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Polymer Devolatilization

THE PROBLEM

The production of many petroleum and biomass based polymers involves contact with chemical solvents. This contact may occur during the polymerization/reaction step, or when extracting impurities from the final product. Typically, the liquid solvent is first removed mechanically by centrifuge or filter. However, after mechanical separation, many polymers still contain 30-60 weight percent solvent. Therefore, a comprehensive solvent extraction method is required to produce the desired end product.

Example Use Case

  • Hexane laden polyethylene
  • Solids rage: 30,000 kg/hr
  • Hexane content: 35% wt
  • Requirement: <25% hexane content wetted powder

Additional Considerations:

  • Polymer flowability was poor in the 25-35% range
  • An existing dryer was to be used as a second stage dryer below 25%
  • Polymer softening temperature was 110-120°C
  • Hexane was to be recovered so low dryer gas flow rate was desirable to improve solvent extraction efficiency and reduce costs

THE SOLUTION

The Twin TorusDisc developed by Bepex International was used to remove hexane from the product. Centrifuge product entered the TorusDisc at approximately 35% hexane and 65°C. The material was then heated to the normal boiling point of hexane (69°C) and dried to approximately 25%. Heat is supplied to the material by conduction between the material and the hollow rotor discs. The rotor discs were heated with saturated steam at 110°C to avoid softening or melting of the material. The exhaust gas from the TorusDisc was then filtered and cooled to recover liquid hexane. The twin-rotor features inter-meshing discs which provide effective mixing and conveyance during the material transition phase.

BENEFITS & RESULTS

  • Reduced hexane content to desired level of <25%
  • Improved flowability of material to the point that could be easily handled by the existing downstream dryer
  • The solvent extraction process allowed for the evaporated solvent to be recovered and recycled back into the upstream process.

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