Technical Solutions to Eliminate Triazinamide Agglomeration in Pymetrozine Production

Triazinamide agglomeration mainly arises from crystal hydrogen bonding, hygroscopic moisture absorption, ultra-fine particle adhesion, improper drying and feeding operations. Below are targeted front-end raw material treatment, process control and reactor operation solutions to guarantee uniform reaction for pymetrozine synthesis.

1. Raw Material Crystal Modification & Anti-Caking Treatment

1.1 Recrystallization to adjust particle size distribution

• Select low-polar mixed solvent (methanol + methyl tert-butyl ether) for recrystallization; control slow cooling crystallization rate (0.5–1 ℃/h) to generate uniform medium-size crystals (80–150 μm), reduce over-fine powder which easily agglomerates.
• Fast quenching crystallization is forbidden, as it produces micro-nano particles with huge specific surface area and strong interparticle adhesion.

1.2 Low-humidity drying to remove bound water

• Replace atmospheric oven drying with vacuum low-temperature drying (45–55 ℃, -0.07~-0.09 MPa). Residual moisture shall be controlled below 0.1%; internal trapped water is the core cause of lumping during storage and feeding.
• Avoid high-temperature drying (>60 ℃): triazinamide partial thermal decomposition generates viscous oligomers that act as binders to glue crystals together.

1.3 Small dosage inert anti-caking dispersant

Add 0.1–0.3% food-grade silica fume or micro talcum powder after drying and sieving. The inert fine powder coats triazinamide crystal surfaces to block hydrogen bond contact between particles, without interfering subsequent acidolysis and condensation reactions.

2. Pre-Feeding Dispersion Pretreatment (Key On-site Process)

2.1 Solvent premixing dispersion before adding to reactor

Prepare triazinamide suspension in anhydrous methanol under high-speed pre-stirring tank for 30–60 min before feeding into synthesis kettle. Fully disperse loose agglomerates via liquid shear force.

• Do not directly feed dry triazinamide powder into acidic mother liquor: rapid local dissolution creates sticky lumps that cannot be broken by normal stirring.

2.2 Online crushing & sieving feeding system

Install vibration sieve (80 mesh) and spiral disperser between storage bin and reactor feeding pipeline. Mechanical shear crushes dry agglomerate lumps into discrete single crystals before entering reaction solvent.

2.3 Strict closed low-humidity feeding environment

Triazinamide is highly hygroscopic. Equip feeding workshop with dehumidifier to keep air relative humidity ≤40%. Open storage drums only during feeding; long-term exposure to humid air quickly regenerates new agglomerates.

3. Reactor Mixing & Reaction Medium Optimization

3.1 Upgrade stirring system for strong shear dispersion

• Replace single-layer paddle stirrer with composite agitator (anchor + high-speed dispersion disc). High shear eliminates solid sediment agglomerates at reactor bottom.
• Maintain stirring speed ≥250 rpm during triazinamide feeding stage; reduce speed only after full dissolution.

3.2 Improve solvent polarity to weaken particle adhesion

Properly increase proportion of non-polar co-solvent in reaction system (e.g. methylbenzene, methyl tert-butyl ether). Reduce hydrogen-bond force between triazinamide crystals in liquid phase to prevent re-agglomeration after dispersion.

3.3 Gradual slow feeding control

Add pre-dispersed triazinamide suspension dropwise within 2–3 h, instead of one-time bulk feeding. Slow addition avoids local oversaturation and secondary crystal agglomeration.

4. Storage & Warehouse Anti-Agglomeration Management

1. Use double-layer PE sealed barrels with aluminum foil inner liner to isolate air moisture; store in constant temperature dry warehouse (temperature 15–25 ℃, RH＜45%).
2. Avoid long-term static stacking of raw material barrels; turn over barrels every 7 days to prevent bottom compression agglomeration caused by gravity extrusion.
3. Control storage period within 30 days; long-term stored triazinamide will gradually harden into massive blocks even with anti-caking agent.

5. Emergency Remedy for Already Agglomerated Triazinamide

If raw materials have formed hard lumps before production:

1. Crush lumps via stainless steel grinder, then vacuum re-dry to remove absorbed moisture.
2. Re-suspend in anhydrous methanol with high-speed stirring for 1 h, filter to remove undispersed hard core residues before putting into synthesis reaction.
3. Discard severely caked materials with oligomer sticky impurities to avoid increasing pymetrozine by-products.