Exploring the catalytic conversion of pyrolytic wax residue: Kinetics and co-pyrolysis

Abstract

This study explores the valorization of pyrolysis waxy residue (PWR), a semi-solid byproduct remaining after the distillation of lighter fractions from paper and plastic waste derived pyrolysis oil, with the aim of optimizing hydrocarbon production. Three strategies were assessed: (1) co-pyrolysis of PWR with sawdust (SD) at varying ratios, (2) catalytic pyrolysis using molecular sieves (MS) and ZSM-5 catalysts, and (3) catalytic co-pyrolysis combining PWR, SD, and catalysts. Thermal decomposition analysis of the PWR revealed maximum volatile release, with complete conversion achieved at 550 °C. Kinetic parameters were estimated using Coats Redfern method and the activation energy was found in the range of 31.3 – 38.9 mol⁻¹ (avg: 35.3 mol⁻¹). Non catalytic fixed-bed co-pyrolysis at the optimum temperature of 550 ˚C showed a 3:1 PWR-to-SD ratio maximizing the hydrocarbon content (79.0 %) but resulted in low oil yields of (∼13 %,). In contrast, catalytic pyrolysis of PWR with MS resulted in a significantly higher hydrocarbon yield with negligible phenolic compounds, while ZSM-5 enhanced the gas production to 32.5 % but slightly reduced hydrocarbon yield to 65.9 %. Catalytic co-pyrolysis using MS provided higher oil yields of ∼40 % with hydrocarbon content at 71.0 %. Despite the challenge of converting long-chain hydrocarbons into oily sludge, the findings highlight the potential for complete conversion and maximized liquid yields through catalysts and co-pyrolysis with biomass mixtures.