Catalytic Fast Pyrolysis of Aspen Lignin Via Py-GC/MS

Aspen lignin extracted by an organosolv process was pyrolyzed in the presence of catalysts and analyzed using Py-GC/MS. The pyrolysis products detected are mostly aromatic hydrocarbons and phenolic compounds. The lignin and catalysts were either mixed or arranged in layers.  Two different micro-porous zeolite catalysts, HZSM-5 and HY, were compared in the study. The effects of the catalysts on the production of aromatic hydrocarbons and phenolic compounds were assessed quantitatively. The HZSM-5 catalyst was found to produce from 2.5 to 40 times more aromatic hydrocarbons than the HY catalyst, by converting  phenolic compounds into aromatic hydrocarbons.  For the HY catalyst, the effect of the catalyst placement is dependent on the catalyst/lignin ratio.For the HZSM-5 catalyst, the effects of placement of catalyst were not as pronounced as were for HY. The data suggest that for any catalyst type and placement there exists an optimum catalyst-to-lignin ratio that maximizes the total production of aromatic hydrocarbons and phenolic compounds. For HZSM-5 in the mixture arrangement, a catalyst-to-lignin ratio of 3:1 was found to maximize both the aromatic hydrocarbons and the aggregate sum of aromatic hydrocarbons and phenolic compounds. At this ratio, 23 wt % yield of aromatic hydrocarbons and 28 wt % yield of the aggregate sum were obtained. Also at these conditions, the products detected have a total oxygen content of about 5 wt % and  Higher Heating Value of 46 MJ/kg, roughly the same as gasoline and diesel. Toluene and p-xylene were the two most abundant hydrocarbons formed in the presence of catalysts. Up to 6.6 wt % and 6.3 wt % of the original lignin were converted into toluene and p-xylene, respectively. We estimate that, if all the lignin produced in pulp and paper mills was catalytically pyrolyzed, the amount of toluene produced would be more than 30 wt % of the current annual production of toluene from fossil sources worldwide.