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Abstract:
The continuous flow synthesis of p-Xylene (pXL) via Diels-Alder cycloaddition of lignocellulosic biomass-derivable 2,5-dimethylfuran (DMF) and acrylic acid (AA) was performed over different type of zeolites, i.e. Beta, ZSM-5 and Y. Among the tested zeolites, Beta zeolite showed an optimum catalytic performance in pXL synthesis from DMF and AA. In this context, Beta zeolite with a Si/Al molar ratio of 150 which is abbreviated Beta(150), resulted in a complete DMF conversion with a pXL yield of 83, and 2,5-dimethylbenzoic acid (DMBA) with yield of 17 as the second product, at 473 K and 10.1 min residence time (τ) and excess of AA (0.7 M). This high catalytic activity is attributed to the high specific surface area of 1180 m2 g-1 with a three-dimensional porous architecture with pore diameter of (6.6 × 6.7 Å) and an acid sites density above 40 µmol g-1. The utilized Beta(150) showed a very stable performance up to 10 h time on stream with minor deactivation after 8 h of TOS, while pXL yield stayed above 70. The original catalytic performance of Beta(150) in DMF upgrading to pXL was restored by applying a regeneration step for the spent catalyst, which is simple in continuous flow reactors. Finally, this sustainable continuous flow process enables an efficient and selective pXL production from DMF and AA as a dienophile at lower reaction temperature (473 K) and shorter residence time (τ = 10.1 min) with respect to batch fashion.
