Fast hydrothermal liquefaction coupled with homogeneous catalysts to valorize livestock manure for enhanced biocrude oil and hydrochar production

Catalytic fast hydrothermal liquefaction (HTL) of cow manure was performed to investigate the effect of reaction temperature (400–450 °C), resident time (10–24 min), and catalyst type (NaOH, Na2CO3, NaHCO3, ZnCl2, citric acid, and H3PO4) on products yields and characteristics. The biocrude oils produced from both non-catalytic and catalytic fast HTL processes were characterized by gravimetric analysis, GC/MS, FTIR, CHNS/O elemental analysis, etc. For instance, by introducing Na2CO3 in the fast HTL process under the same condition, the yield and HHV of the biocrude oil were further enhanced to 21.86 wt% and 31.32 MJ/kg, respectively. The physicochemical properties of hydrochars were estimated by SEM, EDX, FTIR, TGA, and CHNS/O elemental analysis. Importantly, the versatile hydrochar generated from catalytic fast HTL process possessed the porous structure, high HHV (e.g., 18.43 MJ/kg) and great thermal stability, indicating huge potentials as an adsorbent, solid fuel, and even catalyst support. To get more insights into the HTL reaction mechanisms, the aqueous phase as an important byproduct was characterized by GC/MS, TOC, and TN analysis; and gas fraction was identified by GC.