Experimental study on modified lotus stem biochar-based catalysts for heavy oil aquathermolysis

To obtain high-activity catalysts for aquathermolysis at low temperatures, a composite modification method of KOH and silane coupling agent KH570 was used to successfully prepare modified lotus stem biochar (MLSB), and six catalysts with different ZrO2 and MoO3 contents (5–30 %) were synthesized by impregnation method. MLSB and catalysts were analyzed by SEM, N2 adsorption and desorption isotherms, surface pore size, and FT-IR. The results revealed that the pores of raw lotus stem biochar were increased and enlarged, and some -OH on the surface was replaced by hydrophobic groups to form hydrophobic supports. Catalysts had hydrophobic and strong acidic sites. The catalytic activities were evaluated by aquathermolysis experiments. Catalysts exhibited satisfying abilities to catalyze aquathermolysis at low temperatures (130–200 °C). Specifically, 25 % ZrO2−MoO3/MLSB catalyst displayed the optimal heavy oil viscosity reduction rate (86.1 %) at 200 °C, which was attributed to hydrophobicity, more active components and strong acid sites. The highest viscosity reduction rate of heavy oil was obtained with 25 % ZrO2−MoO3/MLSB at 200 °C and a catalyst content of 3 wt%. Continuing to increase the catalyst content decreased the viscosity reduction rate, likely due to catalyst agglomeration hindering the contact between the active component and heavy oil. Moreover, the viscosity reduction effect of the catalyst increased with higher reaction temperatures. Additionally, a reaction network of aquathermolysis catalyzed by ZrO2−MoO3/MLSB was proposed. These findings contribute to the development of efficient catalytic systems for aquathermolysis and provide insights into the application of biochar-based catalysts in heavy oil viscosity reduction.