Fate of bisphenol A pyrolysates at low pyrolytic temperatures

- The pyrolysis behavior of bisphenol A was studied at 240-320 °C.
- Primary pyrolysis of bisphenol A produces phenol and p-isopropenyl phenol.
- p-Isopropenyl phenol is rapidly consumed to produce polymerized compounds.
- Additional phenol is produced via pyrolysis of the polymerized compounds.

Pyrolysis is an important method for breaking down organic waste to obtain useful low molecular weight compounds. To investigate the pyrolysis behavior of bisphenol A (BPA) and BPA pyrolysates at low pyrolytic temperatures, BPA and p-isopropenyl phenol (IPP) were pyrolyzed at 240-320 °C using a batch reactor. BPA decomposition was strongly enhanced at temperatures higher than 240 °C, and was almost complete after 30 min at 320 °C. Theoretically, pyrolysis of BPA gives phenol (PhOH) and IPP in a 1:1 molar ratio, corresponding to yields of 41 wt% PhOH and 59 wt% IPP. However, an unexpectedly low IPP yield (∼10 wt%) was obtained experientially, with a simultaneous increase in the yields of high molecular weight compounds. Compounds resulting from IPP polymerization were detected using electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS), suggesting that IPP was rapidly polymerized into high molecular weight compounds via radical propagation. On the other hand, a maximum PhOH yield of 62 wt% was obtained after 30 min at 320 °C, which is higher than the theoretical yield. As direct dealkylation of IPP is difficult, the excess PhOH is likely derived from thermal decomposition of the IPP polymerization products. Thus, the present work revealed the high reactivity of IPP for polymerization at pyrolytic temperatures, which facilitates increased recovery of PhOH from BPA.