title: Kinetics and mechanism of autohydrolysis of hardwoods.
abstract: Autohydrolysis using water is a promising method to extract hemicelluloses from wood prior to pulping in order to make co-products such as ethanol and acetic acid besides pulp. Many studies have been carried out on the kinetics and mechanism of autohydrolysis using batch reactors. The present study was performed in a continuous mixed flow reactor where the wood chips are retained in a basket inside the reactor. This reactor is well suited to determine intrinsic kinetics of hemicellulose dissolution because the dissolved products are rapidly removed from the reactor, thus minimizing further hydrolysis and degradation of the hemicelluloses in solution. The xylan removal rate follows an S-shaped behavior. GPC analysis of the continuously removed extract shows that the dissolved xylan oligomers have a DP smaller than about 25. Lignin-free xylan oligomers and cellulose oligomers are the major components dissolved in the initial stage of autohydrolysis, while xylan covalently bound to lignin (i.e. an LCC) is the major component removed during the later stage of autohydrolysis. The molecular weight of the dissolved components decreases with time in the second stage. The kinetics of xylan removal are explained in terms of a mechanism based on recent knowledge of the ultrastructure of the cell fibre wall.
authors.affiliation: National Biology Center, National Renewable Energy Lab, 1617 Cole Blvd., Golden, CO 80401, USA. Xiaowen.Chen@nrel.gov
authors.forename: Xiaowen
authors.initials: X
authors.lastname: Chen
authors.forename: Martin
authors.initials: M
authors.lastname: Lawoko
authors.forename: Adriaan van
authors.initials: Av
authors.lastname: Heiningen
mesh_terms: D000107:Acetylation; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008970:Molecular Weight; D014934:Wood