Manageable Conversion of Lignin to Phenolic Chemicals Using a Microwave Reactor in the Presence of Potassium Hydroxide

Sulfonated lignin was converted to phenol and phenolic compounds using a conventional batch or a microwave reactor. In the batch reactor, changing the medium from pure water to an aqueous solution of potassium hydroxide (KOH) dramatically increased the number of liquid products detected by gas chromatography. Similar liquid products were also obtained when a hydrogen peroxide solution was used. In addition to the reaction medium in the batch reactor, the severity factor also plays a critical role in determining the type and the number of liquid products detected. When a microwave reactor was used, lignin conversion resulted in several different liquid products. Of the liquid products, six phenolic compounds (guaiacol, vanillin, homovanillic acid, phenol, acetovanillone, and syringol) were quantitatively analyzed. The mass of the liquid products increased as the temperature increased. Altering the KOH concentration produced mixed results as the amounts of vanillin, acetovanillone, phenol, and syringol decreased, while that of guaiacol increased and homovanillic acid did not change. Thus, the phenolic compounds produced by lignin conversion can be adjusted by varying the operating conditions in a less energy intensive microwave reactor.