Catalytic Hot-Gas Filtration with a Supported Heteropolyacid Catalyst for Preconditioning Biomass Pyrolysis Vapors

Abstract

During ex situ catalytic fast pyrolysis (CFP) of biomass, the separation of reactive char and alkali/alkaline particulates from biomass pyrolysis vapors by hot-gas filtration (HGF) leads to improved vapor stability and quality. HGF in tandem with chemical tailoring (e.g., partial deoxygenation) of the clean pyrolysis vapors, denoted as catalytic hot-gas filtration (CHGF), has the potential to further improve vapor composition by removing reactive oxygen moieties and protect downstream upgrading catalysts from fouling. Downstream upgrading refers to both vapor phase upgrading (e.g., ex situ CFP) and condensed phase upgrading (e.g., hydrotreating). Consequently, CHGF (as a single unit operation) was evaluated for preconditioning pyrolysis vapors for downstream upgrading processes. In order to understand the effective operating conditions that successfully filter and partially deoxygenate pyrolysis vapors, a titania-supported molybdenum heteropolyacid (Mo-HPA/TiO2) catalyst was studied for use in CHGF. Here, pine pyrolysis vapors were generated in a small pilot-scale pyrolyzer and transferred to a CHGF unit via a continuous-flow slipstream. In the CHGF unit, the pyrolysis vapors were filtered and upgraded over a packed Mo-HPA/TiO2 catalyst bed. Real-time monitoring and identification of the products formed were achieved by molecular beam mass spectrometry. The results showed that under a hydrogen-rich environment, the pine vapors were partially deoxygenated and alkylated over the Mo-HPA/TiO2 catalyst. Reactivity studies revealed that an increase in hydrogen concentration and a reduction in weight-hourly space velocity enhanced deoxygenation and alkylation. Time-on-stream (TOS) studies showed stable product formation up to 1 h with little change in catalyst activity. Additionally, the liquid product was collected using a custom fractional condensation unit (built in-house) and analyzed by gas chromatography mass spectrometry to confirm that the product was partially deoxygenated and alkylated. The combination of CHGF and fractional condensation allowed for chemical and physical removal of both foulant and value-added compounds (e.g., phenols, alkylphenols, methoxyphenols, cyclopentenones) for additional enhancement of downstream upgrading processes. The pre- and postreaction catalysts were characterized using temperature-programmed desorption, N2 physisorption, and elemental analysis with results indicating some catalyst coking. A hydrogen-based catalyst regeneration procedure restored the reacted catalyst activity to that of fresh Mo-HPA/TiO2.

Experimental study of fast pyrolysis vapors fractionation through different staged condensation configurations

“…The observed compositions are in good agreement with other studies, confirming the possibility to tailor the oil composition by varying the temperature of the condensation sections [6,11,19].…”

Bioprocessing Separations Consortium Three-Year Overview: Technical Advances, Process Economics Influence, and State of the Science

“…Figure 26 Filtration and conversion results for various filter materials and catalysts (Peterson et al 2019).…”

“…Another alternative, a titania-supported molybdenum heteropolyacid (Mo-HPA/TiO2) catalyst, was developed in FY 2019 to target further improvements in fast pyrolysis vapor quality. The HPA catalyst demonstrated vapor hydrodeoxygenation by reducing the concentration of reactive species such as sugars and acids, alkylation activity allowing the conversion of lighter molecules to liquid range products, and reduced carbon losses to the aqueous phase (Peterson et al 2019). In summary, the catalyst's performance was promising.…”

Catalytic Conversion of Pyrolysis Oil to Alcohols and Alkanes in Supercritical Methanol over the CuMgAlOx Catalyst

“…The PO was sourced from the National Renewable Energy Laboratory (NREL) and produced using the fast pyrolysis of loblolly pine in a fluidized-bed pyrolyzer at 500 °C under a N 2 atmosphere. 27 After condensation and collection, the PO was kept under a N 2 atmosphere with a layer of dodecane to prevent the oxidation of the PO over time. Reactions with the PO were performed the same day when the PO was mixed with methanol to limit degradation.…”