Production of guaiacols via catalytic fast pyrolysis of alkali lignin using titania, zirconia and ceria

The present study is focused on unlocking value added phenolics such as guaiacol and its derivatives from alkali lignin via in situ catalytic fast pyrolysis using TiO2, CeO2 and ZrO2. TiO2 was synthesized by sol-gel technique and calcined at different temperatures, and CeO2 and ZrO2 were synthesized using combustion synthesis protocol. The catalysts were characterized using powder X-ray diffraction, pore size distribution and Fourier transform infrared spectroscopy. Fast pyrolysis of physical mixtures of lignin and the catalysts were conducted in a micropyrolyzer and the products were analyzed using gas chromatography-mass spectrometry (GC/MS). Seventeen phenolic compounds were quantified using pure standards. Guaiacol, methyl guaiacol, ethyl guaiacol, vinyl guaiacol and isoeugenol were the major phenolics produced at 500 °C during catalytic fast pyrolysis. The yield of guaiacols with different catalysts followed the trend: sol-gel TiO2 (36-37 wt.%) > ZrO2 ≈ CeO2 (∼29 wt.%) > Aeroxide TiO2 (26 wt.%) > non-catalytic (18 wt.%). The high selectivity of TiO2 to guaiacols is attributed to multiple interdependent properties such as presence of surface hydroxyl groups, favourable pore size distribution and crystalline phase.