Two-Stage Lab Extrusion Line for Polymer Devolatilization
- Clients in: Devolatilization
Background and Challenges
This project was delivered to a leading chemical industry powerhouse in East China. The client faced significant processing hurdles in developing a high-performance specialty polymer requiring rigorous post-synthesis purification.
- Process Bottlenecks: The nascent polymer contained high levels of residual solvents and impurities, necessitating a continuous multi-stage “washing-extraction-devolatilization” process to achieve optical or medical-grade purity.
- Corrosion Issues: The acidic washing agents and reaction byproducts posed a severe corrosion threat to standard equipment, demanding metallurgy far superior to conventional nitrided steels.
- R&D Flexibility: As a pilot line, the system required an extremely wide operating window to simulate the complete phase transition from low-viscosity solutions to high-viscosity melts.
In-depth Analysis of Material Characteristics
Analyzing the ultra-high L/D configuration (Stage 1: L/D 74, Stage 2: L/D 58), the material processing involves distinct complexities:
- Multiphase Flow & Separation: The process involves complex “solid-liquid-liquid” interactions within the barrel. Precise shear control is critical to achieve efficient mass transfer (washing) followed by phase separation (liquid drainage).
- Extended Residence Time: The combined L/D ratio exceeding 130D indicates that the reaction or purification kinetics require substantial residence time to ensure complete conversion and solvent removal.
- Metallurgical Sensitivity: The polymer system is sensitive to metal ion contamination and operates in a highly corrosive environment, mandating the use of specific chemically inert alloys.
USEON Solution
To address these challenges, USEON engineered a bespoke H-type two-stage washing and devolatilization system:
H-Type Dual-Stage Architecture:
- Stage 1 (LAB35 Twin Screw Extruder, L/D 74): Functions as the primary reaction and washing zone. Its extended length accommodates three high-pressure liquid injection systems (up to 15Mpa) and extensive mixing zones for micro-level solvent dispersion.
- Stage 2 (LAB30 Twin Screw Extruder, L/D 58): Dedicated to deep devolatilization and pressure build-up, ensuring minimal volatile content in the final pellets.
- The H-arrangement optimizes the melt flow channel between stages while reducing the vertical clearance required for installation.
Dynamic Liquid Drainage & Injection:
- The line features three sets of Dynamic Liquid Drainage units. These counter-rotating twin-screw side units force extracted liquids out of the barrel while preventing polymer melt leakage—a significant upgrade over passive drainage methods which often clog.
- Specialized liquid injection barrels allow precise introduction of washing agents even into high-pressure melt zones.
Premium Corrosion Resistance:
- The Stage 1 barrels are constructed from 630 Stainless Steel with Nickel-Based Alloy liners (HRC50), and screw elements are machined from 630 SS. This metallurgy effectively neutralizes intergranular corrosion risks in acidic environments.
- Stage 2 and downstream components utilize 304 Stainless Steel and Nickel alloys to maintain a contamination-free process.