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 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 catalystto-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% yield of aromatic hydrocarbons and 28% yield of the aggregate sum were obtained. Also at these conditions, the products detected are estimated to have a total oxygen content of about 4% 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% and 6.3% 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% of the current annual production of toluene from fossil sources worldwide. (C) 2013 Elsevier Ltd. All rights reserved.