| Phase behavior of polyimide (polyimide, PI) and4,4’-Oxydianiline (ODA) in hot compressed water was investigated in a fused silica capillary reactor (FSCR), respectively. Depolymerization of PI in hot compressed water(HCW) was studied in a batch autoclave reactor under different conditions. The experimental products were analyzed qualitatively and quantitatively by High Performance Liquid Chromatography (HPLC), Gas Chromatography and Mass Spectrometry (GC-MS), Raman spectra and Fourier-transform Infrared Spectroscopy (FT-IR). According to the analysis of depolymerization products and the results of phase behavior, the depolymerization mechanism of PI in hot compressed water with catalyst was proposed.Phase changes of PI and ODA in sodium hydroxide solution were investigated in FSCR. The results showed that with reaction temperature and time increasing, PI gradually melted and dissolved in water, and was not hydrolyzed completely at325℃for90min. Solid particles appeared and gas released in the process of cooling. It was found that ODA started to melt at a low temperature, then eventually became an aqueous fluid coexisting with vapor phases above191.7℃. When temperature up to290℃reaction time of30min,there is no phase change during the process and Solid crystals appeared in cooling process.The depolymerization of PI was studied under the conditions of temperature (295～350℃), pressure (7.5～15.8MPa), reaction time (30～90min), ratio of water/PI (20.0). It was found that PI could be degraded to monomer completely when the experiments were conducted for30min at340℃. The results of kinetic analysis showed that the activation energy of PI catalytic depolymerization was130.6kJ·mol-1. Further stability tests of ODA were carried out at temperature290to330℃under the reaction time range of15to120min. It revealed that ODA was unstable and partially converted to aniline with the reaction temperature and the time increased, reducing its yield. |
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