A THREE-STAGE KLASON METHOD FOR MORE ACCURATE DETERMINATIONS OF HARDWOOD LIGNIN CONTENT

摘要

A three-stage Klason, or 72 wt% sulfuric acid, method is described for hardwoods. As compared to the traditional two-stage method, the primary hydrolysis (PH) stage was modified to improve mixing of the wood meal into the 72% H2SO4. The PH stage was followed by two 1 h secondary hydrolysis (SH) stages. The 72% H2SO4 slurry was first diluted to 40 wt% H2SO4 and heated at 80 °C then diluted to 3 wt% H2SO4 and refluxed. When equivalent PH stages were used, convincing evidence was obtained showing that the hydrolytic intensity in the cleavage of lignin-carbohydrate complexes (LCC) was much higher for the modified SH stages, as compared to the traditional refluxing of a 3% H2SO4 slurry for 4 h. The accuracy in lignin content determination should be equal or superior for the three-stage method, which takes approximately 2 h less time. Results are presented for 4 hardwoods from 3 different genera.