The functionalization and separation of lignin in lignocellulosics were carried out in the two phase system composed of
p-cresol and 72% sulfuric acid. The key point of this process is that lignin and carbohydrates, which are totally different in structures and reactivities, are modified individually in the different phases : lignin is in the organic phase and carbohydrates in the aqueous phase. During this process, carbohydrates are swollen, followed by partial hydrolysis and dissolution in the acid solution, resulting in the decomposition of interpenetrating polymer network structures in the cell wall. Lignin solvated with cresol contacts with acid for a short time only at the interface between sulfuric acid and cresol, whereby the cleavage of only benzyl aryl ethers and selective phenolation at α -positions occur. These lead native lignins to highly phenolic diphenylmethane type materials which still retain basic structures of native lignin formed by the dehydrogenative polymerization. When the stirring of reaction mixture is stopped at the end of the treatment, the system is separated quickly into the organic phase containing functionalized lignin and the aqueous phase having partially hydrolyzed carbohydrates, as cresol and concentrated sulfuric acid are not mixed at room temperature and their specific gravities are quite different.
The functionalization and quantitative separation of lignin were quickly achieved at room temperature, independent of wood species. The resulting lignophenol derivatives had several distinctive properties which conventional lignins did not have, such as highly phenolic properties, no conjugated system, high solubility, white color, etc. This process would be useful for the functionalization of native lignins and industrial lignins aiming at their effective utilization.
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