Highly Selective Conversion from Alkali Lignin to Phenolic Products

In order to realize the high value-added utilization of alkali lignin, the catalytic hydrogenolysis of alkali lignin was performed in this study with assistance of formic acid acting as an internal hydrogen donor over the catalyst Ni-ZrO2/gamma-Al2O3 prepared by the chemical reduction method. Effects of temperature, formic acid, and catalyst on the catalytic performance were investigated, and the recyclability for catalyst was also explored. Results showed that increasing the temperature (from 180 to 240 degrees C) and adding catalyst (0.5 g catalyst/g lignin) were beneficial for bio-oil yield, and the presence of FA was advantageous for lignin conversion. Catalytic abilities of catalyst were weakened due to the recycle reflected on a decrease in bio-oil yield. GC/MS analysis showed that the relative content of vanillin was relatively high (65.65%) at 180 degrees C, while that of alkyl G-type phenols was dominant (around 70%) at 240 degrees C. It was interpreted that the prepared catalyst exhibited excellently catalytic selectivity for specific phenolic products, especially for G-type phenols, due to the highly catalytic performance for the cleavage of C-O-C/C-C bonds in alkali lignin.