Torrefaction-Assisted Fractionation of Material Recovery Facility Waste

Abstract

Material recovery facility (MRF) residues are heterogeneous mixtures of plastics, paper/cardboard, and mineral matter that are difficult to separate and are commonly landfilled. This study evaluated whether torrefaction-induced changes in grindability can enable size-based enrichment of plastic-, biogenic-, and mineral-rich components from MRF-derived municipal solid waste (MRF-MSW). Approximately 150 g batches were torrefied at 300–400 °C for 5–150 min, producing 0–55% mass loss, and then ground and vibro-sifted into >850, 74–850, and <74 μm fractions. Across the investigated torrefaction severities, 60–80% of the recovered ash was concentrated in the <74 μm fraction, whereas the >850 μm fraction at low mass loss had the highest higher heating value (HHV) and was enriched in plastics. Microscopy and elemental analysis revealed that the materials were concentrated into plastic, biogenic, and mineral-rich fractions. Above approximately 20% mass loss, all retained material passed the 850 μm screen. The chlorine contribution from the coarse plastic-rich fraction declined to essentially zero above approximately 25% mass loss, while most residual chlorine was associated with the mineral-rich fine fraction. These results show that torrefaction severity can be adjusted to control grindability and facilitate physical fractionation of heterogeneous MRF-MSW.