Pyrolysis of the palm-based handicraft wastes: structure, reactions, and products

The mannan-rich palm handicraft processing wastes are potential feedstocks to produce high-value anhydrosugars through pyrolysis. However, the correlation between their structural characteristics and the pyrolysis chemistry remains unclear. Herein, two kinds of common palm feedstocks, tagua nut and bodhi root, were taken to explore the structure and pyrolysis characteristics using different characterization and experimental methods. Thermogravimetry-infrared spectroscopy (TG-FTIR) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) were employed to systematically investigate the pyrolysis characteristics and product distribution of tagua nuts and bodhi roots. Notably, the two raw materials exhibited high mannan contents of 87.59% and 88.01%, respectively, which exerted a fundamental influence on their pyrolysis behavior. The TG-FTIR results demonstrated that the maximum weight loss temperatures of the two materials were 301 and 302 °C, respectively. Among the anhydrosugars in the pyrolysis products, the proportion of levomannosan (LM) exceeded 90%. In Py-GC/MS tests, the maximum LM yield from tagua nut was 11.2 wt% (at 600 °C), while that from bodhi root was 10.9 wt% (at 500 °C). During the lab-scale pyrolysis, the highest yields of the organic liquid products were 31.5 wt% and 29.5 wt% for the two feedstocks at 600 °C. In the liquid pyrolysis products, a maximum LM yield of 5.8 wt% and a maximum 5-hydroxymethylfurfural (5-HMF) yield of 2.0 wt% were obtained, with trace furfural (FF, 0.50 wt% for tagua nut, 0.61 wt% for bodhi root). Finally, the pyrolysis mechanism of the two materials, especially the formation of LM, was discussed. The present work lays a foundation for the production of important anhydrosugars from the mannan-rich biomass wastes.