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See detailCatalytic hydroprocessing of lignin under thermal and ultrasound conditions
Finch, Kenneth B.; Richards, Ryan; Richel, Aurore ULg et al

in Catalysis Today (2012), 196

Lignin isolated from Miscanthus x giganteus using acidic (FAL) and alkali (AL) conditions was thereafter subjected to the catalytic depolymerization under thermal or ultrasounds activation. The ... [more ▼]

Lignin isolated from Miscanthus x giganteus using acidic (FAL) and alkali (AL) conditions was thereafter subjected to the catalytic depolymerization under thermal or ultrasounds activation. The characterization of lignins was achieved by thermogravimetric analysis and FTIR. Three different classes of catalysts, containing nickel as active species, have been prepared in this scope: (i) nano-Ni by reduction of NiCl2 with NaBH4 under ultrasonication, (ii) Fe3O4-(NiMgAlO)x and (NiAlO)x by calcination of Mg(Ni)–Al hydrotalcite incorporated Fe3O4 followed by reduction with hydrogen, and (iii) NiO(111) nanosheets by reduction of Ni(NO3)2 with urea in benzyl alcohol. The catalysts were characterized by XRD and XPS techniques. Reduced mixed oxides displayed a moderate activity while a significant increase in conversion (up to 90%) was observed in the presence of nano-Ni(0). NiO(111) nanosheets catalysts performed very close to nano-Ni(0). The conversion and the mass distribution of the reaction products were strongly related to the procedure used for the extraction of ligning. In all the case AL led to a better depolymerization. The performances of the tested catalysts under ultrasound conditions were inferior to those tested under conventional heating conditions. The nature of the solvent was also found to be very important in this process. Thus, ionic liquid [BMIM]OAc led to the best results in autoclave conditions, and methanol under ultrasounds. [less ▲]

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See detailCatalytic conversion of lignin to low molecular weight compounds
Verziu, Marian; Richel, Aurore ULg; Filip, Petru et al

Conference (2011)

Nowadays lignocellulosic materials represent the higher renewable natural resource in the world. These materials consist of 34–50% cellulose, 19–34% hemicellulose and 11–30% lignin. Unlike cellulose ... [more ▼]

Nowadays lignocellulosic materials represent the higher renewable natural resource in the world. These materials consist of 34–50% cellulose, 19–34% hemicellulose and 11–30% lignin. Unlike cellulose, lignin is a three-dimensional aromatic polymer including three main phenylpropane units, namely p-coumaril, coniferyl and sinapyl alcohol which are linked by C-O-C or C-C bonds. To valorize this material it is necessary to achieve its depolymerization to monomers or dimers that typically results from the cleavage of β-O-4 linkages. Literature already reported several approaches to depolymerize lignin using both homogeneous and heterogeneous catalysts. Yuan et all have considered a homogeneous route in this scope using NaOH as catalyst. This solution is however by far non-green leading to no-recyclable wastes. Heterogeneous catalysts offer an alternative. The use of noble metals like Pt or Rh supported on carbon, at 473 K, under H2 pressure, was shown to yield over 50% in monomers and dimers . Cheaper metals as copper represent a more versatile route but the reported example uses high energetic supercritical conditions. The use of inexpensive metals such as Ni may offer another alternative. In this study we propose an inexpensive route presenting results obtained using as active species, nickel in different environments such as NiOx, (NiAl)Ox, (NiMgAl)Ox thus looking also for the effect of basicity in this reaction. These materials were prepared using specific protocols and characterized by several techniques like: XRD, DRIFT, BET, and TEM. The catalysts were tested in autoclave conditions at different temperature (423-473K) under H2 pressure. The lignin was extracted from Miscanthus plants into formic acid / acetic acid / water mixture. Since it is not soluble in water its solubilization was achieved in an [BMIM]OAc ionic liquid, selected from a screening of a series of ILs. On the other side, the analysis of the reaction products is a complicate issue in this chemistry. This was carried out with a chromatographic system equipped with a Detector Triple Quad LC/MS, and a MS Ion Source type, working simultaneously in both APCI and ESI modes. The analysis of the reaction products indicated both polar and less polar compounds with a m/z signal varying from 80 till 900. The population of the different class molecules was carefully analyzed as a function of the nature of the catalyst and the reaction conditions. The higher extent of lignin depolymerization was around 54% and was obtained using a (NiAl)Ox catalyst. Under these conditions the predominant class was that with m/z of 200-300 a.u. Finally the stability of the catalysts was checked looking for their separation and recyclability in several successive cycles. [less ▲]

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