The process of liquefying spruce and birch in SCM was achieved in a simple, single-step reaction that occurs in a batch system until the desired conditions are met, over a few minutes as shown in Fig. 13.1.

Under the batch system studied, methanol goes from a fluid density of 0.791 g/l to a density of 0.325 g/l under supercritical conditions, allowing for complete penetration and saturation of the wood particles in the reactor. As the SCM de — polymerizes and solubilizes the major wood components, it reacts with the derived oligomers and monomers, by methanolysis [21, 25]. The mass balance calcula­tions, based on Eq. 13.1, yielded a conversion constant of solid Sitka spruce into bio-oil of 92 wt%, while Alaskan birch yielded 95 wt%.

Residue(%) = W1/W0 x 100 (13.1)

where W0 is the original amount of biomass introduced into the reactor and W1 is the insoluble solids left after supercritical methanol treatment.