Valorization of tree leaves waste using microwave‐assisted hydrothermal carbonization process

Fallen leaves of landscape trees, as an emerging biomass waste, were valorized using conventional hydrothermal carbonization (HC) and microwave‐assisted hydrothermal carbonization (MHC) pretreatments, and were comparatively characterized for physicochemical properties and thermal degradation kinetics. The results show that MHC is superior to conventional HC operation, because at 200℃, the MHC process not only gives a higher hydrochar yield (45.09 vs. 39.47 wt%) with significantly reduced energy consumption (0.63 vs. 2.74 MJ g−1), but also is more effective in removing K and Si. For isoconversional kinetic analysis, the FWO method provides better results than the KAS method as the latter failed to fit the tree leaves sample (R2 400℃) showed that the hydrochar obtained from the MHC process has a lower average activation energy of ~190 MJ kg−1 than the conventional HC process (~260 MJ kg−1). This study reveals the potential for valorization of the landscape tree wastes via the MHC process. This is a systematic study that reports valorization of fallen leaves of urban landscape trees as a biomass waste, using microwave‐assisted hydrothermal carbonization (MHC) as compared to conventional hydrothermal carbonization (HC). It has been shown that the MHC process is superior to conventional HC operation. Results reported in this study may shed light on turning landscape tree leaves as an environmental pollution source into an energy resource, and facilitating the design of subsequent hydrochar utilization process.