Influence of catalysts on the hydrothermal liquefaction of municipal primary sludge: Upgrading to a higher quality biocrude

Abstract

Effect of homogeneous and heterogeneous catalysts on hydrothermal liquefaction of primary sludge was studied. Biocrude, biochar, aqueous phase and biogas were all affected, in terms of quantity and quality. HTL without any catalyst attained a biocrude yield of 37.7 % (w/wVS). The best improvements in biocrude yield are observed with CuSO4 (10 %), 42.20 % (w/wVS) and TiO2 (20 %), 41.90 % (w/wVS). All experiments with catalyst produced a biocrude with HHV higher than 30 MJ/kg and with carbon content higher than 60 %. The analysis demonstrated that the major fraction of biocrude were asphaltenes, the heavier phase. While, the light phase, oils, in most of the cases, contained more saturates than polars. Biochar and aqueous phase were recuperated with high organic contents, that enables their usages in further applications. Even though gas fractions were small, their compositions varied between CO, CO2 and hydrocarbons. Catalysts were normally recuperated with the solid phase, except some cases due to their particle sizes. Most of the ashes of primary sludge were transferred to biochar. Some parts of them went to the aqueous phase and biocrude during separation process.