Depolymerization Of Polybutylene Terephthalate In Subcritical Aqueous Acid Solution And Sub/superctitical Ethanol

Waste plastic was recovered by supercritical fluid technology. Depolymerization of polybutylene terephthalate was researched by water and ethanol as the solvent, which was environment friendly and inexpensive . The research results on waste plastic recycling utilization were theoretical as well as practical values.Depolymerization of Polybutylene Terephthalate(PBT) was studied in subcritical aqueous acid solution and sub/supercritical ethanol. The influence of depolymerization reaction conditions on PBT depolymerization and products yield was investigated. Depolymerization products were analyzed by FT-IR, GC-MS, GC, LC-MS and HPLC.According to the analysis of depolymerization products, the depolymerization mechanism of PBT in subcritical aqueous acid solution and sub/supercritical ethanol was proposed, respectively. Depolymerization of PBT in subcritical aqueous acid solution was studied under the conditions of catalysis of cupric acetate(0.01g~0.07g), mass ratio of 8.0(24.0g H2O/3.0g PBT) ,temperature (220~280℃), pressure (2.2 ~ 6.4 MPa), reaction time (10~50min). The results showed that the presence of the cupric acetate had an obviously promotion for PBT depolymerization in subcritical water. In the numeral range of experiment design, the optimum dosage of cupric acetate was 0.03g/3.0g PBT. Depolymerization products of PBT were terephthalic acid (TPA) and tetrahydrofuran (THF). Compare to the results of relative literature, 1,4-butanediol did not be detected. With the conditions of temperature 250℃, reaction time 50 min and 0.03g cupric acetate, PBT could be totally depolymerized and the yields of TPA and THF could reach 99.3% and 83.1%, respectively. The results of kinetic analysis showed that the depolymerization followed a pseudo-first-order kinetics with an activation energy of 141.6 kJ·mol-1.Depolymerization of PBT in sub/supercritical ethanol was studied under the conditions of mass ratio of 4.0~12.0, temperature (220 ~ 280℃), pressure (3.1 ~ 9.4MPa), reaction time (5 ~ 60min). The results showed that in the numeral range of experiment design, the optimum mass ratio was 10.0 (20.0g EtOH / 2.0g PBT). The products of PBT depolymerized in ethanol were DET and 1,4-BD, which were partly different with that in water. PBT depolymerization increased with the reaction temperature and time increasing. With the conditions of mass ratio of 10.0, temperature 240℃and reaction time 60 min, PBT could be totally depolymerized and the yields of diethyl p-phthalate (DET) and 1,4- butanediol(1,4-BD) could reach 97.7% and 89.4%, respectively. The results of kinetic analysis showed that the depolymerization followed a pseudo-first-order kinetics with an activation energy of 38.8 kJ·mol-1.Phase behavior changes of PBT was observed and images were recorded in fused silica capillary reactor (FSCR) under a microscope in aqueous cupric acetate solution and ethanol, repectively. PBT could dissolve in water at 280℃for 19min, and in ethanol at 330℃. Hydrolysis and alcoholysis of PBT both occurred in homogeneous phase.