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Title: Comparison of different pretreatments for birch bark: towards more efficient biorefinery.

The current situation Currently, the energy demand in Europe is that energy demand is constantly increasing, and fossil-based fuels are running outthis leads to increasement of the energy insecurity in Europe. In order to fulfill the energy demands also in the future, some new technologies and innovations will need to take place. The use of biomass as a feedstock for energy and other valuable products has been a point of interest for several years now. Also, when considering the European Union’s targeted energy policies, among the national bioeconomy strategies, utilization of biomass seems promising. Pretreatment of biomass is targeting to decompose large molecules in biomass. By cleavage of bonds and fragmentation, the biomass is tried to separate to different fractions. In this study, three different pretreatment methods were studied , and the in order to find the best alternative for bark residue. The formed fractions were identified by using Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The used methods are the following: 1st Steam explosion (SE), 2nd hydrothermal pretreatment (HT) and 3rd organosolv treatment (OS). As a process SE and HT are quite similar, the only difference is that in HT the water is in a liquid form instead of vapor. In OS, organic solvents are used to drive the reaction. The feedstock in this study was silver birch bark (petula pendula), which was obtained from Sweden. Each pretreatment resulted two fractions, solid and liquid. After the FTIR and NMR data was were analyzed, it was noticed that in all pretreatments the total amount of phenolic compounds and extractives was lowered in solid residue. In turn, the concentration of mentioned compound groups in the liquid fraction was increased. The amount of lignin remained unchanged in SE and HT treatments. However, in OS treatment the increased share on lignin was detected in the liquid fraction. This was considered to be related to the nonpolar behavior of lignin, since organic solvents are nonpolar, they have an ability to dissolve nonpolar components.