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

Journal Article · Sat Nov 14 00:00:00 EST 2015 · Catalysis Today

DOI:https://doi.org/10.1016/j.cattod.2015.10.032· OSTI ID:1251593

Engtrakul, Chaiwat ^[1]; Mukarakate, Calvin ^[2]; Starace, Anne K. ^[2]; Magrini, Kimberly A. ^[2]; Rogers, Allyson K. ^[2]; Yung, Matthew M. ^[2]

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1. National Renewable Energy Lab. (NREL), Golden, CO (United States). Chemistry and Nanoscience Center
2. National Renewable Energy Lab. (NREL), Golden, CO (United States). National Bioenergy Center

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 degrees C. The SiO₂-to-Al₂O₃ 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, N₂ 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 toward alkylated (substituted) aromatics (e.g., xylene, dimethyl-naphthalene, and methyl-anthracene) decreased while the selectivity toward unsubstituted aromatics (e.g., benzene, naphthalene, and anthracene) increased. Additionally, the selectivity toward polycyclic aromatic compounds (2-ring and 3-ring) increased as catalyst acidity increased, corresponding to a decrease in acid site spacing. The increased selectivity toward 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 3-ring 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.

• Research Organization: National Renewable Energy Lab. (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Sustainable Transportation Office. Bioenergy Technologies Office; USDOE Office of Science (SC)
• Grant/Contract Number: AC36-08GO28308
• OSTI ID: 1251593
• Alternate ID(s): OSTI ID: 1373341
• Report Number(s): NREL/JA-5900-65796
• Journal Information: Catalysis Today, Vol. 269, Issue C; ISSN 0920-5861
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

09 BIOMASS FUELS
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
biomass
pyrolysis
vapor phase upgrading
acidity
ZSM-5
zeolite