Fluidized bed catalytic pyrolysis of eucalyptus over hzsm-5: effect of acid density and gallium modification on catalyst deactivation

Authors: Mullen, Charles; Tarves, Paul; RAYMUNDO, LUCAS - Federal University Of Rio Grande Do Sul; SCHULTZ, EMERSON - Embrapa; Boateng, Akwasi; TRIERWELLER, JORGE - Federal University Of Rio Grande Do Sul

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2017
Publication Date: 4/1/2018
Citation: Mullen, C.A., Tarves, P.C., Raymundo, L.M., Schultz, E.L., Boateng, A.A., Trierweller, J.O. 2018. Fluidized bed catalytic pyrolysis of eucalyptus over hzsm-5: effect of acid density and gallium modification on catalyst deactivation. Energy and Fuels. 32:1771-1778.

Interpretive Summary: Biomass, such as crop residues, herbaceous grasses and woody materials, is the largest cellulosic based source available. These types of biomass can be readily converted to liquids, known as bio-oil, by rapid heating in the absence of air, otherwise known as fast pyrolysis. Bio-oil is considered a potential intermediate to hydrocarbon drop-in bio-fuels that could be produced at petroleum refineries. However, bio-oils are not yet completely compatible with crude oils or refinery infrastructure. This is mostly due to the high concentration of reactive oxygenated compounds found in the bio-oil that make it thermally unstable. One method for reducing the amount of these oxygenated compounds in the bio-oil is to perform the pyrolysis process in the presence of a catalyst, a material that alters the chemical reactions occurring to remove oxygen as carbon oxide gases and/or water, leaving behind crude-oil compatible hydrocarbons. This process is called catalytic fast pyrolysis (CFP). The catalysts used are often zeolites, acidic materials with a specific pore shape ideal for producing aromatic hydrocarbons. One problem with CFP, is that the catalyst can become less effective with use of only relatively small amounts biomass because the biomass leaves coke deposits on the catalyst. In this work we performed CFP on eucalyptus wood using three variations of the standard catalyst, a zeolite called HZSM-5. One variation was to modify the catalyst with the addition of gallium. This proved very effective at lengthening the catalyst lifetime, and we found that significant deoxygenation of this bio-oil still occurred with this catalyst at least two times longer than the standard catalyst. This information will be useful for anyone considering development of a biomass pyrolysis based biorefinery.

Technical Abstract: Catalytic fast pyrolysis of eucalyptus wood was performed on a continuous laboratory scale fluidized bed fast pyrolysis system. Catalytic activity was monitored from use of fresh catalyst up to a cumulative biomass to catalyst ratio (B/C) of 4/1 over extruded pellets of three different ZSM-5 catalysts by tracking CO, CO2, H2, C2H4 production and bio-oil quality. The catalysts employed were extruded HZSM-5 with two different silica to alumina ratios (30 and 80) as well as one modified with Ga (SiO2/Al2O3 = 30) by ion exchange which was reduced under H2 prior to pyrolysis. The deactivation of the catalysts over the course of the experiment was reflected in the decline in deoxygenation activity following the order HZSM-5 (30) > HZSM-5 (80) > GaZSM-5 (30). HZSM-5 (30) lost most of its activity before cumulative B/C of 2/1 was reached, while HZSM-5 (80) still showed significant deoxygenated activity at this exposure level. GaZSM-5 (30) still showed deoxygenation activity at B/C of > 4/1. The improvement exhibited by HZSM-5 with increasing SiO2/Al2O3 ratio was attributed to reduced acid site density that decreased the propensity for coke formation due to reactions occurring between substrates at adjacent active acid sites. For the reduced GaZSM-5, initial dehydrogenation activity aided in the production of aromatics by the olefin oligomerization and aromatization route up to C/B of approximately 1.5/1 after which the Ga became completely oxidized; however, the oxidized GaZSM-5 catalyst continued to exhibit improved decarbonylation and decarboxylation activity.