Catalytic Hydrothermal Liquefaction of Water Hyacinth Using Fe3O4/NiO Nanocomposite: Optimization of Reaction Conditions by Response Surface Methodology

This research aimed at optimizing the reaction conditions for the catalytic hydrothermal liquefaction (HTL) of water hyacinth using iron oxide/nickel oxide nanocomposite as catalysts. The iron oxide/nickel oxide nanocomposite was synthesized by the co-precipitation method and used in the hydrothermal liquefaction of water hyacinth. The composition and structural morphology of the synthesized catalysts were determined using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and atomic absorption spectroscopy (AAS). The particle size distribution of the catalyst nanoparticles was determined by the Image J software. Three reaction parameters were optimized using the response surface methodology (RSM). These were: temperature, residence time, and catalyst dosage. A maximum bio-oil yield of 59.4 wt% was obtained using iron oxide/nickel oxide nanocomposite compared to 50.7 wt% obtained in absence of the catalyst. The maximum bio-oil yield was obtained at a temperature of 320°C, 1.5 g of catalyst dosage, and 60 min of residence time. The composition of bio-oil was analyzed using gas chromatography-mass spectroscopy (GC-MS) and elemental analysis. The GC-MS results showed an increase of hydrocarbons from 58.3% for uncatalyzed hydrothermal liquefaction to 88.66% using iron oxide/nickel oxide nanocomposite. Elemental analysis results revealed an increase in the hydrogen and carbon content and a reduction in the Nitrogen, Oxygen, and Sulphur content of the bio-oil during catalytic HTL compared to HTL in absence of catalyst nanoparticles. The high heating value increased from 33.5 MJ/Kg for uncatalyzed hydrothermal liquefaction to 38.6 MJ/Kg during the catalytic HTL. The catalyst nanoparticles were recovered from the solid residue by sonication and magnetic separation and recycled. The recycled catalyst nanoparticles were still efficient as hydrothermal liquefaction (HTL) catalysts and were recycled four times. The application of iron oxide/ nickel oxide nanocomposites in the HTL of water hyacinth increases the yield of bio-oil and improves its quality by reducing hetero atoms thus increasing its energy performance as fuel. Iron oxide/nickel oxide nanocomposites used in this study are widely available and can be easily recovered magnetically and recycled. This will potentially lead to an economical, environmentally friendly, and sustainable way of converting biomass into biofuel.

Hydrothermal Liquefaction of Water Hyacinth: Effect of Process Conditions and Magnetite Nanoparticles on Biocrude Yield and Composition

In this work, an efficient way of converting the water hyacinth to biocrude oil using magnetite nanoparticles (MNPs) as potential catalysts was demonstrated for the first time. MNPs were synthesised by co-precipitation and used in the hydrothermal liquefaction (HTL) of water hyacinth at different reaction conditions (temperature, reaction time, MNPs to biomass ratio and biomass to water ratio). The best reaction conditions were as follows: temperature— 320, reaction time—60 minutes, MNPs to biomass ratio – 0.2 g/g and biomass to water ratio – 0.06 g/g. HTL in presence of MNPs gave higher biocrude yields compared to HTL in absence of MNPs. The highest biocrude yield was 58.3 wt% compared to 52.3 wt% in absence of MNPs at similar reaction conditions. The composition of biocrude oil was analysed using GC-MS and elemental analysis. GC-MS results revealed that HTL in presence of MNPs led to an increase in the percentage area corresponding to hydrocarbons and a reduction in the percentage area corresponding to oxygenated compounds, nitrogenated compounds and sulphur compounds. Elemental analysis revealed an increase in the hydrogen and carbon content and a reduction in the nitrogen, oxygen and sulphur content of the biocrude when HTL was done in presence of MNPs compared to HTL in absence of MNPs. The nanoparticles were recovered from the biochar by sonication and magnetic separation and recycled. The recycled MNPs were still efficient as HTL catalysts and were recycled five times. The application of MNPs in the HTL of water hyacinth increases the yield of biocrude oil, improves the quality of biocrude through removal of hetero atoms, oxygen and sulphur compounds and is a potentially economical alternative to the traditional petroleum catalysts since MNPs are cheaper, widely available and can be easily recovered magnetically and recycled. This will potentially lead to an economical, environmentally friendly and sustainable way of producing biofuels from biomass.