Two ways of catalytic depolymerization of native and isolated wood lignins are described: the peroxide delignification of hardwood (aspen, birch) and softwood (abies) in the medium of acetic acidwater over TiO 2 catalyst and the thermal dissolution of organosolv lignins (ethanol-lignin and acetone-lignin) in supercritical alcohols (ethanol and butanol) over solid Ni-containing catalysts. The catalyst TiO 2 in rutile modification has the higher activity in wood peroxide delignification at 100°C as compared to TiO 2 in anatase modification. The results of kinetic studies and optimization of the processes of peroxide depolymerization of hardwood (aspen, birch) and softwood (abies) lignins in the medium of acetic acidwater over catalyst TiO 2 (rutile) at mild conditions (≤ 100°C, atmospheric pressure) are compared. The catalyst TiO 2 initiates the formation of OH • and OOH • radicals from H 2 O 2 which promote the oxidative fragmentation of wood lignin. In this case, the peroxide depolymerization of softwood lignin, constructed from phenylpropane units of guaiacyl-type proceeds more difficult than the hardwood lignins, mainly containing syringyl-type units. The solid and soluble products of peroxide catalytic delignification of wood under the optimized conditions were studied by FTIR, XRD, GC-MS and chemical methods. Regardless of the nature of wood the cellulosic products have a structure similar to microcrystalline cellulose. The soluble products mainly consist of monosaccharides and organic acids. Aromatic compounds are present only in a low amount which indicates the oxidative degradation of aromatic rings of lignin phenylpropane units under the used conditions of wood catalytic delignification. The processes of thermal dissolution of acetone-lignin and ethanol-lignin from aspenwood in supercritical ethanol and butanol over Ni-containing catalyst (NiCu/SiO 2 , NiCuMo/SiO 2) are compared. The composition, structure and thermal properties of organosolv lignins were studied with the use of FTIR, GPC, 1 H-13 C HSQC NMR, DTA and elemental analysis. The influence of a composition of Ni-containing catalyst on the thermal conversion in supercritical butanol and ethanol of ethanol-lignin and acetone-lignin was established. The highest conversion of lignins (to 93% wt.) in supercritical alcohols and the highest yield of liquid products (to 90 % wt.) were achieved at 300 °C in the presence of catalyst NiCuMo/SiO 2. Scheme of green biorefinery of wood based on the use of non-toxic and low-toxic reagents (H 2 O 2 , H 2 O, acetic acid, ethanol, butanol) and solid catalysts (TiO 2 , NiCuMo/SiO 2) is suggested.
Catalytic hydrogenolysis in the medium of supercritical organic solvents is a promising way of wood lignins depolymerization into liquid products.In this study, for the first time, the catalytic properties of bifunctional catalysts Ru/C, Pt/ZrO 2 , NiCuMo/SiO 2 , containing nanosized metal particles on acidic supports are compared in the processes of aspen wood and ethanol lignin hydrogenolysis in supercritical ethanol.The most active catalysts are Ru/C and Pt/ZrO 2 which provide the high conversion of wood (to 78 wt%), significant yield of liquid products (to 50.6 wt%) and low yield of solid rest (to 22 wt%) at temperature 250 °C and H 2 pressure 9 MPa. These catalysts increase the yield of monomeric compounds in liquid products from 9.5 % to 42.9 % on mass of lignin.GC-MS analysis shows that alkyl derivatives of methoxyphenols (mainly propyl syringol and propyl quaiacol) are dominated in liquid products. Solid products of aspen wood catalytic hydrogenolysis contain mainly cellulose (to 82.2 wt%). Therefore, the catalytic hydrogenolysis in supercritical ethanol in the presence of by functional catalysts Ru/C and Pt/ZrO 2 allows to fractionate the aspen wood biomass on cellulose and liquid products enriched with propyl siringol and propyl quaiacol.In catalytic hydrogenolysis of ethanol lignin the yield of alkyl derivatives of methoxyphenols is lower compared to wood. This is probably due to the reduced content of reactive -O-4 bonds in the structure of ethanol lignin compared to native lignin of aspen wood. As follows from the results obtained, native lignin of wood is easier depolymerized to monomeric compounds in the process of catalytic hydrogenolysis than ethanol lignin, isolated from wood.According to GPC data, the catalysts shift to the region of lower molecular mass the molecular mass distribution of liquid products of aspen wood and ethanol lignin hydrogenolysis.
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