Hydrogenation of vanillin to vanillyl alcohol over Pd/PDA/Ni foam in micropacked bed reactors

The micropacked bed reactor (μPBR) with monolithic catalyst hydrogenation technology has received widespread attention due to its high efficiency, continuous operation, and safety. In this study, the Pd/PDA/foam catalyst was prepared via impregnation method and vanillin (VL) hydrogenation was investigated in green water solution based on the μPBRs. The effect of operating temperature, pressure, the number of foam catalyst block, VL concentration, liquid and H₂ flow rate on VL conversion and VA yield was discussed. The highest conversion of VL was 99.4 % and product yield of vanillyl alcohol (VA) reached 84.9 % with 2.8 MPa, 120 °C, 22 blocks of Pd/PDA/Ni foam catalyst, H₂ flow rate of 10 mL min⁻¹ and liquid flow rate of 0.1 mL min⁻¹, and short reaction time (0.106 h) in μPBRs. The kinetic of hydrogenation VL to VA was established. The reaction rate constant and activation energy in μPBRs were from 0.63 to 1.39 min⁻¹ and 16.94 kJ·mol⁻¹. The STY of VA in μPBRs was 0.0824 kg·L⁻¹·h⁻¹·g⁻¹, which was bigger than that of batch hydrogenation devices.