Abstract
p-Xylene is a commodity chemical used for the manufacture of plastic bottles and textiles. For the biomass-based route from 2,5-dimethylfuran (DMF) and ethylene, the properties of the catalyst such as acidity effect, product selectivity and catalyst activity play an important role. To determine the effect of acidity and extraframework position in faujasite zeolite on p-xylene selectivity, type Y (Si/Al = 40 and Si/Al = 2.55) and X (Si/Al = 1.25) zeolites containing the extraframework Lewis acids Na+, K+, Li+, Ag+ and Cu+, and a Brønsted acid-containing zeolite, HY (Si/Al = 40), were prepared and tested for p-xylene production under solvent-free conditions and at low conversions (less than 35%). Here it is reported that NaX zeolite catalyses DMF and ethylene conversion to p-xylene with 91% selectivity at 30% conversion, which is better than the 25% p-xylene selectivity obtained when using HY at similar conversion. ANOVA was used to show that there is a synergistic effect between acidity and extraframework position on the rate of p-xylene production. At 7% DMF conversion, Lewis acids were more selective than the Brønsted acid tested (50 versus 30% p-xylene selectivity). p-Xylene selectivity is optimal when using Lewis acids with moderate acidity and extraframework positions located in the faujasite supercage (sites II and III).
Highlights
Introduction pXylene is an important commodity chemical used to produce terephthalic acid and polyethylene terephthalate (PET)
As an alternative to the conventional petrochemical route, a biomass-based route to p-xylene was demonstrated via the Diels–Alder cycloaddition of 2,5-dimethylfuran (DMF) and ethylene to form 1,4dimethyl-7-oxabicyclo[2.2.1]hept-2-ene, which is subsequently dehydrated to p-xylene over acid catalysts [2]
Faujasite, whose structure consists of six-membered double rings (d6R) and sodalite cages, was characterized by X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), nitrogen adsorption, inductively coupled plasma-atomic emissions spectroscopy (ICP-AES) or energy-dispersive X-ray spectroscopy (EDS), and temperature-programmed desorption thermal gravimetric analysis (TPD-TGA) to assess the structure, morphology, pore volume and chemical composition of the samples
Summary
Introduction pXylene is an important commodity chemical used to produce terephthalic acid and polyethylene terephthalate (PET). The effect of the properties of the catalyst such as acidity and of zeolite catalysts such as framework type, acidity, mesoporosity on p-xylene yield and selectivity in n-heptane solvent has been studied [7,8,9,10]. Density functional theory (DFT) has provided insight into the reaction mechanism, kinetic regime change and the effect of active site type on catalyst activity [12,13]. This biomass-based route to p-xylene has been researched intensively, the solvent-free route to p-xylene has not received much attention despite the decreased p-xylene cost and environmental impact. An experimental study on the effect of active site type and extraframework position in the faujasite zeolite under solvent-free conditions has not been reported and aids computational studies
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