Production of monomeric phenols by formic acid assisted hydrous liquefaction of lignin

Abstract On the one hand, lignin has long been recognised as a possible, promising source material for the production of biogenic chemicals and materials, fine chemicals, bio-fuels and fuel blending constituents due to its broad availability potential and its chemical structure. On the other hand, extensive research over a long period of time has revealed the challenges connected to slow, medium and fast pyrolysis of lignin as well as lignin liquefaction. However, a recently developed thermochemical solvolytic process based on a cheap and environmental friendly solvent system consisting of formic acid (FA) and water provides efficient lignin liquefaction. The lignin derived bio-liquid differs significantly from classical pyrolysis bio-oils in terms of chemical composition. It is formed in high yield and with excellent reproducibility, and an almost quantitative material balance has been accomplished for the liquefaction process. The carbon efficiency for the conversion from lignin to oil has been determined to be up to 96%. Qualitative analysis reveals that the produced liquid consists of a wide variety of monomeric phenols in addition to minor amounts of a nonpolar hydrocarbon fraction. The phenolic fraction can be isolated and quantified, and the yield of the produced monomeric phenols is as high as 50% of the original lignin input. The majority of these compounds have been identified, and have structures of high value from an industrial perspective. These results facilitate a target-oriented approach of the utilisation of world's second largest biomass resource, lignin, towards the production of valuable chemicals.