Insight into Catalytic Hydrothermal Liquefaction of Cardboard for Biofuels Production

Catalytic hydrothermal liquefaction (HTL) of cardboard was carried out in a 300 mL Parr batch reactor using 5 wt % Ni­(NO3)2, Ca­(NO3)2, and NiCl2 in a temperature range of 225–300 °C for H2, biocrude, and bio-oil production. A slurry with cardboard to water weight ratio of 1:30, 1:10, 1:4, or 1:1.5 was loaded in the reactor and pressurized with N2 (40 or 200 psi). HTL was performed at various temperatures for 120 min. While HTL was in progress, gas samples were withdrawn periodically and analyzed by GC. The maximum H2 yield of 11.46 mL/g of cardboard was obtained using Ni­(NO3)2 at 300 °C in 30 min. The percent liquefaction of biomass was quantified by TOC. The liquefaction yields were found to be dependent on reaction temperature, residence time, cardboard to water ratio, and operating pressure. The highest biocrude yield of 47.14% was observed at 275 °C in 30 min. Light bio-oil (LBO) and heavy bio-oil (HBO) were extracted by dichloromethane and acetone, respectively, and characterized by GC/MS and elemental analyzer. LBO contained mainly C4–C11 oxygenated hydrocarbons with a higher heating value (HHV) of 27.71 MJ/kg. HBO consisted of C17–C22 oxygenated compounds with a HHV of 29.62 MJ/kg.