Furan Production from Glycoaldehyde over HZSM-5

Abstract

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°C with several aldol condensation products as co-products (e.g. benzoquinone). However, under typical catalytic fast pyrolysis conditions (>400°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 and this study provides a generalizable mechanism of oxygenate coupling and furan formation over zeolite catalysts. TOC Graphic Synopsis Identifying potential thermochemical pathways of biomass to furan, which can help biomass displace petroleum for fuels and chemicals. While strongly acidic zeolites have been used to completely deoxygenate bio-oils and pyrolysis vapors, other less reactive and/or partially deactivated zeolites have been shown to partially deoxygenate pyrolysis vapors to form furan and alkyl furans. 16-20 French and Czernik evaluated 40 selected catalysts (including HZSM-5) for their hydrocarbon production performance on aspen wood, cellulose, and straw lignin and demonstrated formation of partially dehydrated oxygenates, such as furan, methyl furan, furfural, and methyl furfural in the products. 17 Mukarakate et al. studied the conversion of pine pyrolysis vapors over fixed beds of β-zeolite and HZSM-5 and found the formation of several furan derivatives (furan, methyl furan, dimethyl furan, and trimethyl furan). 19,20 Jae et al. identified 4-methyl-2,3-dihydrofuran, furfural, 5-methyl furfural, 2-furanmethanol, and 5-methyl-2(5H)-furanone in the products during CFP of glucose over 13 zeolites with a variety of pore size and shape. 18 Carlson et al. identified furan, 2-methyl furan, 4-methyl-furfural, furan-2-methanol as the thermally stable oxygenated intermediates in the production of aromatics from

Theoretical Determination of Size Effects in Zeolite-Catalyzed Alcohol Dehydration

“…A unit cell was constructed for each zeolite, with each model containing the zeolite's primary channel(s) at its center ( Figure 2). Bonds at the edge of each cell were terminated with hydrosilane groups (Si-H) for H-AEL and H-BEA and hydroxyl groups (Si-O-H) for H-ZSM-5 to be consistent with previous literature [10,64]. In each case, Al was substituted at a single T site.…”

“…The dehydration reactions at lower temperatures are preferable because they remove oxygen without removing carbon, and carbon yield is highly correlated with fuel selling price [8]. Such dehydration reactions are likely to be rate-limiting for a variety of reaction classes, including Diels-Alder cycloaddition and carbon-carbon coupling reactions of carbonyls [9,10]. Hence, an ability to control dehydration kinetics within zeolite pores can be desirable.…”

O2 Activation and Oxidative Dehydrogenation of Propane on Hexagonal Boron Nitride: Mechanism Revisited

“…Generally speaking, the reactive bond length is related to the bond strength in the TS; the stronger the bond strength, the longer is the bond length in its TS. This is also called “late” TS or “early” TS . Hence, the longer length of O–H in TS2 means a more active state of the B–O species as compared with TS1.…”

“…This is also called "late" TS or "early" TS. 25 In Figure 6, as mentioned above, TS1 corresponds to the transition state of the first dehydrogenation step based on the molecular adsorption state of O 2 . The relative free energy of TS1 is 116.1 kcal/mol, which means that ΔG a is 79.9 kcal/mol for this elementary reaction.…”

Catalytic conversion of acetol over HZSM-5 catalysts – influence of Si/Al ratio and introduction of mesoporosity

“…Glycolaldehyde was shown to yield furans such as furanone below 300 °C, while at >400 °C further reactions to aromatics occurred [37], and general the conversion of model compounds and the yield of aromatics tend to increase with temperature. Chen et al [36] reported a higher yield of coke (~11 C%) and a lower yield of liquid product (9.5 C%) when upgrading acetol over HZSM-5 at 500 °C, with 68% of the liquid products attributed to aromatics (incl.…”