Effect of the Method of Synthesizing a Nickel-Containing Catalyst on Lignin Conversion in Liquid-Phase Hydrodepolymerization

Results of the catalytic hydrogenation of lignin in a hydrogen-donor solvent medium are described. Nickel-containing systems are deposited directly on the lignin surface in an amount of 1.5–3.4 wt %. Nickel systems are deposited by two methods: from a Ni(OAc) 2 × 4Н 2 О aqueous solution and from a colloidal solution in toluene of nickel particles prepared by metal vapor synthesis (MVS). The hydrogen donor solvent is tetralin taken in a tetralin/lignin ratio of 1 : 1. Hydrogenation was carried out in a rotating autoclave at a temperature of 400°C and a pressure of 100 atm. It is shown that the preactivation of nickel-containing lignin by ultrasonication at 39 kHz for 20 min leads to an almost exhaustive conversion of the organic matter: the hydrogenation products comprise 13.1 wt % gas and 86.3 wt % liquid hydrocarbons. The liquid hydrogenation products contain aromatic hydrocarbons and nonvolatile condensed compounds with an average molecular weight of 300 Da. The effect of sonication on nickel-containing lignin and the evolution of nickel-containing components during lignin hydrodepolymerization are studied by electron microscopy and magnetic susceptibility methods.