Stability Of Polymer Monomer Bpa, 1,4-BD, TPA In Super/sub-critical Water

Stability of bisphenol A(BPA), 1,4-butanediol(1,4-BD) and terephthalic acid(TPA), which were the monomers of polycarbonate(PC) and polybutylene terephthalate(PBT) depolymerization in super/sub- critical water, were studied in fused silica capillary reactor(FSCR) under the conditions of different temperture and heating time. Upon examination in water inside a FSCR under a microscope, phase changes were observed during BPA or TPA was heated. The research can provide foundation data for the PC and PBT depolymerization in super/sub-critical fliulds.Stability of BPA in super/sub-critical water was studied in FSCR(1.0 mm ID). It was found that the stability of BPA was influenced by temperature and heating time obviously, phenol and 4-isopropenylphenol were the main decomposition products of BPA. When the temperature of 260-360℃, the pressure of 1.6-18.7MPa and heating time of 15 min, the recovery of BPA decreased from 99.04% to 11.06%. When the temperature of 260℃and heating time of 15-75min, the recovery of BPA decreased from 87.80% to 43.54%.Stability of 1,4-BD in super/sub-critical water was studied in FSCR(1.5 mm ID). It was found that the stability of 1,4-BD was influenced by both temperature and heating time obviously, and tetrahydrofuran synthesis from 1,4-BD via dehydration. When the temperature of 240-340℃, the pressure of 3.3-14.6 MPa and heating time of 15 min, the recovery of 1,4-BD decreased from 95.35% to 55.75%. When the temperature of 260 ℃and heating time of 15-75 min, the recovery of 1,4-BD decreased from 93.35% to 62.84%.Stability of TPA in super/sub-critical water was studied in FSCR(2.3 mm ID). It was found that the stability of TPA was better than BPA and 1,4-BD under the same experiment condition, and the initial temperature for TPA decomposition was 320℃. The decomposition products of TPA was benzoic acid. When the temperature of 320-440℃, the pressure of 10.6^-15.5 MPa, heating time of 15 min, the recovery of TPA decreased from 99.99% to 74.91%. When the temperature of 360℃and heating time of 10-90 min, the recovery of BPA decreased from 95.40% to 75.80%.It was noted that the wall effects of the batch autoclave promoted the decomposition of BPA, 1,4-BD and TPA by comparing the experiment results of FSCR and batch autoclave. Additional kinetic analysis suggests that BPA, 1,4-BD and TPA in super/sub-critical water follows a first-order reaction kinetics with activation energy of 70.1kJ·mol^-1, 73.4 kJ·mol^-1 and 77.2 kJ·mol^-1, respectively. Phase behavior changes of TPA and BPA in water was observed and images were recorded in FSCR under a microscope when BPA or TPA was heated. It started to melt at a low temperature, then dissolved completely in water above 183.7℃and 298.2℃, respectively, and eventually became an aqueous fluid coexisting with vapor phases. 1,4-BD can be soluble in water, so the process of decomposition of BPA, 1,4-BD, TPA in water occurred in homogeneous phase.