Promoting Effect of ZSM-5 Catalyst on Carbonization via Hydrothermal Conversion of Sewage Sludge

An in-depth study on the transformation and distribution of carbons via hydrothermal conversion (HTC) of sewage sludge was conducted to evaluate the catalytic impact of Zeolite Socony Mobil-5 (ZSM-5). All the experiments were carried out between 180 and 300 °C with ZSM-5 catalyst during the HTC. Chars were analyzed for their carbon content distribution, carbonization degree, carbon-containing functional groups, and Raman chemical structural properties. The results revealed that ZSM-5 catalyst could concentrate carbon-containing matter in char and have distinct catalytic effects of ZSM-5 on carbonization degree. The catalyst with an Si/Al ratio of 300 is appropriate for char production at lower reaction temperatures, whereas the char with lower Si/Al ratio catalyst has better performance under higher reaction temperatures. ZSM-5 has a positive effect on the decomposition of C-(C,H) and promotes formation of C-(O,N) structure. Moreover, it can increase the decomposition of functional groups C═N and enhance the formation of −CHn groups. Compared to the pure char, the structure of char converted from a small aromatic ring to a larger aromatic ring with ZSM-5 catalyst assistant.