Conversion of the Estonian fossil and renewable feedstocks in the medium of supercritical water

Two different Estonian oil shales, peat, and willow biomass were submitted to supercritical water conversion at unified operating conditions. The yield and chemical composition of conversion products were investigated by chromatographic, FTIR-spectroscopic and ultimate analysis techniques. The results reveal significant difference in products yield and composition those depending on the feedstock origin and its chemical composition. Common and specific features in conversion of fossil and renewable matter were described. The maximum and the minimum oil yield per organic matter, 62.7 and 18.6%, respectively, were obtained in conversion of oil shales. Willow biomass conversion resulted in the highest yield of gas and water (50%). The solubility of oils despite original feedstock increases with solvents used in the raw: dimethyl ketone < water < benzene. The investigation on group composition of the benzene-soluble compounds demonstrated that various oxygen compounds dominate over hydrocarbons in all cases. The majority of hydrocarbons was represented by polycyclic aromatic ones. Aliphatic hydrocarbons, making 6–11% of the benzene-soluble oil were represented by n-alkanes up to C33. Conversion gases, especially those of peat and willow were characterized by high carbon dioxide content. Supercritical water conversion can be used as an alternative method for the liquefaction and gasification of different feedstocks.