Kinetics and recovery of bisphenol-A from fiber-reinforced polycarbonate using subcritical water

Abstract

Chemical recycling of industrial fiber-reinforced polycarbonate (PC) to produce bisphenol-A (BPA) is carried out in the present study using water and an alkali catalyst (KOH) via hydrothermal processing (HTP). The operating window for the conversion of PC was determined using differential scanning calorimetry (DSC), and batch HTP reactions were carried out under two conditions: neutral sub-critical conditions (260–300 °C) with water and alkaline mild conditions (130–150 °C) with 1 M KOH. Sub-critical conditions led to the formation of a mixture of BPA, phenol and alkylphenols, whereas mild alkaline conditions mainly led to the formation of BPA with >90% recovery. The kinetic parameters for the alkaline conversion of PC to BPA were investigated using high pressure DSC, and six different kinetic models were compared with the experimental data and assessed for their accuracy. The first-order kinetic model was found to be the best to describe the decomposition of PC to BPA, with an average activation energy of 162.1 kJ mol⁻¹. Glass fibers after HTP were recovered and their structural integrity was analyzed using scanning electron microscopy (SEM). Nearly 100% recovery of glass fibers was achieved with neutral water, while more than 10 wt% of glass fibers were lost due to leaching when 1 M KOH was used. Process intensification via recirculation of the aqueous phase proved to be detrimental to the monomer yield.