This paper reports a novel liquefaction process that is capable of depolymerizing the natural biopolymer lignin into a liquid bio-oil with a very low oxygen content, suitable as a blending component to be combined with conventional fossil fuels for motor fuel applications. During the conversion, both depolymerization and removal of oxygen by formation of water occur in a single step. Formic acid serves as both the hydrogen donor and reaction medium in the pyrolysis/solvolysis process. Using an alcohol as cosolvent can improve the liquid yields and H/C ratios. Very little coke (5%) is produced. The liquids produced comprise two easily separable phases, where the lighter organic phase consists mainly of low molecular weight alkylphenols and C8−C10 aliphatics. The process is developed to be combined with ethanol production from lignocellulosic carbohydrates in a biorefinery concept aimed at converting all fractions of the wood into renewably sourced liquid fuels.

Lignin accounts for approximately 25-35 % of the organic matrix of wood and lignocellulosic biomass in itself is the most abundant renewable material on the planet. It has long been recognized as a potential feedstock for producing chemicals, fuels, and materials. Despite this excellent availabilty of lignin it is a low value compound and has so far mainly been used as energy source in combustion applications. Less than 5 % are being processed for other purposes. This article discusses the potential for an increased use of lignin as a renewable raw material, possible conversion routes towards monomeric phenolic compounds, and applications for these products. A brief overview about present state-of-the-art is given and a high-yielding, one-step approach of producing alkylated phenolic compounds from lignin is presented.

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Technical lignins from various sources can be converted into bio-oil with a low O/C ratio by pyrolysis in the presence of formic acid and an alcohol. By application of different analytical techniques, such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI-MS), and size-exclusion chromatography (SEC), it has been shown that a complete degradation of the lignin takes place irrespective of the origin. The resulting bio-oil has a low-molecular-mass distribution with a preponderance of aliphatic hydrocarbon structures. A substantial number of phenolic compounds are, however, also present, and some of these also contain carboxyl groups. The results clearly show that formic acid is a powerful supplier of atomic hydrogen. By further optimization of the pyrolysis reaction, it should be possible to further reduce the content of aromatic structures.