William Curtis Conner

Kinetics and Reaction Engineering of Levulinic Acid Production from Aqueous Glucose Solutions

We have developed a kinetic model for aqueous-phase production of levulinic acid from glucose using a homogeneous acid catalyst. The proposed model shows a good fit with experimental data collected in this study in a batch reactor. The model was also fitted to steady-state data obtained in a plug flow reactor (PFR) and a continuously stirred tank reactor (CSTR). The kinetic model consists of four key steps: (1) glucose dehydration to form 5-hydroxymethylfurfural (HMF); (2) glucose reversion/degradation reactions to produce humins (highly polymerized insoluble carbonaceous species); (3) HMF rehydration to form levulinic acid and formic acid; and (4) HMF degradation to form humins. We use our model to predict the optimal reactor design and operating conditions for HMF and levulinic acid production in a continuous reactor system. Higher temperatures (180-200 °C) and shorter reaction times (less than 1 min) are essential to maximize the HMF content. In contrast, relatively low temperatures (140-160 °C) and longer residence times (above 100 min) are essential for maximum levulinic acid yield. We estimate that a maximum HMF carbon yield of 14% can be obtained in a PFR at 200 °C and a reaction time of 10 s. Levulinic acid can be produced at 57% carbon yield (68% of the theoretical yield) in a PFR at 149 °C and a residence time of 500 min. A system of two consecutive PFR reactors shows a higher performance than a PFR and CSTR combination. However, compared to a single PFR, there is no distinct advantage to implement a system of two consecutive reactors.

The effects of contact time and coking on the catalytic fast pyrolysis of cellulose

The effects of catalyst contact time (WHSV−1) and coking on catalytic fast pyrolysis of cellulose with ZSM-5 were studied in a bubbling fluidized bed reactor. Because coke interferes with catalyst activity, the effect of catalyst contact time was studied at coke loadings known not to deactivate the catalyst. CO and CH4 are favored at low catalyst contact times ( 10000 s). At increased time on stream, the catalyst lost activity due to coking. The majority aromatic-producing activity was lost after site turnovers of 95 (cellulose monomers to Bronsted sites) corresponding to a weight turnover of 2.0 (feed weight to catalyst weight). Accumulated coke deactivates the catalyst by both filling the micropores and blocking the acid sites.

Analysis of the morphology of high surface area solids: studies of agglomeration and the determination of shape

Characterization of the morphology of high surface area solids is most often accomplished by nitrogen desorption and/or mercury intrusion porosimetry. If the void/solid structure is viewed as an interconnected network, ad-de-sorption and retraction/intrusion may be associated with the openings and constrictions within the void network. This more realistic view adds another dimension to the analyses. The data can be analyzed as if the data consisted of agglomerated microspheres. This analysis proves consistent for compacted aerosol silicas but is inconsistent if the solid has a different morphology. More significantly, the ratios of the measured most probable radii of intrusion to those of retraction seem to be characteristic of the void solid structure and pore shapes, and thereby, it may be possible to infer the pore shapes and general structure from this more detailed analysis. A heuristic diagram of these trends is presented. 6 references.

The Effect of Water on Furan Conversion over ZSM-5

Catalytic fast pyrolysis is a method for converting lignocellulosic biomass into renewable aromatics and olefins. Water is a byproduct of this reaction and is also present in the biomass feed. As the water partial pressure is increased from 0 to 212 Torr (0 to 28 kPa), there is an increase in furan conversion from 43.8 to 84.8 % over ZSM‐5. The CO2 and propylene yields also increase from 0.7 to 16.4 % and 2.9 to 44.9 %, respectively, as the water partial pressure increases. Water partial pressures in an industrial catalytic fast pyrolysis reactor should be within the range of water partial pressures used in this study. These results demonstrate that the presence of water promotes hydrolysis reactions in the gas‐phase conversion of furanic pyrolysis vapors over zeolite catalysts.

The effects of ZSM-5 mesoporosity and morphology on the catalytic fast pyrolysis of furan

ZSM-5 catalysts with different morphologies were synthesized and evaluated for the catalytic conversion of furan in a fixed bed reactor to provide insights into the rational design of zeolite catalysts for catalytic fast pyrolysis (CFP). The effects of mesoporosity and morphology of ZSM-5 catalysts on the production of aromatics and olefins as well as catalyst deactivation were investigated. The results suggest that increasing mesoporosity and decreasing crystallite size can increase furan conversion and affect selectivity to products. Improved selectivities to benzene, toluene, xylene and olefins were achieved with mesoporous ZSM-5 and 100 nm ZSM-5 compared to 800 nm ZSM-5. Coke formation on zeolite catalysts during the reaction of furan was also largely reduced (up to 65%) by introducing mesoporosity. It was observed that coke is mainly formed and accumulated inside the micropores of ZSM-5 catalysts rather than on the external surface or within the mesopores. Characterization of mass transport in the coked zeolite samples using cyclohexane as a probe molecule suggested that coke blocks micropores, leading to a decrease in micropore volume during the catalyst deactivation process. However, due to the three-dimensional pore structure of ZSM-5, the mass transport properties of mesoporous ZSM-5 do not exhibit an apparent change. Catalyst deactivation was mainly due to the coverage of active sites by coke, rather than the blockage of the transport pathways by coke.

Nanostructured Basic Catalysts: Opportunities for Renewable Fuels

This research studied and developed novel basic catalysts for production of renewable chemicals and fuels from biomass. We focused on the development of unique porous structural-base catalysts zeolites. These catalysts were compared to conventional solid base materials for aldol condensation, that were being commercialized for production of fuels from biomass and would be pivotal in future biomass conversion to fuels and chemicals. Specifically, we had studied the aldolpyrolysis over zeolites and the trans-esterification of vegetable oil with methanol over mixed oxide catalysts. Our research has indicated that the base strength of framework nitrogen in nitrogen substituted zeolites (NH-zeolites) is nearly twice as strong as in standard zeolites. Nitrogen substituted catalysts have been synthesized from several zeolites (including FAU, MFI, BEA, and LTL) using NH3 treatment.