60-80℃ (lower than the decomposition temperature of the energetic components of the propellant), the outlet air temperature is 30-40℃, and the feed rate is 5-10L / min.

[0024] Compared with the prior art, the present invention has the following technical effects.

[0025] (I) The method of the present invention is simple and efficient: it does not require complete dehydration, and can be operated directly in a water-containing state, shortening the granulation cycle to 2-12 hours (more than 60% shorter than the existing drying + granulation process), and reducing the energy consumption per ton of propellant to 10-20 kWh (a reduction of 75%).

[0026] (II) The method of the present invention has a stable anti-agglomeration effect: the microsphere coating layer forms a physical barrier, and the porous structure modified by mPEG-PLAA further enhances the steric hindrance. After granulation, the particle size distribution is 100-500μm. After 6 months of storage at room temperature and pressure, there is no obvious agglomeration (agglomeration rate <5%, which is far lower than the 30%-50% of the existing drying methods).

[0027] (III) The degradation of the method of the present invention is controllable and safe: the degradation rate of PLA / PLGA microspheres can be controlled by adjusting the ratio (degradation cycle of 3 to 12 months). During subsequent recycling, the coating layer can be removed by natural degradation or mild chemical treatment (such as alkaline aqueous solution), without affecting the reuse of propellant components; and PLA / PLGA does not chemically react with the energetic components of propellant (ammonium perchlorate, aluminum powder, etc.), and there is no safety risk during storage.

[0028] (IV) The method of the present invention has strong industrial adaptability: microfluidic technology can achieve uniformity of microsphere size (variance coefficient <10%), spray granulation / centrifugal granulation can be carried out on a large scale and continuously, the equipment has high compatibility and is easy to connect with existing high-pressure water jet separation production lines.

[0029] (V) The degradation rate of the microsphere coating in this invention is achieved by adjusting the mass ratio of polylactic acid (PLA) to polylactic acid-glycolic acid copolymer (PLGA) and the molar ratio of lactic acid monomer to glycolic acid monomer in polylactic acid-glycolic acid copolymer (PLGA).

[0030] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0031] It should be noted that, unless otherwise specified, all raw materials and equipment used in this invention are those known in the art.

[0032] Currently, the industry faces problems such as agglomerated particles causing obstruction in subsequent processing, equipment blockage, safety risks due to internal moisture accumulation, and high energy consumption (approximately 50-80 kWh per ton of propellant), low efficiency (drying cycle 8-12 hours), and stability damage (decreased stability of energetic components) during the drying process. This highlights the inability of a single technology to achieve efficient anti-agglomeration and safe disposal in a hydrated state. Therefore, the industry practice is to use pre-drying followed by processing (such as hot air drying at 50-60℃ or vacuum drying at 10-20 Pa) or adding inorganic dispersants (calcium carbonate, talc), bio-coating, and other technical solutions. However, these solutions still suffer from poor anti-agglomeration effects (poor compatibility, difficulty in subsequent separation, secondary pollution), low process efficiency (requiring long drying cycles), insufficient safety (high temperature causes component degradation), and inability to operate directly in hydrated conditions. This leads to the development of the direct granulation anti-agglomeration method. Therefore, the industry believes that the integrated technology of "water-containing operation, efficient coating, controllable degradation, and safe recycling" can solve these problems. However, the technology has bottleneck problems such as insufficient adaptability to water-containing operation, difficulty in balancing anti-agglomeration effect and controllable degradation, and difficulty in taking into account the chemical inertness of energetic components. It cannot be applied to the large-scale (ten thousand tons / year) safe disposal needs of waste propellants.

[0033] Therefore, by utilizing the biocompatibility, chemical inertness, and controllable degradation of PLA / PLGA microspheres, a dense coating layer is formed on the surface of aqueous propellant particles. The spatial steric hindrance and physical barrier between the microspheres prevent particle adhesion and aggregation. At the same time, granulation can be completed without complete dehydration, thus achieving the requirements of "adaptability to aqueous operation", "anti-agglomeration effect", "controllable degradation" and "chemical inertness", solving the above-mentioned unsolvable problems.

