Effect of temperature management on the hydrolytic degradation of PET in a calcium oxide filled tube reactor

Poly(ethylene terephthalate) (PET) was hydrolysed and decarboxylised, using a calcium oxide filled column under several thermal conditions, in order to obtain high yields of high purity benzene. The reactions of the hydrolysis of PET and the subsequent decarboxylation of the resulting terephthalic acid were successfully separated by a sophisticated temperature management. While hydrolysis proceeded well at temperatures below 500 °C, the decarboxylation proceeded with a sufficient velocity at about 500 °C. The yield and purity was strongly determined by the extent to which hydrolysis and decarboxylation were separated. At temperatures higher than the optimal temperature for hydrolysis, the resultant side reactions led to both a lower yield and purity of the product, while few by-products were observed when the hydrolysis was completed before the decarboxylation started. The best results were achieved at a heating rate of 2 K min−1 between 300 °C and 500 °C, with a benzene yield of 74% and a purity of 97 wt.%.