Kinetic Regime Change in the Tandem Dehydrative Aromatization of Furan Diels–Alder Products

Abstract

Renewable production of p-xylene from [4 + 2] Diels− Alder cycloaddition of 2,5-dimethylfuran (DMF) and ethylene with H−Y zeolite catalyst in n-heptane solvent is investigated. Experimental studies varying the solid acid catalyst concentration reveal two kinetic regimes for the p-xylene production rate: (i) a linear regime at low acid site concentrations with activation energy E a = 10.8 kcal/mol and (ii) a catalyst-independent kinetic regime at high acid site concentrations with activation energy E a = 20.1 kcal/mol. We carry out hybrid QM/MM calculations with a three-layer embedded cluster ONIOM model to compute the energetics along the main reaction pathway, and a microkinetic model is constructed for the interpretation of the experimental kinetic data. At high solid acid concentrations, p-xylene production is limited by the homogeneous Diels−Alder reaction, whereas at low acid concentrations, the overall rate is limited by the heterogeneously catalyzed dehydration of the Diels−Alder cycloadduct of DMF and ethylene because of an insufficient number of acid sites, despite the dehydration reaction requiring significantly less activation energy. A reduced kinetic model reveals that the production of p-xylene follows the general kinetics of tandem reactions in which the first step is uncatalyzed and the second step is heterogeneously catalyzed. Reaction orders and apparent activation energies of quantum mechanical and microkinetic simulations are in agreement with experimental values.

Diels–Alder cycloaddition of 2-methylfuran and ethylene for renewable toluene

“…d Reaction barriers and adsorption energies are tabulated in units of kcal/mol. Adjustments to parameters shown in parantheses, consistent with the adjustments made in the prior work 37 and within expected computational error…”

“…37 This model can be re-derived for the rate of toluene production from 2-methylfuran and ethylene and reparameterized using values obtained from the QM/MM calculations (Table 3) Figure 4d). 40 ring in methylfuran increases the number of possible side reactions, as compared to the DielsAlder cycloaddition of 2,5-dimethylfuran and ethylene.…”

Production of renewable toluene from biomass-derived furans via Diels-Alder and dehydration reactions: A comparative study of Lewis acid catalysts

“…BTX aromatics are particularly utilized as precursors in the production of polystyrene, polyurethane, and polyethylene terephthalate (PET), for whose demand has increased globally [5]. Recently, a thermochemical route to produce renewable BTX aromatics from biomass-derived furans (i.e., 2,5-dimethylfuran (DMF), 2-methylfuran (MF), furan) and ethylene via Diels-Alder cycloaddition and subsequent dehydration reactions, has been proposed using solid Brønsted and Lewis acid catalysts [6][7][8][9][10][11][12][13][14][15][16][17]. Because ethylene can also easily be obtained by the dehydration of bio-ethanol [18], this route can be considered as a fully sustainable process for the production of BTX chemicals.…”

Production of renewable p-xylene from 2,5-dimethylfuran via Diels–Alder cycloaddition and dehydrative aromatization reactions over silica−alumina aerogel catalysts

“…The yield of p-xylene increased linearly with the density of acid sites. It has been shown that the initial Diels-Alder reaction of DMF and ethylene proceeds uncatalyzed and the overall rate of p-xylene formation is controlled by the catalyzed dehydration of the cycloadduct for H-Y zeolite and WO x -ZrO 2[11,13,15,22]. The rate of p-xylene formation increased with an increase in the concentration of Brønsted acid sites[22] .…”

“…It has been shown that the initial Diels-Alder reaction of DMF and ethylene proceeds uncatalyzed and the overall rate of p-xylene formation is controlled by the catalyzed dehydration of the cycloadduct for H-Y zeolite and WO x -ZrO 2[11,13,15,22]. The rate of p-xylene formation increased with an increase in the concentration of Brønsted acid sites[22] . Thus, the variation of the yield of p-xylene with different Si/Al ratios of the SAAs can be explained by the dependence of the p-xylene production rate on the concentration of the Brønsted acid sites.In addition to the effect of acid site concentrations, the change of the p-xylene yield over SAAs with different Si/Al ratios may be partially caused by the different deactivation performances of the SAAs because the deactivation of the catalysts occurred during the reaction by the formation of heavy oligomers on the catalyst surface (SeeFig.…”