Аннотация:Direct ozonation of wood is considered as a pretreatment of vegetable raw materials with the aim of a subsequent cellulose, monocaccharides and bioethanol processing. The process of ozone absorption by aspen (Populus tremula) and pine (Pinus sylvestris) wood was investigated.
Yields of ozonized wood, water-insoluble wood ozonation product (WOP), water- soluble ozonation products, holocellulose and cellulose were found. The lignin and cellulose content in WOP was determined. Both WOP and cellulose samples were studied by the IR spectroscopy method. The degree of polymerization (DP) of cellulose obtained from ozonized wood was found.
It is shown that ozonation results in delignification of wood. The delignification degree of 93% was achieved by ozonation of aspen wood. At the same time DP of cellulose decreases from 700 to 220. Data on holocellulose yields show that hemicelluloses are also destructed during wood ozonation [2]. Delignification degree of pine wood under ozone impact achieves 65-70%, accompanying by decrease of cellulose DP from 750 to 510.
Water soluble products were investigated by means of UV and HPLC methods. Ozonation of aspen and pine wood results in formation of byproducts of lignin aromatics destruction by ozone (formic, glyoxylic, oxalic, malic acids, etc.). At the same time water soluble aromatic compounds (carbonyl- and carboxyl- derivatives of guaiacol) were found in products of wood ozonation. In the case of pine wood the content of byproducts is three times as large as that of aspen.
Wood degradation enhances as the specific ozone consumption increases. Lignin degrades first of all followed by hemicelluloses. It was shown that cellulose, characterized by the most resistance structure, is also subject to degradation during ozonation of wood.
The yield of cellulose, average degree of polymerization, and supramolecular structure depend on initial MC of wood. The variation of MC allows controlling the properties of the cellulose obtained from the wood treated with ozone. The moisture content of 55% (aspen) and 60% (pine) corresponds to the most effective ozonation process accompanied by the most prominent wood structure transformation.
It is supposed that the wood transformation is caused by reactions of molecular ozone, as well as radical species generated in the course of ozone reactions with water present in the wood structure.