Hydrothermal processing of rice husks: effects of severity on product distribution

• Published in: Journal of chemical technology and biotechnology (1986) Vol. 83; no. 7; pp. 965 - 972
• Main Authors: Vegas, Rodolfo, Kabel, Mirjam, Schols, Henk A., Alonso, J. L., Parajó, J.C.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.07.2008; Wiley
• Subjects: acids; Applied sciences; autohydrolysis; biomass fractionation; Chemical engineering; Exact sciences and technology; Ion exchange; kinetics; lignocellulosic materials; Oryza sativa; product distribution; rice husks; wood; xylo-oligosaccharides; biomass fractionation; product distribution; Molecular weight distribution; Reaction product; Polymerization; Desorption; Biomass; Rice by product; Gel permeation chromatography; Vegetal waste; Refining; Laser; Breakdown; Ion exchange; rice husks; Mass spectrometry; autohydrolysis; Speciation; xylo-oligosaccharides
• ISSN: 0268-2575; 1097-4660
• DOI: 10.1002/jctb.1896

BACKGROUND: Treatment in aqueous media (hydrothermal or autohydrolysis reactions) is an environmentally friendly technology for fractionating lignocellulosic materials. Rice husks were subjected to hydrothermal processing under a variety of operational conditions to cause the selective breakdown of xylan chains, in order to assess the effects of reaction severity on the distribution of reaction products. RESULTS: The effects of severity (measured by the severity factor, R0) on the concentrations of the major autohydrolysis products (monosaccharides, xylo‐ and glucooligosaccharides, xylooligosaccharide substituents, acetic acid, acid‐soluble lignin and elemental nitrogen) were assessed. The interrelationship between the severity of treatment and molecular weight distribution was established by high‐performance size‐exclusion chromatography. Selected samples were subjected to refining treatments as ethyl acetate extraction and ion exchange for refining purposes, and the concentrates were assayed by high‐performance anion‐exchange chromatography and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. CONCLUSIONS The protein equivalent of the products present in liquors accounted for 43 to 51% of the protein present in the raw rice husks. The concentrations of glucose (derived from starchy material) and arabinose (split from the xylan backbone) were fairly constant with severity. Even in treatments at low severity, high molecular weight compounds derived from xylan accounted for a limited part of the stoichiometric amount. Operating under harsh conditions, about 50% of the total xylan‐derived compounds corresponded to fractions with a degree of polymerization (DP) < 9. After refining, saccharides accounted for more than 90% of the non‐volatile components of the sample. The refined products showed a series of xylose oligomers up to about DP 13, and a series of acetylated xylose oligomers up to about DP 15. Copyright © 2008 Society of Chemical Industry