Aromatic hydrocarbon production via eucalyptus urophylla pyrolysis over several metal modified ZSM-5 catalysts – an analysis by py-GC/MS

Authors: SCHULTZ, EMERSON - Embrapa; Mullen, Charles; Boateng, Akwasi

Submitted to: Energy Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2016
Publication Date: 1/12/2017
Publication URL: https://handle.nal.usda.gov/10113/5642500
Citation: Schultz, E.L., Mullen, C.A., Boateng, A.A. 2017. Aromatic hydrocarbon production via eucalyptus urophylla pyrolysis over several metal modified ZSM-5 catalysts – an analysis by py-GC/MS. Energy Technology. 5:196-204.

Interpretive Summary: The largest source of renewable feedstock to produce green fuels and chemical products is biomass, including crop and forest residues. In Brazil, Eucalyptus is the main forest resource cultivated, which is used to produce pulp for the paper industry and charcoal for the steel industry. However, due to the large amount produced, there is still an excess of Eucalyptus available for other applications, such as production of biofuels and chemicals. A promising process to convert biomass into these products is catalytic fast pyrolysis (CFP), which involves heating the biomass in the absence of oxygen in the presence of a catalyst, to make a liquid called bio-oil that contains less oxygen than that produced form the analogous non-catalytic process. The most effective class of catalysts found to date for CFP are materials called ZSM-5 zeolites whose acidity and microscopic shape make them ideal for producing non-oxygenated compounds called aromatic hydrocarbons, similar to components of petroleum based fuels. We used a method called pyrolysis-gas chromatography py-GC to screen various metal-modified catalysts for conversion of eucalyptus to bio-oil. The catalyst modified with gallium via a process called total ion exchange i.e., complete exchange of the zeolite’s acidic sites (named GaZSM-5 TIEx), yielded the highest amount of aromatic hydrocarbons while the catalysts modified with nickel produced the lowest yield of aromatic hydrocarbons. We found that while gallium modified catalysts were most selective for xylenes, nickel based catalysts were most selective for benzene production with a concurrent increase in methane production. Zinc modified catalysts were the most selective for toluene production. This information will be of value to those considering developing a pyrolysis based biorefinery for the production of fuels and chemicals from eucalyptus or other biomass resources.

Technical Abstract: Metal modified HZSM-5 catalysts were prepared by ion exchange of NH4ZSM-5 (SIO2/Al2O3 = 23) using gallium, molybdenum, nickel and zinc, and their combinations thereof. The prepared catalysts were used to evaluate catalytic pyrolysis for the conversion of Eucalyptus urophylla to fuels and chemicals, specifically aromatic hydrocarbons, in a microscale pyrolysis reactor coupled with gas chromatography-mass spectrometry (py-GC/MS). Two different biomass to catalyst ratios (1:5 and 1:10, w:w) were studied. The catalyst prepared with gallium via total ion exchange (GaZSM-5 TIEx) yielded the highest amount of aromatic hydrocarbons, while the catalysts modified with Ni produced the lowest yield of aromatic hydrocarbons. A correlation between methane yield, benzene and p-xylene selectivity was found for the catalysts, what can be observed mainly for nickel, zinc and gallium-nickel catalysts. Gallium modified catalysts were most selective for xylenes, while Ni based catalysts were most selective for benzene production with a concurrent increase in methane production. Zinc modified catalysts were the most selective for toluene production.