Characterization of the lignin obtained by alkaline delignification and ofthe cellulose residue from steam-exploded olive stones

The lignocellulosic by-products (whole stones and seed husks) obtained from pitted table olive and olive oil processing (respectively) were pretreated under various conditions of steam-explosion, with respect to pressure and time and with a dilute solution of sulfuric acid and without previous acid impregnation. The two materials exhibited considerable difference in behavi or. The pre-impregnation of whole stones with low level of acid prior to st eam treatment was necessary to improve the fractionation and the autohydrol ysis of hemicellulose, while the results with seed husks were similar both with and without an acid catalyst. The lignins recovered from water-washed solid residue by alkaline-extraction followed by acidification were charact erized. These lignin preparations from whole stones contained a very high a mount of fat and almost no neutral sugars. The results also showed that the se lignin preparations were guaiacyl-syringyl lignin, similar to exploded h ardwood lignin, with an extensive cleavage of the beta-aryl-ether linkage. The effect of treatment severity on the major physical properties of cellul ose was also investigated. The cellulose fraction derived from steam-explod ed whole stones was rapidly depolymerized as severity increased, leading to a degree of polymerization of 180, at a severity of log R-0 = 4.07. In see d husks, under similar severity conditions, depolymerization of cellulose w as much slower, and only reached a value of 821 (at log R-0 = 4.07) or a va lue of 600 at log R-0 = 4.34 without acid impregnation. The cellulose deriv ed from both steam-exploded materials was moderately crystalline, the relat ive crystallinity index values of seed husks being higher than those of who le stones. The results indicated that the cellulose from seed husks was mor e protected than that of the whole stones in the steam-explosion process, a nd could be used to produce a cellulose with different properties and appli cations depending on severity and on the different treated material. (C) 19 98 Elsevier Science Ltd. All rights reserved.