Catalytic cracking of lignin model compounds and degraded lignin dissolved in inert solvent over mixed catalyst of iron oxide and MFI zeolite for phenol recovery

The catalytic cracking of guaiacol and bibenzyl as lignin model compounds, and degraded lignin, which was obtained through treatment in water/1-butanol co-solvent with silica-alumina, was investigated. During cracking of guaiacol over TiO2-FeOX catalyst using 1-butanol as a solvent, which was employed in the original treatment, 1-butanol reacted, decreasing product selectivity. In contrast, benzene as a solvent did not react, exhibiting a reasonable material balance. In the catalytic cracking of bibenzyl dissolved benzene solvent over TiO2-FeOX and MFI-type zeolite catalysts, MFI slightly exhibited carbon-carbon bond cleavage of bibenzyl. However, the degraded lignin did not dissolve in benzene solvent. Therefore, an investigation was done to find a solvent that could dissolve lignin and yet was inert to the catalyst using Hansen solubility parameters and screening tests with a microreactor coupled to a GC/MS instrument. Results suggested lignin had good solubility in quinoline, which also was inert over TiO2-FeOX and MFI-type zeolite catalysts at the reaction temperature of 673 K. A physically mixed catalyst of TiO2-FeOX and MFI-type zeolite was used for catalytic cracking of the degraded lignin dissolved in quinoline to obtain phenol selectively, with 11.5 mol% yield of monomeric phenols and 55.0% phenol selectivity. [Display omitted] •TiO2-FeOX catalyst was effective for guaiacol demethoxylation.•MFI zeolite could slightly decompose bibenzyl to produce monomeric aromatics.•Quinoline, dissolving degraded lignin, was inactive over TiO2-FeOX and MFI zeolite.•Physical mixture of TiO2-FeOX and MFI zeolite is effective for degrading lignin.•11.5 mol% of monomeric phenols was recovered from lignin using the mixed catalyst.