OPTIMIZING MULTISTEPS MECHANICAL-CHEMICAL FRACTIONATION OF WHEAT-STRAW COMPONENTS

Wheat straw was refined into fibres, hemicellulosic sugars and lignin oligomers by means of a multi-stage fractionation treatment: mechanica l separation of the botanical components followed by one or two stage chemical fractionation process. Yellow winter wheat straw was initiall y separated into two fractions by milling in a Disc Mill: (a) chips, c ontaining mostly internodes and (b) meal, consisting mainly of ground leaves and nodes. The internode fraction (63% of the whole straw) cont ained 8% more cellulose, 9% more lignin and 10% less ash compared with the unfractionated material. Disc mill fractionation was particularly effective with respect to the separation of the non-lignocellulosic c omponents, i.e. protein, extractives, etc. Wheat straw internodes as w ell as whole straw were treated with acidic or alkaline aqueous ethano l in one or two stages; two-stage treatment involved the introduction of a pretreatment step with dilute acid improving, both, the productio n of hemicellulose derived sugars, and the aqueous-ethanol delignifica tion to follow. The fibre yield in the case of internode chemical frac tionation was generally higher in comparison with the one of the whole straw. The fibrous fractionation residues from internodes were in all cases enriched in cellulose compared with whole straw fibres. In spit e of the higher initial lignin content of the internodes, delignificat ion was more extensive than in the case of whole straw. Moreover, vari ations in the residual lignin composition were found, reflecting the i ntensity of the chemical fractionation process, as well as the origin of the raw material. (C) 1998 Elsevier Science B.V.