Thermo-Chemical Recycling of SRM from Mixed Plastic Waste via Entrained-Flow Gasification: A Kinetic Study on Devolatilization and Char Reactivity

Abstract

Entrained-flow gasification of waste allows for high recycling rates towards CO₂-neutral chemical building blocks. In order to engineer such gasifier facilities, experimental analysis of the reaction rates is of great importance. Solid-recovered material (SRM) from commercial mixed plastic waste is prepared cryogenically to a conveyable powder achieving a characteristic particle diameter, suitable for subsequent analysis at pressurized conditions in a wire-mesh reactor, a high-temperature entrained-flow reactor and thermogravimetric analyzer. The pyrolysis behavior of SRM is investigated via a parameter study on temperature, pressure, heating rate and holding time. Kinetic devolatilization data is derived from a wire-mesh reactor, mimicking the reaction conditions of an entrained-flow gasifier at lab-scale. Full devolatilization within 400 ms at 1600 °C despite a particle size of 600 µm is achieved. A representative SRM pyrolysis char is prepared in a unique entrained-flow reactor under relevant near-industrial conditions at 1400 °C, 10 bar and 2.4 s for the first time in literature. The char sample is characterized in its properties and intrinsic reactivity towards O₂, CO₂ and H₂O in a thermogravimetric analyzer at 10 bar. A Power Law model allows for accurate representation of the experimental results, providing a reliable data set for gasifier CFD simulation. Here, the reactivity of SRM is driven by the Alkali-Index, and greater than bituminous coal, lower than lignite, but similar to pine and waste wood. Highly necessary performance indicators like conversion, cold gas efficiency and syngas quality can be determined towards thermo-chemical recycling of plastic waste allowing for stand-alone or co-gasification strategies.

Keywords: Gasification; Kinetics; Mixed plastic waste; Pyrolysis; SRM including SRF; Thermo-chemical recycling.