[0034] The overall inventive concept of this invention is to utilize the biocompatibility, chemical inertness, and controllable degradation of PLA / PLGA microspheres to form a dense coating layer on the surface of water-containing propellant particles. This layer blocks particle adhesion and aggregation through steric hindrance and physical barriers between microspheres, while granulation can be completed without complete dehydration.

[0035] The method of this invention is applicable to the industrial treatment of water-containing waste HTPB propellant after high-pressure water jet separation. It can solve the problem of propellant particle agglomeration during collection, storage and subsequent processing, and improve treatment safety and resource recovery rate.

[0036] The raw material specifications of this invention are as follows.

[0037] Energetic and water-containing waste HTPB propellant: taken from retired solid rocket engines, collected after high-pressure water jet separation, with the moisture content controlled at 55% to 70% (too low a moisture content can easily lead to premature particle agglomeration, while too high a moisture content will increase the energy consumption of subsequent drying).

[0038] Polymer raw materials: PLA (polylactic acid, weight average molecular weight 90,000, crystallinity 40%); PLGA (polylactic acid-glycolic acid copolymer, weight average molecular weight 110,000, the molar ratio of lactic acid monomer to glycolic acid monomer can be selected as 1:1, 2:1 or 3:1); mPEG-PLAA (amphiphilic modified polymer; mPEG, i.e., methoxy polyethylene glycol, molecular weight 2,000; PLAAA, i.e., polyalanine, number average molecular weight is 5,000); PVA (polyvinyl alcohol, number average molecular weight is 70,000).

[0039] Auxiliary materials: safe organic solvent (ethyl acetate, analytical grade, boiling point 77℃, volatile and does not react with the energetic components of the propellant); deionized water (used to adjust the concentration of the microsphere suspension).

[0040] 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.

[0041] Example 1: Small-scale freeze-drying granulation (kg level).

[0042] This embodiment provides a direct granulation method to prevent agglomeration of energetic and water-containing waste HTPB propellant.

[0043] The raw materials in this embodiment are: 1 kg of water-containing waste HTPB propellant (water content 60%, particle size 10-100 μm), 50 g of PLA, 50 g of PLGA (lactic acid monomer: glycolic acid monomer = 1:1), 10 g of mPEG-PLAA, 500 mL of ethyl acetate, and 2000 mL of deionized water.

[0044] The method includes the following steps.

[0045] Step 1: Preparation of microsphere suspension.

[0046] PLA, PLGA, and mPEG-PLAA were added to the safe organic solvent ethyl acetate and stirred at 30°C and 500 r / min for 40 min to form a solution. The mass ratio of PLA to PLGA was 1:1, and the total mass concentration of PLA and PLGA dissolved in ethyl acetate was 15%. The amount of mPEG-PLAA added was 10% of the mass of PLA.

[0047] Using deionized water as the aqueous phase, a microfluidic chip (channel size 80 μm) was introduced. The oil phase flow rate was 0.3 mL / h, and the aqueous phase flow rate was 3 mL / h. The emulsion was collected and dropped into an aqueous solution containing 0.5 wt% PVA. The mixture was stirred at 30 °C for 3 h to obtain a microsphere suspension with a particle size of 10 μm, a pore diameter of 3 nm, and a porosity of 15%.

[0048] Step 2: Mix and coat.

[0049] Energetic and water-containing waste HTPB propellant with a water content of 60% was directly added to the microsphere suspension obtained in step one at a mass ratio of 1:0.4 in a high-speed shear mixer and sheared at 800 r / min for 15 min. It was observed that the propellant particles were uniformly coated with microspheres, forming a microsphere coating layer with a thickness of 8 μm.

[0050] Step 3: Granulation.

