Liquefaction mechanism of lignin in the presence of phenol at elevated temperature without catalysts - Studies on beta-O-4 lignin model compound .3. Multi-condensation

The condensation of the reaction intermediates of GG was traced by using gel permeation chromatography (GPC). It was found that the molecular weights of the reaction products of GG initially increased with the progress of reaction and then gradually approached an equilibrious distribution. The time required to approach the equilibrium was mainly dependent on the reaction temperature, while the molecular weight distribution in the equilibrious state was dominated by the phenol/GG ratio. The self-condensation of the intermediates gave rise to the multi-condensed products with molecular weights ranging from several hundreds to several thousands. The multi-condensed products were characterized by GPC and IR. The results revealed that both the amount of the multi-condensed product and its molecular weight significantly increased with a decrease in the phenol/GG ratio, indicating that phenol played an important role in restraining the self-condensation reaction of the reactive intermediates. IR analysis revealed that the constituent units of the multi-condensed products were similar to those of the reaction intermediates, suggesting that there was no new type of reaction occurring in the formation of the multi-condensed product other than the simple coupling of the reaction intermediates.