Catalytic fast pyrolysis of walnut shell with K/AC catalyst for the production of phenolic-rich bio-oil

Potassium supported on commercial activated carbon (K/AC) catalysts were prepared and used for catalytic fast pyrolysis (CFP) of walnut shell to produce phenolic-rich bio-oil. Pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) and fixed-bed CFP tests were performed to reveal the influences of pyrolytic temperature, potassium loading and catalyst-to-biomass (C-to-B) ratio on the product distribution. The Py–GC/MS results showed that the K5.79/AC catalyst in which the potassium loading was 5.79% exhibited the maximal improvement on the yield of phenolic compounds. Pyrolytic temperature significantly affected the total phenolic yield, which achieved the maximum value at 450 °C whether with or without catalysts. Moreover, the C-to-B ratio also dramatically affected the yield of phenolic compounds. The total phenolic yield raised with increasing C-to-B ratio, whereas the excessive C-to-B ratio (higher than 3:1) would lead to an obvious decrease in total phenolic yield. Overall, the yield of total phenolic compounds achieved the maximum value of 145.65 mg/g (14.57 wt%) at 450 °C under C-to-B ratio of 3:1 in Py–GC/MS runs. Meanwhile, the lab-scale experiments obtained the maximal total phenolic yield of 135.13 mg/g (13.51 wt%) at 450 °C under C-to-B ratio of 1:3.