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Catalytic fast pyrolysis of furan over ZSM-5 catalysts: A model biomass conversion reaction
Due to its low cost and availability, lignocellulosic biomass is receiving significant attention worldwide as a feedstock for renewable liquid bio-fuels. We have recently shown that zeolites can be added to a pyrolysis reactor to directly make aromatics from solid biomass in one single step in a process called catalytic fast pyrolysis (CFP). The advantage of this approach is that valuable petrochemicals can be made directly from solid biomass in a single catalytic step using zeolite catalysts. However, little is known about the conversion chemistry that occurs within the zeolites during CFP. The objective of this thesis is to identify the key catalytic reactions that occur for conversion of biomass inside ZSM-5 zeolite catalysts using furan and its derivatives as model biomass compounds. The kinetic data and chemistry was obtained by using a continuous flow fixed-bed reactor, and an in-situ temperature-programmed reactor system. Furan adsorbs as oligomers at room temperature. These oligomers are converted into CO, CO2, H2O, olefins, monocyclic aromatics, and undesired polycyclic aromatics and coke at 400 - 600°C. An important route to form aromatics at 600°C is Diels-Alder reaction/dehydration where furan reacts with produced olefins and forms aromatics and water. The Diels-Alder reaction can be further utilized by co-feeding olefins with furanic compounds to tune the aromatics distribution. For example, in our experiments we were able to double toluene and triple xylenes selectivity for furan and 2-methylfuran CFP, respectively. Moreover, we synthesized a series of Ga-promoted catalysts to increase the rate of aromatics production. The aromatics selectivity obtained from furan conversion over Ga-containing ZSM-5 was 40% higher than unpromoted ZSM-5. The promotion was also observed in a bubbled fluidized-bed reactor used for pinewood CFP, where the aromatics yield was increased by 50% using a Ga-promoted ZSM-5 FCC catalyst. We finally fine-tuned ZSM-5 pores to impose more space confinement on aromatic products. These modified ZSM-5 increased p-xylene selectivity in xylenes from 32% to greater than 90% for conversion of 2-methylfuran and propylene while the overall p-xylene selectivity was increased from 5% to 15%. The Ga promotional effect was also observed on a spray-dried ZSM-5 catalyst. This study addresses the catalytic chemistry that occurs inside zeolites during CFP of biomass into aromatics using furan as a model biomass compound. Understanding this reaction chemistry can give us insight into how to design more effective zeolite catalysts and reactors for the efficient utilization of our biomass resources.
Cheng, Yu-Ting, "Catalytic fast pyrolysis of furan over ZSM-5 catalysts: A model biomass conversion reaction" (2012). Doctoral Dissertations Available from Proquest. AAI1530357.