The degradation of polystyrene in supercritical toluene was studied at 310—370℃, 3.6—5.2 MPa by using a novel fast reactor. Supercritical solvents have unique properties such as excellent heat and mass transfer. Compared with thermal degradation without solvents, supercritical degradation obtains high conversion in a very short reaction time. The supercritical degradation of polystyrene is a typical free radical reaction mechanism, including chain fission, disproportionation, radical recombination, β-scission, intermolecular abstraction and intramolecular abstraction. Based on the reaction mechanism, the process of polystyrene degradation in supercritical toluene was modeled at the mechanistic level by using population balance equations formulated via the method of moments. The predictions of the degradation conversion of polystyrene were compared with experimental results, and the agreement was good.
Depolymerization of polybutylene terephthalate (PBT) in supercritical methanol was studied using a stainless stirred batch\|type autoclave under high temperature (453～533?K) and high pressure (7～12?MPa) conditions.The main depolymerization products were dimethyl terephthalate (DMT) monomer and ethylene glycol.The effects of different reaction temperature and pressure on depolymerization of PBT were investigated by analysis of the solid phase and liquid phase products.Considering the critical point of methanol (512 6?K,8 09?MPa),the reaction pressure was varied with in the range of 7～12?MPa.The results showed that the reaction pressure had little influence on the depolymerization and the depolymerization rate was affected greatly by the reaction temperature.The depolymerization of PBT was only 30% in 40?min at lower temperatures (453～463?K) but reached 100% in 20?min when the temperature was above 513?K.Depolymerization kinetics of polybutylene terephthalate in supercritical methanol was studied.The results showed that the depolymerization reaction rate constant ( k 1) in the temperature range of 513～533?K was much larger than the rate constant ( k 2) in the range of 453～483?K.The dissolution characteristics of PBT in supercritical methanol were the critical factors for depolymerization of PBT in a short time.These findings suggest that the supercritical methanol treatment for depolymerization of polymers such as PBT will be potential for obtaining useful chemicals.
