Renewable chemical feedstocks from integrated liquefaction processing of lignocellulosic materials using microwave energy†

The objective of this investigation was to find a simple method for the production of phenolic rich products and sugar derivatives (biopolyols) via separation of liquefied lingocellulosic materials. Liquefaction of lignocellulosic materials was conducted in methanol at 180 °C for 15 min with the conversion of raw materials at about 75%. After liquefaction, the liquefied products were separated by addition of a sufficient amount of water. It was found that the hydrophobic phenolics could be largely separated from aqueous solutions. The phenolic products that precipitated from the aqueous phase were mainly composed of phenolic derivatives such as 2-methoxy-4-propyl-phenol and 4-hydroxy-3-methoxybenzoic acid methyl ester. Afterwards, the aqueous solution was distilled under vacuum to remove water and formed a viscous liquid product henceforth termed biopolyol. As evidenced by GC-MS analysis, the biopolyols contained methyl sugar derivatives, including methyl β-D-mannofuranoside, methyl α-D-galactopyranoside, methyl α-D-glucopyranoside, and methyl β-D-glucopyranoside. The effect of glycerol on promotion of the liquefaction reaction was also studied. The yield of residue was significantly decreased from approximately 25 to 12% when a glycerol–methanol mixture was used as solvent rather than methanol. According to the GC-MS analysis, the total content of phenolics and poly-hydroxy compounds (including glycerol and sugar derivatives) in phenolic products and biopolyols was 65.9 and 84.9%, respectively. Therefore, a new method for fractionation of liquefied products was proposed according to the molecular structure of the biomass.