Delignification of rye straw using hydrogen peroxide

Abstract

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% H 2O 2 at pH 11.5 for 12 h at 20, 30, 40, 50, 60, and 70°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 β– O–4 ether bonds together with β–β and β–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.