Effect of palladium-doped magnetite nanoparticles in the hydrothermal liquefaction of mixed spentgrain to bio-oil

Abstract

The mixed spent grain biomass, a mixture of maize and barley, has been used as a feedstock for bio-oil production through a hydrothermal liquefaction (HTL) process in the presence of iron oxide and palladium-doped magnetite nanoparticle catalysts. The study aimed at improving the quality of bio-oil produced through HTL in the presence of palladium-doped magnetite nanoparticles. The palladium-doped magnetite nanoparticles were synthesized by the co-precipitation method. The nanoparticles were characterized using Fourier transform infrared spectroscopy, Transmission electron microscopy, and X-ray diffraction techniques. The central composite design of response surface methodology was used to optimise three reaction parameters. Under the optimum conditions of temperature of 320 ℃, catalyst dosage of 1.5 g, and holding time of 60 min, the maximum bio-oil yield of 61.3% was obtained in the presence of palladium-doped magnetite particles, in comparison to 46.31% in the absence of the catalyst. The elemental analysis of bio-oil showed an increase of elemental carbon from 55.07 wt.% for uncatalyzed liquefaction to 76.47 wt.% for Pd-doped magnetite nanoparticle catalyzed liquefaction. Similarly, the elemental hydrogen increased from 5.32 wt.% for uncatalyzed to 7.63 wt.% for palladium-doped magnetic nanoparticle catalysed liquefaction. The elemental analysis further indicated improved bio-oil quality with the reduction of oxygen content from 36.52 wt.% to 14.33 wt.% and nitrogen from 2.51 wt.% to 1.32 wt.% for palladium-doped magnetite nanoparticle-catalysed liquefaction. The GC-MS showed an increase of hydrocarbons from 60.45% for uncatalyzed liquefaction to 88.03% for palladium-doped magnetite nanoparticle catalyzed liquefaction. The bio-oil produced in the presence of Pd-doped magnetite nanoparticles had a high heating value of 34.23 MJ/kg, the average kinematic viscosity of 4.7±0.11 mm2/s, the average flashpoint of 136 ℃, the iodine value of 122.64 ± 1.45 g I/100g, and the average acid number of 0.32 ± 0.36 mg KOH/g which were all in the permissible limits for crude bio-oils. The application of palladium-doped magnetite nanoparticles in the HTL of mixed spent grain biomass increases the yield of bio-oil and improves its quality by increasing the hydrocarbons and reducing the hetero atoms. This study offers a potential pathway for improving the yield and quality of bio-oils through the application of Pd-doped magnetite nanoparticles.