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Lignocellulosic biomass is a green and renewable energy source, and development of methods of biomass valorization is of a great interest for the industry and production of fine chemicals and materials. Biomass consists of three main components: cellulose, hemicellulose and lignin. In order to be able to utilize all components in an efficient way biomass should be fractionated and each component should be separated in a suitable form for further application. Most fractionation processes are focused on the production of cellulose and hemicellulose, and lignin is usually left non-valorised and used for providing heat for a pulp mill. Lignin constitutes up to 35% of wood by mass and the high carbon content of lignin makes it especially valuable for production of fuels and materials. However due to the complexity of lignin structure and tendency for recondensation reactions under fractionation conditions lignin is difficult to valorize. A promising approach is the in-situ conversion of lignin into stabilized monomers during fractionation process. Here we report wood biomass fractionation in continuous flow reactor under hydrogen free conditions. Methanol/water/H3PO4 mixture is used as solvent and Pd/C as a catalyst. Yield of aromatic monomers reaches up 39 wt%, which is close to the theoretical maximum. Main monomers produced from lignin are: 4-n-propylguaiacol, 4-n-propylsyringol, 4-n-propanolguaiacol, 4-n-propanolsyringol and methyl ethers of 4-n-propanolguaiacol and 4-n-propanolsyringol. Catalyst reusability was studied and it was found that catalyst can be used without drop in activity in 5 consecutive runs. Cellulose is almost completely preserved in a pulp after the reaction completion.