O-26　熱分解による縮合型タンニンのケミカルス変換

抄録

The utilization of woody biomass is extremely important for the prevention of global warming and the establishment of a recycling-oriented society. Utilization of condensed tannins contained in bark as useful chemicals is expected to promote the utilization of bark that is not effectively utilized. This study aims to develop a method to convert condensed tannins into high value-added chemicals by pyrolysis. Commercially available mimosa tannin derived from Acacia mollissima bark was purified using Sephadex LH-20. Pyrolysis of tannins was performed by heating in nitrogen or solvent (sulforane or water). Catalytic pyrolysis over Pd/C were also conducted at 280°C in hydrogen or nitrogen using an autoclave with agitator. Pyrolysis in nitrogen at 350°C produced mainly char, with small amounts of resorcinol (4.4 mol%, based on mole of flavanol unit) and catechol (2.5 mol%). Under the catalytic hydrogenolysis conditions, the yield of low molecular weight products increased, although the results varied depending on the solvent used. Resorcinol and an unidentified 4-substituted catechol derivative were obtained in sulfolane, while resorcinol, catechol, and their 4- methylated derivatives were formed in water, indicating that the A and B rings of the tannin flavanol units were released in good yields (up to 30 mol%). Since resorcinol and catechol degraded further in the trial of model experiments, it is necessary to suppress the over-decomposition of the products to further improve the yields. Resorcinol and catechol are expected to replace petroleum-based chemicals for the production of adhesives and pharmaceuticals.