(127e) Kinetic Regime Change in the Diels-Alder Cycloaddition of Biomass-Derived Furans with Solid Acids

The need for sustainable production of everyday materials in addition to market volatility of petroleum-based feedstocks has motivated research into the production of renewable aromatic chemicals from biomass. Specific chemicals of interest include p-xylene, the feedstock for polyethylene terephthalate (PET). We have proposed a renewable method of producing renewable p-xylene by cycloaddition of biomass-derived dimethylfuran (DMF) and ethylene, which serves as the last step in a complete process for producing p-xylene from cellulose^[1]. The reaction occurs by symmetry-allowed [4 + 2] Diels-Alder cycloaddition of ethylene and DMF and subsequent aromatization by acid-catalyzed dehydration.

            In this work, we highlight enhanced selectivity to p-xylene can be achieved by using microporous catalysts with large pore and tunable acidity. High selectivity to p-xylene (~90%) can be achieved when the conversion of DMF reaches >99%.  It is shown that 2,5-hexanedione, formed by the hydrolysis of DMF in the initial stage of the reaction (conversion of DMF <60%), can reform DMF to maintain the equilibrium between DMF/water and 2,5-hexanedione, which significantly improves overall selecitivty to p-xylene^[2]. This study reveals that the superior performance of large-pore zeolites for selective production of p-xylene can be attributed to: (a) their large pore structure and tunable partilce size for fast mass tranport, (b) their resistance to deactivation, allowing for high conversion of DMF and (c) its ability to catalyze dehydration of the Diels-Alder cycloadduct without catalyzing other side reactions^[4,5]. In addition, it was also found that p-xylene, once formed from DMF, did not readily isomerize to o- or m-xylene at the considered reaction conditions, which provides a significant process advantage by eliminating the expensive separation of xylene isomers^[3]. The discovery that large pore zeolites with tunable acidity exhibits high selectivity with high catalytic reaction rate significantly improve the potential for lignocellulosic biomass to serve as a renewable feedstock for aromatic chemicals.

References:

[1] Williams, C. L.; Chang, C.-C.; Do, P.; Nikbin, N.; Caratzoulas, S.; Vlachos, D. G.; Lobo, R. F.; Fan, W.; Dauenhauer, P. J., "Cycloaddition of Biomass-Derived Furans for Catalytic Production of Renewable p-Xylene". ACS Catal. 2012, 2(6), 935-939.

[2] Chang, C.-C.; Green, S. K.; Williams, C. L.; Dauenhauer, P. J.; Fan, W., "Ultra-selective cycloaddition of dimethylfuran for renewable p-xylene with H-BEA". Green Chem. 2014, 16 (2), 585-588.

[3] R.E. Patet, N. Nikbin, C.L. Williams, S.K. Green, C. Chang, W. Fan, S. Caratzoulas, P.J. Dauenhauer, D.G. Vlachos, “Kinetic Regime Change in the Tandem Dehydrative Aromatization of furan Diels-Alder Products,” ACS Catalysis 2015, 5(4), 2367-2375.

[4] S. Vaitheeswaran, Sara Green, Paul J. Dauenhauer, Scott M. Auerbach, "On the Way to Biofuels from Furan: Discriminating Diels-Alder and Ring-Opening Mechanisms," ACS Catalysis2013. 3(9), 2012-2019.

[5] N. Nikbin, P.T. Do, S. Caratzoulas, R.F. Lobo, P.J. Dauenhauer, D.G. Vlachos, "A DFT study of the acid-catalyzed conversion of 2,5-dimethylfuran and ethylene to p-xylene," Journal of Catalysis 2013, 297, 35-43