Production of phenols from lignin-derived slurry liquid using iron oxide catalyst

• Phenols were obtained by depolymerization of lignin, followed by catalytic cracking.
• Lignin depolymerization in H2O/BuOH solution produced lignin-derived slurry liquid.
• The reactions of the slurry liquid were investigated under high pressure steam.
• Catechols and methoxyphenols in the slurry liquid were converted into phenols.
• The recovery fraction of phenols increased as the FH2O/FFH2O/F value increased.

A two-step process consisting of depolymerization and catalytic cracking without hydrogen addition was carried out to produce phenols from lignin. In the first step, lignin was depolymerized using a silica-alumina catalyst in a water/1-butanol solution at 623 K for 2 h. After the reaction, lignin-derived slurry liquid was obtained in 67 C-mol% yield. From the model studies, it was considered that lignin was mainly depolymerized via hydrolysis of aryl ether bonds between lignin units. For the second step, the catalytic reaction of the 1-butanol phase of the slurry liquid was carried out over an iron oxide catalyst using a high pressure fixed-bed flow reactor at 673 K. The catalytic reaction under high pressure steam conditions was effective for the suppression of the formation of solid products. In addition, the recovery fraction of phenols increased as the FH2O/FFH2O/F value (the flow rate ratio of steam to the slurry liquid) increased, resulting in 17% of phenols at FH2O/F=5FH2O/F=5 for 2–4 h. From the model studies and our previous results, catechol and methoxyphenol in the slurry liquid were considered to be converted into phenols, cresols and other alkyl phenols over the iron oxide catalyst.

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