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Evaluation of Different Sulfur-Free Delignification Methods for Hot-Water Extracted Hardwood

Abstract Hot-water extraction (HWE) of hardwoods may be performed as a part of sequential disintegration of hardwoods in a biorefinery system. In this study, different sulfur-free delignification methods were investigated for their respective effectiveness in lignin removal from unextracted (SM) and hot-water-extracted sugar maple (SMHWE). Peracetic acid and tetrahydrofurfural alcohol were investigated as attractive delignification agents, which may be produced on site (biorefinery products). Oxygen was used in combination with the organic solvents acetone and ethanol, designed sugar fermentation products from hydrolyzed hot-water extracts. The delignification degree and delignification selectivity were compared for SM and SMHWE. SMHWE consistently showed a higher degree of delignification. Also, a higher selectivity was observed in delignification of SMHWE with all investigated agents except peracetic acid. Oxygen delignification in an acetone:water mixture was the most selective in delignification of SMHWE. The delignification results obtained using the acetone-water-oxygen system for sugar maple were confirmed using Eucalyptus (unextracted, Eu, and hot-water-extracted, EuHWE). These results indicate that the structural and chemical changes occurring during HWE of hardwoods provide for a more efficient subsequent delignification with a wide range of delignification agents.