Effect of ZSM-5 acidity on aromatic product selectivity during upgrading of pine pyrolysis vapors

Abstract

The impact of catalyst acidity on the selectivity of upgraded biomass pyrolysis products was studied by passing pine pyrolysis vapors over five ZSM-5 catalysts of varying acidity at 500°C. The SiO 2 -to-Al 2 O 3 ratio (SAR) of the ZSM-5 zeolite was varied from 23 to 280 to control the acidity of the catalyst and the composition of upgraded products. The upgraded product stream was analyzed by GCMS. Additionally, catalysts were characterized using temperature programmed desorption, diffuse-reflectance FTIR spectroscopy, N 2 physisorption, and X-ray diffraction. The results showed that the biomass pyrolysis vapors were highly deoxygenated to form a slate of aromatic hydrocarbons over all of the tested ZSM-5 catalysts. As the overall acidity of the ZSM-5 increased the selectivity towards alkylated (substituted) aromatics (e.g., xylene, dimethylnaphthalene, and methyl-anthracene) decreased while the selectivity towards unsubstituted aromatics (e.g., benzene, naphthalene, and anthracene) increased. Additionally, the selectivity towards polycyclic aromatic compounds (2-ring and 3-ring) increased as catalyst acidity increased, corresponding to a decrease in acid site spacing. The increased selectivity towards less substituted polycyclic aromatic compounds with increasing acidity is related to the relative rates of cyclization and alkylation reactions within the zeolite structure. As the acid site concentration increases and sites become closer to each other, the formation of additional cyclization products occurs at a greater rate than alkylated products. The ability to adjust product selectivity within 1-, 2-, and 3ring aromatic families, as well as the degree of substitution, by varying ZSM-5 acidity could have significant benefits in terms creating a slate of upgraded biomass pyrolysis products to meet specific target market demands.

A study of guaiacol, cellulose, and Hinoki wood pyrolysis with silica, ZrO2&TiO2 and ZSM-5 catalysts

“…The increase in aromatic hydrocarbons from ZSM-5 catalyst is often observed in literature [28][29][30]. The ZrO 2 -TiO 2 has pore sizes of 11 nm, 16 nm, and 121 nm, which is much larger than the ZSM-5 catalysts' pore size of 0.58 nm.…”

“…Lower SAR ratios cause higher acidity. However, changing the SAR ratio does not change the overall structure of the catalyst [10]. By using a ZSM-5 catalyst with high SAR ratio of 1500 we can isolate the steric effects of the catalyst and compare it to the ZSM-5 with increased acid strength and acid site density.…”

Biomass pyrolysis: A review of the process development and challenges from initial researches up to the commercialisation stage

“…They concluded that with the increase of the acidity of zeolite, the content of alkylated aromatics decreased. This could be related to the change of the cyclisation and alkylation reactions [317] .…”

Hydrocarbon Production from Catalytic Pyrolysis-GC/MS of Sacha Inchi Residues Using SBA-15 Derived from Coal Fly Ash

“…In this work, product selectivity is based on percentages of relative peak area of each compound to the total peak areas obtained from the chromatogram as shown in Equation (1) [24]. In this study, the GC set-up did not allow for the separation and quantification of the light gases (e.g., H 2 , H 2 O, CH 4 , CO, CO 2 , C 2 , C 3 ) [39]. For each catalyst, the Py-GC/MS experiment was conducted three times to confirm the reproducibility of pyrolysis products.…”