Reflux-assisted pyrolysis of LDPE with alumina packing: Trade-offs in product quality and energy requirements

This study investigates the combined effect of using a reflux zone with γ-Al 2 O 3 packing during pyrolysis of polyethylene to improve the quality of the condensable product and thus produce a naphtha-rich (C 5 -C 12 ) product with a higher saturation level. LDPE was pyrolyzed in a semi-batch reactor at 450 °C. The reflux zone contained a bed of α-Al 2 O 3 , γ-Al 2 O 3 , or a mixture of both. Under reflux temperature of 350 °C, α-Al 2 O 3 and mixed beds produced similar condensed-product yields (~85 wt%) and comparable product distribution across carbon-number ranges. However, the mixed bed significantly altered the functional-group composition, where linear α-olefins decreased from 28.5 to 1.4 wt%, n-paraffins increased from 14.8 to 22.6 wt%, and aromatics remained low (~4 wt%). Increasing the loading of γ-Al 2 O 3 further increased the saturation level, but reduced the condensed-product yield to approximately 71 wt% and increased gas and aromatic formation. A simplified energy-balance analysis showed that reflux increased reactor energy demand on a feed basis. However, at an estimated reflux ratio of approximately 0.2, the specific energy demand per kilogram of naphtha was comparable to that of the no-reflux case, while the naphtha yield was higher.