Alkaline earth metal-based minerals/wastes-catalyzed pyrolysis of poly(ethylene terephthalate)/poly(butylene terephthalate) for benzenes-enriched oil production

The pyrolysis of poly(ethylene terephthalate) (PET)/poly(butylene terephthalate) (PBT) catalyzed by five alkaline earth metal-based minerals/wastes, namely calcined dolomite, calcite, magnesite, calcium carbide slag (CCS), and ophicalcitum, was conducted by a pyrolyzer-gas chromatography-mass spectrometer (Py-GC-MS) with the objective of recovering benzenes-enriched oil. Compared with magnesium-based catalysts and pure CaO, the calcium-based catalysts with calcium hydroxide as the main component performed better catalytic effect, which could simultaneously promote the hydrolysis of ester products and the decarboxylation of aromatic acids after hydrolysis. For PET, the addition of solid base catalysts at 600 °C promoted the complete degradation of aromatic acids and aryl esters, which accounted for 32.6% and 30.7% of the pyrolysis oil, respectively. The content of benzene in oil increased from 8.8% to 31.7%–78.8%. For PBT, the addition of solid base catalysts at 600 °C completely decomposed the aromatic acids, which accounted for 67.1% of the pyrolysis oil, and the content of benzene in oil increased from 12.3% to 34.5%–81.0%. During the deoxygenation of polyester pyrolysis products, increasing temperature was more effective for the decomposition/conversion of acetone and tetrahydrofuran, while increasing the alkalinity of the reaction environment contributed to the rapid decrease in acetaldehyde and aryl ketone contents.