Unsupported Ni metal catalyst in hydrothermal liquefaction of oak wood. Effect of catalyst surface modification

Hydrothermal liquefaction of oak wood was carried out in tubular micro reactors at different temperatures (280–330 °C), reaction times (10–30 min), and catalyst loads (10–50 wt%) using metallic Ni catalysts. For the first time, to enhance the catalytic activity of Ni particles, a coating technique producing a nanostructured surface was used, maintaining anyway the micrometric dimension of the catalyst, necessary for an easier recovery. The optimum conditions for non-catalytic liquefaction tests was determined to be 330 °C and 10 min with the bio-crude yield of 32.88%. The addition of metallic Ni catalysts (Commercial Ni powder and nanostructured surface-modified Ni particle) increased the oil yield and inhibited the char formation through hydrogenation action. Nano modified Ni catalyst resulted in a better catalytic activity in terms of bio-crude yield (36.63%), thanks to the higher surface area due to the presence of flower-like superficial nanostructures. Also, bio-crude quality resulted improved with the use of the two catalysts, with a decrease of C/H ratio and a corresponding increase of the high heating value (HHV). The magnetic recovery of the catalysts and their reusability was also investigated with good results.