Production of Aromatic Hydrocarbons via Catalytic Pyrolysis of Biomass over Fe-Modified HZSM-5 Zeolites

Iron-modified HZSM-5 catalysts were prepared by partial ion exchange of NH(4)ZSM-5 with Fe(II) at three different loadings (1.4, 2.8 and 4.2 wt %), and their effectiveness for producing aromatic hydrocarbons from cellulose, cellobiose, lignin and switchgrass by catalytic pyrolysis was screened using a microscale pyrolysis reactor coupled with gas chromatographymass spectrometry (py-GC/MS). Two different catalyst to biomass ratios of 10/1 and 5/1 (w/w) were studied to determine the varying effects at full and partial conversion of the primary oxygenated pyrolysis vapors. Among the four catalysts screened (including the parent HZSM-5), the one loaded with iron at 1.4 wt % Fe [Fe-HZSM-5 (1.4)] produced the largest increase in production of aromatic hydrocarbons from cellulose, cellobiose and lignin. From cellulose, a carbon yield of selected aromatics (benzene, toluene, o,p-xylenes, ethylbenzene, 1,2,4-trimethylbenzene, naphthalene and 2-methylnapthalene) of similar to 18% was achieved with Fe-HZSM-5 (1.4), and for cellobiose the carbon yield of selected aromatics using Fe-HZSM-5 (1.4) was 25%. For switchgrass, Fe-HZSM-5 (1.4) catalyst produced a similar carbon yield of aromatics as the standard HZSM-5 (similar to 17%) but higher loadings of Fe decreased the yield. However, for all of the starting materials studied, the chemical selectivity of the aromatic products changed with addition of Fe to the catalyst. Benzene and naphthalenes were favored for the iron containing catalysts compared with the standard HZSM-5, while the selectivities for p-xylene, ethylbenzene and trimethylbenzene were decreased with the addition of iron.