Recent developments in lignin separation processes have enabled efficient recovery of lignin from pulping liquors in industrial quantities. Therefore, the availability of lignin demands for effective utilization to value added applications such as bio-oil containing monoaromatic phenols. Utilizing lignin as a raw material for bio-oil production is challenging due to structural variation in isolated lignins. Hence, it is important to investigate the effect of lignin structure on the production of bio-oils. Within the structure of native lignin, β-O-4 bond is the most abundant linkage and cleavage of this bond is considered to be the most important for producing monoaromatic phenols. This research analysed bio-oil produced from various lignins isolated from harwoods and softwoods with different pulping methods (organosolv, kraft and soda-anthraquinone) in relation to their structure. All lignin samples were characterized with 13C NMR for obtaining important information on structural moieties such as β-O-4 content, methoxy groups, carbonyl groups and aliphatic chains. In a typical experiment, lignin (5 g) was mixed with distilled water (200 mL) prior to carrying out depolymerisation at 310 °C for 120 min (Parr reactor) in the presence of formic acid (5 g) and Ru/γ-Al2O3 (0.5 g). Bio-oil was extracted from the aqueous reaction mixture with ethyl acetate followed by drying. Monoaromatic compounds were quantified with GC-MS and molar mass distribution of bio-oil samples was analyzed with GPC. The results of β-O-4 content in isolated lignin samples obtained in 13C NMR lignin and respective bio-oil yields from depolymerisation experiments are as follows: Eucalyptus organosolv lignin (β-O-4 content = 8 moieties per 100 Ar), 17 wt % bio-oil. Beech organosolv lignin (β-O-4 content = 22 moieties per 100 Ar), 16 wt % bio-oil. Softwood kraft lignin (β-O-4 content = 8 moieties per 100 Ar), 15 wt % bio-oil. Softwood soda-anthraquinone lignin (β-O-4 content was 2 moieties per 100 Ar), 11 wt % bio-oil. Based on above results it is plausible to say that bio-oil yield does not solely dependent on β-O-4 content of lignins. In addition, the results obtained from GC-MS characterization of bio-oils showed that composition of bio-oil samples does not vary significantly with applied pulping techniques but only dependent upon the type of wood (i.e. hardwood or softwood). Weight average molar mass distribution of all bio-oil samples were in narrow molar mass range (215 – 245 g / mol).

Conversion of various lignins to bio-oil through depolymerisation: Comparative analysis

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.