Potential of catalytic oxidation of Kraft black liquor for the production of biosourced compounds

Industrial Kraft black liquor from maritime pine was oxidised in aqueous, alkaline medium, under air, at 150°C, with or without CuO/TiO2 catalyst. The oxidation products were analysed by HPLC, elemental analysis, SEC, FTIR, NMR. The results showed the depolymerisation of lignin, the formation of phenolic compounds in low yields, with vanillin being the main phenolic compound, and the formation of aliphatic compounds in higher yields, with formic, succinic and tartronic acids being the main identified aliphatic compounds. The presence of the catalyst favoured the formation of phenolic and aliphatic compounds. Replacing Kraft black liquor by pure Kraft lignin as a starting material did not improve the performances of the catalytic oxidation, indicating that lignin purification may not be necessary under our conditions. Switching from a batch reactor to a fixed bed reactor, operating under similar conditions, did not increase the yields of oxidation products but did increase the productivity. This work demonstrates the potential of Kraft black liquor to produce a large panel of compounds, including phenolics, aliphatic acids and oxidised lignin, all of which valuable in chemical industry. For the first time, a catalytic process for the chemical valorisation of Kraft black liquor is presented

Depolymerization of Technical Lignins in Supercritical Ethanol: Effects of Lignin Structure and Catalyst

International audienceThree complementary Kraft lignins and a Soda lignin were characterized by NMR (31P, 13C, and HSQC) and GPC. Their theoretical yield in monomers (TMY) assuming a complete cleavage of all β-O-4 linkages was calculated based on these analyses. The most recalcitrant Kraft lignin according to the TMY criteria was depolymerized in supercritical ethanol (250 °C, H2, 110 bar) with Pt/C, Ni/C, and Ru/C catalysts. All catalysts present an important effect on monomers (analyzed by GC/MS), oligomers (by UV fluorescence), and char yields. They promote cracking reactions and the stabilization of the broken bonds by H-transfers. The hydrogenation of the side chains of the monomers is also promoted to notably produce propyl-guaiacol. We show that an oligomeric pool prevails for all catalysts. Then, the effect of lignin structure on the depolymerization mechanism was studied by comparing the 4 lignins with the least precious catalyst (Ni/C). The S/G ratio of monomers is well related to the S/G ratio of lignins. Under our conditions, the β-O-4 content and the TMY do not control the yields in monomers. They are not relevant indicators for the depolymerization of these recalcitrant technical lignins. Future work should focus on novel catalysts and processes to improve the selective conversion of C–C bonds if monomers remain the targeted product

Laccase/HBT and laccase-CBM/HBT treatment of softwood kraft pulp: impact on pulp bleachability and physical properties

Pycnoporus cinnabarinus laccase and a chimeric laccase-CBM were applied in softwood kraft pulp biobleaching in the presence of 1-hydroxybenzotriazole (HBT). The presence of CBM could enhance the laccase biobleaching potential as a decrease in the enzymatic charge and chlorine dioxide consumption, as well as an increase in pulp brightness were observed. Laccase/HBT treatment could be improved by increasing oxygen pressure from 1 to 3bar and pulp consistency from 5% to 10%. Conversely, under the same conditions, no improvement of laccase-CBM/HBT treatment was observed, indicating a different behavior of both systems. However, laccase-CBM/HBT treatment led to a better preservation of pulp properties. This effect was probably due to fiber surface modifications involving the action of the CBM. Transmission electron microscopy examination of pulp fibers indicated a retention of laccase-CBM inside the pulp fibers due to CBM binding and an increased external microfibrillation of the fibers due to enzymatic treatments

Fusion of a family 1 carbohydrate binding module of Aspergillus niger to the Pycnoporus cinnabarinus laccase for efficient softwood kraft pulp biobleaching

International audiencePycnoporus cinnabarinus laccase was fused to the C-terminal linker and carbohydrate binding module (CBM) of Aspergillus niger cellobiohydrolase B (CBHB). The chimeric enzyme of molecular mass 100 kDa was successfully produced in A. niger. Laccase-CBM was further purified to determine its main biochemical properties. The Michaelis-Menten constant and pH activity profile were not modified, but the chimeric enzyme was less thermostable than either the P. cinnabarinus laccase or the recombinant laccase produced in the same strain. Laccase-CBM was able to bind to a cellulosic substrate and, to a greater extent, to softwood kraft pulp. Binding to the pulp was shown to be mainly time and temperature-dependent. Laccase-CBM was further investigated for its softwood kraft pulp biobleaching potential and compared with the P. cinnabarinus laccase. Addition of a CBM was shown to greatly improve the delignification capabilities of the laccase in the presence of 1-hydroxybenzotriazole (HBT). In addition, ClO2 reduction using 5 U of chimeric enzyme per gram of pulp was almost double than that observed using 20 U of P. cinnabarinus laccase per gram of pulp. We demonstrated that conferring a carbohydrate binding capability to the laccase could significantly enhance its biobleaching propertie

Secretome analysis of Phanerochaete chrysosporium strains CIRM-BRFM41 grown on softwood

 Abstract Proteomic analysis was performed to determine and differentiate the composition of the secretomes of Phanerochaete chrysosporium CIRM-BRFM41, a peroxidase hypersecretory strain grown under ligninolytic conditions and on softwood chips under biopulping conditions. Extracellular proteins from both cultures were analyzed by bidimensional gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry. A total of 37 spots were identified. The secretome in liquid synthetic medium comprised mainly peroxidases, while several wood-degrading enzymes and enzymes involved in fungal metabolism were detected in biopulping cultures on softwood. This prompted an analysis of the impact of secretome modulation in the presence of softwood chips. Biotreated wood was submitted to kraft cooking and chemical bleaching using chlorine dioxide. The fungal pre-treatment led to a significant increase in pulp yield and a better bleachability of the pulp. This bleachability improvement could be explained by the production of specific lignocellulose-degrading enzymes