Chemistry, Vol 13, No 2 (2020)

Depolymerization of pine ethanol lignin in the medium of supercritical ethanol in the presence of catalysts NiCu/SiO2 and NiCuMo/SiO2

Angelina Viktorovna Miroshnikova, Sergey Viktorovich Baryshnikov, Yuriy Nikolaevich Malyar, Vadim Anatolyevich Yakovlev, Oxana Pavlovna Taran, Laurent Djakovitch, Boris Nikolaevich Kuznetsov

Abstract


The regularities of thermocatalytic transformation of pine ethanol lignin in supercritical ethanol in the presence of catalysts NiCu/SiO2 and NiCuMo/SiO2 in the temperature range 250–400 °C were established. The composition and structure of ethanol lignin, liquid and solid products of its conversion were studied by methods of elemental analysis and gel-permeating chromatography (GPC). The composition of gaseous products – by method of gas chromatography.

At the process temperature of 250 °C the catalysts do not have a significant effect on conversion of ethanol lignin. The maximal yield of liquid products (83.5 wt.%) was obtained at temperature 300 °C in the presence of catalyst NiCuMo/SiO2 containing 8.8 wt.% of molybdenum. At temperature 350 °C NiCu/SiO2 and NiCuMo/SiO2 catalysts contribute to the almost complete conversion of ethanol lignin into liquid and gaseous products, and the yield of solid products does not exceed 1 % wt.

In liquid products of catalytic conversion there is a decrease in the atomic ratio of O/C and the increase of H/C atomic ratio as compared to initial ethanol lignin due to catalytic intensification of reactions of deoxygenation and hydrogenation of lignin and products of its depolymerization.

According to GPC data on the curves of molecular mass distribution (MMD) of liquid products of thermocatalytic conversion of ethanol lignin at 300 °C there are peaks with highs at 160 and 380 Da, probably related to guiacyle monomers and dimmers, respectively.

From the comparison of MMD of liquid products obtained by ethanol lignin depolymerization at 300 °C over catalysts NiCu/SiO2 and NiCuMo/SiO2 it follows, that the introduction of molybdenum in the catalyst promotes the formation of monomeric guaiacyl products.