Phase behavior and reaction of polyethylene in supercritical water at pressures up to 2.6 GPa and temperatures up to 670°c

Z. Fang, R. L. Smith, H. Inomata, K. Arai

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43 Citations (Scopus)

Abstract

Phase behavior and reaction of polyethylene (PE) in supercritical water were studied with a diamond anvil cell (DAC) technique with visual and Raman spectroscopy. When PE + water (12-30% PE) mixtures were rapidly heated at initial pressures ranging from 110 to 690 MPa, PE first melted and formed a liquid spherule PE phase. The spherule began to expand at above 450°C and underwent a color change to red at about 570°C. At higher temperatures, the red color disappeared and the PE molten phase turned transparent. Upon further heating, the red color returned and other material underwent homogenous reaction as evidenced by a dark color which appeared throughout the cell. Volatile liquids were formed on the surface of the liquid PE phase spherule. For reactions run at higher temperature (645-671°C) at pressures ranging from 1.9 to 2.6 GPa, thin films formed on the anvils after quenching which had C≃C, OH, and C-C Raman bands, which indicated that hydrolysis products formed even though the reaction times were relatively short (290-475 s). Reactions performed at a constant temperature of 423°C and at an initial pressure of 850 MPa showed only a slight decrease (0.03 MPa/s) in pressure with time. The results of this study show, conclusively, that PE and water remain as a heterogeneous system over the polymer (12-30% PE) compositions studied during heating and reaction in supercritical water. Only after PE decomposes to lower molecular weight hydrocarbons, above about 565°C, can homogeneous reaction conditions result. (C) 2000 Elsevier Science B.V.

Original languageEnglish
Pages (from-to)207-216
Number of pages10
JournalJournal of Supercritical Fluids
Volume16
Issue number3
DOIs
Publication statusPublished - 2000 Jan 15

Keywords

  • DAC
  • Phase behavior
  • Polyethylene
  • Raman
  • Reaction
  • Supercritical water
  • Visual microscopy

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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