Efficient catalytic upgrading of municipal sludge hydrothermal biocrude via dual-base modified ZSM-5

Hydrothermal liquefaction (HTL) was identified as a promising technology for the conversion of wet municipal sludge (MS) into liquid biofuel. However, the oil product (biocrude) derived from MS exhibited high O content and low higher heating value (HHV). These issues severely limited its application as a biofuel. In this study, a catalytic hydrogenation process was employed to upgrade the sludge biocrude. ZSM-5 zeolites were selected as catalysts. A series of alkali modification studies were conducted. Furthermore, the mechanism of catalytic hydrogenation upgrading was analyzed. The results indicated that the modified ZSM-5 (NaOH + TPAOH-ZSM-5), prepared via mixed organic and inorganic alkali modification, exhibited the best hydrogenation performance, with synergistic meso -microporous structures. This catalyst significantly enhanced the deoxygenation efficiency, increasing from 33.76% for ZSM-5 to 75.02%% for NaOH + TPAOH-ZSM-5 (300 °C, 40 min). Meanwhile, the hydrocarbons content in the upgraded biocrude exceeded 50%. Additionally, the content of heavy oil fraction (>C20) decreased from 83.68% to 13.66%. The study confirmed that the modification of the ZSM-5 pore structure facilitated the formation of mesopores. This structure allowed macromolecular substrates to enter the catalyst channels and participate in the reaction. Consequently, the catalytic hydrodeoxygenation effect on the biocrude was effectively enhanced. This work provided an experimental basis for the application of dual-alkali modified ZSM-5 in catalytic upgrading of sludge hydrothermal biocrude.