Catalytic hydrothermal liquefaction of municipal sludge by hydrochar to produce biocrude

Hydrothermal liquefaction (HTL) is an effective technology for municipal sludge (MS) conversion. In this study, the performances of biochar catalysts in HTL were investigated using MS as raw material. The solid product (hydrochar) of MS HTL was collected and prepared into three types of catalysts, namely BC, KOH/BC, and H₂SO₄/BC, to investigate the effects of different catalysts and catalyst loadings on MS HTL under fixed reaction conditions (350 °C, 40 min). The results show that the highest yield of biocrude could be achieved at 5 wt% BC, 15 wt% KOH/BC, and 5 wt% H₂SO₄/BC catalysts under used conditions, which could reach 17.84 wt%, 16.99 wt%, and 18.00 wt%, respectively. They were all higher than that of the non-catalytic condition (16.86 wt%). H₂SO₄/BC gave the greatest boost to the biocrude yield (18.00 wt%) and the highest energy recovery (ER up to 51.15% at 5 wt% loading), 8.85% higher than the energy recovery without catalyst (42.30%). H₂SO₄/BC also increased the hydrocarbon content and decreased the phenol content in biocrude.