Kinetics of Polycarbonate Methanolysis by a Consecutive Reaction Model

Polycarbonate (PC) particles were depolymerized by methanol to recover bisphenol A (BPA) and dimethyl carbonate (DMC) in the range of 160-220 degrees C without using a catalyst or toxic solvents. The effect of operation variables Such as methanol/polycarbonate (MeOH/PC) weight ratio and the ethylene glycol/methanol (EG/MeOH) cosolvent system on reaction yields was examined to get better monomer yields. The product yield increased as the amount of methanol increased until the MeOH/PC molar ratio 71. However, the EG/MeOH cosolvent system did not improve the depolymerization yield. A novel kinetic model was proposed to explain the depolymerization reaction, which consists of a series of reactions: random scission from high molecular weight PC to its solid oligomer, dissolution from the solid oligomer to liquid oligomer, and homogeneous degradation from the oligomer to its monomers, BPA and DMC. Continuous distribution kinetics and shrinking core model were employed to describe random scission of PC and dissolution of PC solid particle in methanol solution. The predicted values by the proposed model were shown in good agreement with the experimental ones.