Fast pyrolysis of tannins from pine bark as a renewable source of catechols

Fast pyrolysis of water-insoluble (W-I) tannins-mainly composed of condensed tannins-obtained from Pinus radiata bark methanol-water extraction was carried out in pursuit of a renewable source of high-value chemicals, in particular catechols. Micropyrolysis in an isothermal furnace unit (Py-GC-MS/FID) was performed between 450-600 degrees C. Catechin and W-I tannins were compared to establish thermal degradation behavior between this fraction and its representative monomer constituent. Additionally, W-I tannins were compared with typical sources of renewable phenols such as pine bark and organosolv-lignin in order to highlight its potential. Bench-scale experiments of W-I tannins were performed in a fluidized bed reactor between 400-600 degrees C to provide information related to yield and concentration of catechols. The Py-GC-MS/FID results showed that W-I tannins are prolific of catechol and 4-methylcatechol, similar to their most abundant monomer constituent catechin. However, W-I tannins are not only composed of condensed tannins and some substituted polycyclic aromatic hydrocarbons, triterpenes and carbohydrate-derived compounds were detected. The comparison of pyrolysis products among the renewable sources of phenols showed that W-I tannins yielded the highest relative content of catechols while guaiacols and carbohydrate-derived compounds predominated in the composition of lignin and bark products, respectively. The optimal pyrolysis-oil yield for bench scale assays (37 wt%) was found at 550 degrees C and maximum yield of both catechol (4.4 wt%) and 4-methylcatechol (2.3 wt%) were also obtained at 550 degrees C.