Water density effect on lignin gasification over supported noble metal catalysts in supercritical water

Gasification of lignin and 4-propylphenol, which is a model of low-molecular weight compounds from lignin, over supported metal catalysts in supercritical water was studied at 673 K. Supported ruthenium catalysts were active in supercritical water. The catalytic gasification rate was enhanced by the increase of water density. The gasification of lignin proceeded in supercritical water through two steps: (i) decomposition of lignin to low-molecular weight compounds and (ii) gasification of the low-molecular weight compounds over metal catalysts. The rate of 4-propylphenol gasification was not affected by the water density; this was different from lignin gasification. These results indicated that the first step (decomposition to low-molecular weight compounds) in the lignin gasification was enhanced by increasing the water density.