The effect of solvent and input material pretreatment on product yield and composition of bio-oils from lignin solvolysis

Solvolytic conversion of lignin from wood with formic acid as a hydrogen donor can provide a renewable source of aromatic compounds, especially phenols. In this paper, lignin or lignin-enriched fractions from Norway spruce and white birch are compared with regard to yields of bio-oil in solvolytic conversion. Water as a green solvent is also compared to ethanol as the reaction medium, and the yields and composition of the produced oils are presented. Maximum yields by weight are inversely connected to the oxygen content of the feedstock, showing that pure lignins give the highest yields while carbohydrate-containing feedstocks undergo more deoxygenation and thus give lower yields. The overall composition of the bio-oils produced is quite stable and independent of the feedstock type and pretreatment, though some difference in the quantitative distribution of the individual components is observed. The use of water or ethanol as reaction media has a significant impact on the bio-oil yields and composition due to the alkylation of the aromatic rings by the ethyl group from the solvent.