Phenol recovery by BPA tar hydrolysis in supercritical water

In this paper, we proposed a new process of Bisphenol-A(BPA) tar hydrolysis in supercritical water (SCW) to recover phenol. First, the decomposition of BPA in SCW was studied at 673 K and in the pressure range from 28 to 38 MPa. In SCW, BPA was hydrolyzed to produce phenol and 2-(4-Hydroxy phenyl)-2-propanol (HPP). HPP was further hydrolyzed to produce phenol and, at the same time, dehydrated to produce 4-Isopropenylphenol (IPP), which was stable under the conditions used. With increasing water density, the contribution of HPP hydrolysis became more significant than that of dehydration, and as a result, the yield of phenol increased. Moreover, with increasing water density, the dielectric constant of the solvent increased and the polar-activated intermediate was thus stabilized more than the reactant. This probably was the reason that the hydrolysis rate increased with increasing water density. The SCW treatment of BPA tar was studied also in the ranges of temperature from 473 to 673 K and pressure from 20 to 38 MPa. Although in argon atmosphere polymerization took place, it did not in SCW. The phenol yield in SCW increased with elevating temperature and pressure. The maximum phenol yield was around 60 mol% of the phenol structures in the tar, that corresponded to 40 wt% of the raw tar. Such high phenol yield was obtained even at tar/water ratio as high as above 30 wt% that would be required for the process to be economically feasible.