[0051] Energetic and water-containing waste HTPB propellant with microsphere coating was transferred to a freeze dryer, pre-frozen at -35℃ for 3 hours, and then sublimated under a vacuum of 1 Pa for 10 hours to obtain 0.6 kg of particles (8% moisture content). The propellant particles formed after granulation are monodisperse microparticles. The monodisperse microparticles are prevented from agglomerating during processing and storage by the steric hindrance and physical barrier effect of the microsphere coating.

[0052] Performance testing in this embodiment: The particle size distribution of monodisperse microparticles is 150-400 μm, and the aggregation rate is 3%; after 6 months of storage at room temperature, the aggregation rate increases to 4.5%, the microsphere coating is intact, and there is no component deterioration.

[0053] Example 2: Pilot-scale spray granulation (100kg class).

[0054] This embodiment provides a direct granulation method to prevent agglomeration of energetic and water-containing waste HTPB propellant.

[0055] The raw materials in this embodiment are: 100 kg of water-containing waste HTPB propellant (58% water content, particle size 10-100 μm), 20 kg of PLA, 20 kg of PLGA (lactic acid monomer: glycolic acid monomer = 2:1), 200 mL of ethyl acetate, and 2000 mL of deionized water.

[0056] The method includes the following steps.

[0057] Step 1: Preparation of microsphere suspension.

[0058] PLA, PLGA, and mPEG-PLAA were added to the safe organic solvent ethyl acetate and stirred at 30°C and 500 r / min for 40 min to form a solution. The mass ratio of PLA to PLGA was 1:1, and the total mass concentration of PLA and PLGA dissolved in ethyl acetate was 12%. The amount of mPEG-PLAA added was 10% of the mass of PLA.

[0059] Using deionized water as the aqueous phase, a microfluidic chip (channel size 80 μm) was introduced. The oil phase flow rate was 50 mL / h, and the aqueous phase flow rate was 200 mL / h. The emulsion was collected and dropped into an aqueous solution containing 0.5 wt% PVA. The mixture was stirred at 30 °C for 3 h to obtain a microsphere suspension with a particle size of 8 μm, a pore diameter of 3 nm, and a porosity of 15%.

[0060] Step 2: Mix and coat.

[0061] Energetic and water-containing waste HTPB propellant with a water content of 58% was directly added to the microsphere suspension obtained in step one at a mass ratio of 1:0.35 in a biaxial vibratory mixer and vibrated at 80 Hz for 20 min. It was observed that the propellant particles were uniformly coated with microspheres to form a microsphere coating layer with a thickness of 8 μm.

[0062] Step 3: Granulation.

[0063] Energetic and water-containing waste HTPB propellant with microsphere coating is transferred into a spray granulator with an inlet air temperature of 70°C, an outlet air temperature of 35°C, and a feed rate of 8 mL / min. After granulation, the particles are directly collected in a sealed container. Continuous operation yields 58 kg of particles (8% moisture content). The propellant particles formed after granulation are monodisperse microparticles. The monodisperse microparticles are prevented from agglomerating during processing and storage due to the steric hindrance and physical barrier effect of the microsphere coating.

[0064] Performance testing in this embodiment: The particle size distribution of monodisperse microparticles is 120-450 μm, and the aggregation rate is 4%; the microsphere coating layer has a degradation period of 5 months in neutral aqueous solution, and the coating layer can be completely removed by subsequent treatment with 0.1 mol / L NaOH solution for 2 hours, and the propellant component recovery rate reaches 98%.

[0065] Example 3: Effect of different PLA / PLGA ratios on degradation rate.

[0066] This embodiment provides a direct granulation method for preventing agglomeration of energetic and water-containing waste HTPB propellant. This method is basically the same as the method in Example 1, except that in this embodiment, only the mass ratio of PLA to PLGA is adjusted, and the degradation cycle of the microsphere coating layer in a neutral aqueous solution at 30°C is tested.

[0067] When the mass ratio of PLA to PLGA is 1:0.5, the degradation cycle is 8 months.

[0068] When the mass ratio of PLA to PLGA is 1:1, the degradation cycle is 5 months.

