Catalytic fast pyrolysis (CFP) offers a simple and robust route to convert raw lignocellulosic biomass to aromatic hydrocarbons. During CFP, cellulose, hemicellulose, and lignin are first thermally decomposed to bio-oil vapors that are further converted to aromatics in the presence of a ZSM-5 zeolite catalyst. The high temperatures required for CFP also favor coke formation, an undesired byproduct, through condensation of the oxygenated intermediates on ZSM-5′s outer surface and/or secondary reactions inside its micropores. Introducing mesopores through desilication represents a possible strategy to enhance mass transport and intracrystalline diffusion, and consequently favor aromatic production over undesired coke formation. Here, we study the effect of desilication on the structure, acidity, and performance of aluminum-rich ZSM-5. Detailed characterization of the obtained zeolite catalysts indicates that mild desilication conditions do not significantly affect the elemental composition, crystallographic structure, microporosity, and distribution of aluminum atoms in framework and extraframework sites. However, the number of accessible Brønsted acid sites increased by ∼50% as a result of the enhanced mesoporosity. Desilication increased the aromatic yields obtained for red oak pyrolysis (27.9%) compared to the parent zeolite (23.9%), without impacting the liquid product distribution (67.4% selectivity to benzene, toluene, and xylene). Our results suggest the catalytic performance could be further improved by enlarging the mouth of ink bottle shaped mesopores in order to further enhance mass transport between the gas phase and the zeolite's micropore network.

Microgram‐scale reactors combined with gas chromatography (GC) coupled to mass spectrometry (MS) or flame ionization detection (FID) are used widely in pyrolysis research. Whether these devices meet the expected fast heating rates and short vapor residence times of fast pyrolysis have not been verified. In this study, experiments and simulations are used to investigate heat and mass transfer in a furnace‐based micropyrolyzer. Surprisingly, heating rates obtained from the temperature history of sample cups in the reactor were modest compared to the greater than 1000 K s−1 heating rates sometimes assumed for such reactors. The heating rate at 773 K, employed commonly in fast pyrolysis, was only 180 K s−1. The highest rate observed was 494 K s−1 at a furnace temperature of 1268 K, which is well above typical pyrolysis temperatures. The mass transfer of volatilized samples was studied using both an optically accessible furnace and computational fluid dynamics. The standard sample cups used with these micropyrolyzers impede the escape of vapors. The use of shallow perforated cups overcame this mass transfer limitation to lead to levoglucosan yields ≈10 % higher than usually reported for the pyrolysis of cellulose.

Efforts to understand the reaction mechanisms of cellulose pyrolysis have been stymied by short reaction times and difficulties in probing the condensed phase of cellulose intermediate products.