A new approach for bio-oil characterization based on gel permeation chromatography preparative fractionation

Analyzes of bio-oils obtained by direct liquefaction are obstructed by the interferences of the liquefaction solvent. We therefore developed a new analytical approach based on a preparative gel permeation chromatography (GPC) fractionation to remove the solvent from the bio-oil and, if convenient, separate the resulting bio-oil into several fractions according to molecular size. The bio-oils investigated were prepared by liquefaction of pine wood using guaiacol and a guaiacol/water mixture as reaction media. These bio-oils were fractionated and then analyzed by several techniques such as 13C and 1H NMR, FTIR, C:H:O analysis and carbon residue. The results were compared with those of bio-oils produced via hydrothermal liquefaction (liquefaction in water) and fast pyrolysis. The analyzes showed great differences in product distribution, composition and properties of the bio-oil. For instance, the liquefaction oils appeared to be leaner in sugar-like components and richer in aromatic molecules than pyrolysis oil. Moreover, the aromatic content in the liquefaction oils indicated that carbohydrates react to form these type of compounds. In comparison with pyrolysis, liquefaction yielded bio-oils leaner in oxygen, but with higher content of heavies (compounds with apparent molecular weight > 1000 Da). The higher concentration of heavy products resulted in liquefaction oils with higher coking tendency than pyrolysis oil. A ranking of the severity of the reaction conditions for the liquefaction experiments is proposed: Guaiacol < Guaiacol/water < Water.