[0069] When the mass ratio of PLA to PLGA is 1:2, the degradation cycle is 3 months.

[0070] The results showed that the higher the PLGA content, the faster the degradation rate, which could be flexibly adjusted according to the needs of subsequent recycling cycles.

Claims

1. A method for direct granulation and anti-agglomeration of energetic and water-containing waste HTPB propellant, characterized in that, The method includes the following steps: Step 1, Preparation of microsphere suspension: Polylactic acid, polylactic acid-glycolic acid copolymer and amphiphilic modified polymer mPEG-PLAA were dissolved in a safe organic solvent, and microsphere suspensions were prepared by microfluidic emulsion method. Through the modification of amphiphilic modified polymer mPEG-PLAA, a porous structure was formed on the surface of the microspheres. Step 2, Mixing and Coating: Energetic water-containing waste HTPB propellant with a water content of 55% to 70% is directly mixed with the microsphere suspension obtained in step one. Through shear force or slight vibration, the energetic water-containing waste HTPB propellant particles are uniformly coated by the microsphere network to form a microsphere coating layer. Step 3, Granulation: The propellant particles are granulated, and the resulting propellant particles are monodisperse microparticles. The monodisperse microparticles are prevented from agglomerating during processing and storage by the steric hindrance and physical barrier effect of the microsphere coating layer.

2. The method for direct granulation and anti-agglomeration of energetic and water-containing waste HTPB propellant as described in claim 1, characterized in that, In step one, the microspheres have a particle size of 5–15 μm, the pore diameter of the pore structure is 2–5 nm, and the porosity of the pore structure is 10%–20%.

3. The method for direct granulation and anti-agglomeration of energetic and water-containing waste HTPB propellant as described in claim 1, characterized in that, In step one, the amount of the amphiphilic modified polymer mPEG-PLAA added is 5% to 15% of the mass of the polylactic acid.

4. The method for direct granulation and anti-agglomeration of energetic and water-containing waste HTPB propellant as described in claim 1, characterized in that, In step one, the mass ratio of polylactic acid to polylactic acid-glycolic acid copolymer is 1:(0.5-2).

5. The method for direct granulation and anti-agglomeration of energetic and water-containing waste HTPB propellant as described in claim 4, characterized in that, In step one, the mass ratio of polylactic acid to polylactic acid-glycolic acid copolymer is 1:

1.

6. The method for direct granulation and anti-agglomeration of energetic and water-containing waste HTPB propellant as described in claim 1, characterized in that, In step one, the safe organic solvent is ethyl acetate; the total mass concentration of the polylactic acid and polylactic acid-glycolic acid copolymer dissolved in ethyl acetate is 10% to 20%.

7. The method for direct granulation and anti-agglomeration of energetic and water-containing waste HTPB propellant as described in claim 1, characterized in that, In step two, the shearing rotation speed of the shearing force is 500-1000 r / min, and the shearing time is 10-20 min; the frequency of the slight vibration is 50-100 Hz, and the vibration time is 15-25 min.

8. The method for direct granulation and anti-agglomeration of energetic and water-containing waste HTPB propellant as described in claim 1, characterized in that, In step three, the particle size distribution range of the monodisperse microparticles is 100–500 μm.

9. The method for direct granulation and anti-agglomeration of energetic and water-containing waste HTPB propellant as described in claim 8, characterized in that, In step three, the particle size distribution range of the monodisperse microparticles is 120–450 μm.

10. The method for direct granulation and anti-agglomeration of energetic and water-containing waste HTPB propellant as described in claim 1, characterized in that, In step three, the granulation includes freeze-drying granulation or spray granulation; the freeze-drying process conditions for freeze-drying granulation are: pre-freezing at -35℃ for 3 hours, and sublimation drying at 1Pa vacuum for 10 hours; the inlet air temperature of the spray granulator for spray granulation is 60-80℃, the outlet air temperature is 30-40℃, and the feed rate is 5-10L / min.