Bio-oil by the hydrothermal liquefaction of municipal sewage sludge using hierarchical Fe-Co-ZSM-5 catalysts

Abstract

Hydrothermal liquefaction (HTL), a mimic of natural formation of petroleum is the only thermochemical conversion having ability to convert the wet biomass to bio-oil, which upon hydrotreatment gives drop-in auto fuels. Yield of bio-oil, the energy product of HTL depends on the activity of the catalyst. Hence the synthesis of hierarchical Fe-Co-ZSM-5 was reported for the first time, the same was characterized and evaluated for the HTL of municipal sewage sludge to bio-oil. From their XRD characterization and calculated XRD crystallinity, 3 days was found to be the optimum crystallization time, as its crystallinity was 84% of hierarchical Al-ZSM-5 as standard, maximum among others crystallized at 2 and 4 days. From the characterization of Fe-Co-ZSM-5 obtained at 3 days by N2 adsorption, mesoporosity was found to be 87.7% conforming its hierarchical nature and UV-visible reflectance spectrometry confirmed the incorporation of Fe and Co into the tetrahedral zeolite framework. Hydrothermal liquefaction of municipal sewage sludge studied at 250°C and initial H2 pressure of 40 bar using the hierarchical Fe-Co-ZSM-5 (3 days) catalysts gave higher bio-oil yield of 23.8% compared to 10.26% for non-catalytic HTL.