Green catalytic processing of native and organosolv lignins

Abstract

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.

Production of Aromatic Compounds by Catalytic Depolymerization of Technical and Downstream Biorefinery Lignins

“…Some of the diffusion traces detected in the aliphatic region may also come from C-and O-alkylation under reaction conditions with scEtOH, as it has been previously described [ 39 , 47 , 60 ]. HSQC of SeolA 523 and A 523-Ru in the aliphatic region (see Figure S14 in Supporting Information ) presented cross-peaks that are compatible with alkylated aromatic compounds.…”

Kinetic Studies and Optimization of Heterogeneous Catalytic Oxidation Processes for the Green Biorefinery of Wood

“…In the process of abies wood peroxide delignification in the medium of "formic acid-water" the soluble lignin is formed. In contrast, in the medium "acetic acid-water", lignin undergoes a deep oxidative degradation with the formation of the mixture of organic mono-, dibasic and hydroxy acids [25].…”

Catalytic peroxide fractionation processes for the green biorefinery of wood

“…Optimization was performed with the use of generalized parameter of optimization (W a ) which was calculated as in [23].…”

“…The successful replacement of the dangerous H 2 SO 4 catalyst on non-toxic and non-corrosive TiO 2 catalyst in the process of peroxide fractionation of aspen-wood was demonstrated in[22]. Besides, the similar kinetic regularities of aspenwood peroxide fractionation in the presence of 2 % H 2 SO 4 and 1 % TiO 2 catalysts point on the same mechanism of lignin depolymerization[22].Catalytic properties of TiO 2 samples in anatase and rutile modifications were compared in the process of aspen wood peroxide delignification at 100 °C[23]. At the same process conditions the use of titanium dioxide catalyst in rutile modification with low surface area (2 m 2 /g) gives the cellulosic product with lower content of residual lignin and higher cellulose content, as compared to TiO 2 in anatase modification with higher surface area (89-11 m 2 /g).…”

“…At the same process conditions the use of titanium dioxide catalyst in rutile modification with low surface area (2 m 2 /g) gives the cellulosic product with lower content of residual lignin and higher cellulose content, as compared to TiO 2 in anatase modification with higher surface area (89-11 m 2 /g). The reduced catalytic activity of TiO 2 anatase can be explained by the following reasons[23]. Probably, the smaller size of pores in anatase samples (12.4-13.1 nm) as compared to rutile sample (17.9 nm) reduces their catalytic activity in wood delignification owing to strengthening of diffusion limitations inside pores.…”