m-Phenylenediamine (mPDA) Purification
A patented separation process that isolates m-phenylenediamine from o- and p-isomers with exceptional precision. Using a refined divided-wall distillation column (DWC), the method consistently achieves > 99.98 wt.% purity at commercial scale. First plant successfully commissioned in 2024.
mPDA product purity
Low T, color stability
Process Overview
The legacy route uses three towers (de-tarring → isomer removal → product column). Polywin’s layout integrates the main separation into a single divided-wall distillation column. The middle section is split by a vertical wall: feed enters the prefractionator side, while the main fractionation side delivers a high-purity side-draw of mPDA. Overhead removes light/isomer impurities; bottoms purge heavies and tars. Vacuum operation minimizes thermal stress and discoloration.
Feed Envelope
- mPDA: 65–95 wt% (typ. 75–90 wt%)
- o-/p-isomers: 5–25 wt% (typ. 10–20 wt%)
- Low boilers (e.g., aniline) + water: < 2 wt%
- Heavies/tars: up to ~15 wt% depending on upstream
Column Internals
- Structured packing preferred (lower ΔP, shorter residence time)
- Specific area: 250–500 m²/m³ (range 125–750 m²/m³)
- Packed length: ~10–50 m (example: ~32 m)
- Divider length: ~60% of packed height
- Cross-section split (divided zone): ~38–43% / 57–62% (prefractionator / main)