Selective production of benzene and naphthalene from poly(butylene terephthalate) and poly(ethylene naphthalene-2,6-dicarboxylate) by pyrolysis in the presence of calcium hydroxide

Poly(butylene terephthalate) (PBT) and poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) were pyrolysed in a fixed bed reactor in the presence of calcium hydroxide (Ca(OH) 2) in order to obtain benzene and naphthalene, respectively. In these experiments different ratios of polymer and Ca(OH) 2 were used. Also the temperature was varied in a range between 600 °C and 800 °C. It was found that the highest yield of benzene (67%) was obtained at a temperature of 700 °C and a molar Ca(OH) 2/PBT ratio of 10. The amount of carbon, fixed in the reactor residue after the experiment, was reduced from 56% for pure PBT to 38% under these conditions. Aromatic byproducts were reduced, as well, while the amount of 1,3-butadiene increased. Tetrahydrofuran was just formed under the influence of Ca(OH) 2. For PEN, the optimal conditions were found at a temperature of 600 °C and a molar Ca(OH) 2/PEN ratio of 5. A naphthalene yield of 80% from PEN was obtained. The rise of the naphthalene yield was caused by a more effective decomposition of the polyester by Ca(OH) 2, which led to the reduction of carbon in the reactor residue after the experiment from 59% for pure PEN to 10% under optimised conditions. The part of aromatic byproducts changed just slightly.