Title
A three-stage Klason method for more accurate determinations of hardwood lignin content
Authors
DANIEL J. NICHOLSON AARON T. LEAVITT and RAYMOND C. FRANCIS

Received July 20, 2013
Published Volume 48 Issue 1-2 January-February
Keywords hardwoods, lignin content, sulfuric acid hydrolysis, acid insoluble lignin, acid soluble lignin

Abstract
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.