A custom bench-scale continuous-flow catalytic fast-pyrolysis (CFP) reactor system was implemented for the optimization of ex situ CFP and screening of catalysts to gain insight into commercial scale ex situ CFP processes across various reactor types. Operated in an ex situ configuration, tandem laminar entrained-flow pyrolyzer and vapor-phase upgrading reactors were optimized to successfully demonstrate CFP of pine over two different commercial zeolite catalysts. Mixing-enhancers within the vapor-phase upgrader induced laminar flow dynamics with larger Reynold's numbers, thus enhancing heat and mass transfer and in turn CFP conversion. Real-time analysis of products was accomplished via molecular beam mass spectrometry (MBMS), while light gas yield was determined using nondispersive infrared (NDIR) analysis. The transfer of the pyrolysis vapors to the vapor-phase upgrader was investigated to gain insight into optimal transfer-line conditions for limiting secondary thermal cracking and preserving carbon in the ex situ CFP process. The products were comparable to those previously obtained from fixed bed and fluidized bed reactor systems as well as entrained-flow riser reactor systems (e.g., one-ring aromatics, polyaromatics, and phenolics). Replicate experiments demonstrated a good average mass balance closure: 14 wt % oil, 27 wt % aqueous, 26 wt % char, 12 wt % total coke (system and catalyst coke), and 21 wt % light gas (CO, CO2 and CH4) with overall closure of similar to 100%. Similar trends in catalyst deactivation were observed for the laminar entrained-flow reactor system with decreasing catalyst-to-biomass ratio as reported in the literature. Under optimized continuous-flow conditions, constant catalyst activity was maintained, suggesting that the laminar entrained-flow reactor system was a viable option for the CFP of pine. Minor differences in catalytic activity were observed for the two catalysts tested.

Fast pyrolysis and catalytic fast pyrolysis (CFP) of biomass produce a liquid product stream comprised of various classes of organic compounds having different molecule size and polarity. This liquid, either spontaneously in the case of catalytic fast pyrolysis or by water addition for the noncatalytic process separates into a nonpolar organic-rich fraction and a highly polar water-rich fraction. The organic fraction can be used as a blendstock or feedstock for further processing in a refinery while, in the CFP process design, the aqueous phase is currently sent to wastewater treatment, which results in a loss of residual biogenic carbon present in this stream. This work focuses on the catalytic conversion of the biogenic carbon in pyrolysis aqueous phase streams to produce hydrocarbons using a vertical microreactor coupled to a molecular beam mass spectrometer (MBMS). The MBMS provides real-time analysis of products while also tracking catalyst deactivation. The catalyst used in this work was HZSM-5, which upgraded the oxygenated organics in the aqueous fraction from noncatalytic fast pyrolysis of oak wood to fuels comprising small olefins and aromatic hydrocarbons. During processing of the aqueous bio-oil fraction, the HZSM-5 catalyst exhibited higher activity and coke resistance than those observed in similar experiments using biomass or whole bio-oils. Reduced coking is likely due to ejection of coke precursors from the catalyst pores that was enhanced by excess process water available for steam stripping. The water reacted with coke precursors to form phenol, methylated phenols, naphthol, and methylated naphthols. Conversion data shows that up to 40 wt % of the carbon in the feed stream is recovered as hydrocarbons.

Catalytic fast pyrolysis of biomass over zeolite catalysts results primarily in aromatic (e.g., benzene, toluene, xylene) and olefin products. However, furans are a higher value intermediate for their ability to be readily transformed into gasoline, diesel, and chemicals. Here we investigate possible mechanisms for the coupling of glycoaldehyde, a common product of cellulose pyrolysis, over HZSM-5 for the formation of furans. Experimental measurements of neat glycoaldehyde over a fixed bed of HZSM-5 confirm furans (e.g., furanone) are products of this reaction at temperatures below 300 degrees C with several aldol condensation products as coproducts (e.g., benzoquinone). However, under typical catalytic fast pyrolysis conditions (>400 degrees C), further reactions occur that lead to the usual aromatic product slate. ONIOM calculations were utilized to identify the pathway for glycoaldehyde coupling toward furanone and hydroxyfuranone products with dehydration reactions serving as the rate-determining steps with typical intrinsic reaction barriers of 40 kcal mol(-1). The reaction mechanisms for glycoaldehyde will likely be similar to that of other small oxygenates such as acetaldehyde, lactaldehyde, and hydroxyacetone. This study provides a generalizable mechanism of oxygenate coupling and furan formation over zeolite catalysts.

Catalytic C-C coupling and deoxygenation reactions are essential for upgrading of biomass-derived oxygenates to fuel-range hydrocarbons. Detailed understanding of mechanistic and energetic aspects of these reactions is crucial to enabling and improving the catalytic upgrading of small oxygenates to useful chemicals and fuels. Using periodic density functional theory (DFT) calculations, we have investigated the reactions of furan and acetaldehyde in an HZSM-5 zeolite catalyst, a representative system associated with the catalytic upgrading of pyrolysis vapors. Comprehensive energy profiles were computed for self-reactions (i.e., acetaldehyde coupling and furan coupling) and cross-reactions (i.e., acetaldehyde + furan) of this representative mixture. Major products proposed from the computations are further confirmed using temperature controlled mass spectra measurements. The computational results show that furan interacts with acetaldehyde in HZSM-5 via an alkylation mechanism, which is more favorable than the self-reactions, indicating that mixing furans with aldehydes could be a promising approach to maximize effective C-C coupling and dehydration while reducing the catalyst deactivation (e.g., coke formation) from aldehyde condensation.

During catalytic upgrading over HZSM-5 of vapors from fast pyrolysis of biomass (ex situ CFP), water reacts with aromatic intermediates to form phenols that are then desorbed from the catalyst micropores and produced as products.