Decomposition Behavior of Bisphenol A Under Subcritical Water Conditions: A Response Surface Methodology Approach

The degradation of bisphenol A (BPA), the main monomer of polycarbonate, was investigated under subcritical water conditions to better understand its decomposition as a function of process conditions and to provide useful data for designing a recycling process to convert polycarbonate into valuable products. Hydrothermal experiments were conducted in a batch reactor at temperatures ranging from 250 to 350 °C, with reaction times from 5 to 30 min and water-to-material ratios of 5, 10, and 15 (mL/g), following a Box–Behnken design with response surface methodology (RSM). The influence of process parameters on phase distribution, total carbon content, and product composition was evaluated. The results showed that temperature and reaction time were the most significant factors affecting BPA decomposition, while the water-to-material ratio had a minor effect. The recovery of the DEE (diethyl ether)-soluble phase decreased with increasing temperature and time, accompanied by a corresponding increase in the water-soluble phase yield and total carbon content. Analysis of the DEE-soluble fraction revealed the sequential transformation of BPA into 4-isopropenylphenol, 4-isopropylphenol, and phenol, with phenol becoming the dominant degradation product at higher temperatures. These findings provide new insights into the hydrothermal decomposition mechanism of BPA and form a basis for understanding polycarbonate degradation and developing sustainable subcritical water recycling processes for polymeric materials.