Biomass conversion to bio-oil is evolving as a preferred energy conversion reaction over conventional fossil fuel due to its lower carbon footprint. In this work, lignocellulose biomass from a clean pine was pyrolyzed, and the pyrolysis vapors were upgraded over microporous HZSM-5 zeolite (Si/Al=30) catalyst at 500 °C in a fluidized bed reactor. Porous HZSM-5 is an efficient catalyst converting oxygenated bio-oil to aromatic oil; however, it undergoes rapid deactivation during the conversion process. In this work, we have used electron microscopy and spectroscopy techniques to study the spent zeolite catalysts with SiO<sub>2</sub> binder to understand the deactivation mechanisms. We investigated differences in spent zeolite catalysts that were collected from two different locations of the reactor; (a) vapor-phase upgrading (VPU) vessel (catalyst was collected from the fluidized bed reactor), and (b) receiver for spent catalyst (the catalyst was fed continuously into the fluidized bed and removed via overflow into the receiver). The biomass-to-catalyst feed ratio (B:C) was varied between 1.4 and 2 with the total amount of biomass fed also varied per experiment from 1200 to 2000g. We used a variety of characterization technique such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-Ray spectroscopy (EDS), Raman spectroscopy to study differences between spent HZSM-5 zeolite catalysts as well as fresh and regenerated catalysts. Two types of carbonaceous species were identified in the spent zeolite catalysts: bulk coke, which was present in larger volume not incorporated into the zeolite crystals (zeolite crystals are embedded in the zeolite catalyst particle), and surface coke in the form of a thin film that covered the surface of the zeolite crystals. In addition, some local dealumination was observed at nanoscale level. Moreover, inorganic contaminants such as Na, Mg, Ca were found in local areas, penetrating the zeolite crystals. Thus, our study suggests three different deactivation mechanisms operating on HZSM-5 due to catalytic fast pyrolysis such as coke deposition, dealumination, and inorganic contamination. This work paves the way for studying zeolite deactivation mechanisms using microscopy and spectroscopy techniques.

Study of zeolite deactivation mechanisms due to biomass conversion to biofuel

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