A Mechanism Study on Hydrothermal Carbonization of Waste Textile

In this work, waste textile (WT) was employed as one representative pseudo-component of municipal solid waste (MSW) to investigate the mechanisms during hydrothermal carbonization (HTC) process. The experiments were examined at 230 and 280 °C with the residence time from 30 min to 90 min. The chemical component analysis showed that a significant fraction of fixed carbon was retained within the hydrochar, while ∼98% volatile matter was detected in the soluble fraction. Our results clearly demonstrate that decarboxylation was the most important defunctionalization process, whereas dehydration turned out to be less important. The combustibility index (S) and the combustion stability index (Rw) of the hydrochar were both greater than those of WT, suggesting hydrochar was superior in combustion performance. Fourier transform infrared (FTIR) analysis and solid-state 13C nuclear magnetic resonance (NMR) characterization displayed that large amount of aliphatic compounds decomposed, while enhancements of aromatic and carbonyl types carbons were observed in hydrochar and soluble. Higher temperature enhanced the breakage of unreacted feedstock to fragment and enforced the aromatization and repolymerization reactions to form the solid char and liquid phase. Between char and liquid phase, recombined, polycondensation and repolymerization reactions progressively occupied the dominant effects. These reactions promoted char and oil-range molecules to form hydrochar. On the basis of these outcomes, a conversion pathway of hydrothermal carbonization of WT was proposed.