Delignification of rye straw using hydrogen peroxide

Alkaline peroxide delignification of rye straw has been first investigated in this paper. The results showed that treatment of dewaxed and water-extracted rye straw with 2% H2O2 at pH 11.5 for 12 h at 20, 30, 40, 50, 60, and 70 degrees C resulted in a dissolution of 52.7, 75.7, 81.8, 83.1, 85.8, and 87.8% of the original lignin, and 44.2, 52.5, 70.0, 70.0, 71.3, and 71.9% of the original hemicelluloses, respectively. The isolated pure lignin fractions contained rather low amounts of neutral sugars, 0.4-1.1%, and had weight-average molecular weights between 2420 and 3480 g mol(-1). They contained almost equal amounts of noncondensed guaiacyl and syringyl units with fewer p-hydroxyphenyl units. The beta-O-4 ether bonds together with beta-beta and beta-5 carbon-carbon linkages were found to be present in the lignin structural units. Hydroxycinnamic acids such as p-coumaric and ferulic acids appeared to be strongly associated to lignin molecules. Comparison of these lignin samples indicated that the alkaline peroxide treatment of the straw under the conditions given did not affect the overall structure of lignin. (C) 2000 Elsevier Science B.V. All rights reserved.